Friday 28 February 2014

Areal Flood Advisory valid from Feb 28 1:20 PM to 7:15 PM PST

Interactive NWS Alert Information

New Event for PNW
Areal Flood Advisory valid from Feb 28 1:20 PM to 7:15 PM PST
Sent to SMS and E-Mail at Feb 28 1:20 PM PST
alert map
Radar Time: Feb 28 2014 5:15 PM PST
alert legend
000
WGUS86 KSTO 282120
FLSSTO

FLOOD ADVISORY
NATIONAL WEATHER SERVICE SACRAMENTO CA
120 PM PST FRI FEB 28 2014

CAC005-007-009-017-057-061-063-067-077-091-099-101-109-113-115-
010315-
/O.NEW.KSTO.FA.Y.0005.140228T2120Z-140301T0315Z/
/00000.N.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
STANISLAUS CA-YOLO CA-SIERRA CA-TUOLUMNE CA-NEVADA CA-PLUMAS CA-
SAN JOAQUIN CA-SUTTER CA-EL DORADO CA-PLACER CA-YUBA CA-AMADOR CA-
CALAVERAS CA-BUTTE CA-SACRAMENTO CA-
120 PM PST FRI FEB 28 2014

THE NATIONAL WEATHER SERVICE IN SACRAMENTO HAS ISSUED AN

* URBAN AND SMALL STREAM FLOOD ADVISORY FOR..
  AMADOR COUNTY...
  CALAVERAS COUNTY...
  WESTERN EL DORADO COUNTY...
  WESTERN NEVADA COUNTY...
  WESTERN PLACER COUNTY...
  SACRAMENTO COUNTY...
  SAN JOAQUIN COUNTY...
  STANISLAUS COUNTY...
  EASTERN SUTTER COUNTY...
  SOUTHWESTERN TUOLUMNE COUNTY...
  SOUTHEASTERN YOLO COUNTY...
  YUBA COUNTY...
  SOUTHEASTERN BUTTE COUNTY...
  SOUTHWESTERN PLUMAS COUNTY...
  WESTERN SIERRA COUNTY...

* UNTIL 715 PM PST

* AT 115 PM PST STORMS CONTINUING TO MOVE THROUGH THE AREA BRINGING 
MODERATE TO HEAVY PRECIPITATION. WIDESPREAD SHOWERS AND SCATTERED 
THUNDERSTORMS WILL CONTINUE TO DEVELOP OVER THE AREA THROUGH THE 
AFTERNOON. RAINFALL AMOUNTS AROUND HALF AN INCH AN HOUR ARE 
POSSIBLE. 

SMALL STREAMS AND CREEKS WILL HAVE RAPID RISES AND MAY OVERFLOW 
THEIR BANKS. STREET FLOODING ESPECIALLY NEAR STORM DRAINS IS ALREADY 
OCCURRING. PONDING OF WATER IN POOR DRAINAGE AREAS AND LOW LYING 
SPOTS IS ALSO EXPECTED. 

PRECAUTIONARY/PREPAREDNESS ACTIONS...

MOST FLOOD DEATHS OCCUR IN AUTOMOBILES. NEVER DRIVE YOUR VEHICLE INTO
AREAS WHERE THE WATER COVERS THE ROADWAY. FLOOD WATERS ARE USUALLY
DEEPER THAN THEY APPEAR. JUST ONE FOOT OF FLOWING WATER IS POWERFUL
ENOUGH TO SWEEP VEHICLES OFF THE ROAD. WHEN ENCOUNTERING FLOODED
ROADS MAKE THE SMART CHOICE...TURN AROUND...DONT DROWN.

EXCESSIVE RUNOFF FROM HEAVY RAINFALL WILL CAUSE ELEVATED LEVELS ON
SMALL CREEKS AND STREAMS...AND PONDING OF WATER IN URBAN AREAS...
HIGHWAYS...STREETS AND UNDERPASSES AS WELL AS OTHER POOR DRAINAGE 
AREAS AND LOW LYING SPOTS.

&&

Thursday 27 February 2014

Very Strong Low to Slam California Tonight Through Saturday


Very Strong Low to Slam California Tonight Through Saturday

 FEBRUARY 27, 2014
While we're in a break through this evening, don't be fooled: one heck of a strong storm is offshore, and it’s going to pack a punch when it nears shore and slows down early Friday morning. This secondary storm is much stronger than the previous; to compare, the last system dropped to around 998mb. The next system offshore is already down to around 986mb, and dropping in pressure by around 1mb an hour… possibly more at times.
As you can tell from the satellite image above, this system is already looking very impressive, and by late tonight it should be a fully wrapped up, mature cyclone. In the early morning hours of Friday, the surface low is currently forecast to dip down to around 968mb by the 18z NAM. Other models indicate a depth of around 970 – 974mb. Either way, it’ll still be a very powerful storm – one of the deepest lows offshore in a few years, and the biggest precipitation event for southern California in at least a year.
18z 4km NAM’s forecast MSLP, 10m winds, and 10m wind vectors arrows. At this given time, (around 6am), the low’s depth is forecast at 968mb.

