textproduct: Portland

SYNOPSIS

Onshore flow persists through much of the next week, while high pressure building offshore will see temperatures trend warmer through Friday. A frontal system Saturday will bring the next chances for light rain and usher in a broad pattern change favoring warmer weather into next week.

LONG TERM...Saturday through Wednesday

A more substantial pattern shift will be underway by Saturday morning as an upper trough moves from the Gulf of Alaska inland over the Pacific Northwest. This system will bring a cold front into the coast on Saturday. Chances for rain peak during the day on Saturday, most notably along the coast and within coastal terrain, as well as inland to the north of Portland. There are 50% or greater chances of accumulating (0.01 inches or more) rain from Newport northward on the coast, and 80-90% chances from Tillamook north through the Long Beach Peninsula. Inland, the probability of accumulating rain rises from only 5% in Portland to 55-65% in the Lewis and Cowlitz Valleys. Rainfall amounts are very likely to be 0.05-0.10 inches or less, with only a 10% chance of seeing 0.20 inches in coastal Clatsop and Pacific Counties. During and behind the frontal passage, below normal high temperatures in the low to mid 60s along the coast and mid to upper 70s inland are expected through the weekend.

As the progressive upper trough exits eastward, there is higher uncertainty in the evolution of the pattern by early next week. Long-range ensembles depict a high probability of strong upper ridging developing over the Four Corners, but whether that will translate to hot weather locally is lower confidence. While temperatures are very likely to be warmer compared to the weekend, the spread of potential solutions remains somewhat wide. At this point, there is an 80% chance of highs in the 80s within inland valleys on Monday and a 75% chance of reaching the 90s on Tuesday, before the potential envelope of outcomes widens substantially on Wednesday, when highs anywhere in the 80s or 90s remain possible. In the warmer solutions, inland ridging and resultant coastal thermal troughing may be sufficient to drive periods of offshore flow, resulting in potential gusty north winds along the coast and within the Willamette Valley. -36

AVIATION...Through 18Z Friday

VFR conditions with scattered low clouds over the airspace continue late this morning. Expect continued VFR through the TAF period for most terminals. The only exception will be KAST and KONP, where there is a 20-30% chance of MVFR conditions between 11-16Z Fri. Light winds this morning will build to 5-10 kt out of the north to northwest this afternoon, then ease below 5 kt after 04-09Z Fri (earliest along the coast).

KPDX AND APPROACHES...VFR conditions and clear skies continue through the period. Diurnal northwest winds expected to rise to around 7 kt by 00Z Fri, then ease after 07-09Z Fri. -12

MARINE

Buoy observations continue show seas of 4-5 ft early Thursday morning, which are expected to persist through much of the week with a dominant west to northwest swell at 7-9 seconds and a secondary long-period south-southwesterly swell. Backing winds are expected today ahead of a frontal system approaching the waters Friday into Saturday, mainly for the waters north of Cape Falcon and the waters beyond 30-40 NM south of Cape Falcon. Chances for light rain peak Saturday morning during the frontal passage, with 10% or less chances of rain beginning before dawn.

Behind the boundary, initial westerly flow will veer out of the north through the weekend as surface high pressure builds offshore. Chances for maximum wind gusts of at least 20-25 kt are greater than 90% across the waters from Sunday through at least Tuesday. Chances that peak afternoon gusts reach gale-force are the highest on Monday afternoon and increase to the south, from less than 5% north of Cape Falcon to 35-50% south of Cape Foulweather. -36

PQR WATCHES/WARNINGS/ADVISORIES

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