Unsettled Pattern Through Thursday

Unsettled Pattern Through Thursday

 MARCH 2, 2014

A moist zonal flow will take hold of our weather through Thursday, with several embedded shortwaves traveling along the moist westerly flow. The first is pushing through today (Sunday), with a stronger system Monday and another notable system Wednesday into Thursday.

The Monday system will be associated with the nose of a 100kt+ westerly jet nosing into California, which combined with a broad sub-tropical moisture plume (PWAT values between 1 – 1.4″) and a weak shortwave-trough will support some moderate precipitation across the state from mid to late-morning through the rest of the day. Very good moisture and bands of decent vertical motion should be enough to dump .25 – .5″ of rain across much of the lower elevations, with .5 – 1.5″ of rain in the foothills and mountains, and 2 – 3″ in orographically favored slopes/mountains in the northern sierra/foothills and coastal mountains. Locally breezy winds are also possible Monday as a band of 20 – 35kt 850mb winds pushes through… especially from Sacramento north to Redding. No significant winds are expected, more likely just some 20 – 25mph gusts, and in an extreme case an isolated 30mph gust.

700mb vertical velocities and 500mb heights valid for Monday afternoon. Warm colors indicate upward motions.

Showers linger into into the overnight hours of Monday into early Tuesday, drying out for the late morning and afternoon. A weak cold front slides through late Tuesday, which for the most part may bring some scattered showers. No significant precipitation is expected from this system.

For the most part, Wednesday morning and afternoon should be dry, however another system slams into the Pacific Northwest by afternoon, and may spread some rain over the far northern mountains by the afternoon. By evening, this system’s front slides through northern California. This system could drop another .25 – .5″ of rain Wednesday evening through Thursday in the valley, with .5 – 1″ in the foothills and mountains… possibly up to 2″ in orographically favored regions. A deep low off the OR/WA coast (~985mb) could send a band of moderate-strength mid-level winds in the valley Wednesday evening, perhaps enough combined with precipitation to drive down some 20 – 30mph gusts in the northern and central Sacramento valley.

4km NAM’s forecast QPF through Wednesday. Does not include the Thursday system, which would add another .25 – 1.5″ to these amounts (more in the higher elevations).

Drought wise, while these few systems will dump some additional much-needed precipitation atop recent storms, we are, and will remain in a rather severe drought, and still need a broad 10″ swath of precipitation across the lower elevations of northern California, with much more in the mountains (more than double that). These recent storms have added many feet of additional water to reservoirs across the state, and add several feet of sierra snow of which will melt and bring reservoirs up further this spring during the melt. Even after that, reservoirs will remain well below normal, and water conservation will be especially needed to reduce the risk of major shortages.

Right now it appears strong ridging returns to the state by this coming weekend, and may remain dominant through at least mid-month with perhaps a weak storm here and there. Temperatures in the 70s will become more common in inland lower elevations over the coming weeks given the sun has been slowly staying up longer and longer.

There is a bit of potential for convection with Wednesday’s/Thursday’s system, but it’s a couple days out and things could change. If this potential still appears possible Tuesday or Wednesday, I’ll put out another post regarding that potential. Otherwise, if convection looks limited, this post should cover most of the action this week.