Portland, OR 97280 Weather

Synopsis

Dry weather is expected through much of Saturday, before rain chances increase through the latter half of the weekend with persistent seasonable temperatures. By the start of next week, there is a 10-20% chance of very light precipitation across the forecast area through at least Wednesday. A relatively stronger system looks to drop down by mid-week, which looks to bring a slightly higher probability (20-30%) for showers.

Discussion

Today through Thursday...Dry weather looks to take hold over the area as a transient, upper level ridge moves across the region through Saturday. Expect daytime highs today in the low 50s to upper 50s on the coast, into the low to mid 60s for inland valleys and upper 40s to upper 50s for the Cascades. As the ridge axis shifts inland, light offshore flow will develop, peaking overnight in the Cascades and Coast Range. This will result in daytime high temperatures on Saturday warming into the upper 50s to low 60s on the coast, into the low to mid 60s for inland valleys and low 50s to low 60s for the Cascades. Overnight temperatures will again fall into the low to mid 30s for most locations across the CWA tonight, with Freeze Watches and Frost Advisories remaining in effect; Freeze Watches may be upgraded to Freeze Warnings if confidence increases in temperatures falling to near or below freezing.

There remains good consensus among long-range ensembles that another cutoff low will develop over the Gulf of Alaska on Saturday and track to the southeast offshore of Vancouver Island. By Sunday, there is less agreement on how the low will evolve as it nears the Pacific Northwest. For now, There are modest chances, near 50%, for rain on Sunday across the region, decreasing through the first half of next week as troughing may linger overhead. Cool air aloft will also likely continue to support seasonable temperatures for late October.

Looking beyond the weekend and into the start of next week, uncertainty in the forecast remains high. Ensemble clusters are split on the overall pattern with the ECWMF maintaining a ridge over the region as a broad, upper level low persists near 40N/140W which would bring a return of a warm and dry pattern. While the GFS ensembles lean into a broad trough spreading southward from far Western Canada thus maintaining a cooler and wetter pattern. As a result NBM is keeping a broad, 15-20% chance for precipitation, with little to no QPF across the forecast area, along with slightly warmer than seasonal daytime highs and overnight lows through the remainder of the forecast period. /42-36

Aviation

Through 12Z Friday...Generally VFR conditions expected across the airspace through the majority of the TAF period. Stratus will continue to linger over the Cascades through around 15Z Friday. Until those clouds scour out, there will be a 5-10% chance for intermittent low-end VFR/high-end MVFR conditions for KPDX, KTTD and KUAO. Any lowered flight conditions that do develop, should improve to VFR around 16Z-18Z Friday. Otherwise, widespread VFR conditions are expected. There also is a 5-10% chance of MVFR conditions developing between KUAO and KEUG as well as KAST starting around 11Z Saturday.

KPDX AND APPROACHES...Generally VFR conditions with a 5-10% chance for intermittent low-end VFR/high-end MVFR conditions until around 15Z Friday. Any lowered flight conditions that do develop, should improve to VFR around 16Z-18Z Friday. /42

Marine

Buoy observations as of 1 AM PDT Friday shows north/northwest winds with gusts up to 30 kt. In addition to the winds, seas are around 10 to 12 ft around 9 to 11 seconds. These conditions are resulting in steep and hazardous conditions that are expected to persist through at least 8 AM PDT Friday morning. Therefore, will maintain the current Hazardous Seas Warning. Will also maintain the trailing Small Craft Advisories, which will come on-line around 8 AM PDT Friday and continue through at least Friday afternoon. The main channel of the Columbia River Bar will also maintain a Small Craft Advisory through 8 AM PDT Friday. Seas will be relatively less steep with significant wave heights of 7 to 9 ft at 8 to 10 seconds.

Northerly winds weaken by late Friday morning with a continued northwest swell and seas becoming less steep. Northerly winds will then persist through at least Saturday afternoon as an approaching low stalls west of the coastal waters. There is still uncertainty on the exact strength and track of this low heading into Saturday evening and Sunday. However, models are showing that winds and seas look to re-build as the next system moves through the waters. This could lead to a brief period of Small Craft Conditions across all waters. /42