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  Friday April 11 2014     7 SVR T-STORM WARNINGS Today …

Severe Warnings Issued More Than Three Hours Ago

SVR T-STORM WARNING MEMPHIS TN - KMEG 414 PM CDT FRI APR 11 2014
SVR T-STORM WARNING MEMPHIS TN - KMEG 411 PM CDT FRI APR 11 2014
SVR T-STORM WARNING MEMPHIS TN - KMEG 334 PM CDT FRI APR 11 2014
SVR T-STORM WARNING PADUCAH KY - KPAH 324 PM CDT FRI APR 11 2014
SVR T-STORM WARNING MEMPHIS TN - KMEG 323 PM CDT FRI APR 11 2014
SVR T-STORM WARNING PADUCAH KY - KPAH 244 PM CDT FRI APR 11 2014

SVR T-STORM WARNING SPRINGFIELD MO - KSGF 222 PM CDT FRI APR 11 2014

Active Tuesday, Strong Thunderstorms Possible

Active Tuesday, Strong Thunderstorms Possible

 MARCH 31, 2014

A cold upper low off the northern Californian coast will slowly work southeast along the coast overnight tonight into Tuesday, spiraling bands of convective clouds and precipitation into northern California beginning late tonight into Tuesday morning. Snow levels have already dropped off to 2000 – 3000ft across the sierra, and may flutter down lower at times through Tuesday, especially with convection, which is expected to be widespread.

IR satellite, mosaic radar with precipitation-typing, LSRs, METARs, and MSLP analysis from 8:55pm Monday.

Short range high-resolution models such as the 4km NAM indicate potential for at least partial clearing by mid to late-morning, and indicates pockets of strong surface heating with temperatures rising into the upper 50s to locally low 60s across the Sacramento and northern San Joaquin valley. These surface temperatures would support some very steep low-level lapse rates, with lapse rates remaining steep into the mid-levels given -30 or so 500mb temperatures aloft associated with the upper-level and surface low. Dewpoints are lacking given the pretty cold environment, however there’s enough low-level moisture to promote surface-based CAPE values between 200 – 400 j/kg according to the RAP and 4km NAM, which combined with decent buoyancy via strong diurnal heating would promote a risk of strong thunderstorm development itself.

0z 4km NAM’s forecast MLCAPE valid around 2pm Tuesday, indicating widespread modest values.

Upper jet of 100 – 120kts swings around the low into central California, with weaker upper level winds in northern California Tuesday. However, a band of modest upper-level winds wrapping directly around the low supports a bit of upper-level wind dynamics. Perhaps a bit more important, directional shear will be quite favorable give the low offshore, including locally breezy south surface winds, and westerly to southwesterly mid/upper level winds. Hodographs do show some small clockwise hooks and loops, in coordination with with pockets of 0 – 3km storm relative helicity (SRH) values in the 75 – 150 M2/S2 range… locally higher in favored terrain.

4km NAM’s forecast 0 – 3km SRH and 10-meter wind speed/directional arrows.

NAM’s forecast sounding for the Sacramento area with hodograph, valid Tuesday afternoon for the Sacramento area.

With that said, if clearing does occur in parts of the valley Tuesday morning and afternoon between convective bands, sufficient instability could evolve and support the development of strong enough thunderstorms to work with available shear. Main threats from thunderstorms Tuesday will be hail given the low freezing level, and yet again the threat for funnel clouds or weak brief tornadoes. I currently believe the highest threat appears to be from Stockton north to Redding given lift decreases a bit as you work your way further south.

Another 6 – 12″ of snow may fall Tuesday across the sierra/mountains above 4000ft, with locally upwards of 2 – 4″ between 2500 – 3500ft… locally some accumulation down to 2000ft. In the lower elevations, additional rainfall amounts between a few hundredths and perhaps more than a half inch are possible depending on convective/thunderstorm coverage. Thunderstorms would be rather slow moving (possibly as slow as 5 – 10mph in general) Tuesday, and could drop significant amounts of rain and hail over impacted areas.

Occluded convective band rotates in during the evening, which itself may roll through the valley and mountains with some thunderstorms. Low dives south through the morning hours Wednesday, shunting lift and moisture to our south. Weak trough may bring a round of light precipitation to northern California Thursday night into Friday.

Warming is expected by weekend into next week, with 80s possibly returning to the valley by early next week.

