textproduct: Portland

SYNOPSIS

Seasonably cool and dry weather continues though Thursday morning/afternoon before a low pressure system moves onshore Thursday evening/night. Confidence is high this system will bring widespread rain and increasing winds to all of northwest Oregon and southwest Washington late Thursday into Friday, however exact rain amounts and peak wind speeds remain uncertain. High confidence for a return to dry weather on Saturday and Sunday as high pressure builds back in. Chances for rain then return to the forecast on Tuesday.

LONG TERM...Saturday through Tuesday night

The weather pattern becomes quiet heading into the weekend as model ensemble guidance remains in excellent agreement for a quick return to high pressure with dry weather. Temperatures will likely remain slightly cooler than average with highs in the mid 60s Saturday through Monday, with only a 5-10% chance for highs near 70 degrees over inland valleys. Chances for rain have lowered and now hold off until Tuesday, peaking near 20-35% Tuesday evening.

Morning frost remains possible in the Upper Hood River Valley each morning Saturday through Monday as light winds and mostly clear skies will allow for excellent radiational cooling overnight. The frost potential is mainly confined to the Parkdale and Dee Flat area where probabilities for lows of 36 degrees or colder range anywhere from 25-50%. Chances near Odell are lower at around 5-10%. -23

AVIATION...Through 12Z Thursday

West to southwest flow aloft will persist through 12Z Wednesday. As of 12Z Wednesday, a broken low stratus deck along the coast was beginning to lift ahead of an incoming cool front approaching the north Oregon coast from the west. Radar observations continue showing a narrow band of light rain showers extending along the frontal boundary. It now appears this front and the associated rain showers will arrive at KAST sometime between 13-14Z Wednesday, with ceilings likely lowering back to MVFR thresholds or lower (70% chance). Ceilings will improve back to VFR after 19-20Z at KAST, while most likely remaining VFR at KONP this morning.

Confidence is lower for inland TAF sites in regards to the potential development of a low stratus deck sometime between 13-16Z Wednesday. As of 12Z Wednesday, conditions remained VFR inland with scattered to broken high clouds around 20 kft. A very brief period of fog developed at KSLE and KEUG early Wednesday morning, but has since lifted. The probability for ceilings below 3000 ft peak between 30-40% around 14-15Z Wednesday at all inland TAF sites. Even if low clouds do develop later this morning, expect widespread VFR conditions to make a quick return after 18-19Z Wednesday.

KPDX AND APPROACHES...VFR conditions are expected to persist through at least 13Z Wednesday with scattered to broken high clouds. There is around a 30% chance for MVFR ceilings or lower to return at any time between 13-16Z Wednesday. Even if low clouds do develop later this morning, expect VFR conditions to make a quick return after 18-19Z Wednesday. Northwest winds around 3-6 kt are expected through the TAF period. -23

MARINE

High pressure will maintain northerly winds across the waters through Wednesday night before becoming northeasterly for a period of time early Thursday morning through early Thursday afternoon ahead of an approaching low pressure system. This system will move somewhere over the coastal waters late Thursday into Friday, bringing rapidly increasing winds and seas along with widespread rain. Guidance has not come into agreement yet on the exact track and strength of this low pressure system, which means exact wind speeds and wave heights are uncertain Thursday night into Friday. With that being said, confidence is high for at least small craft advisory level wind gusts of 21 kt or stronger with this system given probabilities for gusts over 21 kt have increased to 80-95%. In fact, chances for gale force wind gusts of 34 kt or stronger have also increased and now range between 45-55% given an increased potential for a relatively strong low pressure system tracking somewhere over the coastal waters. Potential low tracks could range anywhere from over the southern waters towards Florence to the northern waters towards the Columbia River Bar. A narrow belt of high winds will be possible on the south side of this low pressure system if it rapidly strengthens as it approaches the coast, however confidence is low regarding the location of these higher winds if they do materialize. Nevertheless, this helps explain why chances for max wind gusts of 48 kt or stronger are non-zero, currently ranging between 10-20%.

If this low takes a favorable track and strengthens as it approaches the coast, then hazardous seas as high as 15-20 ft would be possible (5-10% chance). If the low comes in weaker, peak winds would likely range somewhere between 25-35 kt and seas would likely peak closer to 10-13 ft. The latter is currently the most likely outcome, however the forecast should be monitored over the coming days for updates. -23

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...None.