textproduct: Portland

SYNOPSIS

A cool and somewhat unsettled pattern will persist through the weekend as upper-level troughing remains over the Pacific Northwest. Periodic marine pushes will continue to bring morning cloud cover inland, while weak disturbances may produce occasional light precipitation along the coast and at higher terrain. Forecast uncertainty increases into early next week as ensemble solutions are pointing towards a low pressure system bringing precipitation into the region.

DISCUSSION...Today through Thursday

Upper-level troughing remains the dominant feature over the northeast Pacific, maintaining a cool air mass and persistent onshore flow across the region. While cloudier and cooler days remain in the forecast through the weekend, precipitation chances remain low, with most locations staying dry. Temperatures today look to top out in the upper 70s to low 80s across the interior, 60s along the coast and upper 60s to mid 70s for the Cascades.

This broad troughing will remain in place through Saturday, a weak, embedded perturbation within the overall flow could briefly enhance precipitation chances, particularly north of a line from McMinnville and Molalla. Ensemble guidance currently gives a 20-60% chance of total rainfall amounts across these areas of 0.05 inches to 0.20 inches. Any precipitation that develops is expected to be light, with the coast, Coast Range, and Cascade foothills favored for the highest chances. Continued onshore flow will also maintain the potential for morning marine stratus across the interior. By Sunday, the upper-level low shifts eastward of the Cascades and a shortwave ridge builds over the region for the start of the week. This transition will result in daytime highs on Sunday to be a few degrees warmer than Saturday and further warming is expected on Monday with daytime highs in the upper 70s to low 80s across the interior, 60s along the coast and into the 70s for the Cascades.

Looking towards next week, ensemble guidance continues to favor a cooler and potentially wetter pattern, but confidence remains low, even with most models and their ensembles showing some amount of measurable precipitation. While a majority of ensemble members support measurable precipitation across a larger portion of the forecast area, there remains substantial spread in the finer details such as timing, strength, and position of the upper- level trough.

Probabilistic guidance suggests at least 0.01 inches of rain over 48 hours from late Tuesday to late Thursday ranges from 70-90%. As for chances of higher amounts of rain, there is a 45-80% chance for 0.25 inches, 30-65% chance for 0.50 inches, and a 15-45% chance for 1 inch. While this isn't shaping up to be a "fire season ender", the amount of rainfall will at a minimum will be looked upon as favorable by most. Still, while the pattern continues to look favorable for precipitation, it must be pointed out that we are talking about rain on days 4-6 and the forecast will most likely change between now and then. /42~12

AVIATION...Through 12Z Saturday

An upper-level trough extending over the Pacific Northwest will continue to support onshore flow through the TAF period. Current observations as of 11Z Friday show scattered areas of MVFR to LIFR conditions across the airspace. Coastal locations are expected to fill in with IFR/LIFR conditions over the next few hours, with scattered MVFR conditions for inland locations. KEUG, KPDX and KTTD have the highest probability for these MVFR conditions to develop through 15Z Friday, with KTTD already showing MVFR conditions at this time. Any lowered flight conditions are expected to improve towards VFR by 17Z-19Z Friday for inland locations and 18Z-21Z Friday for coastal locations. North to northwest winds will build to 5-10 kt inland and 8-12 kt along the coast by midday Friday. Could see some gusts along the coast (KONP) and inland (KHIO and KSLE) up to 20 kt between 20Z Friday through 06Z Saturday.

Persistent onshore flow, will bring a return of MVFR to LIFR conditions to the coast starting around 06Z-08Z Saturday, with MVFR conditions expected to return to KEUG, KTTD and KPDX after 12Z Saturday.

KPDX AND APPROACHES...VFR conditions expected to persist, with a 45-60%, for MVFR cigs developing around 13Z-15Z Friday with backbuilding clouds developing. Flight conditions expected to improve to VFR around 16Z-18Z Friday and remain until MVFR conditions could return after 12Z Saturday. Northwest winds to 5-8 kt by Friday afternoon. /42

MARINE

Broad troughing continues in across the NE Pacific bringing north-northwesterly winds today. Winds are expected to remain around 10-15 kt or less. A weak front drops into the northern coastal waters late tonight into Saturday with little to no impact expected. Northerlies persist through the weekend while predominately wind driven seas remain at around 3 to 5 ft. The pattern may become a bit more active as a broad upper level trough approaches the region towards the start of next week and is followed by an Alaskan Low moving southeast from the Gulf of Alaska into the Pac NW. This second system could bring low end Gale Force gusts across our waters by the middle of next week as well as result in seas building towards 10 ft. /42-DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...None.