Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
832 FXUS66 KPQR 231029 AFDPQR Area Forecast Discussion National Weather Service Portland OR 329 AM PDT Thu May 23 2024 .SYNOPSIS...Weak high pressure brings a brief period of warmer and sunnier conditions today. Cooler and cloudier conditions quickly return as another trough brings a chance of showers back to the area Friday and Saturday. Medium range models hint at a more sustained period of warmer and drier weather Sunday into early next week. && .SHORT TERM...Now through Saturday Night...Shower activity has mostly ended across the area early this morning as an upper level trough departs east of the Cascades, with a few lingering radar echos noted over the High Cascades in the vicinity of Mt Hood. Otherwise, partial clearing is depicted on satellite imagery in the lee of the Coast Range as drier northwest flow starts to work into the region. Conditions will continue to improve through the day today as a transient shortwave ridge moves overhead, with cloud cover gradually eroding and revealing mostly sunny skies by later this afternoon. Modest height rises and sunny skies will allow for much warmer temperatures than recent days as highs climb into the upper 60s to near 70 across much of the area. The shift to warmer and drier weather will be short lived as the next trough embedded in the large scale northwest flow regime arrives early Friday. This will bring a return of showery weather with cooler and cloudier conditions Friday into the weekend as temperatures trend back down into the upper 50s to low 60s through Saturday. QPF amounts remain fairly modest through the weekend, with guidance generally depicting around a quarter to a half inch of rain in the higher terrain of the Casacdes and Coast Range and lighter amounts of a tenth or two at best in the lowlands from Friday through Saturday. Snow levels may briefly lower to around 4000 feet Friday night into Saturday morning, allowing for a dusting of snow as low as the Cascade passes. Conditions will begin to improve by later Saturday as the trough departs to the east and makes way for the next period of shortwave ridging. /CB .LONG TERM...Sunday through Wednesday...Sunday looks to feature drier conditions and rebounding temperatures as benign zonal flow develops in the wake of the departing trough. WPC ensemble clusters are in reasonably strong agreement on a warming trend continuing into the early part of next week as a stronger ridge builds somewhere between the Great Basin and the Rockies, leaving the Pacific Northwest in warmer and drier southwest flow aloft. Therefore expect temperatures to reach well into the 70s for most area both Monday and Tuesday, with probabilistic guidance depicting a 30-40 percent chance to reach 80 degrees in the Portland area and closer to a 20-30 percent chance over other parts of the Willamette Valley. Guidance remains in reasonable agreement into the middle of next week as most models hint at some semblance of upper level troughing returning to the region, albeit with some differences in timing, strength, and position. In terms of sensible weather, look for increasing shower chances again by Wednesday of next week, with temperature falling back into the 60s. /CB && .AVIATION...VFR conditions generally prevail early this morning with satellite and surface observations indicating continued expansion of a 4-6kft AGL stratus deck across the region. Going forward predominant CIGS will largely fluctuate in this 4-6kft range although high-end MVFR conditions are more likely to materialize along the coast between roughly 14-19z. Current HREF guidance does project around a 30-50% chance for MVFR cigs inland this morning as well, however, these probabilities are likely overdone as the aforementioned stratus deck already in place is currently higher than some of the more pessimistic HREF ensemble members would seem to indicate - ground truth and persistence leans towards VFR CIGS continuing. Still, wouldn`t be surprised if CIGS flirted with a FEW-SCT 3-4kft layer between 14-18z inland. Winds stay fairly light, generally less than 5-10 knots at all sites. PDX AND APPROACHES...VFR conditions are expected to continue through the forecast period. Current stratus deck backbuilding from the Cascades over the terminal area has stayed above 4-5kft so far(as of 9-10z) and should largely remain there before breaking up this afternoon. Would put the probability of MVFR cigs at 20-30% between 14-18z. Winds remain fairly light. -Schuldt && .MARINE...Today the region will see a brief break from the active conditions as a transitory shortwave ridge of high pressure shifts overhead leading to lighter winds, and decreasing seas to 4-5 feet at 8 seconds by the afternoon hours. However, another low pressure system and attendant frontal boundary swings into the region from the NNW Friday and Saturday bringing a return of active weather. Seas build towards to 7 to 9 feet at 8 to 9 seconds on Saturday before subsiding towards 3 to 5 feet on Sunday into early next week. Given the wave heights/periods on Saturday seas will once again be fairly steep. Looking ahead, large scale upper-level flow then turns more W-SW towards the middle of next week with some guidance hinting at yet another weak weather disturbance moving into the region around Wednesday - confidence in timing and impacts remain low at this time. -Schuldt && .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