Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
266 FXUS66 KPQR 210952 AFDPQR Area Forecast Discussion National Weather Service Portland OR 252 AM PDT Fri Jun 21 2024 .SYNOPSIS...High pressure will maintain above normal temperatures for inland areas through Saturday. Moderate heat risk expected from Portland to Salem. More seasonable temperatures return Sunday into early next week as onshore flow strengthens and chances for morning cloud cover increase. Conditions will remain mostly dry through Tuesday aside from areas of drizzle Saturday night into Sunday morning for the coast, west slopes of the Coast Range, and Cascade foothills. Precipitation chances increase across northwest OR and southwest WA Wednesday into Thursday as an upper level trough moves inland, which will also bring relatively cooler temperatures. && .DISCUSSION...Friday through Thursday night...High pressure continues to build overhead Friday, which will remain the dominate weather feature over the next couple of days. With little change to the weather pattern and 850 mb temps today, expect high temps very similar to what was observed yesterday (upper 80s to lower 90s across the interior lowlands, mid 60s to lower 70s at the coast). Still expecting temps to be a few degrees cooler on Saturday as onshore flow strengthens slightly and 850 mb temps decrease, but still rather hot with highs well into the 80s. As such, HeatRisk remains in the moderate category from Portland to Salem and for the Columbia River Gorge and Upper Hood River Valley. While high temps in the lower 90s in mid to late June isn`t hot enough to warrant a Heat Advisory, those extremely sensitive to heat could suffer from heat exhaustion or heat stroke if exposed to the heat for long enough, especially in direct sunlight. Be sure to stay hydrated and for those who must work outside, plan on frequent breaks during the afternoon hours. Conditions begin to change Saturday night into Sunday morning as low-level onshore flow strengthens and a weak upper level shortwave deepens the marine layer to 1-1.5 km according to NAM/GFS soundings. This will help spread cloud cover inland Sunday morning, which should limit high temps to the 70s despite afternoon sunshine. Cannot completely rule out highs in the lower 80s if morning cloud cover scatters out fast enough (5-15% chance over the Willamette Valley and Portland metro according to the NBM). Although conditions should remain dry over the interior lowlands, it still appears areas of drizzle will impact the coast, western slopes of the Coast Range, Willapa Hills, and south WA/north OR Cascade foothills Saturday night into Sunday morning due to the deepening marine layer, moist westerly upslope flow at low levels, and lift associated with the upper level shortwave. NBM PoPs seem a bit too low in the aforementioned areas given the pattern in place and the latest ensemble guidance for QPF. Therefore decided to increase PoPs a bit in these areas by nudging towards CONSShort, ensuring there is a mention of drizzle in the forecast. Dry and seasonable on Monday before temps trend a bit warmer again on Tuesday. This is in response to another ridge of high pressure amplifying overhead. However, this ridge looks to be transient as the next upper level trough will be approaching from the northeast Pacific. This trough will bring the return of cooler temps and precip chances late in the week. However, confidence is low in regards to the exact timing and exact rain amounts as there is currently a large degree of model spread for QPF. Nevertheless, the NBM is showing a 10-40% chance for 24-hr rain amounts in excess of 0.25" from 5pm Wednesday through 5pm Thursday (highest chance in the mountains, lowest chance in the Willamette Valley). -TK && .AVIATION...VFR prevailing except along the coast where IFR/LIFR cigs persist. Surface high pressure offshore will maintain onshore flow, but with a subsidence the coastal stratus not expected to make it past the coastal mountains. The coastal stratus is expected to dissipate around 16-19Z Fri in the KAST-KTMK area. But towards KONP, IFR conditions likely (50-80% chance) last through 20Z Fri. Chances for IFR decrease to around 30-50% chance after 20Z Fri. Otherwise, northwesterly winds will pick up along the coast up to 10-15 kt by 18Z Friday, with gusts up to 20 kt more prominent at KONP. PDX AND APPROACHES...VFR with nearly clear skies throughout the TAF period. Northwest winds increasing to around 8-10 kt this afternoon and evening. /mh && .MARINE...High pressure offshore is expected to persist through the week. Northerly winds around 15-20 kt will continue today, strongest offshore beyond 10 NM. Expect periods of winds gusting up to 25 kt early this morning. As such, will maintain the Small Craft Advisory for the outer coastal waters through 8 AM Friday. Seas around 4 to 6 feet will generally be wind driven through the week. A weak front is expected to approach the coastal waters Saturday, weakening the high pressure. Winds will likely become more onshore and ease to below 15 kt. The front will also bring an increasing westerly swell, though seas are only likely to build up to 8 ft on Sunday. High pressure gradually rebuilds early next week. /mh && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory until 8 AM PDT Friday for PZZ271>273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland