textproduct: Portland

SYNOPSIS

A fast moving cold front will cross over the region through this morning. This will bring a return of light rain across northwest OR and southwest WA. Temperatures cool down behind this system, dropping snow levels towards 4000 ft by Sunday night, resulting in light snow through the Cascade passes. Expect a chilly Monday night into Tuesday morning. The next system arrives Tuesday night into Wednesday, with wet weather continuing through the end of the week. Looking beyond and into the start of December, some models are hinting at winter weather across the forecast area. However, there is a wide range of model solutions and the forecast will change.

LONG TERM...Tuesday through Saturday

Tuesday morning will be the chilliest night of the week, with low temperatures forecast to drop into the low to mid 30s across interior lowland valleys. With moist surface conditions, there will be potential for frost development Monday night into early Tuesday morning especially on grasses and elevated metal surfaces. By late Tuesday afternoon and evening, the majority of ensemble members suggest upper level ridging will build over the U.S. West Coast, however, the Pacific Northwest appears to be right at the top of the ridge. While 500 mb heights will climb and bring relatively warmer temperatures, we will be far from dry.

The next system will ride the periphery of the ridge and enter the Pacific Northwest from the northeastern Pacific. This will bring widespread rain back into the forecast Tuesday into Wednesday. This system is expected to be on the warm side with 850 mb temperatures around 2-4 C. As a result, snow levels will climb above 6000 ft. Conditions remain showery through the latter part of the week as this system moves through the region.

Chances for 48-hour liquid precipitation exceeding 1" from 4 AM Tuesday to 4 AM Thursday are around 45-80% along the coast, Coast Range, Willapa Hills, and Cascades, 20-50% across the Willamette Valley, southwest WA lowlands and Upper Hood River Valley. Similar, 48-hour liquid precipitation exceeding 1" probabilities are forecasted from 4 AM Wednesday through 4 AM Friday.

Ensemble members maintain wet weather through the end of November and into the start of December. However, there is a lot of uncertainty as to how exactly how the end of November/start of December will greet the Pacific NW. At this time, the 06Z deterministic GFS is bringing -8 to -17 C (18 to 1 F) 850 mb temperatures into the CWA. Looking at the 06Z deterministic ECMWF is bringing -2 to -7 C (25 to 19 F) 850 mb temperatures. So, when looking at any forecast for the end of November into the start of December, be aware that uncertainty is high. With that in mind, now is the perfect time to make sure that your are ready for any winter weather. /42

AVIATION

As of 10Z Sunday, the airspace has a mixture of flight conditions ranging from VFR to LIFR which will result in a very challenging TAF package. Generally, LIFR/IFR conditions are being observed south of KCVO. At the same time, areas north of KSLE are seeing everything from VFR to LIFR. Along the coast, expect VFR/MVFR conditions. A front is slowly moving into the region with light rain already being reported at KAST as of 10Z Sunday. This precipitation will slowly push inland, with terminals in the northern Willamette Valley expecting to see precipitation around 13Z-15Z Sunday, central Willamette Valley and central OR coast terminals around 17Z-19Z Sunday, and southern Willamette Valley terminals by 18Z-21Z Sunday.

The variable flight conditions should start to mix and lift more towards MVFR/VFR as the front moves through the airspace. However, there could be brief periods of IFR/LIFR conditions throughout the TAF period. South/southwest winds will become northwest behind the front. Inland winds will remain mainly less than 10 kts. Along the coast, expect winds to increase for a few hours as the front passes with gusts up to 25 kts. The front should move out of the airspace around 10Z Monday and should result in a mixture of low- end VFR/high-end MVFR conditions for the remainder of the TAF period.

KPDX AND APPROACHES...Expect MVFR conditions to persist. Around 13Z-15Z Sunday, an incoming front will bring light rain along with a mixture of MVFR/VFR conditions. Winds remain less than 10 kts from the south/southeast, shifting westerly after the frontal passage. The front should move out of the airspace around 10Z Monday and should result in a mixture of low- end VFR/high-end MVFR conditions for the remainder of the TAF period. /42

MARINE

High pressure over the area is maintaining fairly stable conditions with minimal change expected through Sunday. Seas will remain around 10 to 13 ft through the remainder of the weekend before falling to 8 to 9 ft on Monday and then 6 to 8 ft on Tuesday. A weak cold front will move over the waters Sunday morning, bringing southwest becoming northwest wind gusts up to 25 kt. A relatively stronger front arrives Tuesday night into Wednesday, bringing wind gusts up to at least 25-30 kt with a 30-50% chance for gale force wind gusts up to 35 kt. Confidence in gale force wind gusts materializing is not high enough to issue a Gale Watch at this time. /42-23

BEACH HAZARDS

An energetic westerly swell is expected along the northwestern Oregon and southwestern Washington coasts through Monday. Seas 10-14 ft at 14-16 seconds are forecast and resulting in a high sneaker wave threat. These energetic waves can run significantly farther up a beach than normal, including over rocks and jetties, creating potentially life-threatening conditions in the surf zone when beachgoers can be unexpectedly knocked off their feet and pulled out into cold ocean waters.

A Beach Hazards Statement has therefore been issued through 10 AM Monday. Caution should be used when in or near the water, and beachgoers with children should be especially watchful. Never turn your back on the ocean, and be sure to keep an eye on the waves. Those participating in razor clam digs should additionally exercise caution. /42

PQR WATCHES/WARNINGS/ADVISORIES

OR...Dense Fog Advisory until 10 AM PST this morning for ORZ116>118.

WA...None.

PZ...Small Craft Advisory until 10 AM PST Monday for PZZ210-251>253- 271>273.