Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
075 FXUS66 KPQR 261544 AFDPQR Area Forecast Discussion UPDATED National Weather Service Portland OR 844 AM PDT Wed Jun 26 2024 ...UPDATED, for morning aviation weather. .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. && n 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 .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...Strong onshore flow across the region this am, with widespread MVFR (CIGS 1500 to 2500 ft) as marine layer stratus spreads inland. As of 8 am, still holes in the stratus from Portland area to Kelso, but that will fill in by 18Z. Stratus will slowly lift to VFR before breaking apart this afternoon. Meanwhile, low pressure offshore will spread a few showers inland this am. Better chance of showers later this afternoon along the coast and inland over the Cascades, with that chance of showers for all areas overnight. Generally, will remain VFR with broken decks from 3500 to 6000 ft tonight into Thu am. PDX AND APPROACHES...Onshore flow will dominate weather pattern today, with mix of low VFR and MVFR CIGS this am into early afternoon, then mostly VFR after 21Z. Will maintain VFR tonight, but CIGS likely to reform at 3500 to 4000 ft. Will maintain a small chance (25% or less) for showers today into the evening, but that goes up a bit more tonight. /Rockey && .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