Area Forecast Discussion
Issued by NWS Portland, OR

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000 FXUS66 KPQR 021208 AFDPQR Area Forecast Discussion National Weather Service Portland OR 318 AM PST Tue Mar 2 2021 .SYNOPSIS...Mild and mainly dry Spring-like weather will hold through early Thursday before a series of storm system bring a return to valley rain and mountain snow late in the week into next weekend. && .SHORT TERM...Today through Thursday...Water vapor satellite imagery early this morning reveals an upper level low pressure digging southward off the California coast and cutting off from the mean jet stream currently plowing into British Columbia. This has left a dying front more or less stalled along our north coast. Weak onshore flow should continue to allow marine clouds tied to this dying front to expand inland this morning before gradually scattering out this afternoon. Surface observations and the KRTX and KLGX radars have detected few, if any, precipitation returns overnight and do not see a big reason that will change today so kept PoPs below mentionable thresholds. A low amplitude shortwave trough currently centered near the Aleutian Islands will dig southeastward into the eastern Pacific over the coming days. This will result in shortwave ridging transitioning across the Pacific Northwest and amplifying over the Rocky Mountain states through Thursday. This will leave the region under a quiet weather regime with high temperatures gradually climbing from the mid 50s today to the low 60s by Thursday. As the aforementioned shortwave trough approaches the region, the next front and accompanying band of rain will most likely reach the coast Thursday afternoon per the latest ensemble guidance. Strong southerly flow tied to the front will minimize orographic precipitation. In fact, NBM guidance suggests just a 40-50% chance that one inch of rain will fall in the Willapa Hills and our wetter points in the north Oregon Coast Range Thursday afternoon through early Friday despite this atmospheric river likely falling into the low end moderate category per the GEFS and EPS. As a result, hydrology concerns remain relatively low for most of the region. Nonetheless, will need to watch the Grays River, particularly considering how responsive it was less than a week ago and there is still some snow lingering in the upper elevations of the basin per NOHRSC. Theoretically, the past couple of days and next several days of dry weather will allow some of the rain this coming Thursday to soak in vs. runoff as efficiently as it did last week, but how much so, remains quite uncertain. Despite 50-70 kt 925-850mb southerly winds developing offshore ahead of the front late Thursday, modeled pressure gradients appear unfavorable to result in these stronger winds surfacing along most, if not all, of our coastline. As a result, we may be able to scrape by without any wind headlines Thursday. /Neuman .LONG TERM...Thursday night through Monday...Models and their ensembles are in good agreement the aforementioned front and attendant band of rain will slowly shift eastward into the rest of northwest Oregon and southwest Washington Thursday night into Friday. This will result in temperatures returning closer to average with off and on light valley rain expected Friday. Snow levels will generally be above the Cascades passes to begin, but should lower below the passes some time late Friday or Saturday. However, the bulk of the precipitation will likely be over at that point so winter travel impacts will be quite a bit more limited than our most recent storm cycle. Model and ensemble guidance suggests a series of colder storm systems dropping southeastward out of the Gulf of Alaska appear likely to impact the Pacific Northwest late in the weekend into early next week. Timing and details remain uncertain, but most model and ensemble guidance suggests temperatures will drop back below average, at least a couple bouts of valley rain and more significant mountain snow will move through the Pacific Northwest late in the weekend into early next week. /Neuman && .AVIATION...Remnants of a dying front with MVFR to IFR cigs on the north Oregon and south WA coast. Clouds expected to lift and dissipate around midday today. Up the lower Columbia river to KPDX poses a more challenging forecast. Will it be VFR or MVFR this morning. There is enough model support to say yes with weak lift in the lower levels and enough moisture to form the lower cigs. But the observed onshore flow is weak, would like to see KAST-KPDX near 2 mb, it is near zero. But that is not the tell all for determining cigs reaching KPDX and vicinity. For now, with moderate confidence, think cigs will develop around 1500-3000 ft from 15-19Z. For the remainder of the interior should remain VFR today with patchy fog for a few hours this morning, best TAF locations for fog would be KHIO and KEUG. For detailed regional Pac NW aviation weather information, go online to: https://weather.gov/zse KPDX AND APPROACHES...VFR to start the TAF forecast, but there is enough guidance showing MVFR cigs 1500-3000 ft for a few hours this morning what does form should dissipate around 19Z for a return to VFR. Surface winds should remain light today. /mh && .MARINE...Winds will trend more northwest today as high pressure builds in from the west. Seas still holding at 10 to 12 ft today through this evening. Not much change into Wed, as winds stay relatively benign with weak pressure gradients. But, it is still March, a month of transitions. As such, transition is Thursday, as a strong but slow moving cold front approaches. Moderate to high potential for strong southerly gales, along with seas building back to 17 to 22 ft. A Gale Watch will likely be needed in the next 24 hours. Winds and seas will drop back a bit on Fri, but unsettled weather continues into the coming weekend. Still though some models variations, but various models are in better agreement then 24 to 48 hours ago. /mh && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory until midnight PST tonight for coastal waters from Cape Shoalwater WA to Florence OR out 60 NM. Small Craft Advisory until midnight PST tonight for Columbia River Bar. && $$ Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland

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