Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
446 FXUS66 KPQR 180441 AAA AFDPQR Area Forecast Discussion...UPDATED National Weather Service Portland OR 941 PM PDT Tue Sep 17 2024 Updated short term and aviation discussions. .SYNOPSIS...A weak frontal system will continue to bring clouds, cool temps, and light rain showers overnight. Dry weather returns Wednesday through Friday with onshore flow and slightly below normal temps. Rain potential returns this weekend, but confidence is low in the overall pattern. && .SHORT TERM...Now through Thursday Night...Radar is showing the showers moving through the area but are currently concentrated more to the southern portions of the forecast area. Satellite shows a weak meso-low along the coast, with the main low pressure system (that is the weather maker) sits right over the OR/CA border. Expect light rain showers to gradually move over the area through the night. Precipitation amounts are forecast to be very light as models suggest the track of the upper trough will be slightly offshore and moving southward, minimizing rainfall amounts across northwest Oregon and southwest Washington. The highest forecast amounts are are around 0.10-0.40 inch, generally south of a line from Tillamook to Oakridge. Northward, expect less than 0.10 inch of rain. Winds will also be from the south/southwest, with the strongest gusts (25-30 mph) through the central Columbia River Gorge and over the Cascade crest. Tonight into tomorrow (Wednesday), the upper level trough will exit our area and continue moving into California. High pressure will re-build as a positively-tilted ridge noses into the region from the Pacific. Winds will gradually weaken and shift back to a north/northwest direction. Expect decreasing PoPs and a return to dry conditions. Will also see decreasing cloud cover overnight, so some locations could see patchy fog development given the moist conditions and calm winds. HREF currently suggests spotty chances (10-30%) of visibility falling below 1/2 mile for locations east of the Cascades. Otherwise, expect a mostly sunny day tomorrow with high temperatures rebounding to the low to mid 70s for interior lowland valleys and mid 60s along the coast. Thursday remains benign as high pressure lingers, with continued onshore flow and similar high temperatures as Wednesday. -Muessle/Alviz .LONG TERM...Friday through Tuesday... Friday through Tuesday...Friday looks to be another warm and pleasant September day characterized by increasing onshore flow as a positively tilted ridge axis slowly shifts south of the region. Expect temperatures slightly below seasonal norms with inland highs in the low 70s. Forecast confidence remains below normal this weekend into the early part of next week as model solutions continue to diverge significantly with regard to how the upper level pattern will evolve beyond Friday. Ensemble clusters remain just about evenly split in depicting ridging, troughing, and zonal flow regimes over the Pacific Northwest from Saturday through Monday. This obviously will have large implications for the forecast as anything ranging from warm and dry weather to a cooler and wetter pattern remains on the table for days 5-7. This continues to be reflected in the NBM interquartile ranges for temperatures which range anywhere from the upper 60s to the upper 70s between the 25th and 75th percentile guidance. As such, and until models begin to converge on a solution, have opted to stick with the NBM mean which splits the difference between these solutions and depicts broad- brushed chance to slight chance PoPs over the area late this weekend through early next week. -CB && .AVIATION...An upper level low over the Oregon coast will drop south tonight toward the northern CA coast, resulting in southeast flow aloft shifting to the northeast by Wednesday morning. Light rain will gradually dissipate this evening, with widespread MVFR stratus settling in across the area, with higher chances of IFR along the central Oregon coast. Probability of conditions improving to VFR increase late Wednesday morning to early afternoon around 18-20z. Winds become light and variable overnight, becoming northwest by Wed afternoon. PDX APPROACHES...Light rain should dissipate by 06z while MVFR stratus expected to settle in with CIGs around 1500 ft through late Wed morning. Expect conditions to improve to VFR after 18-19z Wed. Winds becoming light and variable overnight, before becoming northwest 6-8 kt by Wed afternoon. -DH && .MARINE... A weather system drops down from British Columbia tonight into Wednesday. However by the time it reaches the waters, it will elongate and weaken. Winds have shifted southerly as the front nears. Peak wind gusts up to 15 kt along the coastal waters will relax tonight as the system falls apart. There is a slight chance for thunderstorms tonight primarily over the outer zones. Northerly winds return Wednesday as high pressure rebuilds offshore. Winds may gust 20 to 25 kt at times, primarily over the outer zones. Seas around 4 to 6 ft today and tonight, increasing to around 8 ft later Wednesday into Thursday, then settling to around 5 ft late in the week. -Hall/mh && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...None. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland