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

Scattered showers linger east of I-5 this evening with rain mainly falling along the Cascade foothills and the higher terrain. Overall looking at an overcast region with VFR CIGs. Some areas of lower CIGs but in generally upper level MVFR and hovering right around that 3000 ft AGL mark. Over the next several hours, skies will continue to improve and lift even further above 5000 ft AGL. One area to continue to watch though is along the coast and westerly flow dominates. Could see more prolonged periods of MVFR conditions as is depicted by some higher resolution models. However, overnight the flow will become southerly and usher in warmer and slightly drier air and thus, less of a trend towards IFR or even low MVFR CIGs.

After 20Z Thu, inland terminals will begin to clear with many expected to see CIGs well above 5000 ft AGL.At this time, winds will also shift to the north as high pressure begins to form.

KPDX AND APPROACHES...VFR with no concerns through the period. Winds shift late in the TAF period but remain elevated and therefore fog is not a threat at this point. -27

MARINE

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>253-272-273. Hazardous Seas Warning until 5 AM PDT Thursday for PZZ271. Small Craft Advisory from 5 AM to 5 PM PDT Thursday for PZZ271.