textproduct: Portland

SYNOPSIS

Seasonably cool and dry weather continues into Thursday before a frontal system moves onshore Thursday afternoon. Confidence remains high in a widespread soaking rain and breezy winds across the region, with lower confidence in the placement of potential strongest winds along the coast. Dry weather then very likely returns this weekend with additional chances for rain next week.

LONG TERM...Saturday through Wednesday

As the trough lifts into the Canadian Prairie Provinces by Saturday morning, low amplitude and transient shortwave ridging will see a return to dry conditions in the Pacific Northwest. Seasonably cool weather will persist into the workweek, with afternoon high temperatures only reaching the low 60s along the coast and mid 60s within interior valleys through Monday. Overnight lows will similarly remain cool, largely in the 40s Saturday night through at least Monday night, with the coolest temperatures occurring in the Upper Hood River Valley. Chances for frost with morning lows of 36 degrees or cooler remain at 5-10% in the Odell area, and 35-55% near Parkdale and Dee.

Additional upper-level troughing next week may bring additional chances for rain to the region some time during the first half of the workweek. Uncertainty in the evolution of the large-scale pattern remains high at this lead time, resulting in 10-30% chances for rain across much of the region during this time. -36

AVIATION...Through 00Z Friday

West to southwest flow aloft continues through the TAF period. High broken clouds continue to move across the area. Current widespread VFR conditions will continue through at least 10Z Thu. Around 10-12Z Thu, chances of deteriorated conditions increase, primarily at KONP. Probabilistic guidance suggests a 20-30% chance of LIFR and 30-40% chance of IFR conditions at KONP, 10-20% chance of LIFR/IFR conditions at KEUG, and just a 5-15% chance of MVFR CIGs at all other terminals. Any deteriorated conditions should lift and clear out by 17-19Z Thu, although there is a 30-40% chance of MVFR conditions hanging around at KONP past 19Z Thu. Otherwise, north to northwesterly winds around 5-10 kt today will become light and may become more northeasterly by 06Z Thu. Brief gusts up to 18 kt are possible late this afternoon at KONP. Winds looks to be light and variable Thu afternoon.

KPDX AND APPROACHES...VFR conditions with scattered to broken high clouds. Northwest winds around 4-7 kt through the TAF period. ~12

MARINE

Northerly winds continue across the waters tonight, then become northeasterly early Thursday morning through early Thursday afternoon as a low pressure system approaches. This system will move over the coastal waters late Thursday into Friday, bringing rapidly increasing winds and seas along with widespread rain. Guidance has not come into agreement yet on the exact track and strength of this low pressure system, which means exact wind speeds and wave heights are uncertain Thursday night into Friday. With that being said, there is high confidence for at least small craft advisory wind gusts of 21 kt or stronger with this system. Given a 30-50% chance of gale force wind gusts of 34 kt or stronger, a Gale Watch has been issued from 8 PM Thursday to 11 AM Friday for all of the waters, and 11 PM Thursday to 11 AM Friday for the Columbia River Bar. Uncertainty remains mainly due to location, where a relatively strong low pressure system is expected to track somewhere over the coastal waters. Additionally, with low chances of a narrow belt of high winds developing on the south side of this system, there is low confidence on where and how strong wind gusts could materialize over the waters. With this system, the low chance of a narrow belt of high winds is well represented by a 10-20% chance of max wind gusts of 48 kt or stronger.

If this low takes a favorable track and strengthens as it approaches the coast, then hazardous seas as high as 15-17 ft would be possible (5-10% chance). If the low comes in weaker, peak winds would likely range somewhere between 25-35 kt and seas would likely peak closer to 10-13 ft. The latter is currently the most likely outcome, however the forecast should be monitored over the coming days for updates. ~12/23

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.

WA...None.

PZ...Gale Watch from Thursday evening through Friday morning for PZZ210.

Gale Watch from Thursday evening through Friday morning for PZZ251>253-271>273.