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 gusty winds. Trailing this system, a broad pattern change favoring warmer weather into next week is expected with Moderate HeatRisk potential and northerly winds. .

LONG TERM...Saturday through Thursday

A bit more of an active pattern this weekend as a broad trough aloft over the northeast Pacific will be the weather driver. This trough is producing a cold front that will push inland on Saturday which will cause temperatures to lower and increase chances for rainfall through the day. This trough is coupled with a ridge over the four corners region of the US which is fairly amplified. The combination of cooler next to warmer air, and the pressure gradient, will cause winds to increase significantly. Winds will blow west to east through the day and increase through the afternoon. The typical areas will see the gustiest winds (Upper Hood River Valley, Columbia River Gorge, gaps of the Coast Range). The NBM Max Wind Gusts show a mean of around 30 mph within the Columbia River Gorge with slightly higher values around the windiest of locations like Crown Point. However, if we look at the 90th percentile (10% chance of occurring), gusts could reach as high as 45 mph in Hood River and the more exposed terrain. For the Willamette Valley, there is a 10% chance of gusts up to 25 mph but based on the wind direction, for most areas this may be a bit overdone. In addition to the wind, rain is expected with the frontal passage though accumulation will be minimal. Overall looking at high confidence (>80%) for the north coastal areas for accumulating rain, 60% for southwest Washington, and less than 10% for most of the interior portions of Oregon.

Sunday will be a transitional day with dry and slightly warmer conditions. Very little impact expected. However, Monday and Tuesday will see more change. On Monday we will see the progressive upper trough exit eastward which leads to 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. -27/36

AVIATION...Through 00Z Saturday

VFR conditions with scattered low clouds over the airspace continue into Thursday evening. Expect VFR conditions to continue through the TAF period for most terminals. The only exception will be along the coast, where there is a 25-35% chance of MVFR CIGs for any given hour between 12-16Z Fri. Northwesterly winds around 5-11 kt will then become light and variable after 04-09Z Fri (earliest along the coast, latest inland).

KPDX AND APPROACHES...VFR conditions with mostly clear skies continue through the period. Diurnal northwest winds around 6-9 kt will ease after 05-08Z Fri. -12/03

MARINE

Buoy observations as of 3 PM Thursday continue to show seas of 3-4 ft, which are expected to persist through much of the week with a west to northwest swell at 7-9 seconds and a secondary long-period south-southwesterly swell. A frontal system approaching the waters Friday into Saturday will bring increased winds, mainly for the inner waters north of Cape Falcon and all of the outer waters. Chances for rain peak Saturday morning during the frontal passage, likely clearing out through the afternoon.

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. -12/36

PQR WATCHES/WARNINGS/ADVISORIES

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