Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
950 FXUS66 KPQR 161023 AFDPQR Area Forecast Discussion National Weather Service Portland OR 323 AM PDT Sun Jun 16 2024 .SYNOPSIS...Low pressure maintains cool and showery conditions today, with a chance of thunderstorms across much of the area this afternoon and evening. A few showers linger into Monday then much warmer and drier weather returns Tuesday through the end of next week. && .SHORT TERM...Now through Monday Night...An elongated upper level trough has shifted southward from British Columbia to Washington and remains the dominant feature over the Pacific Northwest this morning. Latest satellite imagery shows broken cloud cover lingering across northwest Oregon and southwest Washington, with a lull in shower activity as radar echos are mainly confined to northern coastal areas and parts of the Cascades as of 2 AM Sunday. Expect a similar day to Saturday as unseasonably cold air aloft yields another day of highs topping out in the mid 60s. Shower activity will increase in coverage with daytime heating as the trough axis shifts southeast across the area, with steep mid level lapse rates and modest instability again contributing to a chance of thunderstorms. The best thunderstorm potential will reside from roughly Salem north through early evening, but can`t rule out a few lightning strikes with southward extent towards Eugene as well. Shower activity will trend downward through Monday with temperatures remaining in the 60s as northwest flow takes hold in the wake of the departing trough. Showers will remain light and mostly be confined to the higher terrain through Monday afternoon, then wind down through Monday night and set the stage for the next stretch of warmer and drier weather beginning Tuesday. /CB .LONG TERM...Tuesday through Saturday...More summerlike weather returns to the region on Tuesday as WPC ensemble clusters continue to show broad agreement on the weakening of the trough over the western CONUS and subsequent increasing 500 mb heights across the Pacific Northwest. This will send temps back above seasonal norms as highs climb into the mid to upper 70s across the interior lowlands on Tuesday afternoon. Wednesday through Friday looks to be the hottest stretch for the coming week as most ensemble and deterministic solutions continue to depict a weak Rex Block characterized by a low amplitude ridge over western Canada and an open trough over northern California. Ensemble temperature spreads have nudged slightly upward for the latter half of the week, with probabilistic guidance now peaking with around a 50 percent chance to reach 90 degrees in the Portland area on Thursday and a 25-35 percent chance both Wednesday and Friday. Notably, the probability to reach 95 degrees on any of these days is less than 10 percent from Portland to Salem and closer to one percent in other locations, serving to underscore the relatively high confidence in the range of temperature outcomes for the coming week. The bulk of the guidance then suggests that temperatures will begin to trend back down next weekend with the approach of another trough. /CB && .AVIATION...A weak front is currently in the process of moving ashore, and the next few hours (before 19z Sun) will see around a 15-30% chance of intermittent MVFR ceilings at all terminals, but this will be very patchy and ceilings will bounce between low-end VFR and MVFR during this time. Some intermittent fog can`t be ruled out before the front fully pushes ashore, and could produce around a 20% chance of IFR visibilities at times before 15z Sunday. However, threat is low, and exact area of fog formation will be difficult to predict. Afterwards, with increasing precipitation and daylight heating kicking in soon after, threat of fog ends by 15z. Low chance for some weak thunderstorms at times after around 18z Sun as instability develops due to post frontal conditions. Daytime hours Sunday could see around a 25% chance of thunderstorms at time, which could potentially produce hail and brief gusty winds. Threat ends by 03z Mon. PDX AND APPROACHES...10% chance of fog developing within the next few hours, possibly reducing conditions to IFR briefly. However, a frontal passage around 15z ends threat of fog. A few showers associated with frontal passage begin at that time, allowing for a 15-30% chance of intermittent MVFR ceilings before 20z Sun or so. Afterwards, around a 25% chance of weak scattered thunderstorms are possible once daylight heating begins, ending around 03z Sun. /JLiu && .MARINE...Seas around 5 to 7 ft at 9 to 11 seconds for the near future. Winds are currently negligible, but will increase following the frontal passage up to just under Small Craft Advisory level Sunday evening. A stray gust or two above SCA criteria may be possible Sunday night, but by and large the majority of waters will remain under, with only a 10% chance of SCA level winds. Next chance at more impactful conditions will be Tuesday night, though uncertainty is still relatively high. Marginal SCA winds look possible from Tuesday evening onwards, with breezier marginal winds possible until at least the weekend. /JLiu && .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