FXUS66 KPQR 231758 AFDPQR Area Forecast Discussion National Weather Service Portland OR 1058 AM PDT Wed Oct 23 2024 .UPDATED AVIATION DISCUSSION... && .SYNOPSIS... Generally dry today and tonight through light showers are possible for the Cascades later in the morning, and a few showers at the coast tonight. Friday starts out dry but will be last dry period before a wet pattern returns. Fog chances in low lying valleys most mornings this week with frost possible this morning, becoming more widespread Thursday and Friday mornings. && .SHORT TERM...Now through Thursday night...A mix of high and mid-level clouds streaming across the area this morning. These clouds are associated with a low off the WA/OR coast and a long fetch extending southwest to a low north of Hawaii. Within the mid and high level clouds, a few showers may develop today mainly over the Cascades in Lane county as the upper low just offshore nudges closer. Forcing is weak so PoPs are low, <20%. Ensemble and deterministic guidance is in good agreement that the low should move into Idaho later today with weak ridging building behind it. Clearing skies tonight into Thursday morning and a slightly cooler air mass will allow for more widespread frost Thursday morning for most locations out of populated areas (such as Portland/Vancouver metro, Salem, Eugene, etc.) There is a 60-95% chance of low temperatures falling to at least 36 degrees. The Frost Advisory most of the CWA except for the coast and high Cascades for midnight through 8 AM Thursday looks good. A few locations have the potential to reach Freeze Warning criteria with anywhere from a 40- 90% chance of temperatures falling to 32 degrees in portions of Hood River Valley as well as the southeastern portion of the Willamette Valley south of Corvallis (outside of Salem and Eugene population areas) and adjacent Cascade foothills. The Upper Hood River Valley has forecasted temperatures in the upper 20s to low 30s later tonight into Thursday, so have upgraded the Advisory to a Freeze Warning. Friday should be another frosty morning in the same areas as today. .LONG TERM...Friday through Tuesday...Pattern change begins Friday from from dry, cool weather to a wetter pattern over the weekend into early next week. Snow levels lowering to near or below Cascade passes Monday and Tuesday. Also potentially windy offshore flow Friday across the Gorge and nearby Cascades as high pressure inland impinges against approaching system. Coastal areas too appear has a chance for windy conditions later Friday. WPC 500 mb clusters in good agreement with the progression of an upper level trough over the northeast Pacific, moving into the western CONUS early next week. Deterministic models fill in the details, showing a surface cutoff low currently near 34N 143W lifting to the PacNW later Friday to bring breezy conditions at the coast. There is about a 10% chance for wind gusts to 40 mph reaching the coastline Friday night. Once this goes through the upper trough should slide into the PacNW to bring periods of rain. Saturday night into Sunday looks to be the wettest day with NBM mean 24-hr rain amounts around 0.5" to 1" in the valley and 1" to 1.5" in the mountains. Cooler temperatures are expected behind this frontal system, with snow levels falling to near or below Cascade passes Monday into Tuesday. Snow amounts could potentially reach advisory criteria (6"/12hr) at pass levels Monday. && .AVIATION...Currently observations show a mix of LIFR to MVFR conditions across the northern Willamette Valley into Portland metro area associated with lingering fog and stratus. Conditions will likely improving in the coming hours (18-20z) with higher confidence in widespread VFR cigs/vis this afternoon into the evening hours. It's also worth noting there is a 10-15% chance for pop-up shower activity at most terminals this afternoon - minimal impacts. However, with clearing skies, ample surface moisture, and light winds tonight into sunrise Thursday morning fog formation will be a concern throughout the Willamette Valley - the best chances for fog will be KHIO/KUAO southward and after 10 to 12z. Winds remain fairly light at all sites, generally less than 10 knots through the TAF period. PDX APPROACHES...Lingering stratus likely persists for the next couple of hours with IFR CIGS gradually increasing to MVFR before breaking up ~21z. Otherwise, VFR conditions expected and will likely persist through at least 10Z Thursday. After this point we'll have to watch for degraded conditions due to fog/low stratus however compared to other portions of the region confidence in timing/impacts locally are low at this time. -Schuldt && .MARINE... Surface high pressure will persist across the northeast Pacific and result in relatively light winds and benign seas through early Friday. Northerly winds will strengthen each afternoon and evening, but will generally remain below 20 kt. A surface low pressure is expected to develop over the eastern Pacific and that low is expected push north/northeastward towards Vancouver Island late Friday into early Saturday. This will result in increasing southerly winds and building seas across all waters. Currently there is around a 60%-70% probability for for Gale Force southerly wind gusts during this time. However, there still remains some uncertainty as to the overall timing and location of the low, but models and their ensembles are coming into better agreement when compared to 24 hours ago. While, confidence in the Gale conditions manifesting, the timing remains in flux. As such, will not be issuing a Gale Watch at this time, but if the trends continue, then expect a Gale Watch to be issued in the near future. In addition to the elevated winds, seas will also build towards the low to mid teens by late this week/weekend. Currently, there is only a 5%-10% probability of seas building into the upper teens. A large upper level system will settle across the region over the weekend into early next week. This will bring a return to north/northwesterly winds, which will remain elevated, but will likely not result in Gale Force conditions. Winds and seas will slowly subside, but expect seas to remain in the 9 to 11 ft range through the start of next week. /42 && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Frost Advisory from midnight tonight to 8 AM PDT Thursday for ORZ104>107-109-114>118-123>125. Freeze Warning from midnight tonight to 8 AM PDT Thursday for ORZ121. WA...Frost Advisory from midnight tonight to 8 AM PDT Thursday for WAZ203>205-208. PZ...None. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland