textproduct: Portland

SYNOPSIS

Rain shifts south this afternoon, diminishing this evening. Morning clouds give way to mostly sunny skies Thu afternoon as conditions are expected to trend warmer and drier later this week. Temperatures generally expected to remain near to slightly above seasonable normals for late April. Chances for showers increase this weekend, particularly over the higher terrain of the Cascades and foothills. Similar conditions persist into early next week.

DISCUSSION...Now through Wednesday

Rain associated with a weak backdoor cold front will continue to slide south this afternoon, while the upper low shifts east across Idaho and into the northern Rockies, allowing for precipitation to gradually diminish by this evening. A few lingering showers will exist through tonight, mainly over the Oregon Cascades and foothills, and into the southern Willamette Valley. Snow levels will remain near the passes with 1-2 inches of snowfall possible through late this afternoon.

Conditions are expected to trend warmer and drier Thursday and Friday as an upper level trough dropping out of Canada remains east of the Pacific NW. Expect morning clouds will give way to mostly sunny skies Thu afternoon with temperatures trending back toward seasonable norms, with further warming likely into Friday. Early morning min temperatures are expected to remain elevated enough into the upper 30s to lowers 40s to limit any widespread frost, although could be flirting with some frost in the Upper Hood River Valley where there is around a 50% chance of temps falling to 36 F or below.

The amplified upper level pattern continues into Friday with an anomalously steep upper level ridge over the NE Pacific pushing north into Alaska, undercut by the subtropical jet moving into southern California. With a weaker upper ridge, most ensemble clusters are showing shortwave troughing dropping out of western Canada across the Pacific NW by this weekend. But, conditions are still expected to remain mostly dry with seasonable to slightly warmer than normal temperatures through Sunday. There is potential for shower activity over the central Oregon Cascades Saturday afternoon: 20-40% PoPs with a 10-20% chance of thunder. Depending on the strength of the upper shortwave and amount of mid-level moisture, chances for showers may increase on Sunday, with around a 10-25% chance of rain showers across the lowlands into Sunday afternoon.

Uncertainty continues into early next week, but ensembles do indicate weak, perhaps transient, upper level ridging works its way across the Pacific NW. Afternoon high temperatures generally will fall into the range from the mid-60s to lower 70s through the middle of next week, with afternoon shower chances likely confined to the higher terrain. /DH

AVIATION

A frontal system continues to move through the airspace from north to south, bringing rain and lowering conditions to VFR/MVFR at a few terminals. Expect rain and mixes of VFR/MVFR conditions at inland terminals to persist until 00Z Thu, followed by VFR and dry conditions through at least 18Z Thu. As for coastal terminals, rain showers have mostly tapered off at all coastal terminals, but MVFR conditions still linger. Most guidance suggests that MVFR conditions at the coast will persist through the TAF period. With NBM only suggesting a 30-40% chance of MVFR CIGs beyond 06Z Thu and higher chances before, there is high confidence that MVFR will linger until 06Z Thu, and lower confidence through the rest of the TAF period.

Current southwesterly to south-southwesterly flow at the surface will gradually shift to mostly southerly by 07-09Z Thu. Winds remain around 8-12 kt with gusts up to around 20 kt, but will gradually decrease to under 8 kt after 03Z Thu. Winds will likely shift back to southwesterly to westerly around 18Z Thu.

KPDX AND APPROACHES...Rain and a mixed bag of VFR/MVFR conditions continue until 00Z Thu, then VFR and dry conditions through the rest of the TAF period. Breezy southwesterly to south- southwesterly winds of 8-12 kt with gusts up to around 20 kt, then weakening to sustained winds under 8 kt after 03Z Thu. ~12

MARINE

Winds and seas have increased over the coastal waters today with a cold front still moving through the region. A northwest swell continues to push seas to around 9 to 11 ft with westerly to northwesterly winds around 15 to 20 kt and gusts up to 25 kt over the central and northern outer waters. The southern waters have also seen increasing winds and seas through the afternoon.

Seas will peak between 9-13 ft this evening into tonight at 10 to 12 seconds, bringing steep and hazardous seas. The highest seas will remain over the northern outer waters beyond 20-30 nm. Winds will gradually decrease this evening into tonight, however seas will remain elevated. Expect seas to fall below 10 ft by late Thursday afternoon and continuing to subside into Thursday night.

A Hazardous Seas Warning remains in effect for the outer waters north of Cape Falcon until 5 AM PDT Thursday, followed by a Small Craft Advisory from 5 AM to 5 PM PDT Thursday. The remaining marine zones north of Cape Foulweather have Small Craft Advisories in effect until 5 PM PDT Thursday. For the marine zones south of Cape Foulweather, a Small Craft Advisory will be in effect from 5 PM Wednesday to 5 PM PDT Thursday.

For the Columbia River Bar, seas will increase to around 9 to 10 ft over the main channel late today and remain elevated into early Thursday. As a result, a Small Craft Advisory remains in effect until 5 PM PDT Thursday. ~12/23

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 5 PM PDT Thursday for PZZ210-251-252- 272.

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

Hazardous Seas Warning until 5 AM PDT Thursday for PZZ271.

Small Craft Advisory from 5 AM to 5 PM PDT Thursday for PZZ271.