textproduct: Portland

SYNOPSIS

Cool and generally dry weather will continue through Monday as temperatures gradually moderate. The next chance for rain arrives Tuesday into early Wednesday, with the best chances along the coast, Coast Range, and northern Cascades while most inland valleys likely remain dry. Forecast uncertainty increases toward the latter half of next week.

DISCUSSION...Now through Friday

A weak ridge and surface high pressure are settling over the region, resulting in a quiet and dry remainder of the weekend. Temperatures will gradually recover from the chilly conditions of the past few days, with highs generally in the upper 60s to low 70s Sunday and Monday across the interior lowlands. Despite the slight warm up, temperatures will remain below seasonal average through the weekend.

Clear skies and light winds will promote efficient cooling tonight and again Sunday night, particularly across sheltered valleys. The Upper Hood River Valley remains the primary area of concern for frost, especially Sunday and Monday morning as temperatures could again fall into the 30s. However, chances are much less, with only a 5-15% chance of temperatures dropping to 36 degrees or below Sunday and Monday morning. Patchy fog is also possible during the morning hours where low-level moisture and favorable radiational cooling overlap, with the central and southern Willamette Valley, Coast Range valleys, and Cascade valleys among the more favored locations. Any fog should be localized and dissipate with daytime mixing.

The next meaningful change arrives Tuesday as a weak upper- level trough and associated frontal boundary move into the region. The highest confidence for measurable precipitation remains along the north Oregon coast and Coast Range into southwest Washington, where precipitation probabilities increase to around 50-75% Tuesday morning and then decrease Tuesday night into Wednesday morning. Some precipitation may extend into the northern Oregon Cascades as well. Farther inland, the signal is much weaker, with only around 15-35% of ensemble members indicating more than a trace of precipitation in the Portland metro and Willamette Valley Tuesday afternoon through Wednesday morning. Most inland locations therefore remain more likely to stay dry.

The front and associated trough weaken as they move through Wednesday, with dry conditions expected to return by Wednesday afternoon into Thursday. Ensemble guidance becomes increasingly spread out late next week as the larger-scale flow remains fairly progressive. Some solutions favor another weak trough and cooler conditions with a few light rain chances along the coast on Thursday, while others maintain zonal flow or weak ridging and generally dry weather. Specifically, current ensemble clusters are as such: 25% weak troughing, 25% weak ridging, and 50% roughly zonal. There is not yet enough agreement to favor a specific outcome of ridging or troughing, but the overall pattern remains relatively cool compared to seasonal averages. ~12

AVIATION...Through 00Z Monday

Primarily VFR conditions expected through the TAF period. A broken mid to high level cloud deck will spread across the region through this afternoon and evening, remaining through most of the overnight hours. This is expected to clear over the area sometime on Sunday morning. Similar to this morning, if it clears by 10-13z Sun, patchy fog/low stratus could quickly develop again by 12-15z with MVFR/IFR/LIFR conditions. There's around a 15-25% chance of this occurring at any terminal. If any fog/low stratus does occur, expect it to dissipate by 17-19z Sun. North winds today 10-15 kt at the coast and across the central and southern Willamette Valley with gusts up to 20-25 mph, decreasing after 03-06z Sun. North winds increase again along the coast to 10-15 kt by 19-21z Sun, though they remain generally less than 10 kts inland.

KPDX AND APPROACHES...Predominately VFR conditions expected through the TAF period. There's a 10-15% chance of MVFR/IFR low fog/stratus returning after 10-12z Sun if the high cloud deck that moves in tonight dissipates early enough Sunday morning. North to northwest winds increase to around 8-10 kt after 21z, decreasing after 02-05z Sun. -03

MARINE

Weak high pressure continues over the waters through Sunday. Northerly winds increase this afternoon and evening and remain elevated through Sunday evening with gusts up to 20-25 kts. There could be a short lull in wind gusts Sunday morning before they increase again Sunday afternoon/evening. Small Craft Advisories remain in effect through 11 PM PT Sunday, except through 5 AM PT Sunday for the Columbia River Bar. Wave heights will remain around 4-6 ft at 8-10 seconds through Sunday night.

A weak front approaches the waters Monday, shifting winds more westerly then southerly as the front moves through the waters on Tuesday. There are high chances (70-90%) of wind gusts exceeding 21 kts, Small Craft Advisory criteria late Monday into Tuesday for the coastal waters north of Cape Falcon, with gusts most likely peaking around 25-30 kts. A longer period west to northwesterly swell of 5-8 ft at 12-16 seconds will also move into the coastal waters late Monday into Wednesday, resulting in a moderate sneaker wave threat and increasing seas to 6-8 ft. -03

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 5 PM this afternoon to 5 AM PDT Sunday for PZZ210.

Small Craft Advisory from 5 PM this afternoon to 11 PM PDT Sunday for PZZ251-271.

Small Craft Advisory until 11 PM PDT Sunday for PZZ252-253-272- 273.