Area Forecast Discussion
Issued by NWS Portland, OR

Current Version |  Previous Version |  Graphics & Text |  Print | Product List |  Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
792 FXUS66 KPQR 212351 AAA AFDPQR Area Forecast Discussion...UPDATED National Weather Service Portland OR 451 PM PDT Fri Jun 21 2024 Updated short term discussion. .SYNOPSIS...
-- Changed Discussion --
High pressure maintains above normal temperatures for inland areas on Saturday with widespread heat still present. Temperatures though will be a few degrees cooler than what we saw today. More seasonable temperatures return Sunday into Monday as onshore flow strengthens and chances for morning cloud cover increase. Conditions will remain mostly dry through Tuesday aside from areas of light rain and drizzle Saturday night into Sunday morning for the coast, west slopes of the Coast Range, and Cascade foothills. The eastern Portland metro may see a little light rain as well, but confidence is low. Our next precipitation chances return to northwest OR and southwest WA Wednesday into Thursday as an upper level trough moves inland, which will also bring relatively cooler temperatures yet again.
-- End Changed Discussion --
&& .SHORT TERM...
-- Changed Discussion --
TONIGHT THROUGH TUESDAY...Through the weekend into next week the large scale upper-level pattern stays fairly progressive overall beginning with the gradual departure of a high pressure ridge tonight into Saturday. As a result conditions will start to change by Saturday afternoon as westerly flow near the surface becomes more prominent and high temperatures decrease several degrees compared to today(Friday), although the mid to upper 80s projected inland is still roughly ~10 degrees above normal for mid-June. Come Saturday night into Sunday morning low-level onshore flow strengthens further and a weak upper level shortwave passing into western Washington deepens the marine layer to 1-1.5 km according to deterministic NAM/GFS soundings. This will help spread cloud cover inland by Sunday morning, which should limit high temps to the 70s despite afternoon sunshine - a welcome change. Still cannot completely rule out highs reaching into the lower 80s Sunday afternoon if the westerly push is weaker than expected and morning cloud cover rapidly scatters. There`s a 5-20% chance to meet or exceed 80 degrees over portions of the the Willamette Valley and Portland metro according to the NBM. Although conditions should remain mostly dry over the interior lowlands, it still appears areas of drizzle and/or light rain 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. We`ll also need to watch for light precipitation extending towards I-5 in western Clackamas County early Sunday morning as well due to models like the GFS, NAM, and HREF indicating an area of converging surface-925mb winds which would locally enhance upward lift and thus provide better forcing for drizzle/light rain. The latest NBM PoPs still appear a bit too low across portions of western OR/WA given the aforementioned set-up, especially when guidance like the EPS and HREF are significantly more bullish for light QPF by comparison. Decided to increase PoPs to better match the model consensus during this Saturday night through Sunday morning time period. Dry and seasonable on Monday before temps trend a warmer again on Tuesday. This is in response to another transitory ridge of high pressure amplifying and moving overhead. Tuesday afternoon temperatures likely push into the mid 80s across the inland valleys although there is an outside chance(15-35%) Salem up to the Portland/Vancouver metro could touch 90 degrees again. At least these probabilities are a little lower than previous runs on the NBM and the overall spread of temperatures for Tuesday afternoon has tightened indicating increased confidence in the current forecast. However, it still appears likely we`ll see a cooler and wetter pattern return later next week bringing a swift end to any early to mid week warm-up. -Schuldt .LONG TERM...WEDNESDAY THROUGH FRIDAY...00z Fri WPC Cluster analysis reveals high confidence in a shortwave trough moving in near the end of the workweek, but uncertainty regarding the exact timing still exists. 80%+ confidence in the shortwave trough arriving by Thursday at the latest. Rainfall rates look fairly mild; around a 30% chance of rainfall exceeding 0.25" each day from Wednesday onwards (24-hr periods), decreasing to 10% in the Willamette Valley. Temperatures show a 75% chance of being below 75 degrees on Thursday and Friday, though Wednesday sees slightly more uncertainty due to uncertainty in the timing of the trough arriving. -JLiu
-- End Changed Discussion --
&& .AVIATION...
-- Changed Discussion --
VFR prevailing except along the coast where IFR/LIFR marine stratus lingers. Northwesterly winds persist along the coast with gusts up to 20 kt. Generally north winds across the airspace for inland locations. 35-45% probability of IFR/LIFR marine stratus returning to the coast starting around 03Z Saturday, which will likely develop into a mixture of MVFR/IFR conditions around 12Z Saturday. Temperatures will remain elevated through Saturday so cannot rule out low level eddies forming along the runways and other dark surfaces. PDX AND APPROACHES...VFR with mostly clear skies. Northerly winds around 8-10 kt. -42
-- End Changed Discussion --
&& .MARINE...
-- Changed Discussion --
High pressure offshore remains anchored over the region through early Saturday. A weak front is expected to approach the coastal waters Saturday afternoon, which will weaken the aforementioned high pressure. This will result in onshore flow developing with northwesterly winds around 10-15 kt with gusts up to 20 kt. General seas through Saturday around 4 to 6 ft, but the weak front will also bring an increasing westerly swell. As a result seas are only likely to build toward 5 to 8 ft ft on Sunday. High pressure gradually return for the stat of next week. -42
-- End Changed Discussion --
&& .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