textproduct: Portland

SYNOPSIS

Rain, strong winds, and heavy Cascade snow tonight into early Thursday as a frontal system impacts the area. Heavy snow will also continue in the Upper Hood River Valley tonight before transitioning to rain shortly before sunrise. Stratiform rain will transition to scattered rain showers and isolated thunderstorms late Thursday morning into the afternoon, some of which will have the potential to produce brief heavy rain, small hail and gusty outflow winds. Another weather system will push into the region late Thursday night into early Friday, with more rain and gusty winds, however uncertainty is high regarding exact wind speeds. Unsettled weather continues through the weekend into early next week, though heaviest rainfall likely to shift southward over southwest Oregon and far northwest California. Snow continues at times over Cascades.

EVENING UPDATE

As of 730 PM PST Dec. 25th, around 6 inches of snow has already fallen in the Parkdale area. Accumulating snow is also occurring in Odell, with snow mixing in with rain in Hood River. Another 2 to 6 inches of snow is possible Wednesday night from Odell to Parkdale, heaviest in Parkdale. A dusting to one inch of snow is possible in Hood River. Therefore, a Winter Storm Warning has been issued for the Upper Hood River Valley through 5 AM Thursday, Dec 26th. Temperatures should warm above freezing towards sunrise Thursday with snow transitioning to rain. -TK/Alviz

LONG TERM...Saturday through Tuesday

Ensemble guidance indicates another weak, quick- hitting weather system will move through NW Oregon and SW Washington late Friday into early Saturday right on the heels of the previous system. Although this system looks to be associated with an atmospheric river, the main stream of moisture will be quickly pushed south to funnel into southern Oregon and northern California. Then again, another similar round of moisture will move into the PacNW Sunday, where again the main stream of moisture is trending south of the forecast area. There remains around a 10-40% chance of river flooding for rivers along the Coast Range and Willapa Hills due to the consecutive rounds of moisture around December 28-31, but these chances are decreasing as the heavier rain trends to the south. Monday and Tuesday are much more uncertain as some guidance shows weather drying where others show a chance of continued wet weather. -HEC

AVIATION

At 0445z Thursday, a strong frontal system was moving over northwest OR and southwest WA. This system is bringing widespread stratiform rain impacting all TAF sites, heavy at times. In addition, high winds will occur at the coast with southerly wind gusts likely peaking between 45-55 kt from KAST to KONP tonight. Wind gusts will likely peak closer to 30 kt for inland TAF sites, except 35-40 kt at KTTD where winds will be out of the east. Very strong low-level wind shear remains a concern at all TAF sites through 14-15z Thursday, mainly around 2000 ft. This will mainly be in the form of speed shear, except at KPDX, KTTD, KHIO and KUAO where directional shear will also be a factor. The aforementioned frontal system should finish moving through the area around 15-18z, bringing an end to low-level wind shear concerns and a transition from stratiform rain to scattered rain showers and isolated thunderstorms. Heavier showers or thunderstorms will have the potential to produce small hail, heavy rain and gusty outflow winds as high as 35-40 kt. Winds will also begin to decrease late Thursday morning through the afternoon while veering to the west-southwest. In regards to cigs, expect a mix of MVFR/VFR throughout the TAF period.

PDX AND APPROACHES...Expect gusty southeast winds now through 18z Thursday with surface wind gusts as high as 35 kt. In addition, very strong low-level wind shear remains a concern around 2000 ft (both directional shear and speed shear). The strong winds and low-level wind shear will also be accompanied by steady stratiform rain, heavy at times with surface visibilities falling down to 4-6 SM. Steady stratiform rain will transition to off and on rain showers by 15z Thursday. Stronger showers will have the potential to produce brief heavy rain, small hail and gusty outflow winds as high as 35-40 kt. There is also a 15% chance of thunderstorms late Thursday morning into the afternoon. -TK

MARINE

A Storm Warning remains in effect across the coastal waters through late Thursday morning as a very strong frontal system continues to bring high winds and very large/steep waves. Buoy observations from 9 PM PST Wednesday showed southerly winds gusting between 45-60 kt, strongest at buoy 050. Winds briefly gusted as high as 68 kt at buoy 050, however winds of that magnitude are not expected to last longer than one hour. Therefore, have decided NOT to upgrade the Storm Warning to a Hurricane Force Warning for the southern waters as wind gusts of this magnitude are isolated and very short-lived. Significant wave heights ranged between 20-25 ft with wave periods between 11-14 seconds. These observations generally match the forecast well, albeit wind gusts are over- performing at buoy 050.

After the Storm Warning expires late Thursday morning, seas and winds will come down slightly Thursday afternoon/evening as we remain between weather systems, however seas will still be steep and hazardous with gale force wind gusts. Conditions worsen yet again Thursday night into Friday morning as a strong surface low pressure system moves over the waters and brings strong wind gusts up to at least 40-45 kt. However, uncertainty is high regarding max wind gusts and there is the potential for storm force wind gusts over 48 kt (30-60% chance, highest chance over the central and southern waters). Depending on the exact track and strength of this low, there is a possibility the Gale Warning could be upgraded to another Storm Warning. In fact, cannot completely rule out hurricane force wind gusts over 64 kt (5-15% chance). While the probability for hurricane wind gusts is very low, it is non- zero and worth mentioning given the high uncertainty involved with this particular low pressure system. Due to uncertainty regarding exact wind speeds, there is also uncertainty regarding exact wave heights. The current forecast calls for seas peaking between 24-27 ft Thursday night/Friday morning, however seas around 30 ft are possible if high-end storm force winds materialize. Regardless of the outcome, seas will remain elevated through Saturday before slowly coming down Saturday night. While active weather continues into next week, seas and winds after Saturday look much lower/weaker. -TK

BEACH HAZARDS

A strong mid period swell is currently pushing onto the coast with seas currently around 20-25 ft at 11 to 13 seconds. The ongoing High Surf Advisory remains on track; no High Surf Warning expected, with even high end scenarios remaining below Warning thresholds. The high Surf Advisory continues through Friday afternoon; though seas come down slightly Thursday afternoon. The next low pressure system arrives Thursday night into Friday morning, with swells peaking around 20-22 ft or greater. Beachgoers should stay far away from incoming waves while remaining observant and vigilant. Sneaker waves will be a threat and can catch beachgoers off guard, potentially knocking you off your feet and pulling you out to sea.

Additionally, with Toke Point forecast to reach 12 ft at high tide around 9 am Thursday, a Coastal Flood Advisory for tidal overflow has been issued for the south Washington Coast. Minor flooding up to one foot above ground level will be possible at that time. Coastal flooding is not expected for the Oregon coast at this time. -TK

PQR WATCHES/WARNINGS/ADVISORIES

OR...High Surf Advisory until 4 PM PST Friday for ORZ101>103.

High Wind Warning until 8 AM PST Thursday for ORZ101>103.

Winter Storm Warning until 5 AM PST Thursday for ORZ121.

Winter Weather Advisory until 10 PM PST Thursday for ORZ126>128.

WA...High Surf Advisory until 4 PM PST Friday for WAZ201.

High Wind Warning until 8 AM PST Thursday for WAZ201.

Winter Weather Advisory until 10 PM PST Thursday for WAZ211.

Coastal Flood Advisory from 6 AM to noon PST Thursday for WAZ201.

High Wind Warning from midnight tonight to 10 AM PST Thursday for WAZ203.

PZ...Storm Warning until 10 AM PST Thursday for PZZ210-251>253- 271>273.

Gale Warning from 10 AM Thursday to 10 AM PST Friday for PZZ210- 251>253-271>273.