textproduct: Portland

SYNOPSIS

Largely dry weather expected through midweek while temperatures remain near to above average for mid-October. Chances for rain and cooler temperatures ramp up late in the work week.

SHORT TERM...Now through Monday Night

A band of mid to high level cloud cover will push east of the region later this evening. Between this, decreasing winds overnight and and dewpoints currently hovering in the low to mid 40s in some locations, we should see some of our colder valley locations, particularly across the north Oregon coast range and valleys of southwestern Washington, drop into the mid to upper 30s towards daybreak. As a result, opted to expand the Frost Advisory to cover the threat for surfaces reaching freezing in some of these typically colder spots. Higher dewpoints and more persistent wind in the Willamette Valley should make it difficult for temperatures to drop into the mid to upper 30s and allow temperatures near the ground to reach freezing for all but the coldest spots.

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 30s for many valleys away from the core urban centers.

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 06z Monday

Breezy northerly winds at many taf sites should continue to diminish overnight. As a band of mid-high level clouds currently over the region moves east of the area between 06-08z, valleys should begin to cool off more efficiently with some patchy fog and low clouds developing in more wind sheltered valleys. The probability for IFR conditions to develop by daybreak is highest at KEUG with a 25-30% chance at any given hour in the 13-17z Sunday timeframe. The probabilities are closer to 20% for other inland taf sites. Whatever fog and low clouds do develop overnight should lift and scatter out rather quickly on Sunday, most likely in the 17-20z Sunday timeframe.

KPDX AND APPROACHES...Expect mainly VFR conditions through 06z Monday. However, clearing skies, decreasing winds and current dewpoints in the mid 40s will lead to a threat of some patchy fog and low clouds trying to develop later tonight in the vicinity of the airport. However, there is only a 15-20% chance at any given hour for IFR conditions at the terminal between 13-17z Sunday so will keep the TAF VFR for the time being.

MARINE

Northerly flow continues through the weekend. In addition, northerly wind gusts of 20-25 kt are beginning to occur at Buoy 50 and are expected to persist for several hours so a Small Craft Advisory was issued for the waters off the central coast of Oregon. A building mid-period west-northwesterly swell will push seas to 8-9 ft at 11-12 seconds tonight through Sunday. Chances for seas higher than 10 ft are only ~10% 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 dropping southward off the coast Monday into Tuesday will generate another swell that push into the region. There is a 50% chance for seas to push to 10 ft across the waters, particularly beyond 20 NM Tuesday. In addition, there is a >75% chance for wind gusts to climb into the 21-25 kt range Tuesday. Winds and seas appear to trend downward midweek with more active weather late in the work week.

PQR WATCHES/WARNINGS/ADVISORIES

OR...Frost Advisory from 3 AM to 9 AM PDT Sunday for ORZ104-105.

Frost Advisory until 9 AM PDT Sunday for ORZ121.

WA...Frost Advisory from 3 AM to 9 AM PDT Sunday for WAZ205-208.

PZ...Small Craft Advisory until 5 AM PDT Sunday for PZZ253-273.