textproduct: Portland

SYNOPSIS

A weak shortwave trough will continue to bring increased cloud cover and slightly cooler temperatures today. Temperatures rebound on Monday and Tuesday as high pressure re- builds, with the warmest temperatures on Tuesday. Precipitation chances return on Wednesday as a trough approaches the West Coast. Another trough from the Gulf of Alaska will maintain precipitation chances and a trend toward cooler temperatures by the end of next week.

DISCUSSION...Today through Saturday

Satellite imagery as of early Saturday afternoon depicts scattered low stratus and a band of mid to high level clouds moving over northwest Oregon and southwest Washington as a shortwave trough brushes the Pacific Northwest. Don't expect any precipitation with this shortwave since most of the moisture is directed toward British Columbia while we remain in a drier airmass. Given the increased cloud cover today, temperatures will be a few degrees cooler than yesterday but remain near or slightly above seasonal normals across interior valleys. Afternoon highs are forecast in the upper 60s to low 70s for interior valleys and upper 50s to low 60s along the coast.

Monday to Tuesday, deterministic and ensemble guidance remain in agreement with upper-level ridging re-building over the Pacific Northwest. We'll see a return of sunny skies while dry weather prevails. There is high confidence that temperatures across interior valleys will re-bound into the upper 70s to low 80s on Monday. Tuesday is looking to be the hottest day of the week with afternoon highs forecast in the mid 80s to near 90. There is currently a 30-50% chance that high temperatures exceed 90 degrees on Tuesday across the Portland/Vancouver Metro Area. The rest of the Willamette Valley, southwest Washington lowlands, Columbia River Gorge, and Upper Hood River Valley have a 5-10% chance of exceeding 90 degrees. If KPDX (Portland Airport) ends up at or above 90 degrees, this would tie or break the daily record of 90 degrees which was set in 2023. Given the warmer forecast temperatures on Tuesday, there is now Moderate HeatRisk across the Portland/Vancouver Metro Area, Cowlitz Valley, and Columbia River Gorge. Those who are sensitive to heat will be affected, especially those without cooling and hydration.

The next chances for precipitation return on Wednesday as the next trough approaches the West Coast. The majority (78%) of ensemble members show this trough tracking south of our area and becoming a closed low towards Northern California. As a result, chances for precipitation are 15-25% west of the Cascades and 25-45% across the Cascades. In addition, southerly/southeasterly flow from this pattern would bring increased mid-level moisture and instability, bringing a 15-25% chance for thunderstorms across the Linn and Lane County Cascades Wednesday afternoon. The other scenario depicted by the remaining 22% of ensemble members has the trough swinging directly through the Pacific Northwest; if this were to occur, we would see increased chances for precipitation over our area and cooler temperatures.

There is greater uncertainty in the pattern Thursday-Saturday, however, most ensemble members are showing another trough dipping down from the Gulf of Alaska by the end of the week. This will maintain chances for precipitation across the area and bring lower 500 mb heights, resulting in temperatures cooling down to seasonal normals. However, the exact track of this system, timing, and precipitation amounts are still uncertain. About 30% of ensemble members have ridging re-building by the weekend. -10

AVIATION

Southwesterly flow aloft has maintained clouds over the region causing CIGS to bounce between MVFR and VFR and thus will see TAFs unrepresentative at times. Satellite shows a number a breaks though so will see a steady dissipation inland. However, based on the flow, the coastal terminals, especially from KTMK north may struggle to break out of the stratus. Trend towards VFR conditions inland after 20Z Sun. Winds will gradually increase from the north as high pressure continues to build. Around 12-15Z Mon some models are suggesting a 50% chance of IFR/MVFR CIGs returning however, this will greatly depend on whether the clouds today dissipate. If we maintain even broken high clouds it could be enough to limit radiational cooling.

KPDX AND APPROACHES...A mix of MVFR and VFR with CAC levels changing throughout the morning. Will see CIGs hover around 2500-4000 ft AGL before clearing out. There is a 40-50% chance of MVFR/IFR CIGs tonight after 14Z Mon but those chances significantly decrease around 17Z Mon. -27

MARINE

Southwesterly winds over the waters today around 5-10 kt with gusts around 15 kt. Some periods of gusts up to 20 kt within the inner waters as a weak disturbance passes through but will be isolated and not widespread. Seas will remain below 8 ft.

Monday, weak high pressure returns across all waters which will maintain northerly winds resulting in gusts up to 25 kt for all inner and outer marine zones (though at slightly staggered times). Have included the northern waters in the advisory as it appears there will be around a 6 hour period where they could branch into those zones. Looking towards Tuesday through at least Thursday conditions return to a more benign pattern with north to west winds, with gusts below 20 kt and seas 5 to 7 ft. -27/42

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 5 PM to 11 PM PDT Monday for PZZ251- 271.

Small Craft Advisory from noon Monday to 2 AM PDT Tuesday for PZZ252-253-272-273.