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Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
664 FXUS66 KPQR 290933 AFDPQR Area Forecast Discussion National Weather Service Portland OR 233 AM PDT Sat Jun 29 2024 .SYNOPSIS...Aside from some light drizzle across the northern portions of the CWA late Saturday into Sunday, onshore flow will maintain near average temperatures into early next week. There is 40-60% 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...Saturday through Monday...Satellite data early Saturday morning shows mid to high level clouds pushing into NW Oregon and SW Washington as a broad upper level trough approaches the coast. Latest guidance now shows two distinct shortwaves pulsing through the PacNW with this trough, one later this afternoon or evening and the second tomorrow. These features will produce a 15-20% chance of light drizzle or rain showers at times this afternoon through tomorrow morning, mainly along the coast and Coast Range north of a line extending between Mt Jefferson and Newport as well as the Cascades into central Oregon. There`s not much cold air aloft with this system, so temperatures this weekend into early next week will remain right around normal for this time of year, even on Monday as the upper trough moves to the east. This equates to upper 70s to right around 80 degrees for inland valleys and 60s along the coast. -HEC .LONG TERM...Tuesday through Friday...WPC 500 mb cluster analysis remains in very good agreement of upper level ridging building over the Eastern Pacific early next week with generally zonal flow over NW Oregon into SW Washington, leading to little change in the forecast for Tuesday. Uncertainty in the forecast begins to grow dramatically midweek as ensemble members begin to diverge substantially on potential scenarios. While nearly all of the ensemble guidance has above average 500mb heights over the Pacific Northwest by Thursday, about 25% of the ensemble guidance suggests an upper level trough will either be approaching the region from the northwest or a different shortwave trough will be lingering across the northern Rockies to keep temperatures across the area near average. The rest suggest a pattern conducive for above normal temperatures but with varying degrees of heat. Latest NBM probabilities have risen for temperatures reaching 90F across inland valleys with a 40-60% on Thursday and 60-75% on Friday. Probabilities for reaching 100F on Friday have also risen to 30-45% for inland valleys. The NBM deterministic forecast is on the warm side of the probability distribution come next Friday, but not enough to change it so have left the forecast as is. However, it`s important to note that the forecast temperature spread is very wide with mid 80s at the 25th percentile and low 100s for the 75th percentile distributions. -Neuman/HEC && .AVIATION...High pressure continues to shift eastward as a weak upper-level trough approaches from the west and crosses the region late Saturday afternoon into the overnight. VFR conditions will prevail everywhere through 20Z or so when MVFR or lower CIGs move in along the coast as the weak disturbance moves eastward. HREF and MOS guidance suggest low end VFR to high end MVFR CIGs developing inland around 2000-5000 feet after 6Z Saturday night. HREF probabilities within the Willamette Valley are 30-60%, so still some uncertainty but still possible. A few light showers will also be possible Saturday night, mainly along the coast and north of the metro. Light north winds at 5 kts or less will become west/northwest at 10-15 kts today. PDX AND APPROACHES...High pressure shifting eastward will continue to support VFR conditions through most of the day. Winds will be north/northwesterly becoming more westerly at around 10 kts. CIGs will gradually begin to drop as an upper level disturbance passes overhead. VFR conditions are expected to prevail through around 6Z Sunday when MVFR CIGs will be possible (40-70%). -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 front will temporarily try to clip the waters today and turn winds more out of the west. Otherwise, expect north to northwest winds across the waters 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. Pressure gradients appear increasingly likely to increase by early to mid next week so that there is a >90% chance that northerly wind gusts of 20-30 kt spread northward across the waters. 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. /Neuman/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