textproduct: Portland

SYNOPSIS

Near normal temperatures expected today, then increasing Monday and Tuesday as a ridge amplifies over the northern Plains. The temperature and precipitation forecast becomes more uncertain late Wednesday into Thursday, however chances for rain showers during that time have increased with the latest forecast update. Trending warm and dry Friday and Saturday.

LONG TERM...Wednesday through Saturday night

The upper level low responsible for warmer temperatures Monday and Tuesday will be the same low responsible for uncertainty in the forecast late Wednesday into Thursday, particularly in regards to the temperature and precipitation forecast. Although model ensemble guidance is in good agreement regarding the development of a closed low somewhere over the far northeast Pacific early in the week, guidance begins to vary more when it comes to the strength and track of this low late Wednesday into Thursday. Around 60% of the multi-model ensemble (GEFS/GEPS/ENS) suggests the low will track directly over the WA and/or north OR coast, while the remaining 40% suggests the low will stay nearly stationary offshore while weakening. If the low does move inland and takes a track towards western WA or northwest OR, expect temperatures to end up cooler than the current deterministic forecast with increasing chances for rain showers. If the low stalls offshore and weakens, conditions will trend warmer and mainly dry, aside from chances for showers and isolated thunderstorms in the Cascades given the persistent southerly flow aloft this set-up would result in. Total model spread for high temperatures on Thursday remains large due to this uncertainty, with inland highs ranging anywhere from the upper 70s to mid 90s per the NBM 10th-90th percentile.

One thing worth noting is chances for a low track that is more favorable for showers in southwest WA and northwest OR, including locations west of the Cascades, have increased when compared to yesterday. The latest NBM guidance reflects this well and has increased PoPs to 20-40% Wednesday night into Thursday. Chances for at least 0.25 inches of rain or more have also increased and now range between 10-20% across all of northwest OR and southwest WA from the coast to the Cascade crest, with the highest probabilities over southwest WA, the north OR coast/Coast Range, lower Columbia, and Portland metro. There is a 1-10% chance for 0.50 inches of rain or more, which represents the wettest model solutions.

Confidence in the forecast actually increases a bit Friday into Saturday. This is when model ensemble guidance is in good agreement for dry and warm conditions, with high temperatures somewhere in the 80s or 90s for inland valleys. Chances for highs of 90 degrees or warmer peak on Saturday at 50-60% across the Willamette Valley, Portland metro, Columbia River Gorge, and Upper Hood River Valley. Chances for highs above 100 degrees are around 1-10%, suggesting extreme heat and significant heat-related impacts are unlikely to occur next weekend. -23

AVIATION

High pressure builds over the region with widespread VFR conditions. Winds are largely northerly around 5-8 kt, but areas that are north-south aligned like the Willamette Valley are already seeing gusts up to 15 kt. This will be the trend through the day with winds increasing along the coast this afternoon up to 25 kt. Uncertainty moves in tonight with whether or not MVFR conditions return. Based on the pattern, there is around a 40-50% chance of MVFR and around a 10% chance of IFR CIGs after 08Z Mon along the coast. High resolution models though are not projecting pervasive clouds but rather patchy. Therefore, terminals like KONP and KAST could see more variable conditions overnight. KTTD will see similar struggles with any backbuilding off of the Cascades. Largely though, VFR conditions will prevail inland.

KPDX AND APPROACHES...VFR with northerly winds over the next 24 hours. Less than a 20% chance of MVFR CIGs tonight. -27

MARINE

High pressure over the waters with a typical summer time pattern. Flow remains north to northwest with a thermal trough forming along the coast. Winds are generally 8-10 kt but will continue to rise through the afternoon with gusts up to 25 kt. Along the coastline and moorages, gusts up to 25 kt have been reported. Small Craft Advisory (SCA) winds are expected with sustained winds of 15-20 kt and gusts to 25 kt over much of the waters, but latest models have reduced coverage in the northern waters. Overall, the SCA is marginal and will likely fluctuate below and above criteria. Winds will ease overnight into Monday morning and therefore have shortened the length of time for the hazard. Seas will be around 5-7 ft at 6-8 seconds. Could see periods of choppier seas, but not necessarily widespread enough for hazardous seas. Conditions the rest of the work week are expected to be benign with wind waves ramping up on Saturday.

A SCA has been issued as well for rough seas in the Columbia River Bar due to a strong ebb and seas of 7 ft. -27

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 1 AM to 7 AM PDT Monday for PZZ210.

Small Craft Advisory until 2 AM PDT Monday for PZZ251>253- 271>273.