textproduct: Portland

SYNOPSIS

Dry and benign weather is expected across the region through much of the next week as high pressure builds over the Northeast Pacific, resulting in a warming trend. Weak systems aloft may bring enhanced cloud cover on some days, but rain chances are minimal.

DISCUSSION...Now through Sunday night

Concerns for hazardous weather remain minimal through the upcoming week. There is high confidence that upper-level ridging and surface high pressure will build over the Northeast Pacific, although uncertainty in the amplitude and position of the upper ridge increases later in the forecast period. Through the end of the workweek, while the ridge axis remains well offshore, upper shortwaves within northwesterly flow aloft may produce increased cloud cover on certain days including Tuesday into Wednesday morning, but chances for rainfall remain 5-10% along the Clatsop and Pacific County coasts and in the Willapa Hills, and lower elsewhere. On clearer nights, areas of fog are most likely to develop within sheltered valleys. As the ridge axis shifts east, temperatures will trend upward through at least Thursday, reaching the 60s on the coast and upper 70s to low 80s along the I-5 corridor. At this time, there is Minor HeatRisk forecast across the region, meaning those who are most sensitive to heat may be affected, however there are 15-25% chances Moderate HeatRisk occurs in some urban areas along I-5 if daytime highs end up slightly hotter, including the Portland/Vancouver metro, Salem, and Albany/Corvallis areas.

Later in the forecast period, from Friday through next weekend, uncertainty in the evolution and possible break-down of the upper-level ridge introduces similar uncertainty in forecast temperatures and precipitation. Forecast daytime highs currently trend downward through the holiday weekend as chances increase that ridging deamplifies or is replaced by an upper trough, but there is an increasingly wide range of possible outcomes. The 80%-confidence envelopes (the difference between the 10th and 90th percentiles) in temperature widen from 8-13 degrees on Friday and Saturday to 16-18 degrees on Sunday and Monday along the I-5 corridor. There is greater consensus that the ridge will break down late Sunday into Monday, yielding increasing chances of cooler temperatures as well as the highest chances of rainfall, 25-50%, in over a week. -36

AVIATION

High pressure will maintain fair conditions with high level clouds moving overhead through the day. Northwest flow of 5-10 kt through the day with wind gusts along the coast up to 20 kt possible. Winds relax this evening and overnight. Marine stratus pushed back toward the coast this evening, mainly along the northern Oregon and southern Washington coast. Probabilities increase to 60-90% for development between 02-06z Wednesday for KAST and much lower at 20-30% for KONP. Guidance suggests stratus developing along the Columbia River toward the Portland/Vancouver Metro between 10-1z Wednesday.

KPDX AND APPROACHES...VFR conditions expected through at least 06z Tuesday. High clouds expected to clear out this afternoon. Light northwest winds expected to increase to 8-10 kt by 22z this afternoon. Stratus pushing inland along the Columbia River could reach the metro between 10-16z Tuesday with a 30-60% chance for sub-VFR CIGs, mainly for KTTD and KPDX. -19

MARINE

Northerlies are expected to persist through much of the week as the summer-like pattern settles in. Strongest winds are expected during the afternoon and evening periods as a surface thermal trough strengthens over the southern Oregon coast. A Small Craft Advisory is in effect for the inner coastal waters south of Cape Foulweather later this afternoon into this evening for gusts up to 25 kt. Similar conditions are expected on Tuesday. Seas around 6 to 8 feet are expected through the week as well. Chances increase on Wednesday and Thursday for more widespread wind gusts for all marine zones.

Small Craft Advisories is in place for the Columbia River Bar for early Tuesday morning due to strong ebb currents which will produce conditions hazardous to small craft. Strong ebb currents are possible during the morning hours each day this week. -19/DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.

WA...None.

PZ...Small Craft Advisory from 5 AM to 9 AM PDT Tuesday for PZZ210.

Small Craft Advisory until 11 PM PDT this evening for PZZ253.