Tonight, as the low deepens, the cold front begins to surge east, sending it’s associated precipitation band inland with it. Currently appears precipitation will begin to push eastward between 11pm and 1am for most of interior northern California. Cold frontal precipitation continues into Friday morning until the front clears to the east by the mid to late morning. As this front comes through, a belt of strong belt of low/mid-level winds streams over the region, including 50 – 60kt winds at 850mb and 925mb (closer to the surface) winds of 45 – 55kts from around Colusa southward. Given moderate to heavy precipitation along/ahead of the front, currently believe 40 – 50mph gusts are possible in the southern Sacramento valley south through the San Joaquin valley. 40 – 50mph winds are also likely in coastal areas.
18z 4km NAM’s forecast 850mb winds/vector arrows, and MSLP for around 4am.

Between the cold front and the occluded front associated with the deep low lies a little vort max along a band of cold-core convection. This is expected to rotate into northern California some time Friday, bringing the next round of precipitation. Between the cold front and the small vort-max Friday morning and perhaps early afternoon there could be some clearing. Any clearing behind the cold front given proximity to the very strong low offshore and -20 to -25c cold pool aloft. If we see any sunshine Friday morning, surface warming beneath the cold pool would lead to some rapid destabilization across the lower elevations.

Models are somewhat conflicted on whether or not any clearing will occur. The 4km SPC WRF indicates sufficient clearing for the development of most unstable CAPE values in excess of 200 – 500 j/kg. The 12z NAM 4km indicated close to the same, but the 18z run indicates cloud cover and showers continuing through most of the day, limiting instability. The SREF is up there with the SPC WRF being quite bullish with clearing… and supports 400 – 800 j/kg MUCAPE values from Yuba City to Modesto.

If clearing occurs and sufficient instability is able to arise, thunderstorms would be very likely given strong large-scale accent to get things going on top of any robust buoyancy. Given the deep low offshore directional shear is decent, with surface winds out of the southeast and 700 – 500mb winds out of the southwest by afternoon. 0 – 1km and 0 – 3km AGL SR helicities of 75 – 200 M2/S2 support some clockwise hodograph curvature, which is indicates potential for some rotating storms. Temperature/dewpoint spreads of only a few degrees also support deep convective development, and smaller T/D spreads have also been tied to better tornado potential in combination of course with other thermodynamic and kinodynamic indicies.
4km NAM’s forecast 0 – 3km AGL helicity for mid-afternoon Friday. Yellow colors and deeper are 100 M2/S2 values plus.

There may be some issues with some veer-back-veer in some portions of northern California, so in some regions rotational development could be hindered. Even if notably rotation were to be hindered, 20 – 30kts of effective bulk shear would support hail development… and given the decent cold pool aloft, hail (potentially large) would be possible.

In short, if sky’s can at least partially clear for a few hours Friday morning/early afternoon ahead of a vort-max between fronts, thunderstorms would be quite likely from around Chico or Yuba City southward through at least the southern or central San Joaquin valley. Thunderstorms Friday afternoon/early evening, if any were to develop and become strong, could become capable of producing hail (possibly large), very heavy rain as most convection does, gusty winds, and a tornado threat depending on location. Generally the further south you were the better veering and less veer-back-veer shear vertical wind patterns occur.
Along the coast, convection is likely as soon as Friday morning, continuing through the day even into Friday night until the low finally pushes inland. Coastal storms also pose a hail and waterspout/weak tornado threat given proximity to the deep surface low and ample available low/mid-level instability and steep lapse rates.

The low itself fills/weakens through the day Friday, and is expected to push into the central California coast Friday evening into the overnight. The low’s occluded front rotates in with the low, bringing precipitation from around Chico southward through from Friday evening through Saturday morning. Precipitation with this feature could be heavy at times given it’s directly associated with the low, even though it fills rapidly as it nears the coast. Low impacts the central coast Saturday afternoon after the osculated front falls apart inland through the morning. As the low impacts, it’s last bit of lift and instability ahead of the low may keep showers going through the rest of the afternoon across northern California, with heavier rain along the south-central coast where the strong south/southwest flow southeast of the low provides the best lift. Can’t rule out some additional thunderstorms from the southern Sacramento valley southward throughout the San Joaquin valley Saturday afternoon into the evening as the low pushes through northern California.

Wintry precipitation wise, snow levels in the sierra are expected remain around 5500 – 6500ft for the most part. Generally they’d dip under the 6000ft mark more often during periods of intense precipitation or convection. Friday night as the low comes inland and the occluded front wrapped directly around the low pushes inland, snow levels are forecast to drop a bit more… perhaps down to 5000ft or near the Blue Canyon level by then, though accumulation down to 5000ft may be tricky.

While this system has a significant sub-tropical moisture tap, with precipitable water values in excess of 1.3 – 1.4″ off the southern California coast, the best moisture will be shunted south of northern California, rather blasting southern California with the best moisture, thus they’ll score the best precipitation of this system… especially in the mountains. Even so, strong lift combined with the moisture we have available (.6 – .9″ precipitable water values through Saturday) will still produce some decent QPFs across the region. .75 – 2″ of rain is possible across the valley depending upon convective coverage… with 1.5 – 3″ in the foothills/mountains/sierra. Locally 3 – 5″ is possible in orographically favored regions/south/southwest facing slopes. Along the central coast amounts of 2 – 5″ are possible… with several inches in the southern California mountains, even a couple inches in the lowlands.
Periods of very heavy rainfall could lead to some flooding problems across California over the next 48 hours or so. In addition to flooding potential, strong winds combined with heavy, soaking rain will also likely lead to many power outages… especially in regions that have already seen some rain in the last 24 hours.

