Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
339 FXUS66 KPQR 091019 AFDPQR Area Forecast Discussion National Weather Service Portland OR 319 AM PDT Sun Jun 9 2024 .SYNOPSIS...Expect warm and dry conditions inland today with marine stratus along the coast. Cascades will see a 15-30% chance of showers this morning. Warm and mostly dry weather continues through Thursday, but coastal areas could see a 15-30% chance of precipitation on Tuesday. Toward the end of the week, ensemble guidance suggests an overall cooler and wetter pattern. && .SHORT TERM...Today through Monday night...500mb analysis as of 230 AM PDT depicts an upper level shortwave trough beginning to push into the Pacific Northwest, with SW-SSW flow aloft. This shortwave could provide some lift to support isolated showers or thunderstorms over the Cascades early this morning. However, CAMs are suggesting that most shower and thunderstorm activity will remain east of the Cascades. The westerly component to flow aloft will provide an eastward push any showers or thunderstorms that do develop over our Cascades. Thus, the forecast includes low (15-30%) PoPs across the Cascades this morning, along with a low (15-20%) chance for thunderstorms in the Lane County Cascades. As the axis of the shortwave trough moves directly overhead, winds aloft will shift northwesterly and mid-level moisture will exit our area. This should end chances for elevated showers and/or thunderstorms for the west side of the Cascades by mid-morning. Dry, quiet weather continues today. Satellite imagery as of 230 AM PDT shows a marine layer moving toward the coast, so expect low stratus for coastal areas this morning. Model soundings suggest that coastal stratus will linger throughout the day due to a capping inversion and persistent onshore flow. This will maintain mild temperatures along the coast with afternoon highs peaking in the low 60s. Meanwhile, it will be another warm and sunny day for interior valleys with high temps forecast in the upper 70s to low 80s. High pressure will begin to re-build by this afternoon and strengthen into tomorrow (Mon). This will maintain warm temps inland with sunny skies. NBM suggests a 40-60% chance that temps exceed 80 degrees for interior valleys tomorrow. We may see another marine layer along the coast tomorrow morning, but model soundings are suggesting that increased mixing throughout the day will support clear skies at the coast by the afternoon. -Alviz && .LONG TERM...Tuesday through Saturday...WPC cluster analyses are in agreement of 500mb heights remaining above average through Thursday, supporting near to above average temperatures and mostly dry conditions. However, on Tuesday a trough from the Gulf of Alaska will dip south and push into British Columbia. This will flatten the ridge over the Pacific Northwest and lead to a slight cooling trend. In addition, this will support a 15-30% chance for light precipitation over far northwest Oregon and southwest Washington (mainly along the coast). Wednesday, most of the clusters agree on zonal flow and/or slight re-building of a ridge. By Thursday, ensemble members agree on shortwave ridging over the region, supporting drier and warmer conditions. Friday, this ridge begins to shift eastward as another trough near the Gulf of Alaska dips southward toward the Pacific Northwest. By Saturday, most ensemble members (65%) agree on troughing entering the region with below-average 500 mb heights. If this scenario pans out, then we would see increasing chances for widespread precipitation along with potentially below average temperatures. For now, the NBM`s 15-45% chance of PoPs across northwest Oregon and southwest Washington at the end of the week look reasonable. -Alviz && .AVIATION...A weak front will move inland today which will bring MVFR/IFR stratus to the coast, and high level clouds inland. Already starting to see MVFR CIGs north of KTMK, while a bit further south conditions are clear. Over the next few hours, the marine stratus will begin to fill. There is nearly a 90% chance of IFR CIGs along the coast between 12-18Z Sunday. With the strengthening westerly flow, cannot rule out the stratus moving along the Columbia River to near KKLS. There is around a 30% chance of MVFR CIGs there. Otherwise, all other locations will be VFR through the period with stratocumulus. Along the Cascades, winds will be a bit more gusty. Based on the track of the low pressure, precipitation is not likely, however, there is around a 20% chance for thunderstorms right along the ridges of the Willamette National Forest. Late in the forecast, backbuilding is suggested in the models which could bring increased chances for stratus around KTTD and KPDX. However, confidence is low. PDX AND APPROACHES...VFR through the period with high level stratocumulus. After 05Z Monday, winds just off of the surface will be around 15 kt up to 3000 ft AGL. There is a 20% chance of MVFR CIGs between 14-18Z as the marine stratus moves along the Columbia River. Higher likelihood of this stratus would be on the west side of the terminal. -Muessle && .MARINE...The weak front is settling in over the waters. Low level clouds cover will develop which may reduce visibility through the morning at times. Winds will remain elevated around 15 kt with gusts to 20 kt from the northwest through the day. Based on high resolution models, looks like we will remain just below small craft advisory criteria. Seas will remain around 6-9 ft at 15 seconds through Monday morning. High pressure reforms on Monday which will settle both winds and seas. The next period of concern will be on Tuesday into Wednesday. Tuesday will bring yet another front, but this time there is a chance for some precipitation. Wednesday has the potential to bring breezier winds from the north-northwest. Gusts up to 30 kt are possible from Cape Falcon southward. Seas too will build to around 8-9 ft. During periods of strongest winds, cannot rule out seas up to 10 ft. -Muessle && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory until 11 AM PDT this morning for PZZ210. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland