Area Forecast Discussion
Issued by NWS Portland, OR

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000 FXUS66 KPQR 070439 AAB AFDPQR Area Forecast Discussion...UPDATED National Weather Service Portland OR 938 PM PDT Thu May 6 2021 Updated Aviation and Marine discussions .UPDATE...Made a few adjustments to the forecast this evening, mainly to take out the mention of thunder for most of our inland areas tonight into Friday morning. Without any lightning to speak of being detected within the cold pool, it is tough to justify much lightning at all in our forecast, especially inland during the coolest hours of the night and morning. Based on 18z NAM and GFS, the core of cold air aloft and thus the greatest instability appears to be headed for the Olympic Peninsula and Puget Sound. Will maintain the mention of thunder for portions of SW Washington and the eastern PDX metro Friday afternoon, as diurnal surface heating should provide the best chances although the coldest air aloft will already be crossing the Cascades at that point. Weagle && .SYNOPSIS...Today`s cold front will move east of the Cascades by mid-evening. Low pressure and another cold front cross the region Friday to bring additional showers and possible thunderstorms. High pressure starts to build beginning Saturday, but another very weak front will cross the region Sunday for a final round of potential showers. The upper high then builds in earnest Monday through at least Wednesday for dry weather and bringing temperatures near to, and slightly above, normal. && .SHORT TERM...Tonight through Sunday...No significant surprises as the anticipated cold front is currently aligned with roughly I-5. Showers and breezy winds accompanied the front and will see this boundary continue to push eastward this afternoon and evening. There is a very narrow secondary boundary trailing just along the coast now, also moving east. It has shown brief moments of convective enhancement and would not be surprised to see a one hit wonder bit of lightning come out of it. This would easily be the exception rather than the rule. Broad low pressure over the NE Pac will drift across the PacNW tonight and Friday bringing cooling temperatures aloft. As the trough axis nears the coast late tonight and Friday, may get enough dynamic enhancement to produce a better chance of thunderstorms mainly north of a Tillamook to Salem line, including the Portland Metro. Am not super enthused about these chances as implied by the NBM as equilibrium levels stay somewhat limited in depth, but also do not have strong reasons to go against the calibrated guidance either. As such, will keep the suggested thunderstorm mention in the forecast for our northern areas through early Friday evening. Snow levels will also drop to around 3500 feet later tonight with a couple inches of snow possible under a heavier shower. The upper trough departs late Friday as an upper ridge tries to assert it`s influence through Sunday. However, weak shortwaves cross from the northwest to southeast to hold it at bay and also bring modest rain chances but generally minimal qpf amounts. Temperatures through this weekend will be on the cooler side of normal. /JBonk .LONG TERM...Sunday night through Thursday...Currently not much debate between the operational models and their supporting ensemble casts. They all agree on high pressure progressing east from off the Pacific, though they differ in the details on the strength of the ridging. Regardless, next week`s temperatures will start on the cooler side of normal to then build to a few degrees on the warmer side of normal. Also would expect repeating periods of afternoon and evening onshore sea breezes to work through the Coast Range for pseudo-summer diurnal wind patterns. /JBonk && .AVIATION...
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Post-frontal showers now mainly over the Cascades and offshore. VFR conditions prevailing, but Cascades will likely remain mostly obscured as westerly flow continues through Friday. Next batch of more organized showers will arrive to the coast 06-09Z and likely bring occasional MVFR conditions with heavier showers. These showers spread inland overnight as well but expect primarily VFR conditions. There is a slight chance for thunderstorms for the north Oregon coast and south WA coast later tonight through Fri afternoon, and a slight chance for thunderstorms inland Fri afternoon and north of about KUAO. Showers decrease Fri evening as high pressure briefly builds into the region. Wind westerly generally 10 kt or less but gustier winds towards the east end of the Gorge this evening. For detailed regional Pac NW aviation weather information, go online to: https://weather.gov/zse KPDX AND APPROACHES...VFR with cigs 4000-7000 ft expected. Will see with showers increasing after 09Z, then a slight chance for thunderstorms after 18Z. Showers tapering off Fri evening as high pressure builds into the region. Westerly winds expected to prevail tonight but generally below 10 kt, winds pickup a little Fri later morning to around 10-13 kt and may gust to 15-20 kt briefly Fri afternoon.
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&& .MARINE...
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Winds easing over the waters this evening, but will pick up some overnight as the next batch of showers move in. But do not expect winds to reach advisory criteria. However steep waves have not quite gone away. Buoy 46243 off the Columbia River mouth around 7 feet at 7 seconds so will have an advisory for that. Seas remain 6 to 8 ft with a dominate period of near 10 seconds through Friday then slowly falling into the 4 to 6 ft through the weekend. /42
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&& .PQR WATCHES/WARNINGS/ADVISORIES...
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OR...None. WA...None. PZ...Small Craft Advisory until 2 AM PDT Friday for coastal waters from Cape Shoalwater WA to Florence OR out 60 NM.
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