Things clear out Saturday night into Sunday, though another weak storm is possible Monday or Tuesday. A stronger storm is possible by mid-week, but we'll look into that after we've dealt with this current beast of a storm.


Wednesday 26 February 2014

Additional strong showers and thunderstorms are expected through the night.

A line of showers racing up the I-80/Highway-50 corridor northeast towards Folsom, Roseville, Citrus Heights, and Orangevale, may be producing some rather strong winds, perhaps in excess of 35 - 40 mph. Along with the strong winds, very heavy rain is also expected.

Additional strong showers and thunderstorms are expected through the night.



Flood advisory for east-central Shasta and Tehama counties due to a persistent band of heavy rain sitting over the area. Attached image is one-hour rainfall estimates by radar.

Full statement text:

FLOOD ADVISORY
NATIONAL WEATHER SERVICE SACRAMENTO CA
958 PM PST WED FEB 26 2014

CAC089-103-270900-
/O.NEW.KSTO.FA.Y.0003.140227T0558Z-140227T0900Z/
/00000.N.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
SHASTA CA-TEHAMA CA-
958 PM PST WED FEB 26 2014

THE NATIONAL WEATHER SERVICE IN SACRAMENTO HAS ISSUED 



Tuesday 25 February 2014

Mid-Latitude Cyclones to Affect Northern California Wednesday – Saturday


Mid-Latitude Cyclones to Affect Northern California Wednesday – Saturday

FEBRUARY 24, 2014

Another round of storms is on the way to northern California beginning Wednesday, however once again, these systems won’t have major impacts on our drought. Nonetheless, any precipitation we can get helps in some way, whether it be temperately moistening the ground and watering yards, to adding a few feet to reservoirs.

These systems will be the closest we’ve been to some deep mid-latitude cyclones this winter season, with Wednesday’s system dipping to between 996 – 1000mb before weakening and swinging northward. Friday’s/Saturday’s is forecast to drop to around 980 – 984mb, but it’ll remain at it’s deepest offshore before weakening and sliding south. Mid-latitude cyclones sound a bit ominous, but they’re generally the number one culprit of larger scale storms in the mid-latitudes… this will just be the closest we’ve come to some of these deeper low centers.


0z NAM’s forecast 500mb relative vorticity and MSLP valid Wednesday evening. Warm colors indicate counter-clockwise circulation.

Wednesday’s system will take the furthest north track, thus bringing us in northern California the best dynamics, and thus precipitation. This first system will have access to a decent sub-tropical moisture plume, with precipitable water values of 1 – 1.1″ making their way inland. The low itself will track east towards what would be Fort Bragg through the late afternoon, however begins to rotate northward offshore overnight Wednesday and weaken. The only reason this low rotates north is due to Friday/Saturday’s system pushing eastward into the eastern Pacific, bringing the weaker low into it’s cyclonic flow, pulling it back to the northwest and causing it to dissipate.

Before it dissipates off the Oregon/Washington coast, however, it swings a few waves of energy into northern California on the lows southeastern flank. The first wave is the initial precipitation shield, which swings into the coast early to mid-morning along the coast, and into the valley and mountains by afternoon. This first band will bring the most widespread precipitation, however another wave of energy contained in the low rotates inland during the late afternoon into the early to mid-evening. This is when things get interesting.


Models are growing increasingly bullish with the amount of instability behind the initial precipitation shield given a modest mid/upper level cold pool associated with the low. Plume of steeper mid-level lapse rates pushes overhead during the evening and overnight hours promoting surface based CAPEs of 100 – 300 j/kg in general, with smaller pockets of around 500 j/kg SBCAPE. While the low will be reenforced by a 130kt jet, most of the jet stream layer winds will be blasting southern and central California, with weaker upper level winds over northern California. However, given the low being near the coast, 250 mile pressure gradients of 5 – 8mb are forecast, bringing a band of 40 – 50kt 850mb winds, with 45kt winds extending down to 925mb Wednesday evening from the central Sacramento valley into the northern San Joaquin valley. Given the likely presence of moderate to locally heavy to even convective precipitation, enough downward energy should be available to drive down some 30 – 45mph wind gusts from around Yuba City to Stockton.

0z NAM’s forecast 850mb winds and MLSP early Wednesday evening.

Convective potential appears highest from late evening Wednesday through early Thursday afternoon, peaking in the pre-dawn hours (2 – 5am). Given a decent (though not extreme) surface low off the CA/OR coast, this promotes veering winds in the mid-levels that promote rather decent directional shear, with 0 – 3km storm relative helicities of 100 – 250 M2/S2, and notable low-level shear (0 – 1km bulk shear) of 20 – 35kts… hodographs are clockwise curved and hooking, indicative of an environment supportive of supercellular structures. Since this is a nocturnal setup, instability is a bit elevated… above 900mb it appears. Given the potential for slightly-elevated convection, I believe tornadic potential will be limited. However, robust updrafts could support some hail… possibly near severe levels if enough instability is present.

