textproduct: Portland

SYNOPSIS

High pressure will maintain dry and warm conditions through early next week. A weak shortwave trough will bring increased cloud cover and slightly cooler temperatures tomorrow. Temperatures rebound on Monday and Tuesday as high pressure re- builds. 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 shows a weak shortwave trough slowly moving into the region today. This shortwave will slightly brush the Pacific Northwest and bringing mid to high level clouds across the CWA. While we will likely see no precipitation with this shortwave, we will get a brief reprieve from the warmer daytime highs thanks in part to widespread cloud cover an relatively cooler onshore flow. So, while we will remain dry, said cloud cover and onshore flow will drop daytime highs towards the upper 50s to mid 60s along the coast and in the Cascade. Interior valley locations are expected to see daytime highs in the upper 60s to mid 70s.

Looking towards Monday and Tuesday, there has minimal changes in model ensemble guidance. Said guidance is showing a return of high pressure over the Pac NW, which will bring a return of clear skies, warm daytime highs for Monday and Tuesday. Temperatures return to the 70s to near 80s by Monday from the coast to the Cascades, with the warmest temperatures expected within the interior valleys. Looking at Tuesday, models are still showing this as the hottest day of the week. Current guidance is showing highs in the low to upper 70s along the coast, mid 70s to low 80s for the Cascades and low to upper 80s for the interior valleys.

Looking towards the middle part of next week, 500 mb WPC clusters show at least some weak troughing or a weak low moving over the northwestern coast of CONUS shown via lowering 500 mb heights. This continues to support at least some cooling off, think highs in the 70s rather than the 80s, for the middle of the week and continuing through the end of the week.

The next chances for precipitation return on Wednesday as the aforementioned trough approaches the West Coast. The majority, approx 70%, of ensemble members show this trough tracking south of our area, either toward the California/Oregon border or further south into California. As a result, chances for precipitation are currently 15-25% west of the Cascades and 25-40% across the Cascades. In addition, southerly flow from this pattern would bring increased instability and thus a 15-25% chance for thunderstorms for the Willamette Valley and across the Cascades. The other scenario depicted by 25% of ensemble members has the trough swinging directly through the Pacific Northwest; in this case, we would see increased moisture and chances for precipitation.

Continuing to look at the WPC 500 mb clusters, show a more significant pattern change for Thursday and Friday. However, while the Grand Ensemble does favor more troughing over the Pac NW, approx 30% of ensemble members are favoring a ridge of high pressure returning to western CONUS. Overall, am maintaining the cooling trend for the latte part of the week, but as for precipitation chances and timing, that remains uncertain. /42

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.