textproduct: Portland

SYNOPSIS

A strong frontal boundary will move across the CWA through tonight, bringing widespread rainfall to the coast and the inland valleys. This front will also push snow levels down towards 2000-3500 ft and bring heavy snowfall to the Cascades and portions of the Cascade Foothills. Due to the expected snowfall impacts for the Cascades, have issued some winter weather hazard products, which start early this evening. Behind the front showers return along with a 15-30% chance for thunderstorms starting late Wednesday morning through Wednesday night. Afterwards, concerns shift to cooler overnight temperatures and possible frost/freeze conditions to round out the week. After a brief stint of dry and warmer weather Saturday, precipitation chances return by early next week.

LONG TERM...Thursday through Monday

By Thursday, the upper level low and associated front have left the CWA, but will leave the region under cooler conditions with increasing clearing. Thursday into Friday looks to have overnight lows below normal bottoming out in the mid 30s across the lowlands and spelling a potential for frost. Below freezing temperatures are even forecast for the higher coast range/Cascade valleys, including the Hood River Valley. The latest NBM probabilities for temperatures below 36 degrees F Wednesday night into Thursday morning for the Portland/Vancouver Metro is 10-30% chance. From the Portland/Vancouver Metro areas southward towards Salem and Eugene, OR, expect a 15-75% chance. For locations north of Vancouver, expect a 15-60%. Additionally, there is a 80-95% chance of at least freezing temperatures in the Upper Hood River Valley for Wednesday night into Thursday morning. Similar conditions may develop again Thursday night into Friday morning, though with similar probabilities.

Looking towards the weekend, temperatures gradually warm, reducing these morning frost concerns. Ensembles show a shortwave ridge of high pressure moving quickly overhead on Saturday, but being quickly followed by another low pressure system on Sunday originating from the Gulf of Alaska. Now, beyond Sunday and into the start of next week, WPC Cluster Guidance is favoring this low holding just off the OR/WA coast or moving over the inland Pac NW, which means that cooler and moister conditions are favored for the start of next week. /42-99

AVIATION

Westerly flow aloft ahead of an upper level trough today as a cold front pushes across the area with rainfall increasing later this afternoon through tonight. As of 20z, conditions remain a mix of MVFR and VFR with CIGS around FL025-FL035, along with rain reducing visibility at the coast to around 3-5 SM. Chances for widespread MVFR inland quickly increase to 50-70% later this afternoon/evening, after 00z Wed; while chances for IFR at the coast increase to around 30-40% around the same time. Southerly winds are also expected to remain breezy through this evening, with gusts up to 30 kt likely. The cold front is expected to slide southward across the area overnight, with winds behind the front shifting to the WNW and steady rain quickly decreasing, with the front exiting the area by 18z Wed. Conditions are likely (70-80% chance) to return to VFR by around 15z Wed, followed by increasing showers later Wed morning.

KPDX AND APPROACHES...As of 20z, lower VFR CIGs with light rain. Conditions are expected to deteriorate as a cold front pushes increasing rain across the area. Probs for MVFR increase to around 60-80% by 00z Wed, and continue through at least 10-12z Wed. Southerly winds are expected to remain breezy with gusts up to 25-30 kt through at least 08z tonight. Around 10-12z Wed, expect the front to push through with west to northwest winds and a return to VFR conditions likely. /DH

MARINE

Gusty southwest winds continue to increase this afternoon as a strong cold front approaches the coastal waters. Latest guidance increased winds enough to warrant a Gale Warning for the northern coastal waters, as well as the inner central waters and the Columbia River Bar. Expect southwest wind gusts up to 35 kt there, while elsewhere, widespread gusts to 30 kt is expected, with isolated gusts up to 35 kt possible, especially over the inner waters as the front impinges along the coast. The increased wind waves are expected to build seas to around 8 to 10 ft with a period of around 8-10 seconds. Seas remain steep and choppy through tonight.

Behind the frontal boundary, expect an abrupt shift to the northwest as the front drops south overnight. Breezy northwest winds with gusts up to 20-25 kt continue through Wednesday as an area of low pressure drops along the Canadian coast toward the Puget Sound. This will also bring a 15-25% chance of thunderstorms over the waters through Wed evening. Seas are expected to persist at around around 8 to 10 ft on Wednesday, building slightly to around 10 to 12 ft Wed night as a northwest swell moves through the waters. The Small Craft Advisory remains in place into Thursday morning. High pressure then builds over the waters later this week as northerly winds return and seas gradually subside to around 3 to 6 ft Friday into Saturday. There is potential for another weather system to impact the waters later this weekend, possibly increasing winds and seas. /DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...Winter Weather Advisory from 3 AM to 11 AM PDT Wednesday for ORZ123.

Winter Storm Warning from 5 PM this afternoon to 5 AM PDT Thursday for ORZ126>128.

WA...Winter Storm Warning from 5 PM this afternoon to 5 AM PDT Thursday for WAZ211.

PZ...Gale Warning until 8 PM PDT this evening for PZZ210-251-252-271.

Small Craft Advisory from 8 PM this evening to 5 AM PDT Wednesday for PZZ210.

Small Craft Advisory from 8 PM this evening to 5 AM PDT Thursday for PZZ251-252-271.

Small Craft Advisory until 5 AM PDT Thursday for PZZ253-272-273.