0z NAM’s forecast ML (mixed-layer) CAPE valid for around 4am Thursday morning.

0z NAM’s forecast 0 – 3km storm relative helicity valid early Thursday morning (4am-ish again), indicating a wide swath of 100 M2/S2+ values (yellow).

Diurnal heating combined with another weak rotating inland before the low rotates too far north to affect northern California. This last wave will bring another increase in showers during the day Thursday before clearing out by evening.

Snow levels with the Wednesday/Thursday system primarily start out around 6000 – 7500ft Wednesday afternoon and evening, but lower quickly overnight into Thursday to around 4000ft as cooler, more unstable air moves overhead. 1 – 2ft of snow appear likely above 6000ft, with 3 – 9″ above 4000ft.

QPF wise, .5 – 1″ of rain is possible in the lower elevations including the coast and valley, with 1 – 2″ in the foothills and 2 – 3″ of liquid in the mountains (see winter precipitation in previous paragraph). Locally higher and lower QPFs are possible due to what could be a little or a lot of convection.


Next system pushes toward the coast Thursday night, with precipitation rotating northward into northern California as early as the pre-dawn hours of Friday. Deep subtropical moisture plume will remain confined to southern California with this system, however strong lift will still wring out moderate precipitation. Models are still fluttering with the track of the second low, hovering between the central coast and southern coast… but as long as impact is south of SFO, the best dynamics will be directed at southern California. Even then, we aren’t in too bad a position ourselves here in northern California, and we shouldn’t do too bad precipitation wise.


It appears another pocket of instability will move overhead the Sacramento/San Joaquin valley Friday… but I find it too early to call out convective potential just yet, as models have been all over the place with how exactly this system sets up.


It appears snow levels with the Friday/Saturday system generally stick around 5000ft, but could flutter up or down by a thousand feet depending on the track of the low.

It appears another .75 – 1.25″ of rain could fall across the valley Friday into Saturday, with 1 – 3″ in the mountains (falling as another 1 – 3ft of snow above 5000ft). The initial front Friday could bring some gusty winds given a 980 – 984mb low offshore, with 850mb winds in the 40 – 50kt range, I wouldn’t rule out another band of 30 – 45mph gusts Friday morning from Yuba City southward.

We should start to dry out Saturday night into Sunday as the trough ejects east, however the GFS wants to keep some leftover instability for some showers across the area Sunday. GEM/ECMWF try to indicate another system early next week, but confidence is very low on that system right now.

I’ll have another update out Wednesday specifically regarding the convective threat overnight into Thursday, and another update Thursday on the Friday – Saturday system.


Widespread Thunderstorm Threat Wednesday & Thursday

 FEBRUARY 25, 2014

A very dynamically strong, subtropical moisture plume supported system off the California coast will rotate northward along the northern coast of the state through the day and overnight Wednesday, putting northern California in the perfect region for the system’s best available large-scale accent, moisture, and with this system, especially instability.


Latest models now indicating precipitation onset a bit sooner… perhaps by mid to late morning as some pre-frontal moisture combined with increasing lift combine to develop the first round of showers. This seems possible given cooling cloud tops noted on GOES-west IR imagery are noted just 200 – 300 miles offshore.

Behind the first round of showers, the cold frontal precipitation band is expected to rotate into the coast by mid to late afternoon, and deeper inland through the evening. As the surface low nears closer to the coast during the evening, a band of strong low to mid-level winds pushes overhead along with the cold front, which combined with very strong lift and decent moisture should promote heavy precipitation, which will likely drive down some 35 – 45mph surface wind gusts across the valley as a belt of 40 – 50kt 850mb winds slides through.

0z 12km NAM’s forecast 850mb winds for around 10pm Wednesday evening.

In the mid/upper levels, -20 to -25c 500mb temps associated with the low slide overhead behind the cold front, which combined with surface temperatures in the mid-50s across the lower elevations due to decent low-level moisture return, promotes a plume of relatively steep mid-level lapse rates which pushes overhead just ahead of and especially behind the cold front through the night Wednesday into Thursday.

Decent lapse rates along with surface dewpoints in the 50s promote SBCAPE values in the 200 – 500 j/kg range in general from the coast inland into the Sacramento and northern San Joaquin valley overnight into Thursday, and lifted indexes between -1 and -4c. This amount of instability combined with large amounts of lift on the southeastern flank of the surface low provides a prime environment for thunderstorm development; both along the cold front, and behind it from Wednesday night through Thursday afternoon.

Forecast mixed-layer CAPE and 10-meter winds for around 10am Thursday plotted through the 0z 12km NAM.

Forecast sounding with surface based parcel highlighted. for the southern Sacramento valley for around 10am Thursday.

Along the cold front, while instability isn’t as strong as what lies behind it, very strong lift and a decent low-level jet should prove favorable for at least somewhat in the way of embedded convection. If colder air aloft pushes in somewhat faster aloft over the cold front, a large-scale line of thunderstorms could embed themselves within the frontal precipitation band. Storms such as these would be capable of driving down even stronger winds than what you’d see in stratiform precipitation… possibly near severe criteria if such an event were to occur given the strong mid-level winds.