California Drought to end by an El Nino? Just may happen. Read the story.

California Drought to end by an El Nino? 

Just may happen. Read the story.

There are indications that an El Niño is on the way for the middle and latter parts of 2014. 

The phenomenon may impact the weather in portions of the United States, starting this summer. 

Fluctuations in the sea surface temperature over the tropical Pacific Ocean have been observed and recorded for approximately the past 60 years. 

These fluctuations are known as the El Niño Southern Oscillation or ENSO. 

When the waters are cooler than average for a several-month period, the event is called La Niña. 

Opposingly, when the waters are warmer than average over several months, the event is called El Niño.

There are indications that an El Niño is on the way for the middle and latter parts of 2014. 

The phenomenon may impact the weather in portions of the United States, starting this summer. 

Fluctuations in the sea surface temperature over the tropical Pacific Ocean have been observed and recorded for approximately the past 60 years. 

These fluctuations are known as the El Niño Southern Oscillation or ENSO. 

When the waters are cooler than average for a several-month period, the event is called La Niña. 

Opposingly, when the waters are warmer than average over several months, the event is called 

El Niño.

While El Niño will not have an impact on this spring and summer's severe weather, it may come on early enough and strong enough to have impact on the upcoming hurricane season in the Atlantic and Eastern Pacific.

Disruptive winds, known as wind shear, often develop off the Atlantic coast of the United States and sweep over a large part of the basin during El Niño. 

El Niño is generally not a major player in determining the number and strength of storms that originate over the Gulf of Mexico and much of the Caribbean. 

While the number of storms tends to be lower in the Atlantic during an El Niño, it is not uncommon for the Eastern Pacific to have a very active hurricane season. 

An El Niño may also enhance the summer monsoon over the Four Corners region of the Southwest as tropical moisture funnels in from the Eastern Pacific. 

Whether monsoon moisture is enhanced over drought-stricken California is less certain at this time.

However, there is some hope for rain later in the year that could impact the California drought, which has been weighing heavily on ranchers. 

The greatest effects on the weather pattern in the Lower 48 states, including California, occur during the cold season.

As far as impact on next winter, it is too early in the game to make a call one way or another, but some El Niño patterns in the past [1997-98] have produced significant storms in California. 

El Niño winters are noted for wet and stormy conditions in the South and less-frequent, less-severe cold episodes in the Northern states.

The pattern has been known to bring outbreaks of severe weather in the South during the winter. 

There is a tendency toward dry conditions in the Northwest and North Central states during an El Niño winter.

 

Quick Update: Thunderstorms Possible This Afternoon

Quick Update: Thunderstorms Possible This Afternoon

MARCH 30, 2014

It’s been one heck of a week thunderstorm wise, and even today (Sunday), we may not be out of the woods completely.

Cold air aloft combined with mostly sunny conditions across the region will promote moderate to very steep low-level lapse rates, with mid-level lapse rates in the 7 – 7.5c range, which is moderately steep. A bit of lower-level moisture combined with the decent lapse rates will also support surface-based CAPE values to climb into the 100 – 300 j/kg range, locally a bit higher, from around Sacramento north. Shear today isn’t too strong, however winds do veer decently with height, and terrain-enhanced winds in the lower levels may be sufficient for some robust updrafts today, even with limited general upper support.

Mesoscale analysis most-unstable CAPE (fill) and visible satellite in the background, from 10:30am.

Convection allowing high resolution models including the 4km NAM, NSSL WRF, and HRRR indicate showers and possible thunderstorms developing along the west side of the Sacramento valley this afternoon, moving east to northeast through the early evening. HRRR indicates slight potential for some rotating thunderstorms given terrain enhanced shear in the central and northern Sacramento valley.

Modest instability and shear could be sufficient enough to support thunderstorms capable of hail and gusty winds, however if the HRRR is near-correct, cannot rule out a rotating storm or two in the Sacramento valley this afternoon/early evening, generally north of Sacramento with the hotspot highlighted by the HRRR being between Yuba City and Redding.

15z HRRR’s forecast radar reflectivity for around 5pm.

Things decay after around 7 – 8pm ahead of our next, stronger system. I’ll have an update out this evening regarding this system, I just didn’t want to let today’s threat go unposted.

2 Storms: First this Weekend, Second Next Week

<<<<2 Storms: >>>>

First this Weekend, Second Next Week

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.