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...Now through Monday

Tonight into Wednesday, a Frost Advisory is in effect for the Upper Hood River Valley (notably above 1000 ft in elevation) from 1 AM to 8 AM Wednesday. Lows there are expected to drop into the 33 to 36 degree range, which is cold enough for frost development. Frost may harm sensitive outdoor vegetation; protect or bring in sensitive plants.

Wednesday and Thursday bring a sharp turn toward warmer, sunnier weather as high pressure builds overhead and a drier air mass settles in. Confidence is moderate to high (greater than 60%) that inland highs reach the upper 60s to low 70s Wednesday, then climb into the upper 70s to near 80 Thursday. The Greater Portland metro down to Aurora still has the best odds of hitting 80 on Thursday (about 50-80%), while the remainder of the I-5 corridor is lower (roughly 20-40%). Overnight lows should continue to drop comfortably, keeping heat-related impacts limited.

Friday into Saturday, model and ensemble guidance remains consistent in showing the ridge weakening as a weak trough drops in from Canada. Moisture with this feature appears limited, so most areas should stay dry. The only location with a meaningful precipitation signal remains the Cascades (including the Cascade foothills), where chances for light showers are around 20-40%; elsewhere probabilities remain below 15%. Temperatures ease back a few degrees but remain seasonably warm.

Sunday into Monday, many ensemble solutions depict a closed low shifting southeast towards California while high pressure rebuilds across the Pacific Northwest. That favors another warm- up locally with dry weather for most lower elevations; the Cascades could still see occasional light showers if any moisture wraps north. Guidance continues to support high confidence (>90%) for greater than 80 degrees along the I-5 corridor Sunday, with Monday maintaining a 50-80% chance, again highest near the Greater Portland metro.

During 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. ~12

AVIATION

Moderate to high confidence in persistent VFR flying conditions across the region throughout the period. Few-sct low clouds at 3-5 kft expected overnight beneath high pressure offshore, with 30-50% chances for MVFR cigs at coastal terminals and 10-30% inland. Any low clouds will quickly mix out Wednesday morning, with clear skies expected by 18z Wed. Light north winds will ease below 3 kt overnight, then build out of the northwest to 5-10 kt inland and 10-15 kt with gusts to 20 kt along the coast by Wednesday afternoon.

KPDX AND APPROACHES...High confidence in VFR flying conditions throughout the period. Few-sct low clouds at 3-5 kft expected overnight, with a 10-15% chance of MVFR cigs if cloud coverage exceeds expectations. Low clouds will dissipate quickly through Wednesday morning with clear skies expected by 18z Wed. Light northwest flow of 5 kt or less overnight will build to 5-10 kt by Wednesday afternoon. -36

MARINE

Northwesterly winds today turn northerly by Wednesday as high pressure persists offshore. 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 Wednesday morning. From Wednesday evening through at least Friday, there is a 70-90% chance for at least isolated small craft wind gusts up to 20-25 kt. The strongest gusts would mainly be south of Cape Falcon. The highest probabilities for SCA winds are for Thursday and Friday. Seas of 6 to 8 ft are expected to persist through the week with a northwesterly swell. Mid-period swells of 13-16 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. DH/10

PQR WATCHES/WARNINGS/ADVISORIES

OR...Frost Advisory until 8 AM PDT Wednesday for ORZ121. WA...None. PZ...None.