Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
438 FXUS66 KPQR 292152 AFDPQR Area Forecast Discussion National Weather Service Portland OR 252 PM PDT Sun Sep 29 2024 .SYNOPSIS...Westerly flow aloft will maintain dry weather with variable clouds today. High pressure will build inland over Pac NW tonight into Monday, with light offshore flow with bit warmer temperatures for Monday and Tuesday. Mild and dry weather continue to end of the week, but does appear cooler wet weather returns next weekend. && .SHORT TERM...(Today through Tuesday)...A weak trough continues to pass through, creating slightly cooler and more moist conditions throughout today. Temperatures show only a 20-30% chance of exceeding 70 in the Willamette Valley today. This pattern won`t last long, as ridging begins to build in tonight going into Monday. Temps gradually warm Monday and Tuesday, with Tuesday seeings temperatures in the upper 70s for most areas. RH values will also be drier, with daytime minimum RHs around 20-30%. Winds will shift more northeasterly beginning late tonight into Monday morning as the thermal trough redevelops at the coast, with breezy easterly gusts at times through the Columbia Gorge and Cascades channels aligned east to west. Gusts at those locations may get up to 25 mph on Monday afternoon. In the Willamette Valley, northerly winds may produce gusts up to 20 mph Monday afternoon. On Tuesday, flow gradually becomes onshore again as the thermal trough returns east of the Cascades. High pressure will build into western Washington later today and tonight, and remain in that position for next few days. At the same time, will see thermal low pressure along the south Oregon coast that will strengthen and build north along the Oregon coast. While this will turn our flow more lightly offshore, with bit warmer conditions for Monday and again Tuesday. Winds not likely to be all that strong, with mostly 10-20 mph for more east-wind prone areas such as the mid/lower slopes of the Cascades, western Columbia Gorge into far east Portland/Vancouver metro, and over the Coast Range for Monday into early Tuesday. But, as is often the case during this time of the year, main effects of such patterns is more noticeable during the overnight hours. That is for drier conditions overnight, with milder temperatures and lower humidity in the windy areas. In areas where winds are light (ie, those sheltered from offshore winds), temperatures will drop into the upper 30s to middle 40s. But, in area where wind stays up, overnight temperatures likely to remain in the 50s. Ahhh, fall weather, with cool nights and warm afternoons, or in other words: great pumpkin patch weather. .LONG TERM...(Wednesday through Saturday)...Wednesday to Thursday, the majority of ensemble members from WPC cluster analyses show a ridging/zonal flow pattern with above average 500 mb heights. In this case, we would continue to experience warm and dry fall weather. Increasing agreement on troughing returning next Thursday night into Friday morning, with some better potential for cooler and showery weather for next weekend. Precipitation still looks fairly light, and temperatures will likely return to around 70. /Batz/Liu .AVIATION...Upper ridge building offshore with dry northwest flow over the region. Low level onshore flow from the north Oregon coast into Washington bringing some cumulus with BASES around 4000-5000 ft, generally north and west of KPDX-KUAO. VFR expected to prevail inland through 00Z Tue at TAF sites. Coastal areas also expected to remain VFR but patchy fog or low stratus may develop overnight. Winds north to northwest in the inland valleys with gust 10 to 25 kt through this evening, strongest wind toward the KEUG area. && .MARINE...High pressure centered offshore gradually strengthens as it pushes northeast toward the Washington coast this weekend. Pressure gradients begin to strengthen tonight with gusts up to 20-25 kt possible for the waters south of Cascade Head through Monday. Overall, breezy northerly winds this week as the thermal trough strengthens along the Oregon coast. However pressure gradients weaken Tuesday as a weak front pushes through the high pressure. This front associated with a low pressure moving into the Gulf of Alaska Monday, Tuesday. Also with this system, a developing northwesterly swell will likely push seas up again over 10-15 ft across the coastal waters beginning late Tuesday and into Wednesday. /mh && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory from 5 AM to 8 PM PDT Monday for PZZ252. Small Craft Advisory until 8 PM PDT Monday for PZZ253. Small Craft Advisory from 5 AM Monday to 3 AM PDT Tuesday for PZZ272. Small Craft Advisory until 3 AM PDT Tuesday for PZZ273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland