119 FXUS66 KPQR 231734 AAB AFDPQR Area Forecast Discussion...UPDATED National Weather Service Portland OR 933 AM PST Sun Feb 23 2020 Updates to the short term, aviation and marine discussions. .SYNOPSIS...A pacific front will bring breezy conditions, valley rain and mountain snow to the region today. Large waves will bring increasingly hazardous surf conditions to the beaches this afternoon and tonight. High pressure will then return to the West Coast of the US and result in cool nights, mild days, and mainly dry weather this upcoming work week. && .SHORT TERM...Today through Wednesday...Satellite imagery early this morning shows a rather impressive ~990mb low pressure moving eastward between Vancouver Island and Haida Gwaii. This front brought considerable rainfall to much of the forecast area with accumulations upwards of a quarter of an inch. With significant lift and convection along the leading edge of the front, conditions quite gusty, especially along higher terrain like Mt. Hood. Behind the cold front there will be a brief lull in the wet weather and even an hour or two of sunshine is likely. With clearing skies and daytime heating, instability will increase so cannot rule out a thunderstorm or two across the northern zones and northern waters. This instability will gradually deepen through the day so expect showers to spread eastward across the area this afternoon. Brief heavy rain and small hail will likely accompany the most intense showers. With the coldest temperatures aloft remaining over Washington today, expect showers this afternoon to be more numerous and more intense across our northern zones when compared to our southern zones. Snow levels around 4000-5000 ft range will begin to drop into the 2000-3000 ft range later this afternoon and evening behind the cold front. Thus, the main winter weather impacts at the Cascade passes will likely hold off until late this morning/midday. Snowfall amounts in the Cascades do not appear overly impressive with this storm system and will likely be marginal for an advisory at pass level. Nonetheless, the rapidly falling snow levels this afternoon and evening will likely enable to snow to stick rapidly under any heavier or more persistent showers. Models remain in good agreement that a shortwave ridge will build over the eastern Pacific and Pacific Northwest tonight and Mon. This will result in decreasing showers with most of the area drying out entirely by Mon afternoon or evening. As is common with a ridge building in behind a front, there is a chance of late night and morning valley fog on Tue giving way to mostly sunny skies. Models suggest that this ridge will flatten Tue afternoon as a shortwave trough advances towards the area. While weak, it could bring precipitation to the area but in a high PoP, low QPF format. NBM guidance has struggled to capture these type of events on several occasions over the past year so opted to trend PoPs a bit higher than NBM guidance across our northwestern zones Tue evening into Tue night. Ridging will again build over the area Wed. -Neuman/Muessle .LONG TERM...Wednesday night through Sunday...Models and their ensembles are in good agreement shortwave ridging will be the dominant feature over the Pacific Northwest Wednesday night through Friday. This will bring predominantly dry conditions, morning valley fog in spots and mild temperatures. In fact, temperatures appear likely to top out in the upper 50s to low 60s next Thursday and Friday. Models and their ensembles suggest a more active weather pattern will try to take hold next weekend as a shortwave trough slides into the ridge. However, there are still substantial differences in how this will play out among the models with some scenarios keeping us dry through the weekend while many others result in valley rain and high mountain snow next weekend. NBM PoPs were maintained as it seems to capture the uncertainty well. /Neuman && .AVIATION...Radar is showing the front has crossed the middle of the CWA and is continuing to move southeast at a good pace. MVFR conditions ahead of the front is still being observed in central and southern valley sites. The front is expected to be fully out of the area by 19Z. VFR conditions in the post-frontal air mass is already being met in KAST with inland sites not too far behind. An MVFR-VFR mix should be expected for a couple of hours between 18-20Z. Pockets of rain showers will continue through the morning as the unstable air mass moves across the area. LLWS has been reported across the area as well as moderate to severe turbulence. There is an increased chance of thunderstorm activity mainly to the north coast and southwest WA near the Columbia River. Gusty westerly winds along the coast and gusty southwesterly winds inland will continue until around 02Z Mon. VFR conditions will continue through the afternoon and into this evening. KPDX AND APPROACHES...VFR conditions prevailing through the day. South to southwest winds will continue to produce gusts around 30 kt through 00Z Mon. LLWS as well as moderate to severe turbulence has been reported over KPDX as the front moves through. These conditions should diminish through the afternoon. -BPhillips && .MARINE...Gale force winds looking likely today for the waters north of Cascade Head. Coastal and buoy obs at 3 am showing south wind gusts to 33 kt. Wind should switch to west then northwest this morning after the cold front moves through but winds will continue to gust to 35 kt into the early evening. This a all brought about by a deep low heading to Vancouver Island with the associated front trailing into the WA & OR waters. Swell generation occurring not too far offshore is producing a fresh swell that will move into the waters this afternoon. Expect seas to peak around 18 to 23 ft late this afternoon. The higher waves will be over the northern zones. Spectral wave guides for buoy-29 are indicating seas will reach 22 ft at 14 sec around 4 pm and fall below 20 ft around 10 pm tonight. Winds and seas will drop through Monday reaching sub-SCA criteria by Monday night. /mh -BPhillips && .PQR WATCHES/WARNINGS/ADVISORIES... OR...High Surf Advisory from 1 PM this afternoon to midnight PST tonight for North Oregon Coast. Winter Weather Advisory until 10 PM PST this evening for Northern Oregon Cascades. WA...High Surf Advisory from 1 PM this afternoon to midnight PST tonight for South Washington Coast. Winter Weather Advisory until 10 PM PST this evening for South Washington Cascades. PZ...Gale Warning until 6 PM PST this evening for coastal waters from Cape Shoalwater WA to Cascade Head OR out 60 NM. Small Craft Advisory until 10 AM PST Monday for coastal waters from Cascade Head OR to Florence OR out 60 NM. Small Craft Advisory until 6 AM PST Monday for Columbia River Bar. && $$ Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland This discussion is for Northwest oregon and Southwest Washington from the Cascade crest to 60 nm offshore. This area is commonly referred to as the forecast area.
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