textproduct: Portland

SYNOPSIS

Largely dry weather expected through midweek while temperatures remain above average for mid-October. A system moving south well offshore is unlikely to result in widespread rain, with only low chances for precipitation along the coast. Chances for unsettled weather return Thursday into next weekend.

SHORT TERM...Now through Monday Night

Zonal flow will develop over the region through today in the wake of a departing cold front exiting to the east through this afternoon. Following a few days of unusual warmth, much more seasonable but still above normal temperatures expected through this weekend as afternoon highs reach the upper 50s to upper 60s. Overnight temperatures will also be sharply cooler tonight, falling to the upper 30s to low 40s for most. The coldest locales are likely to be in the Hood River Valley, where there is high confidence in multiple hours of temperatures of 36F or colder which could support widespread frost, and a Frost Advisory remains in effect for the Upper Hood River Valley from 11 PM PDT this evening until 9 AM PDT Sunday. While there is lower confidence in the occurrence of widespread frost, other areas which have locally higher chances of falling into the mid 30s for a few hours tonight are valleys within the north Oregon Coast Range including the Nehalem Valley near Vernonia and along OR-18/OR-22 near Grand Ronde. Increasing cloud cover on Sunday night will see overnight temperatures remain a few degrees warmer and result in lower chances for frost, with the exception of 50-75% chances for lows in the mid 30s in highest elevation portions of the Upper Hood River Valley near Parkdale and Dee.

On Monday, there is good consensus that an upper-level trough approaching the coast will elongate and pinch off into a closed upper low which will track south toward California. As the trough and its associated surface low make their closest approach, chances for rain will largely remain offshore, with coastal and Coast Range communities seeing only 5-15% chances for rain. Rainfall amounts are not expected to be significant. Reinforcing cool air aloft within the trough will continue to push temperatures downward, with near-normal highs expected on Monday. Monday night will bring more widespread chances for overnight lows in the mid 30s, to additionally include some Cascade valleys, portions of the Willamette Valley, and northern lowland areas in Clark and Cowlitz Counties.

LONG TERM...Tuesday through Saturday

While the upper low drifts southward over California, heights aloft rebound locally as transient upper-level ridging develops overhead. This will maintain dry conditions through midweek and support a warming trend with temperatures returning to the low 70s inland by Wednesday. Overnight lows look to remain seasonable, yielding nightly chances for frost within inland valleys.

Through the latter half of the workweek, there remains decent consensus among long-range ensembles that troughing will redevelop over the Gulf of Alaska but with uncertainty in its location and amplitude. The pattern nonetheless supports modest chances for rain for Thursday and Friday, as well as favoring a return to seasonable temperatures each day. Nightly chances for frost continue within inland valleys. -36

AVIATION...Through 18z Sunday

A weak cold front straddling the airspace will continue to track eastward, exiting by the early afternoon. Very light rain showers with largely VFR cigs and sct low clouds at 1-3 kft will likely prevail through 20-21z Sat. Behind the boundary, skies are expected to trend clearer aside from sct high clouds. North to northwest winds will rise to around 10 kt with gusts up to 20 kt along the coast this afternoon, as well as in the southern Willamette Valley by this evening, and to around 5 kt elsewhere.

KPDX AND APPROACHES...VFR conditions favored to prevail throughout the period with low chances for MVFR cigs with very light rain showers before a frontal boundary exits eastward by 21z Sat. Scattered high clouds otherwise expected with northwest winds rising to around 5 kt this afternoon. -36

MARINE

Northerly flow continues through the weekend while a building mid-period west-northwesterly swell pushes seas to 8-10 ft at 11-12 seconds from tonight through much of Sunday. Chances for seas higher than 10 ft are only 5-15% beyond 30 NM north of Cape Lookout. This swell will also continue to pose a moderate risk for sneaker waves along the coast; caution should be used by those in or near the water along beaches through this weekend.

Another weather system tracking to the south well offshore on Monday may generate a larger westerly swell yielding a period of steeper seas from Monday into Tuesday, with 20-40% chances of significant wave heights above 10 ft, highest beyond 20 NM south of Cape Lookout. Benign conditions are then expected midweek, with increasing confidence in another period of active marine weather late in the workweek. -36

PQR WATCHES/WARNINGS/ADVISORIES

OR...Frost Advisory from 11 PM this evening to 9 AM PDT Sunday for ORZ121.

WA...None.

PZ...None.