textproduct: Portland

SYNOPSIS

High pressure strengthens over the region Wednesday and Thursday, delivering the warmest weather of the week. A weak, moisture-limited trough brushes the Pacific Northwest Friday into Saturday, bringing a slight cool-down and low-end Cascade shower chances. With warm and dry conditions returning Sunday and Monday, continue to keep cold water safety in mind as local rivers remain cold enough for cold water shock.

DISCUSSION...Today through Tuesday

Satellite imagery as of early Wednesday morning depicts a few/scattered clouds across northwest Oregon and southwest Washington as skies slowly begin to clear out. These clearing skies are supporting efficient radiational cooling, especially across the Upper Hood River Valley. This morning's low temperature forecast for the Upper Hood River Valley was adjusted slightly colder to the low to mid 30s based on current observations. A Frost Advisory remains in effect for the Upper Hood River Valley through 8 AM this morning, with the highest threat for frost being above 1000 feet elevation where temperatures are coldest.

Warm and sunny weather returns today and Thursday as an upper- level ridge builds overhead and a drier airmass settles in. There is high confidence (80-90% chance) that afternoon temperatures reach the upper 60s to low 70s today, then climb into the upper 70s to near 80 on Thursday. The Greater Portland/Vancouver Metro down to Aurora have the best chances of exceeding 80 degrees on Thursday (about 80-90%), while the remainder of the I-5 corridor is lower (roughly 30-50%). Winds remain light and generally northerly. Overnight lows should continue to drop comfortably, keeping heat-related impacts limited.

Friday into Saturday, ensemble guidance remains consistent in showing the ridge weakening and shifting eastward as a weak trough drops in from Canada. Moisture with this trough appears limited, so most areas should stay dry. The only location with a meaningful precipitation signal remains the Cascades (including the Cascade foothills), where orographic lift will support a 15-30% chance for light showers; elsewhere probabilities remain below 10%. Temperatures will cool a few degrees with the passage of this weak trough, but remain seasonably warm.

Sunday into Monday, the majority of ensemble members depict the aforementioned trough shifting southeast and becoming a closed low towards California while upper-level ridging rebuilds over the Pacific Northwest (rex block pattern). This will favor another warm-up with dry weather prevailing for most lower elevations; the Cascades could still see occasional light showers due to wrap-around moisture from the south. Guidance continues to show very high confidence (>95%) for temperatures exceeding 80 degrees across interior valleys on Sunday, with a 50-70% chance for exceeding 90 degrees across the Portland/Vancouver Metro Area. If KPDX (Portland Int'l Airport) reaches 90 degrees on Sunday, May 3rd, not only would this break the daily record of 89 degrees set back in 1992, it would also be the second earliest day of the year where the airport reached 90 degrees. The earliest KPDX reached 90 degrees was April 30, 1998. The upper-level ridge breaks down Monday to Tuesday, gradually cooling temperatures back down into the 70s.

During this late-week warmth, those recreating on area rivers should remain aware of water temperatures, which remain cold enough for cold water shock, even on hot afternoons. Wear a personal floatation device and use extra caution around fast, cold water. -10/12

AVIATION

Satellite imagery as of early Wednesday morning depicts FEW/SCT clouds across northwest Oregon as conditions gradually clear up. High confidence for predominately VFR conditions through the TAF period, as chances for MVFR CIGs are only 10-20% for all terminals through 16-17z Wed. High pressure will build today, leading to sunny skies by this afternoon. Northerly winds under 5 kt across the region through 17-18z Wed, then strengthening in the afternoon as pressure gradients tighten. Northerly winds for inland terminals remain under 10 kt this afternoon, while the coast remains breezier with gusts up to 20 kt between 21z Tue-02 Wed.

KPDX AND APPROACHES...VFR conditions through the TAF period with mostly clear skies. 10-20% chance for MVFR CIGs this morning through 16-17z Wed. Northerly winds under 10 kt today. -10

MARINE

High pressure offshore will maintain northerly winds across the waters through the end of the week. Northerlies strengthen each afternoon and evening as pressure gradients tighten over the coastal waters due to strengthening surface thermal trough near the southern Oregon coast. Wind gusts are expected to remain below 20 kt through this afternoon. This evening through at least Friday, there is high confidence (70-90% chance) for at least occasional small craft wind gusts up to 20-25 kt. The strongest gusts would mainly be south of Cape Falcon. A Small Craft Advisory has been issued for the waters south of Cape Falcon beginning 2 PM this afternoon and lasting through 11 PM for the inner waters (from shore to 10 NM) and through early Friday morning for the outer waters (beyond 10 NM offshore). A Small Craft Advisory has also been issued for the Columbia River Bar due to a strong ebb current between 2-7 AM Thursday.

Seas of 6 to 8 ft are expected to persist through the week with a northwesterly swell. Mid-period swells of 12-15 seconds will also result in a moderate sneaker wave threat at beaches Wednesday and Thursday. Those participating in razor clam digs should take extra precaution. -10/DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...Frost Advisory until 8 AM PDT this morning for ORZ121.

WA...None. PZ...Small Craft Advisory from 2 AM to 7 AM PDT Thursday for PZZ210.

Small Craft Advisory from 2 PM this afternoon to 11 PM PDT this evening for PZZ252-253.

Small Craft Advisory from 2 PM this afternoon to 5 AM PDT Friday for PZZ272-273.