Behind the front, moisture and lift still exists, nearly as strong as the cold front, which will continue to support waves of showers and thunderstorms through the night. Low-level shear is strongest with the band of strong mid-level winds that accompanies the cold front, but even behind the front 850mb winds remain elevated – in the 20 – 40kt range, with winds increasing in strength with height. Given there being a 992 – 996mb low off the northern CA/OR coast Wednesday night into Thursday, winds will certainly veer with height… with surfave winds from the south to southeast in the valley and winds from 850mb to 500mb being out of the west-southwest to dew west by Thursday morning. This notable veering creates some helicity (essentially horizontal rotation in the atmosphere, or a “rolling” motion), with 0 – 3km storm relative helicity values in the 100 – 250 M2/S2 range Wednesday night into the early afternoon Thursday. These shear parameters combined with the instability forecast would technically make for a decent environment for rotating thunderstorms, however a lack of surface heating during the nighttime hours may inhibit stronger updrafts, thus limiting vertical rotation potential.
0z 12km NAM's forecast 0 - 3km SRH valid for around 10am Thursday. Orange and red indicates 150 - 200 M2/S2 values, which support some notable hodograph clockwise curves.
0z 12km NAM’s forecast 0 – 3km SRH valid for around 10am Thursday. Orange and red indicates 150 – 200 M2/S2 values, which support some notable hodograph clockwise curves.
Once we get into Thursday morning, a break between waves of energy is possible… and this is where our period for any sunshine opens up. Currently, the NAM is being rather aggressive in generating some 300 – 600 j/kg SBCAPEs between 8am and 1pm Thursday before weakening as one last band rotates inland during the late morning and early afternoon. This last band should be enough to get at least some convection going in the Sacramento valley and surrounding mountains, however it’s hard to tell if there would have been enough heating of the low-levels to get some some stronger buoyancy available to storms. In any outcome, thunderstorms Thursday could be capable of hail, strong winds, very heavy rain, and possibly somewhat in the way of a tornado threat. Wednesday night/pre-dawn hours of Thursday should promote a favorable environment for hail/wind producing storms, but probably little in the way of a tornado threat.
0z 12km NAM's forecast hodograph for the southern Sacramento valley. In coordination with above 0 - 3km SRH values, there is indeed a clockwise hooking feature.
0z 12km NAM’s forecast hodograph for the southern Sacramento valley. In coordination with above 0 – 3km SRH values, there is indeed a clockwise hooking feature.
Precipitation wise, .5 – 1″ of rain appears likely across much of the lower elevations from this system. In the foothills and mountains, 1 – 2″ looks to be a good bet, with 2 – 3″ along west and south/southwest facing slopes. Snow levels start out around 6000ft Wednesday, but drop off to around 5000ft by late Wednesday into Thursday. 1 – 2ft of snow appears possible above 5500 – 6500ft Wednesday/Thursday with this system.
February 23rd
A much deeper, stronger cyclone takes aim at California set to slam into the California coast late Thursday/early Friday with more strong winds, heavy rain, mountain snow, and thunderstorms Friday into Saturday. Since this system requires a large amount of time to write up a blog, I’ll put out a separate blog Thursday evening regarding this system. For now,...............

Sunday 23 February 2014


Severe weather possible overnight Thursday into Friday morning
Posted: Feb 20, 2014 8:03 AM PST

By JULYA JOHNSON
6 Storm Team Meteorologist

KNOXVILLE (WATE) - After a warm a breezy day, a few isolated thunderstorms will pop up this evening (20%) ahead of a main line of strong storms back to our west.

Middle Tennessee will get severe weather during the evening hours today, and that system tracks east into our viewing area by midnight.

These storms will pack a punch with potentially damaging winds in excess of 60 mph, heavy rain, and loud thunder.

We can't rule out an isolated tornado, although we are not expecting a widespread tornado outbreak in our viewing area.

The timing on this looks to be from 11 p.m. until around 3 a.m., and then some rain showers will linger until around 9 a.m. on Friday morning.

Since this is happening during the nighttime hours, it's a good idea to have either a NOAA weather radio or our WATE Weather App. Our WATE App is free, just search "Knoxville Weather" in your phone's store. One of the neat things about this app is that you can set it to follow your current location. It will sound an alert to wake you up if a warning is issued. You can also set it for other counties if you have family in other parts of the state.

Wednesday 19 February 2014

Thursday's Severe Weather Threat Is Concerning. When To Expect The Storms & The Main Threats...

Thursday's Severe Weather Threat Is Concerning. When To Expect The Storms & The Main Threats...
2/18/2014
Thursday is going to be an absolute wild ride with temperatures soaring into the upper 60s, very windy conditions, then dropping nearly 20 degrees in 2 hours. The front is a monster and it will be roaring across our area at nearly 50 mph on Thursday night. All of these conditions look favorable for severe weather and I am concerned. In tonight's blog, I want to give a timeline so you know when to expect the storms and I will talk about the main threats.

Storm Prediction Center Severe Weather Risk For Thursday

As expected, the Storm Prediction Center has placed us in the severe weather risk again for Thursday and has our entire area in the 30% chance of severe weather. I agree with the placement, but I think an upgrade is necessary.

