Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
221 FXUS66 KPQR 270944 AFDPQR Area Forecast Discussion National Weather Service Portland OR 244 AM PDT Thu Jun 27 2024 .SYNOPSIS...Scattered showers continue across NW Oregon and SW Washington through Thursday with another day of below normal temperatures, peaking in the upper 60s to low 70s inland. Temperatures raise to near to above normal Friday into Saturday, back into the 80s inland, before another weak weather system lowers temperatures a few degrees and brings another round of scattered showers, mainly for the coast and higher terrain late Saturday into Monday. Rising temperatures and dry weather returns Tuesday into at least midweek. && .SHORT TERM...Thursday through Saturday...Water vapor satellite imagery as of 2 AM Thursday shows the upper level trough axis has pushed inland, and surface observations indicate the surface front has done the same. Scattered showers did spread inland ahead of the front Wednesday evening, and radar imagery shows showers continuing currently, mainly along the coast and higher terrain with a few showers in down to valley floors around and north of the Portland metro area. A weak shortwave along the back end of the upper trough will allow showers to continue through this afternoon for the mentioned areas and the northern Willamette Valley. Daytime temperatures will be similar to yesterday with inland valleys only peaking in the upper 60s to low 70s and upper 50s to 60s along the coast. Additional rain accumulation will be limited with anywhere from a trace to 0.15 inch, up to 0.25 to 0.5 inch for localized spots in the Cascades north of Santiam Pass that have consistent showers. After the trough moves to the east tonight, upper level flow becomes more zonal Friday into Saturday with a surface thermal trough forming over southern Oregon. This will bring dry and warmer weather to the region. Inland temperatures are expected to rise into the upper 70s to low 80s with mid to upper 60s along the coast. Skies will be mostly sunny Friday, but another approaching upper trough will bring increasing cloud cover across the region Saturday with the return of onshore flow. -HEC .LONG TERM...Sunday through Wednesday...Ensemble guidance is in very good agreement of a weak upper level trough moving through the PacNW Sunday as 100% of the WPC 500mb clusters indicate this pattern. Another round of scattered showers are expected with this trough, though coverage looks to be less expansive than the current trough as the surface forcing looks to be limited. About a 15-30% of showers is forecast along the coast and terrain as orographics will be the main forcing for showers. Temperatures may lower a few degrees back to near normal (mid to upper 70s). Some ensemble members as well as deterministic models indicate the potential for another shortwave on the back end of the trough Monday which would allow shower chances and near normal temperatures to continue. By Tuesday into Wednesday, 85% of the WPC clusters indicate a ridge building over the eastern Pacific with the other 15% indicating zonal flow. Dry weather is expected to return with either of these patterns with temperatures rising back into at least the low 80s. -HEC && .AVIATION...Onshore flow persists through Thursday as an upper level trough axis shifts farther east through the day. Conditions inland will be mainly VFR with a brief period of MVFR CIGs this morning between 15-20Z with CIGs dropping to around 1500-3000 ft. The coast will be trickier with conditions fluctuating between VFR with mid level clouds at 3000-6000 ft and MVFR/IFR (or lower) with clouds below 2000 ft. Scattered light rain showers will continue to plaque the region into Thursday afternoon before tapering off this evening around 3Z. Winds will remain south/southwesterly at 5-10 kts through 18-22Z before turn to the west/northwest late this morning and into the afternoon. PDX AND APPROACHES...VFR deck with main deck at 3000 to 5000 ft to start before CIGS likely drop below 3000 ft Thursday morning around 15-20z. Showers remain largely in the vicinity of the site through the morning before increasing in coverage slightly early Thursday afternoon before drying out by the evening. -Batz && .MARINE...South/southwest flow around 10-15 kts will continue through the morning before turning to the northeast as high pressure offshore will return briefly through early Sat. At same time, will see thermal low pressure over far southwest Oregon into northwest California. As such, will get back into some northerly winds, with gusts 20 kt in afternoons/evenings. Yet another weak low pressure arrives later Sat, with winds flipping back to the west or southwest. Gradients weaker, so winds not expected above 15 kt. Seas stay in the 4 to 6 ft range. && .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