textproduct: Portland

SYNOPSIS

The back edge of a cold frontal boundary which has spread ample precipitatiion and mountain snowfall across the Pacific Northwest quickly progresses through the region this morning followed by a showery airmass and a 15-30% chance for thunderstorms this afternoon. A Winter Storm Warning remains in effect for the Cascades through tonight. 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 although forecast confidence Sunday onward is low.

LONG TERM...Friday through Tuesday

Looking towards the weekend confidence is high among both deterministic and ensemble guidance in a ridge of high pressure continuing to build aloft allowing temperatures to gradually warm and reduce frost concerns. However the pattern remains rather progressive as models show the ridge quickly followed by another low pressure system on Sunday originating from the Gulf of Alaska. WPC Cluster Guidance does favor this low dropping almost straight southward across the eastern Pacific favoring this low holding just off the OR/WA coast. How far this low holds off the coast will heavily modulate conditions locally. Should it stay more to our west, warmer conditions and broad southerly flow would be favored, That said, any moisture riding south to north within this flow pattern could spell the return of convection. Thus forecast confidence Sunday onward into the middle of next week is low. -99/42

AVIATION

As we move through the morning hours steadier rain will transition to showers behind the frontal boundary moving overhead - KAST has already seen an improvement back to VFR as a result. Expect a south to northwest wind switch when the front passes this morning as well. However, as bands of showers move overhead, especially during the afternoon and evening hours, brief drop to MVFR or IFR can be expected. On the whole there is a 20-40% chance for MVFR conditions at the coast this afternoon with a 15-25% inland. It's also worth highlighting there is also a 20-30% chance for thunderstorms for all terminals after roughly 18-21z today with lightning and gusty/erratic winds the primary impacts. Chances for these storms quickly drop off around 4-6z Thur.

KPDX AND APPROACHES...MVFR conditions and breezy southerly winds likely persist until 14-16z this morning while the primary precipitation band sits overhead. After his point winds gain a westerly component while rainfall turns more showery, but at least it trends more towards VFR the remainder of the TAF period. Keep in mind there will be a 20-25% chance for thunderstorms locally after ~20z through -4z this evening. Any robust showers or storms may briefly drop conditions to MVFR/IFR. -99

MARINE

A cold frontal boundary is quickly progressing across the coastal waters early this morning with winds switching northwesterly in its wake. Expect gusts between 20-30 knots the remainder of the day as an area of low pressure drops along the Canadian coast toward the region. This feature will also bring a 15-25% chance of thunderstorms over the waters into the evening hours. Seas are expected to persist at around around 9 to 10 ft, building slightly to around 10 to 12 ft tonight as a fresh northwest swell moves through the waters. The Small Craft Advisory remains in place through Thursday morning for both the inner and outer waters, including the Columbia River Bar. High pressure then builds over the waters Thursday into the weekend as northerly winds return and seas gradually subside to around 3 to 6 ft Friday into Saturday. It appears there's a 40-60% chance for north winds to gust above 21 knots into Small Craft Criteria on Saturday. Looking ahead there is potential for another weather system to impact the waters later this weekend, possibly increasing winds and seas. -99/DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...Frost Advisory from 1 AM to 9 AM PDT Thursday for ORZ104>107- 109-114>118-123. Freeze Watch from late tonight through Thursday morning for ORZ121-124-125. Winter Weather Advisory until 11 AM PDT this morning for ORZ123. Winter Storm Warning until 5 AM PDT Thursday for ORZ126>128. WA...Frost Advisory from 1 AM to 9 AM PDT Thursday for WAZ204-205- 208. Winter Storm Warning until 5 AM PDT Thursday for WAZ211. PZ...Small Craft Advisory until 5 AM PDT Thursday for PZZ210. Small Craft Advisory until 11 AM PDT Thursday for PZZ251>253- 271>273.