Area Forecast Discussion
Issued by NWS Portland, OR

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000 FXUS66 KPQR 080511 AAA AFDPQR Area Forecast Discussion...UPDATED National Weather Service Portland OR 911 PM PST Sun Mar 7 2021 Updated aviation discussion. .SYNOPSIS...Low pressure dropping south offshore will keep a threat of showers over the region through the early part of the week. Upper level high pressure is expected to bring drier weather for Wednesday through early Friday, and possibly extend into the weekend. && .SHORT TERM...Tonight through Wednesday...Radar and surface observations continued to show scattered showers across the area early Sunday afternoon. Water vapor pictures showed a shortwave that grazed the northwest part of the forecast area this morning, lifting north through western Washington. The primary upper low was still centered out near 49N 138W, slowly moving south. As we lose daytime heating, models continue to indicate air mass rapidly stabilizing this evening across the region, with the focus of shower activity shifting back offshore closer to the main upper trough. This will lead to showers ending this evening, with the resulting low level stable atmosphere conducive to some patchy fog development late tonight into Monday morning. An increasingly southerly upper level flow as the offshore low pressure system continues to drift south will ultimately lead to a return of deeper moisture Monday and Tuesday. A few weak shortwaves will likely lift north through the forecast area in that time period leading to chances for showers, but with the best energy associated with the upper low directed to the south, the best chances for showers will tend to remain across the south part of the forecast area. Models soundings continue to hint at some minimal CAPE values both days, but this appears to marginal at best, and so will continue to omit any chances for thunder. Tuesday night into Wednesday models show the closed low consolidating and headed south to off the north California coast. The loss of the southerly influx of moisture will tend to diminish pops, with the primary threat of showers by Wednesday shifting to the Cascades as a result of some wrap around moisture and instability on the north side of the low. .LONG TERM...Wednesday night through Sunday...GEFS 500 mb clusters supported by EC operational and ensemble mean clearly signaling an upper ridge over the Pacific Northwest from Wednesday night through Friday, for a period of dry and seasonably mild weather. A majority of these members suggest the dry weather continuing into Saturday, but enough of the cluster members showing a breakdown of the ridge to need to include some low chances for rain by Saturday. By Sunday model solutions diverge considerably, with enough members showing some form of a trough to modestly increase chances for rain for the end of the weekend. && .AVIATION...Shower all but gone at 05Z with radar showing isolated showers over the Cascades and coast range. VFR conditions prevailing with mid and high level clouds. Tonight would be a good night for fog development with a cool air mass, recent rains and stabilizing air mass. But with mid and high clouds overhead radiational cooling will be limited. However there are gaps in the cloud cover currently over the north OR coast and coast range into sw WA. Satellite trends and HREF model cloud cover show this persisting through the night, so may see some IFR fog develop in these areas. But for the remainder of the area the cloud cover should remain thick enough to limit fog considerably. For detailed regional Pac NW aviation weather information, go online to: https://weather.gov/zse KPDX AND APPROACHES...Expect VFR overnight into Monday. As long as the mid and high level clouds remain as forecast, fog threat will be low. But if clouds become thin enough may see some fog or low stratus. && .MARINE...Tonight into Monday marks the last period of active weather over the waters for much of the next week. A weak low pressure and associated cold front are moving inland this afternoon bringing gusty winds, showers, small hail and increased wind waves. Winds are generally 15 to 20 kt with gusts to 25 kt, but with showers, observing gusts to 30 kt in some locations. The general background swell is around 10 to 13 ft but will rise to 16 to 18 ft at 16 seconds through the overnight hours. Most model guidance is showing 18 ft really being the maximum combined wave heights but there is a chance that the top 10% could reach 20 ft or so. These seas will ease as fast as they rise and should reach 10 to 12 ft at 14 seconds by Monday afternoon. Into next week, more settled weather expected with little influencing systems approaching. Seas will remain 9 to 11 ft at 13 seconds Tuesday through Wednesday then ease even further on Wednesday. -Muessle && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory until 4 AM PST Tuesday for coastal waters from Cape Shoalwater WA to Florence OR out 60 NM. Small Craft Advisory until 4 PM PST Monday for Columbia River Bar. && $$ Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland

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