textproduct: Portland

SYNOPSIS

Upper level high pressure remains the controlling feature this late afternoon, keeping the overall pattern dry and warmer than normal through Thursday. Each night will still bring a marine surge, clouds expanding across the coast and pushing inland through gaps, followed by partial to substantial clearing during the day. The next period to watch is Friday into Saturday, when a weak disturbance undercuts the ridge and brings a modest cool-down plus very low-end rain chances (mainly coast and higher terrain north of a line from Lincoln City to Salem). Ridging is favored to rebound late this weekend, returning the region to warmer and dry weather for Sunday into early next week, with some potential for 80 degrees along parts of the I-5 corridor.

DISCUSSION...Now through Tuesday

The big picture hasn't changed since this morning: broad ridging holding firm over the Northeast Pacific into the Pacific Northwest, and it's keeping meaningful precipitation at bay. The day to day weather continues to be shaped by marine air near the surface rather than any nearby storms. Expect the coast to stay coolest with lingering low clouds at times and occasional late-night/early- morning mist or drizzle, while interior valleys spend more time dry with afternoon sunshine once the morning cloud layer retreats.

From tonight through Thursday, plan on a similar repeated cycle compared to previous days. Low clouds expand inland overnight, especially through the Coast Range gaps and into the Willamette Valley, then gradually erode back toward the coast late morning into afternoon. How quickly that burn-off happens will still be the main driver of temperatures each day. If clearing is quicker, inland highs will push toward the upper 70s; if clouds hang on longer, mid to upper 60s becomes more likely. Along the coast and higher terrain, highs generally hold in the upper 50s to upper 60s. Heat impacts remain limited for most, with the main concern confined to those very sensitive to warmer temperatures.

Attention then shifts to late Friday and Saturday. Ensemble guidance continues to cluster around a shortwave disturbance sliding over the top of the ridge and knocking temperatures back closer to seasonal levels. Moisture with this feature looks limited, so rain chances stay on the very lower side, highest at the coast and across higher terrain, mainly north of a line from Lincoln City to Salem (roughly 15-25%). The rest of the area has probabilities less than 10%. East of the Cascades, including the Upper Hood River Valley and the central Gorge, rain chances remain near zero (under 5%). If rain does develop, the most likely scenario brings showers to the coast sometime Friday afternoon and evening, then nudging inland within a few hours. Amounts look light where it does rain, generally under a tenth of an inch. In general, there is lower confidence for precipitation as recent model guidance has trended drier.

By late weekend into Monday, the broader signal returns to rebuilding ridging and another warm-up. Sunday currently looks like the better day for warmer temperatures, with probabilities for 80 degrees along the I-5 corridor around 35-70%, highest within the Portland-Vancouver metro. Confidence in the warm/dry trend is better than the details of exactly how warm each inland valley gets, which will still depend on how far inland morning clouds manage to reach and how quickly they clear. Tuesday continues to support the cooling trend, with zonal aloft and high pressure at the surface over the Northeast Pacific. ~12

AVIATION

At 22Z Tuesday, an expansive marine stratus deck remained firmly in place across the Willamette Valley and along the coast. However, satellite observations showed the edges of marine stratus deck beginning to erode with breaks in cloud cover beginning to show up. This suggests this low stratus deck is still on track to scatter out sometime between 23Z Tuesday and 00Z Wednesday, giving way to VFR flight conditions for the remainder of the day. One potential exception is at the coast, where there is a 40-50% chance marine stratus will remain in place through the rest of today and into tonight. There is also around a 10% chance low clouds will fail to scatter out at inland TAF sites by 00Z Wednesday, however current satellite observations suggest this will most likely not occur.

For inland areas where clearing skies is more likely to occur, expect low clouds to fill back in quickly this evening into early tonight (most likely between 06-09Z Wednesday). This will result in another round of persistent MVFR cigs inland. Ongoing MVFR cigs at the coast will likely lower to IFR tonight, even if MVFR cigs do briefly scatter out towards 00Z Wednesday. Winds are expected to remain light and variable around 5 kt or less through the 00Z TAF period.

KPDX AND APPROACHES...Light and variable winds around 5 kt or less will persist through 00Z Wednesday. Low stratus with cigs around 3000 ft remains in place as of 22Z Tuesday, however the ongoing cloud cover is still on track to scatter out by approximately 00Z Wednesday before quickly returning sometime between 05-10Z Wednesday. Note there is a 10% chance ongoing low clouds will fail to scatter out late this afternoon. If this were to occur, MVFR cigs would persist now through at least Wednesday morning. -23

MARINE

A continued southerly surge will bring persistent low stratus through Wednesday with chances for fog and/or drizzle during the overnight and morning hours. Winds late Tuesday afternoon have become westerly around 5 kt. Winds look to turn northerly late Wednesday through much of Thursday, before a weak system moving onshore Friday into Saturday will see southerly flow return with gusts of 15-20 kt and low chances for rain showers.

High pressure rebuilding this weekend will yield strengthening northerly flow, which may become hazardous to small craft late Sunday into Monday with gusts up to 20-25 kt. Chances for gusts to reach 21 kt or higher increase slightly from 50-80% on Sunday to 60-90% on Monday, with higher chances to the south.

Seas will remain fairly steady at 4-7 ft with a persistent westerly to northwesterly swell through this weekend. -36/23

PQR WATCHES/WARNINGS/ADVISORIES

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