SPC Categorical Severe Weather Risk Thursday 7 AM - Friday 7 AM

Notice SPC has a giant risk area that covers our entire area.
SPC Probabilistic Severe Weather Risk Thursday 7 AM - Friday 7 AM

Notice SPC has our entire area in the 30% chance of severe weather for Thursday making this an enhanced severe weather risk.
A Discussion Of The Thursday Storm System / Severe Threat

Severe weather happens in our area in the winter, but only a few times a winter. Since these are not all that common, I want to refresh you on the ingredients I look for when assessing a severe weather risk for our area. Remember, these three ingredients are all needed if we are to have an outbreak of severe weather in the Ohio Valley.
Forcing

The forcing Thursday comes from an powerful front that will be racing across the area and a very favorable upper level low. The upper level low is what we call a negatively tilted low and these lows provide extreme lift in the atmosphere and can overcome weaker instability, so this is important to note. First, check out the monster front late Thursday. Notice the amazing difference in temperature ahead and behind the front!
To determine the tilt of a low, we draw a line from the center of the low to the edge. If that line is up and down, there is no tilt. If that line goes from top right to bottom left, then the low is positively tilted. If the line goes from top left to bottom right, then the low is negatively tilted. Notice this low is VERY negatively tilted.
Wind Shear / Energy

The data continues to show fierce winds only a mile above the ground on Thursday. The GFS and NAM computer models show winds of nearly 85 mph just 1 mile above the ground on Thursday and that is very concerning. We also see a little of the more dangerous directional wind shear in our area on Thursday night. Directional wind shear is defined as winds changing direction with height and this kind of wind shear can result in rotating t-storms.

GFS Surface Winds Late Thursday

Notice the winds at the surface are from the south at nearly 15 - 30 mph late Thursday. The surface winds alone are very strong late Thursday.
GFS Winds 1 Mile Above The Ground Late Thursday

Notice the winds shift to the southwest just 1 mile above the ground and increase to nearly 75 knots or 85 mph! These are ferorciously strong winds for this height and we do see a direction change of about 45 degrees on Thursday as the storms approach.

Here is an interesting look at the amount of rotation potential called "Helicity" for Thursday with the actual wind vectors on the map. You can see the green or orange arrows from the south at the surface and the winds at 3 km above the ground in hot pink. These winds shift about 45 degrees from the surface to about 3 km above the ground. Helicity measures the potential for the individual storms to rotate and anything over 200 is impressive... the NAM shows over 500 on Thursday.
The bottom line is the wind energy is extremely supportive of severe weather on Thursday. We genenerally see a small change from a south wind at the surface to a southwest wind over the lowest 1 mile of the atmosphere. This is not a huge shift in direction in the lowest part of the atmosphere, but it is something we do need to note. With the low pressure intensifying so fast on Thursday, I feel confident we will continue directional wind shear in the data.

Instability

The temperatures are going to push into the 60s by Thursday and this is a big part of the equation. The latest data does suggest we will dry slot in the afternoon. What this means is that the clouds will likely break a little in the afternoon on Thursday helping push those temperatures higher. Advance Trak is showing the breaks in the clouds well on Thursday afternoon.
This means instability values could get pushed even higher. The NAM and GFS have both increased instability for Thursday with the NAM the highest. The NAM tends to have a better grasp on instability with these storms, so I will heavily rely on that data.

NAM Instability Late Thursday

The NAM has about 1,000 units for the western part of our area with up to 700 near Louisville. This is an increase in instability and another reason for concern.
GFS Instability Late Thursday

The GFS has also increased instability to near 500 units in Louisville as the storms approach and nearly 750 units for our western counties.
One interesting tidbit, the data drops the temperatures about 5 degrees from the high to when the storms pass. In Kentuckiana, the temperatures nearly never drop when it is windy ahead of a storm even if it is at night. That potentially could mean temperatures will be as much as 5 degrees higher when the storms approach lending more energy to those storms.

My Thoughts On Severe Weather Chances For Thursday

The low that will move to our west on Thursday and bring this front is what we call a "cyclogenic bomb". That means the storm intensifies at an extremely fast pace that meteorologists call "bombing out". This low is no joke. The storm system itself has extremely favorable lift for severe weather and winds that are extremely strong. Both are highly supportive of severe weather. This instability continues to rise in the data and as I suggested above, I still think it could go higher. To be honest, I am concerned.

To me, this storm system is looking more and more like it could produce a severe weather outbreak in our area. That does NOT mean a March 2nd style event, but it does mean we could see a lot of warnings on Thursday. The type of wind energy and the instability present makes the main threats damaging winds on this system. With that said, isolated tornadoes absolutely can and do occur in these conditions. In fact, the NAM is showing a very solid chance of rotating storms called "supercells" on Thursday. Notice the large orange area over our region on Thursday indicating rotating storms are a good possibility.
The latest runs from AdvanceTrak show a line of strong and severe storms moving through late Thursday. You can also see there are some "renegade" storms ahead of the line and if that occurs, these tend to be the storms that can quickly produce tornadoes. Notice the timestamp on the top right part of each image.





It is worth noting again that the main threat in this kind of a setup is damaging winds, but isolated tornadoes cannot be ruled out. Based on the latest data, I do not think a slight risk of severe weather is enough for our area and I feel we should be upgraded to a moderate risk. The intensity of the severe weather threat will be highly dependent on how much instability we see. Monitoring the amount of instability in the coming days for Thursday will be key and I will be watching closely. As it stands now, I think an outbreak of severe weather is on the table.

