textproduct: Portland

SYNOPSIS

Largely dry weather expected through midweek. Near normal temperatures today will warm above average Tuesday and Wednesday. Chances for wetter and cooler weather return late in the week with potential for a more robust system next weekend.

DISCUSSION...Now through Sunday

An upper level trough continues to move toward the PacNW, which has increased mid and upper level cloud cover across the region. This increased cloud cover has kept the surface insulated with temperatures ranging from the low 40s in the more sheltered valleys to mid to upper 40s elsewhere. Agreement among the ensembles remains very high in the trough elongating and pinching off into a closed upper low that drifts southward toward northern California through mid week. Precipitation chances remain low over land with the best chance over the Lane County Cascades at 15-20%. Cooler air associated with the trough will drop highs near normal today with the interior lowlands reaching the low to mid 60s and the coastal areas the mid to upper 50s.

Heading into Tuesday and Wednesday, the upper low will continue to drift toward California while heights rebound locally. This will keep conditions dry and will help temperatures jump back above normal into the upper 60s to low 70s across the interior lowlands. Overnight lows drop into the low 40s for most locations but the typical cool spots like the Upper Hood River Valley and portions of the coast range may drop into the upper 30s. Lows at this time could drop below 37 degrees briefly so not expecting widespread frost development so will hold off on Frost Advisories at this time.

The latter half of the week again trends toward cooler temperatures and modest chances for rain. Cluster analysis shows good agreement in troughing developing over the Gulf of Alaska and dropping southeast toward the PacNW Thursday into Friday. This pattern would favor a return to near normal temperatures and chances for light precipitation. Overnight lows Thursday and Friday night are expected to be much cooler with more widespread temperatures in the mid to upper 30s. If trends continues, will likely need Frost Advisories for portions of the lowlands, coast range valleys and other typical cool spots. Potential remains low for a more robust system to impact the PacNW this weekend as a trough drops out of the Gulf of Alaska. This system could be the first atmospheric river of the season, bringing substantial rain and possibly some gusty winds across the region. Uncertainty remains high at this time but details should become clearer in the coming days. -19

AVIATION...Through 18Z Tuesday

A low pressure system dropping southward well offshore will continue to send scattered high clouds over the area through 18Z Tuesday. High clouds should become thicker tonight, helping to prevent fog development. Confidence is high (>90%) for continued VFR flight conditions through 18Z Tuesday. Winds will remain light today and tonight at less than 5-10 kt before offshore winds develop sometime between 15-18Z Tuesday, bringing increasing easterly winds to KTTD and increasing northeast winds to KUAO. Winds will increase out of the north from KSLE to KEUG.

KPDX AND APPROACHES...VFR flights conditions will continue through 18Z Tuesday with scattered high clouds becoming broken tonight. Light south winds this morning should become northwesterly sometime between 22Z Monday and 00Z Tuesday, sustained around 5 kt. Easterly winds are expected to develop at KPDX around 18-19Z Tuesday, sustained around 8-11 kt. -23

MARINE

Southerly winds today with a northwest swell that continues to decrease to around 5-6 feet at 11-12 seconds. A low pressure system dropping southward well offshore will generate a stronger westerly swell arriving this evening which will push seas to 8-11 ft, highest beyond 10 NM and south of Cape Falcon where a Small Craft Advisory (SCA) is in effect starting at 5 PM today.

Winds turn northerly later today and increase noticeably tonight in the wake of the passing system. Widespread wind gusts up to 25 kt will be possible beyond 10 nm for PZZ271-273 into Tuesday evening. Therefore, have extended the SCA for the waters south of Cape Falcon to 5 PM Tuesday while also adding a second SCA for waters north of Cape Falcon up to Cape Shoalwater in effect from 2 AM to 5 PM Tuesday.

Conditions otherwise improve midweek as winds and seas ease, but a more active pattern looks to return late in the week. Increasing northwesterly winds and a northwesterly swell could push seas close to 10 ft again from Thursday into Friday, and a more potent weather system next weekend will bring increasing chances for seas above 10 ft and potentially gale-force winds. -19/36

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 2 AM to 5 PM PDT Tuesday for PZZ271.

Small Craft Advisory from 5 PM this afternoon to 5 PM PDT Tuesday for PZZ272-273.