National Weather Service (2024)

Area Forecast Discussion
Issued by NWS Portland, OR

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-- Discussion containing changed information from previous version are highlighted. --075FXUS66 KPQR 261544AFDPQRArea Forecast Discussion UPDATEDNational Weather Service Portland OR844 AM PDT Wed Jun 26 2024...UPDATED, for morning aviation weather..SYNOPSIS...A weak weather system will bring cooler temperaturesand scattered showers to NW Oregon and SW Washington today intoThursday. Best shower chances for inland valleys will betonight. Dry and warmer conditions Friday and Saturday withanother weak weather system bringing lower temperatures andscattered shower chances again late Saturday into Sunday. Mildtemperatures and limited shower chances continue early nextweek.&&n approaching front will bring increasing mid to high level cloudsthis morning with a 50-70% chance for a period of MVFR cigs around15-19Z. Light and variable winds will increase from the southwest 5-8 kts by 15Z. -Batz.SHORT TERM...Wednesday through Tuesday...Satellite data earlyWednesday morning shows an upper trough approaching theWashington and Oregon coasts. Ensemble guidance indicates thistrough will slowly move onshore today into Thursday, with thetrough axis moving onshore late tonight and the associatedsurface front not long behind. Onshore flow will return today asthis system approaches, with many inland locations alreadybeginning to show a wind shift from northerly to southerlywinds. Cooler temperatures expected with this weather systemtoday and tomorrow. Coastal locations are forecast to only reachthe upper 50s to low 60s, and inland valleys are expected toremain in the 70s (both NBM and HREF indicate less than 5%chance of temperatures reaching 80 degrees anywhere in NW Oregonand SW Washington). Showers are also expected today intotomorrow. Pre- frontal showers through this afternoon willmostly be limited to over the ocean and the coast north ofTillamook with an occasional shower possible over the northernCoast Range, Cascades, and NW Washington. CAMs then indicatechances of scattered showers will increase in these areas and assouth as the Salem area this evening into early tomorrowmorning as the trough axis and surface front approach. The bestchances in the Willamette Valley remain along and north of thePortland metro area (30-45%). Precipitation accumulation throughThursday will be limited with these showers, anywhere from atrace to 0.15 inch for inland valleys and a trace to 0.3 inchfor the coast and higher elevations, except for locally up to0.5 inch in the Cascades north of Marion County.Dry and warmer weather returns Friday into Saturday as thetrough moves to our east and upper level flow becomes morezonal. Temperatures are forecast to rise to near to slightlyabove daily normals, hovering within a couple degrees of 80F forinland valleys. NBM indicates a 35-50% probability oftemperatures reaching 80 degrees on Friday and 50-65%probability for the same on Saturday.Weak troughing returns later Saturday into Sunday. This wouldmoderate temperatures back into the 70s for inland valleys and60s for the coast. Ensemble members suggest the potential forthe return of scattered showers, 40-60% for the coast and higherelevations and 15-35% for inland valleys according to the NBM.Again, amounts look very limited at this time. Ensembles showbit more uncertainty in the pattern early next week, though ingeneral the suggested patterns would bring continued mildweather. Temperatures look to remain in the 70s for inlandvalleys with mostly dry conditions, except for the potential forlingering scattered showers Monday. -HEC &&.AVIATION...
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Strong onshore flow across the region this am, withwidespread MVFR (CIGS 1500 to 2500 ft) as marine layer stratusspreads inland. As of 8 am, still holes in the stratus from Portlandarea to Kelso, but that will fill in by 18Z. Stratus will slowlylift to VFR before breaking apart this afternoon.Meanwhile, low pressure offshore will spread a few showers inlandthis am. Better chance of showers later this afternoon along thecoast and inland over the Cascades, with that chance of showers forall areas overnight. Generally, will remain VFR with broken decksfrom 3500 to 6000 ft tonight into Thu am.PDX AND APPROACHES...Onshore flow will dominate weather patterntoday, with mix of low VFR and MVFR CIGS this am into earlyafternoon, then mostly VFR after 21Z. Will maintain VFR tonight, butCIGS likely to reform at 3500 to 4000 ft. Will maintain a smallchance (25% or less) for showers today into the evening, but thatgoes up a bit more tonight. /Rockey
-- End Changed Discussion --&&.MARINE...Weakening low pressure will send a cold front throughthe waters today, supporting scattered rain showers. Northwestwinds will turn southwesterly this morning as the front approachesfrom the west. Winds are expected to remain below 20 kt. Highpressure builds across the waters again for Thursday and Friday,bringing a return of northerlies. Seas remain in the to 4 to 6 ftrange through most of the week as a westerly swell moves acrossthe waters.&&.PQR WATCHES/WARNINGS/ADVISORIES...OR...None.WA...None.PZ...None.&&$$www.weather.gov/portlandInteract with us via social media:www.facebook.com/NWSPortlandwww.twitter.com/NWSPortland