Tuesday 18 February 2014

Severe Weather Threat Outlook

Severe Weather Threat Outlook 
(Central and Southern Plains, Mid to Lower MS, TN, Ohio Valleys, and portions of the Gulf States through Friday)

Good Tuesday afternoon to everyone. discussion of the upcoming severe weather threat across the Mid to Lower MS Valley into the Tennessee/Lower Ohio Valley and portions of the Gulf States. There is a major warm-up on the way and it is current on-going across the mid section of the country with the pattern shift bringing the warmer air inland. The consequences are reluctant to spawn up some strong to severe thunderstorms beginning on Wednesday evening in the Southern Plains and then advancing as a powerful cold front with linear convection ahead of the front for Thursday afternoon and evening.

A very strong low pressure center will bring some very strong pressure gradient in the form of some powerful, gusty winds just above the surface across the Central Plains and then pulling warm, moist, unstable air from the Gulf of Mexico into the Southeast, Mid to Lower MS Valley and into the Lower Ohio Valley. These ingredients will set the stage up for the severe weather.

Strong storms are in the forecast for mainly Wednesday evening the beginning of the three-day event with Kansas and Missouri getting into action first. Mainly damaging winds will be threat, nothing more. Thursday begins the height of the actual threat. By the graphics, you can see where the main line of severe storms will fire and the main threat being damaging winds in excess of 70 miles per hour or greater, and along comes embedded tornadoes along the linear convection with some large hail possible as well. 

Friday, this system is expected to weaken gradually as it pushes eastward into the Eastern Seaboard of Florida to the Southern Mid-Atlantic. Damaging winds is the strong indication of the main threat. We should be done and over with this threat by dusk on Friday. 
The set-up ingredients for the severe weather is like this. The Northern Jet Stream is retreating Northward into the Southern Canada, as it does so, warm, moist, and unstable Gulf of Mexico air will begin to emerge Northward ahead of the frontal boundary beginning tomorrow afternoon and evening ahead of the strong cold front moving across the Mid-section of the country and advancing eastward. The low pressure center will continue to amplify and strengthen as it pulls Northeast into the Upper Great Lakes for Thursday afternoon and evening. Placing a higher, elevated risk for severe weather.
Thursday Thunderstorm Outlook including a marginal threat of strong storms, and the indicator of severe.
Closer view of the cities including in the Severe Weather threat for Thursday indicates pretty substantial area of high-dense population. The threats including damaging, straight-line winds of 70 miles per hour or greater. Large hail. Heavy rainfall with localized flooding, and a few embedded tornadoes in the strongest cells.
Dew point temperatures and the Energy Helicity are both in the favor category for a good substantial event especially across Northeastern LA, Southwestern MS, and into most of the Tennessee Valley. We can't occlude the Ohio Valley with this potential risk factor for severe storms as well.


Weekend rain to bring rising streams

Weekend rain to bring rising streams

by KGW Meteorologist Rod Hill
Follow: @kgwrodhill
Updated Friday, Feb 14 at 11:47 AM

Steady rainfall took a break Friday, but will return Saturday. The heaviest weekend rain will fall Sunday evening and night. 

The National Weather Service has issued a Flood Watch from the coast to the Cascades. Large rivers, such as the Willamette and Clackamas, are expected to rise an average of 3 to 5 feet through Monday, but remain below flood stage. 

The Willamette river at Salem will likely rise to near bankful Sunday night, while the Willamette at Portland is forecast to rise to near 11 feet, well below the flood stage of 18 feet. 

Smaller streams draining out of the Coast Range should be watched closely. Current projections show the Wilson River at Tillamook to rise within 2 feet of flood stage. Please be alert for areas of high water, especially Saturday and Sunday nights.

The above satellite photo shows a stream of moisture aimed at the Northwest. Combined with Portland rainfall from Thursday night, totals through Monday morning could reach 2 to 3 inches, which would be the heaviest rain since more than 3 inches fell in the last three days of September.

Possible rain totals from Thursday through Monday could reach 2 to 4 inches at the coast, 4 to 6 inches over the Coast Range, 2 to 3 inches across the metro valley and 4 to 7 inches over the Cascades. 

Current forecast models show long enough dry breaks between periods of steady rain to reduce the risk of any widespread flooding. However, motorists should be aware of likely high water spots, especially at night, and small streams should be closely watched.

Monday 17 February 2014


An impressive satellite view over the airmass spectrum this evening where a deep trough axis expanded far south into NW Africa. It is behaving as an upper low which will translate towards the northern Mediterranean in the next days, bringing more heavy rain as well as Saharan dust over parts of south-central Europe!

