Upper level low is shifting onshore this evening. The freezing level is not all that different from this time yesterday, but temperatures aloft are noticeably colder. Kuil sounding this evening shows 500 millibar temperatures around -37c which is a good 10c colder than 24 hours ago. This colder air aloft explains the occurrence of some small hail and graupel that we`ve seen around the region this afternoon and evening.
Surface gradients are light southerly, but one doesnt have to travel more than a couple thousand feet above the surface to encounter west-southwest flow. This west-southwest flow is producing a convergence zone this evening from near port townsend eastward to snohomish county. Mesoscale models lift the pscz slowly to the northeast overnight before dissipating it over the north cascades early tomorrow morning. Well have to keep an eye on it over the next few hours as convective precip often has a habit of yanking the snow level down a few hundred feet pretty quickly.
Apart from that, there isnt much in the way of organized precipitation over the next 24 hours as the core of the upper low shifts east of the cascades by late tomorrow afternoon. Well finally begin drying out by tomorrow evening with shortwave ridging bringing us a dry but still relatively cool weekend. 27
Wa...none. Pz...small craft advisory until 4 am pst friday for coastal waters from cape flattery to james island 10 to 60 nm-coastal waters from james island to point grenville 10 to 60 nm- coastal waters from point grenville to cape shoalwater 10 to 60 nm.
Upper level low is shifting onshore this evening. The freezing level is not all that different from this time yesterday, but temperatures aloft are noticeably colder. Kuil sounding this evening shows 500 millibar temperatures around -37c which is a good 10c colder than 24 hours ago. This colder air aloft explains the occurrence of some small hail and graupel that we`ve seen around the region this afternoon and evening.
Surface gradients are light southerly, but one doesnt have to travel more than a couple thousand feet above the surface to encounter west-southwest flow. This west-southwest flow is producing a convergence zone this evening from near port townsend eastward to snohomish county. Mesoscale models lift the pscz slowly to the northeast overnight before dissipating it over the north cascades early tomorrow morning. Well have to keep an eye on it over the next few hours as convective precip often has a habit of yanking the snow level down a few hundred feet pretty quickly.
Apart from that, there isnt much in the way of organized precipitation over the next 24 hours as the core of the upper low shifts east of the cascades by late tomorrow afternoon. Well finally begin drying out by tomorrow evening with shortwave ridging bringing us a dry but still relatively cool weekend. 27
/issued 300 pm pst thu mar 7 2019/
Synopsis...a cool upper level low over the area will weaken tonight and shift east of the area on friday. Mostly dry conditions over the weekend with a weak upper level ridge over british columbia and northeasterly flow aloft over western washington. Next front arriving later monday with the trailing upper level trough over the area on tuesday.
Short term /today through saturday/...well...this morning went a long way to display that this winter is like a bad house guest that just will not leave. While current radar shows scattered precip activity over portions of w wa this afternoon...temps around the area are generally in the upper 30s to lower 40s...with a couple of exceptions even climbing into the mid 40s. As such...any activity out there should be in the form of rain...although cooler locations might see a flake or two mixed in...but nothing significant or having any impact.
Looking into tonight...lingering low pressure aloft will keep the risk of scattered showers over the area tonight and into tomorrow. with temperatures cooling off and snow levels falling again...any activity overnight and early friday morning will fall in the form of snow. The difference between friday morning and what we saw this morning is that coverage is expected to remain scattered and not as widespread with pops only in the 30-40 pct range...so little to no impacts or accumulations are expected. Will see activity gradually taper off throughout the day friday as the low continues its slow progress eastward...with models in agreement that it should be game over friday night. Saturday morning looks like another cold start...but the good news is that conditions are expected to be dry. saturday will see upper level ridging and dry nw flow aloft over the area helping to ensure an uneventful weekend.
Temps in the short term will see some gradual increase with a degree or two of warming each day...with lower 40s still present friday but getting into the mid 40s saturday. Overnight lows will offset this though...with low temps staying in the upper 20s to lower 30s. smr
Long term /sunday through wednesday/...dry conditions will persist sunday and into sunday night before the next frontal system makes its approach monday as models starting to agree a bit better on timing...having it reach the far nw tip of the state late monday morning...making its way inland and resulting in more widespread precip by monday night. This system looks to be bringing with it higher snow levels...ranging from just under 2000 to around 3000 feet which would keep any precip as rain...which is welcomed news indeed. The associated upper level trough will keep showers in the forecast into tuesday and fortunately models agree on keeping the system pretty progressive...ejecting by tuesday night with another pacific upper level ridge ready to move into the area for wednesday to bring a return of dry conditions.
Temps in the extended actually look to rise with highs sunday approaching 50 in many lowland locations. Likewise...snow levels throughout this period look to remain above 1000 feet. While all of this seems promising...much the story of this winter has been models agreeing on an optimistic scenario for days 7 and 8 only to yank the rug out from many an unsuspecting forecaster and perpetuating this slog of a winter. Still...with it now being march...one would hope that spring would indeed be on the doorstep...so there is reason for cautious optimism. Although...not helping this argument is that there will not be a whole lot of fluctuation in overnight lows...maybe a little bit of headway into the mid to upper 30s monday night/tuesday morning...but the remaining days look to be ranging in the upper 20s to lower 30s still...so the ritual scraping of frost and preheating the car each morning will likely continue. smr
Aviation...flow aloft will continue to be westerly tonight, then become light and variable friday as an upper level low over vancouver island weakens and moves east. Weak southerly and onshore surface flow this afternoon will become weakly offshore tonight and friday as a low pressure center develops off the coast and moves south. The air mass is moist and slightly unstable, with scattered showers and also sun breaks.
Scattered showers will continue tonight and friday. At times these showers could be snow or mixed rain and snow. Some spots, especially hills, could get snow accumulations of an inch or less, but there should be no widespread snowfall. Ceilings are mvfr and vfr this afternoon, and will remain that way this evening, with a trend toward more mvfr by morning. Vfr ceilings are forecast friday afternoon. Ceilings could briefly fall below 1k ft in showers.
Ksea...discussion above applies. Scattered showers will continue, and at 400 ft elevation ksea is one of the places that could get a dusting of snow tonight or friday morning, especially 09z-15z. southerly wind 7-12 kt. Chb
Marine...a weak low pres center off the north coast will move south tonight and friday, with weak offshore flow developing. Moderate offshore flow will develop over the weekend as a deeper low far to the southwest moves into california. A front will move through the area monday and monday night, with small craft advisory strength winds likely over most waters. These winds will probably extend into tuesday. Westerly swells of 15 ft or so may reach the coast monday and tuesday. Chb
Hydrology...river flooding is not expected for the next 7 days.