textproduct: Portland

SYNOPSIS

A progressive weather pattern with prevailing onshore flow continues through the weekend. Broad southwest flow aloft will allow temperatures to peak in the mid to upper 80s today before a frontal system slated for Saturday ushers in cooler temperatures, chances for light rain, and locally gusty west winds over the weekend. Wind related impacts are highest in the central Columbia Gorge. Trailing this frontal system, a broad pattern change favoring warmer and drier weather is expected by the middle of next week with a period of northerly to northeasterly winds as well - a combination we'll have to watch closely.

LONG TERM...Sunday through Thursday

The broader upper-level low feature passing to our north continues to influence the region on Sunday with similarly cool conditions overall compared to the start of the weekend - very little in the way of weather related impacts. However, Monday and Tuesday will see more change. Early next week the progressive upper trough exits eastward while a ridge of high pressure amplifies over the eastern Pacific and Four Corners region. It's around this point deterministic and ensemble systems begin to show growing deviations in the upper-level pattern going forward which leads to higher forecast uncertainty by the middle of the week. While temperatures are very likely to be warmer compared to the weekend, the spread of potential solutions remains somewhat broad, especially on Wednesday. At this point, there is an 80-90%+ chance of highs in the 80s within inland valleys on Monday and a 75-80% chance of meeting of exceeding 90 on Tuesday. Mid to late week it'll all come down to the exact pattern amplification and longitudinal placement of the ridge over the far eastern Pacific. In the warmer solutions (favored by GFS and more GEFS members), stronger inland ridging and the resulting coastal thermal trough may be sufficient to drive decent offshore flow and potential gusty north to northeast winds along the coast and within the Willamette Valley. The EPS keeps this ridge flattened comparatively but still shows a signal for north to northeast winds, albeit weaker. At least the bulk of deterministic and ensemble guidance depict a return to W-NW winds by late Thursday signaling moderating conditions.

From a fire weather prospective the pattern early to mid week does raise some concerns, especially on Tuesday, as notable N-NE winds during the afternoon hours and minimum relative humidity values below 25% could combine for a period of elevated to critical fire weather conditions in the central and southern Willamette Valley (a 30-50% chance according to the latest NBM). Much of this hinges on the placement/strength of the ridge axis and accompanying near surface thermal trough over southwest Oregon as mentioned earlier. Additionally, the weak offshore component to the low to mid level flow (surface to 700mb) has the potential to adversely impact overnight humidity recoveries in the Cascades, adjacent foothills, and tops of the coast range. We'll have to watch this late Monday through Wednesday period closely the next several forecast cycles as models converge on a solution and forecast confidence increases. -99

AVIATION...Through 12Z Saturday

Current satellite and surface observations early this morning show widespread VFR conditions across the region as coastal stratus hangs off the coastline. There's only a 10-20% chance for degraded flight conditions at KONP/KAST prior to 16-17z, after which point VFR conditions are favored through most of the daytime hours. That said, a westerly surge of low stratus late day (after 23z) likely leads to MVFR CIGs/VIS or lower along the coast by the evening hours. Otherwise, VFR conditions are heavily favored at all inland sites through the TAF period.

KPDX AND APPROACHES...Expect VFR conditions with mostly clear skies and northwest winds generally less than 5-10 kts through the TAF period. -99

MARINE

Fairly benign conditions continue across the waters today as winds remain out of the W-NW. Headed into the first half of the weekend a frontal system approaching the waters brings increasing winds, mainly for the outer waters and the inner waters north of Cape Falcon. Chances for rain peak Saturday morning during the frontal passage, likely dissipating during the afternoon hours.

Behind the boundary, initial westerly flow will veer out of the north by Sunday as surface high pressure builds offshore. Chances for maximum wind gusts of at least 21 kt are around 70-90% from Sunday afternoon/evening through at least Tuesday evening - highest probabilities outer waters. We'll still have to watch for a period of marginal Gale Force northerly winds late Monday afternoon (5-25% chance south of Cape Foulweather). Wave heights through this time period remain around 5-7 ft at 7-9 seconds. -99/12

PQR WATCHES/WARNINGS/ADVISORIES

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