Source: EUMETSAT

                   AWESOME 

Watch a Live Feed of an Asteroid Fly-By Tonight

Watch a Live Feed of an Asteroid Fly-By Tonight

Asteroid Blue FI
by  on FEBRUARY 17, 2014
An asteroid three times the size of a football field will fly by earth tonight, and we all get to watch. The skywatching site Slooh, which allows amateur astronomers to remotely utilize robotic telescopes, will be broadcasting the event on their website beginning at 9:00 PM EST. The broadcast will also be available on Space.com.
The asteroid is named 2000 EM26 and is zipping towards our neighborhood at a brisk 27,000 MPH. Luckily, the space rock will miss us by quite a bit, 8.8 lunar distances to be exact. The average lunar distance is 238,000 miles, so 238,000 X 8.8 = we’re fine.
2000 EM26 will sail by Earth just about a year after an asteroid with a 65 foot diameter exploded over the Russian city of Chelyabinsk. Though not a direct impact, the asteroid’s close shave with humanity still managed to cause a few million dollars in damage and injure 1,500 people. More than anything, the event served as an unfortunate reminder of the solar system’s ability to throw devastating death rocks our way at any given moment.
Russian Meteor IN POST
In light of the heightened concern over asteroid impacts, scientists are discussing possible prevention tactics, including blowing up an oncoming asteroid with a nuclear bomb or hauling one into our moon’s orbit where it can’t cause any trouble.
Will you be tuning in to watch 2000 EM26′s fly by this evening? If so we’d love to hear your reactions below.

2 Storms: First this Weekend, Second Next Week

Rain graphic<<<<2 Storms: >>>>Rain graphic




Warm, moist, even humid conditions expected to persist into Friday as a long fetch of sub-tropical moisture (an atmmospheric river) extending to Hawaii pounds far northwestern California into the Pacific Northwest with heavy rains. While this has, and will continue to bring showers to the northern sierra, northern mountains, and quite a bit in the northwestern corner of the state, the valley should remain mostly dry minus a few showers here and there.

A more elongated trough and associated deep low in the Gulf of Alaska will sufficiently stretch out vertically to allow a cold front to slide through northern California through the day Saturday in the far northern reach of the state, and by evening in the Sacramento valley and adjacent regions. 1.1″ precipitable water band slides down the coast with the front, with .9 – 1″ values working their way inland along and ahead of the frontal precipitation band. Vertical motion with the frontal band are looking pretty intense, however somewhat narrow. Nonetheless, I expect the front to slide with with a period of 1 – 3 hours of precipitation for most locales across the lower elevations, with a 3 – 6 hour period in the foothills and mountains north of Tuolumne county, as the front pretty rapidly decays south of the northern San Joaquin valley due to the front loosing lift with increasing distance from the parent low.


Convective wise, if the front were to come in a bit faster, during the late afternoon for instance Saturday or within a couple hours of sunset, some pre-frontal instability may promote some convection ahead of the front. Current timing in the early to mid-evening doesn’t look very favorable for pre-frontal convective action… but sometimes fronts such as these move a bit faster than modeled. If the system was to come in much later, during the early morning hours of Sunday for instance, it would prove much more favorable for convection during the morning and afternoon Sunday in the cold pool. However that’s a little more far-fetched than the faster timing idea. I’ll monitor timing compared to model data as the system nears during the day Saturday in case any changes occur for the better convective wise.

Snow levels will start out around 7000 – 8000ft Saturday afternoon/early evening, then fall off rapidly as colder air mixes out the lingering mid and low-level warmth, allowing snow levels to dip to around 3500 – 4000ft by mid to late-evening with the tail end of the front and any post-frontal showers overnight.

Precipitation amounts from this system won’t be nearly as significant as the last system, however in the mountains widespread amounts of .5 – 1″ are possible in the mountains/foothills/sierra north of Tuolumne county. Orographically favored slopes of Butte, Plumas, Shasta, and Sierra counties could see around 1 – 2″ locally. In the valley, a generally .1 – .3″ are possible from the center of the valley east, with local amounts of up to a half inch along the eastern side where lift is maximized.
4km NAM’s forecast QPF through the weekend. Note some of the precipitation from Butte county north falls from the Friday system, not just the weekend front.

These QPFs will equate to 6 – 12″ of snow in the sierra, with locally higher amounts up to 16″ possible along favored slopes.
4km NAM’s forecast snowfall through the weekend.

850mb winds increase to 30 – 45kts in the central and northern Sacramento valley ahead of the front… some of which could be mixed down to the surface with pre-frontal dynamics/precipitation, perhaps allowing some 35 – 45mph gusts north of Sacramento. From the sierra crest east into western Nevada, 700mb winds of 60 – 70kts could be drove down by strong downward forcing along the east slope of the sierra, where 50 – 70mph winds are possible Saturday afternoon into the evening.
4km NAM’s forecast surface wind gusts for the later afternoon hours of Saturday.

Cooler post-frontal airmass slides overhead Sunday, cooling things down compared to what we’ve experienced most of the week into the upper 50s to low-60s in the valley.

Things remain dry into early next week while the Gulf of Alaskan low reloads, sending another weak, but cold trough south into the western U.S. At the moment, models aren’t in very good agreement with the system, with the ECMWF being a bit wetter than the U.S.’s GFS., however the ECMWF has been trending further inland over the last couple runs, while the GFS has been pretty consistent with trajectory… and the GFS’s trajectory is actually a bit colder than the ECMWF’s. The GEM keeps the trough further north, not generating much precip for us in northern California.

I shall wait for better agreement for next week’s system, and once agreement has been met, as long as the GEM isn’t closest to correct, I’ll have an update out by early next week regarding the trough, as potential for low elevation snow exists.

Portland Radar. NEXRAD Radar.

Weather On The One, Current National Temperatures

Weather.com Radar

Northern Weather