Area Forecast Discussion
Issued by NWS Portland, OR

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000 FXUS66 KPQR 221815 AAA AFDPQR Area Forecast Discussion...UPDATED National Weather Service Portland OR 1115 AM PDT Sun May 22 2022 Updated aviation discussion .SYNOPSIS... Spring has sprung with more seasonable weather expected over the next several days. Continued warming today with a slight chance for rain on Monday. Warming further into midweek with Wednesday likely to see the hottest temperatures of the week. A stronger front expected on Friday. && .SHORT TERM /THROUGH TUESDAY NIGHT/...
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High pressure remains over the region which means one thing...spring is here! Saturday brought near normal temperatures with that trend continuing today. Broad upper level jet ridging is present today with a jet streak over eastern Oregon. This ridge, both at the surface and aloft, expecting little change in the weather between yesterday and today. More consistent northerly winds though possible today, with temperatures only slightly warmer than those experienced on Saturday. One slight difference though will occur late tonight or early on Monday. 500 mb heights and absolute vorticity show a weak shortwave and associated enhanced vorticity max moving southeast over the area early Monday. This shortwave may bring periods of showers to the area, generally north of Salem, OR. However, models have backed off of both PoPs and QPF for this system over the last few runs. For example, the NAM 12Z May 21st run showed rain starting in Portland around Sunday morning, but now the latest output shows chances for precipitation around Monday morning. The shortwave also appears to be tracking further north with a bulk of the cooler air aloft over northern Washington. Because of this trend, any precipitation will likely skirt southwest Washington and stay north of the forecast area. Could still see some cumulus forming to the north and along the Cascades though. One thing that has gained some confidence in regards to this pattern shift is the chances for winds. At the surface, the pressure gradient between the Dalles and Troutdale is around +3 mb on Monday afternoon. This means that we could see some breezier winds through the day, especially in the Columbia River Gorge and Hood River Valley. As this shortwave passes late Monday, a vertically stacked ridge will once again build over the area. Winds will begin to shift to the south in the afternoon which will usher in warmer air from the southwest. This warm air development will form a thermally induced trough over southern Oregon and northern California. As the thermal trough forms, will likely see winds follow the standard pattern of intensifying in the afternoon due to the thermally induced enhanced pressure gradient. But what about temperatures...a thermal trough means it will get warmer right? That`s correct! Still looking at temperatures rising on Tuesday and relative humidity dropping. While temperatures will be warmer than those experienced on Monday (due to less cloud cover), because there is still some slight northwesterly flow, they are not going to be remarkable by any means. -Muessle .LONG TERM...(WEDNESDAY THROUGH SATURDAY NIGHT)... Dry mild weather continues into Thursday. The thermal trough will redevelop through the day which will bring temperatures to the warmest levels for the week. Could see high temperatures in the Willamette Valley in the mid to upper 70s, with the coast closer to 60 degrees. A shift in the pattern though will start on Thursday as clouds will increase along the leading edge of a weakening front. The front will push across the region on Thursday, with some spotty rain possible - mainly pre-frontal showers. But, the big player in the long term arrives late Thursday into Friday. A closed low aloft, stemming from the Gulf of Alaska, will make its way southward extending a negatively tilted trough over the region. This low is wrapped in cooler air from the north and it will be advected over the region. As of late, models have come into better agreement, especially in regards to QPF. The ECMWF has backed off of the storm total QPF while the GFS has increased. Because conditions are ever shifting, not settling on any numbers as of right now, but can say that the Cascades will likely see the most rainfall due to the southwesterly flow and orographic lift. This front is slower moving with a few shortwaves passing over the region sequentially. This means that we could see the precipitation linger through the weekend, but it is too soon to truly tell. -Muessle .LONG TERM /WEDNESDAY THROUGH SATURDAY/...Dry mild weather continues into Thursday. The thermal trough will redevelop through the day which will bring temperatures to the warmest levels for the week. Could see high temperatures in the Willamette Valley in the mid to upper 70s, with the coast closer to 60 degrees. A shift in the pattern though will start on Thursday as clouds will increase along the leading edge of a weakening front. The front will push across the region on Thursday, with some spotty rain possible - mainly pre-frontal showers. But, the big player in the long term arrives late Thursday into Friday. A closed low aloft, stemming from the Gulf of Alaska, will make its way southward extending a negatively tilted trough over the region. This low is wrapped in cooler air from the north and it will be advected over the region. As of late, models have come into better agreement, especially in regards to QPF. The ECMWF has backed off of the storm total QPF while the GFS has increased. Because conditions are ever shifting, not settling on any numbers as of right now, but can say that the Cascades will likely see the most rainfall due to the southwesterly flow and orographic lift. This front is slower moving with a few shortwaves passing over the region sequentially. This means that we could see the precipitation linger through the weekend, but it is too soon to truly tell. -Muessle
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&& .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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Marine stratus has all but eroded away from the coast, leaving VFR conditions across the forecast area. Expect high clouds to increase today as cirrus spreads out in front of a weather system approaching the coast later today. Marine stratus will once again push back in late this afternoon...HREF probs show a roughly 60-70% chance for IFR cigs along the coast after 03Z, improving to low end MVFR after 12z. Further inland, only high clouds today, with ceilings lowering early Monday morning, but remaining VFR. For detailed regional Pac NW aviation weather information, go online to: https://weather.gov/zse KPDX AND APPROACHES...VFR through the period with only high clouds and light winds. /Kriederman
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&& .MARINE...
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Wind will generally diminish to 10 kt or less across the coastal waters today as offshore high pressure shifts closer to the coast and weakens the gradient. Could see some 15 kt gusts in the central waters during the afternoon as the thermal trough continues to reside to the south over northern CA, but do not anticipate conditions approaching small craft headlines at this time. Moderate northerly breezes will return Monday as high pressure becomes re- established offshore. A weak front may clip the waters late Tuesday as an area of low pressure passes well north toward the BC Coast, which could bring about a brief shift to southerly winds Tuesday night. Seas will remain relatively tame through the next several days as a modest 3-5 ft W swell moves through the waters, with little short period contribution given the generally light winds. -CB
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&& .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...None. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland

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