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 showers increase Sunday to Tuesday, with the highest chances over the Cascades. Drier and potentially warmer temperatures return by Wednesday into Thursday as high pressure builds.

DISCUSSION...Now through Friday

Mostly sunny skies today will allow for temperatures to warm into the mid to upper 60s this afternoon as the region remains under dry, northerly flow. A large upper level low will persist over central Canada while high pressure exists over the NE Pacific. Expect breezy northerly winds along the coast and through the Willamette Valley this afternoon and evening with gusts up to 20-25 mph. Pressure gradients relax overnight as light winds in the valleys and mostly clear skies allow for radiational cooling. Have issued a frost advisory for portions of the southern Willamette Valley, including the Lane and Linn County lowlands where temperatures are likely to fall to around 34-36 degrees. Have also issued another frost advisory for the Upper Hood River Valley for tonight into Saturday morning. Patchy frost is more likely for rural areas from the central Willamette Valley north into the south Washington lowlands.

Within the northerly flow aloft on Saturday, a relatively dry shortwave trough will drop south across the region. A few afternoon showers may develop over the Cascades, highest chances in southwest Washington. With the relatively cooler air aloft, surface temperatures will remain very seasonable, with afternoon highs once again warming into toe mid to upper 60s on Saturday. Very similar pattern continues into Sunday, except with slightly more moisture available in the mid-levels increasing chances for afternoon and evening showers over the Cascades and foothills.

Monday 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 with highs around the mid-60s for interior valleys early next week, though 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 some uncertainty and a wide range of high temperatures. High-end max temperatures for late next week are currently in the upper 70s to lower 80s, with around a 20-30% chance of exceeding 80 degrees on Thursday, while low-end max temperatures remain in the lower to mid 60s. DH/10

AVIATION

VFR conditions and clear skies continue throughout the airspace. Expect VFR conditions to persist through at least 18Z Sat for most terminals, with the only exceptions being KAST and possibly KONP. Guidance suggests a 20-40% chance of MVFR and 10-30% chance of IFR/LIFR CIGs between 10-18Z 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, clear skies tonight into Sat morning brings the potential for frost development over metal surfaces.

Breezy winds continue across the area today, with generally northerly winds with gusts up to 20-25 kt south of KUAO/KTMK and northeasterly to easterly winds with gusts up to 20 kt at terminals near the Columbia River Gorge. Terminals west of KTTD may struggle to shift northeasterly. Expect these breezy winds to weaken towards 03-06Z Sat.

KPDX AND APPROACHES...VFR and clear skies continue through the TAF period. Current northwesterly winds may shift northerly to northeasterly during the afternoon. Before 03-06Z Sat, winds will remain around 8-10 kt and possibly gust up to 18 kt. Thereafter, expect northerly to northwesterly winds around 4-6 kt through at least 18Z Sat. ~12

MARINE

High pressure over the waters combined with a thermal trough along the coast is producing north to northeasterly winds across the waters this afternoon. Pressure gradients will continue to tighten into this evening and persist through early Saturday morning, leading to breezy northerly winds with gusts up to 25 kt. The strongest winds are expected south of Cape Falcon, where Small Craft Advisories remain in effect for the central and southern marine zones through 2 AM Saturday.

Pressure gradients will gradually ease late tonight into Saturday morning, with northerly winds weakening through the day. Seas are currently around 6 to 7 ft at 9 to 10 seconds will gradually subside to around 5 to 6 ft into Saturday and continue into next week. High pressure will persist through the remainder of the weekend into early next week. Winds will shift more west- northwesterly on Monday and remain below 15 kt. A northwesterly swell will continue through next week.~12/10

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 until 2 AM PDT Saturday for PZZ252-253-272- 273.