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Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
757 FXUS66 KPQR 300935 AFDPQR Area Forecast Discussion National Weather Service Portland OR 235 AM PDT Sun Jun 30 2024 .SYNOPSIS...Light shower chances continue across the northern portions of the CWA today. Onshore flow will maintain near average temperatures into early next week. There is 50-60% chance that stronger high pressure offshore will shift over the region towards the end of next week and bring the hottest temperatures of the Summer so far. && .SHORT TERM...Sunday through Tuesday...Upper level trough continues moving over the PacNW today. Scattered showers dissipated by late last night but are expected to return later this morning into the afternoon as surface heating produces enough localized instability. Showers will mainly be located over the Coast Range and Cascades as orographic forcing will be the main lifting mechanism for showers, but a few could meander into the valley. NAM soundings show significantly less instability for today than yesterday, so thunderstorm or heavy shower chances are very limited with today`s scattered showers. As the upper trough moves east Monday into Tuesday, ensemble guidance continues to indicate strong ridging building over the eastern Pacific with lower heights over the PacNW. This will bring dry weather but will keep temperatures stable at right around normal. Expect high temperatures for inland valleys in the upper 70s to low 80s today through Tuesday with 60s along the coast. -HEC .LONG TERM...Wednesday through Saturday...The overall pattern remains the same on Wednesday, according to the WPC 500 mb cluster analysis, though the ridge axis looks to shift slightly east over the Pacific which would allow widespread 80s for inland valleys. Thursday into Saturday remain a little uncertain as ensemble members continue to struggle to handle the specifics of the pattern. However, consensus in the WPC clusters is increasing on either the upper ridge moving over the region or remaining close enough to the region to warm temperatures into the 90s, though the timing of the ridge moving inland remains uncertain. NBM and LREF also agree with this scenario as both indicate around a 50-60% chance of temperatures reaching or exceeding 95F Friday and Saturday for inland valleys, which would be the warmest temperatures of the summer so far. NBM also indicates a 30-40% chance of inland valleys reaching 100F at least one of those days. It still needs to be mentioned that there`s a 5-15% chance of a shortwave trough breaking through the ridge and approaching the region Friday or Saturday, bringing stronger onshore flow and lowering temperatures back to near normal. -HEC && .AVIATION...VFR prevails inland as a weak upper level disturbances tracks across the region. Marine stratus has begun to settle into the coast with a mix of IFR to LIFR cigs/vis already in place a KAST and KONP. These should see gradual improvement through the day Sunday with MVFR to low VFR conditions prevailing come the mid to late afternoon hours. Inland VFR conditions with CIGs around 4000-6000 ft will deteriorate as winds shift west/southwest at low and mid levels to spread marine clouds with MVFR cigs inland roughly after 10-13Z Sun, then gradually improving to VFR after 18-19Z Sun. The HREF projects a 60-80% chance for CIGS at or below 3kft between 12-18z before the aforementioned improvement finally takes place. PDX AND APPROACHES...VFR conditions will begin to deteriorate around 10Z with increasing chances for MVFR cigs 2000-3000 ft to develop. Chances for MVFR peak at around ~70-80% 12-18Z Sun, then rapidly decrease by 18Z Sun for high chances of VFR. -Batz && .MARINE...Weak high pressure over the northeast Pacific with lower surface pressure over California and the Great Basin will more or less maintain itself into next week. A weak area of surface low pressure will pass over the area today, supporting initially southwest winds before turning to the west in its wake. Otherwise, expect north to northwest winds across the waters as high pressure strengthens toward the middle of next week, with the strongest winds generally off the central coast of Oregon and lighter winds farther north. Winds will generally peak in the afternoon and evening hours each day. A thermal low develops along the northern California/southwest Oregon coast on Tuesday and strengthening/spreading north into Wednesday and thereafter. This will increase the pressure gradient along the coast and over the waters with a >90% chance that northerly wind gusts of 20-30 kt spread northward across the waters by mid week. This will in return develop steep wind driven seas of 5-8 ft with a dominant period of 7-8 seconds by late Tuesday or Wednesday. -Batz && .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