textproduct: Portland

SYNOPSIS

A strong frontal boundary arrives today and tonight ushering in widespread rainfall across the coast through the inland valleys, and heavy snowfall to the Cascades. Due to the expected snowfall impacts for the latter area, a Winter Storm Warning is in effect. In the wake of the front showers and a slight chance (15-25%) for thunderstorms follow on Wednesday then concerns shift to cooler overnight temperatures and frost to end the week. After a brief stint of dry and warmer weather on 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. Currently, the Portland/Vancouver Metro there is a 10-40% chance of overnight lows at or below 36 degrees F. From the Portland/Vancouver Metro areas southward towards Salem and Eugene, OR, expect a 45-85% chance of overnight lows at or below 36 degrees F. For locations north of Vancouver, expect a 50-75% chance of overnight lows at or below 36 degrees F. 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 slightly lower probabilities (only 10-30% lower).

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. -99/42

AVIATION

Conditions are generally VFR across the region this morning with increasing southerly flow ahead of a quickly approaching cold-frontal system. Chances for MVFR CIGs along the coast quickly increase to 70-80% by 14-16z this morning as rain moves overhead with a 40-60% chance for IFR conditions during the afternoon and evening. Inland terminals will hold on to VFR conditions a bit longer with MVFR probabilities increasing after 18z to 40-60% as rain increases, but CIGs may fluctuate until the later afternoon and evening when more uniform cloud cover is expected to move in overhead and MVFR conditions likely settle in. Along with rain, winds will increase also increase today with gusts along the coast reaching to 25-35 kt after 18z and 20-25 kt for inland locations.

KPDX AND APPROACHES...VFR conditions likely persist through the morning hours however stratiform rainfall increases midday into the mid afternoon. CIGs are expected to respond in-kind with chances for MVFR conditions rising after 16-18z - probabilities between 70-80% after 20z. Southerly winds also increase during the afternoon with gusts between 20-25 knots persisting through the evening. -99

MARINE

The focus today remains on the arrival of a robust cold-frontal boundary slowly spreading across the waters north to south. As a result expect southwest winds to increase with gusts up to 30 kt across all coastal waters. Winds are expected to be strongest this afternoon into early Tue evening. During this time, there will be around a 3-6 hour period when gusts could (30-50% chance) exceed 34 kt, producing marginal Gale Force wind gusts. A Small Craft Advisory is in effect across the inner and outer waters including the Columbia River Bar starting this morning. The increased wind waves are expected to build seas to around 7 to 10 ft with a period of around 8-10 seconds. Seas remain steep and choppy through Tue night as well.

Behind the frontal boundary Tuesday night winds abruptly shift northwest with gusts increasing back up to 20-25 kt 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 9 to 11 ft Wed night as a northwest swell moves through the waters. Given these seas the Small Craft Advisory was extended out 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 the second half of the weekend into early next week likely increasing winds and seas yet again. -99/DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...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...Small Craft Advisory from 8 AM this morning to 5 AM PDT Wednesday for PZZ210. Small Craft Advisory from 5 AM early this morning to 5 AM PDT Thursday for PZZ251-271. Small Craft Advisory from 8 AM this morning to 5 AM PDT Thursday for PZZ252-253-272-273.