Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
123 FXUS66 KPQR 261021 AFDPQR Area Forecast Discussion National Weather Service Portland OR 321 AM PDT Wed Jun 26 2024 .SYNOPSIS...A weak weather system will bring cooler temperatures and scattered showers to NW Oregon and SW Washington today into Thursday. Best shower chances for inland valleys will be tonight. Dry and warmer conditions Friday and Saturday with another weak weather system bringing lower temperatures and scattered shower chances again late Saturday into Sunday. Mild temperatures and limited shower chances continue early next week. && .SHORT TERM...Wednesday through Tuesday...Satellite data early Wednesday morning shows an upper trough approaching the Washington and Oregon coasts. Ensemble guidance indicates this trough will slowly move onshore today into Thursday, with the trough axis moving onshore late tonight and the associated surface front not long behind. Onshore flow will return today as this system approaches, with many inland locations already beginning to show a wind shift from northerly to southerly winds. Cooler temperatures expected with this weather system today and tomorrow. Coastal locations are forecast to only reach the upper 50s to low 60s, and inland valleys are expected to remain in the 70s (both NBM and HREF indicate less than 5% chance of temperatures reaching 80 degrees anywhere in NW Oregon and SW Washington). Showers are also expected today into tomorrow. Pre- frontal showers through this afternoon will mostly be limited to over the ocean and the coast north of Tillamook with an occasional shower possible over the northern Coast Range, Cascades, and NW Washington. CAMs then indicate chances of scattered showers will increase in these areas and as south as the Salem area this evening into early tomorrow morning as the trough axis and surface front approach. The best chances in the Willamette Valley remain along and north of the Portland metro area (30-45%). Precipitation accumulation through Thursday will be limited with these showers, anywhere from a trace to 0.15 inch for inland valleys and a trace to 0.3 inch for the coast and higher elevations, except for locally up to 0.5 inch in the Cascades north of Marion County. Dry and warmer weather returns Friday into Saturday as the trough moves to our east and upper level flow becomes more zonal. Temperatures are forecast to rise to near to slightly above daily normals, hovering within a couple degrees of 80F for inland valleys. NBM indicates a 35-50% probability of temperatures reaching 80 degrees on Friday and 50-65% probability for the same on Saturday. Weak troughing returns later Saturday into Sunday. This would moderate temperatures back into the 70s for inland valleys and 60s for the coast. Ensemble members suggest the potential for the return of scattered showers, 40-60% for the coast and higher elevations and 15-35% for inland valleys according to the NBM. Again, amounts look very limited at this time. Ensembles show bit more uncertainty in the pattern early next week, though in general the suggested patterns would bring continued mild weather. Temperatures look to remain in the 70s for inland valleys with mostly dry conditions, except for the potential for lingering scattered showers Monday. -HEC && .AVIATION...An upper level trough moving inland across the PNW will support increasing southwest, onshore flow at the surface. Marine stratus in place along the coast is trying to push inland through the gaps in the Coast Range. MVFR/IFR CIGs are impacting the KONP and KAST sites respectively and will remain at sub-VFR conditions through much of the day. HREF guidance suggests the best chance (70-90%) for stratus to reach the Willamette Valley is around the Eugene area where MVFR CIGs reach by 12Z. Sporadic MVFR CIGs develop through the Willamette Valley between 15-20Z, fluctuating between 30-70%. Winds remain light and variable through 15Z or so before increasing from the southwest at 10-15 kts. Light rain showers will increase through the day but shouldn`t bring any major impacts to the terminals. PDX AND APPROACHES... An approaching front will bring increasing mid to high level clouds this morning with a 50-70% chance for a period of MVFR cigs around 15-19Z. Light and variable winds will increase from the southwest 5-8 kts by 15Z. -Batz && .MARINE...Weakening low pressure will send a cold front through the waters today, supporting scattered rain showers. Northwest winds will turn southwesterly this morning as the front approaches from the west. Winds are expected to remain below 20 kt. High pressure builds across the waters again for Thursday and Friday, bringing a return of northerlies. Seas remain in the to 4 to 6 ft range through most of the week as a westerly swell moves across the waters. && .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