textproduct: Portland

SYNOPSIS

Dry conditions with mostly sunny skies through Saturday. Potential for frost tonight across the Upper Hood River Valley and southern Willamette Valley. High temperatures remain near or slightly above seasonable normals for late April. Chances for light, non-impactful showers increase Sunday to Tuesday, with the highest chances over the Cascades. Drier and potentially warmer temperatures return by Wednesday to Thursday as high pressure re-builds.

DISCUSSION...Today through Thursday

Satellite imagery as of early Friday morning depicts mostly clear skies with a few low clouds across northwest Oregon and southwest Washington. Given the clear skies and light winds, there should be some decent radiation cooling early this morning. However, the vast majority of the area will remain warm enough to prevent frost development. An exception is the Upper Hood River Valley, where temperatures have fallen to around 33-35 degrees for locations above 1000 feet (south of Odell). Closer to river level, temperatures are relatively warmer in the mid to upper 30s, but can't rule out some patchy frost. A Frost Advisory has been issued for the Upper Hood River Valley through 10 AM this morning. Meanwhile, along the I-5 corridor, the highest threat for frost will be across the southern Willamette Valley, with chances for temperatures dropping below 36 degrees in this area being around 15-25% this morning.

Expect dry weather with mostly sunny skies across northwest Oregon and southwest Washington today and Saturday. The upper level pattern over the Pacific Northwest remains northerly to northwesterly, mainly due to an amplified ridge over far northwest Canada and the northeast Pacific, and a stalled closed low over south-central Canada and the northern Plains. Since we're in a drier airmass and far removed from the low, conditions remain dry through Saturday. Temperatures are forecast near to slightly above normal this weekend, with highs in the mid to upper 60s for interior lowland valleys, and upper 50s to low 60s along the immediate coast. Since skies will remain clear Friday night, there will be renewed chances for frost development across interior valleys heading into Saturday morning. Chances for temperatures falling below 36 degrees are higher Friday night: 30-40% for the southern Willamette Valley, and 50-80% across the Upper Hood River Valley with the highest chances above 1000 feet elevation. Will need to potentially consider another Frost Advisory for the Upper Hood River Valley for tonight. Yesterday's cloud cover resulted in uncertainty for frost in the Upper Hood River Valley this morning, but there is higher confidence that conditions will be clear going into tonight.

Sunday through Tuesday, additional weak shortwave troughs extending from the parent low over south-central Canada will swing through the Pacific Northwest and bring increased chances for light, non-impactful showers. Chances for showers peak around 10-20% along the I-5 corridor and 20-40% across the Cascades, with the highest chances on Monday. Temperatures remain seasonable and in the mid to upper 60s for interior valleys early next week, but could be a few degrees cooler on Monday due to potential showers.

Wednesday to Thursday, the majority of LREF ensemble members suggest that upper level ridging will build over the northeast Pacific and shift into the Pacific Northwest. Most ensemble members also show above-average 500 mb heights over the area, suggesting warmer temperatures by mid to late next week. There still remains some uncertainty on the exact strength and placement of the ridge axis, thus leading to a wide range of high temperatures: high end max temperatures for Thursday next week are currently in the upper 70s to low 80s, while low end max temperatures are in the low to mid 60s. -10

AVIATION

Expect VFR conditions to continue through most of the period for most terminals. The only exception will be KAST and possibly KONP, with a 30-50% chance of MVFR and 20-30% chance of IFR/LIFR after 12Z Sat. With clear skies continuing through the TAF period, there is moderate to high confidence for another shot of low stratus and/or fog tonight along the coast. Additionally, similar to this morning, clear skies bring the potential for frost development over metal surfaces overnight into Sat morning.

Expect breezy winds across the area today before 03Z Sat, with northerly winds across much of the area and gusts up to 20-25 kt south of KUAO/KTMK, as well as easterly winds along the Columbia River Gorge with gusts up to 20 kt at nearby terminals.

KPDX AND APPROACHES...VFR and clear skies through the TAF period. Northerly to northeasterly winds around 8-10 kt with gusts up to 18 kt before 03Z Sat. The strongest wind gusts (20-25 kt) will be near the mouth of the Columbia River Gorge. Winds will gradually shift more northwesterly beyond 03Z Sat.~12

MARINE

High pressure over the waters and a thermal trough along the coast will result in north-northeasterly winds across the waters today. Pressure gradients will tighten tonight into early Saturday morning, resulting in breezy northerly winds with gusts up to 25 kt. The strongest winds will be south of Cape Falcon, so Small Craft Advisories have been issued for these central and southern marine zones through 2 AM Saturday. Pressure gradients gradually ease throughout Saturday morning, weakening northerly winds. Seas remain around 6-8 ft at 9-10 sec today, building to 8-9 ft tonight south of Cape Falcon as wind waves increase. High pressure continues late this weekend into early next week, with winds turning more west-northwesterly and remaining under 15 kt. A northwesterly swell also persists through next week, with seas falling to 5-6 ft by Monday to Tuesday. -10

PQR WATCHES/WARNINGS/ADVISORIES

OR...Frost Advisory from midnight tonight to 9 AM PDT Saturday for ORZ117-118-121.

WA...None. PZ...Small Craft Advisory from 3 PM this afternoon to 2 AM PDT Saturday for PZZ252-253-272-273.