textproduct: Portland

SYNOPSIS

Persistent onshore flow will continue to yield dry and seasonable weather through this weekend. Temperatures trend warmer early next week as high pressure builds over the Plains. Beyond midweek, forecast uncertainty increases but dry and hotter weather is favored.

DISCUSSION...Now through Wednesday

Pleasant, seasonable, and benign weather is expected to continue through this weekend as zonal flow aloft turns southwesterly ahead of an upper-level trough moving onshore into British Columbia on Saturday. Temperatures will remain near seasonal norms, reaching afternoon highs in the upper 70s to low 80s in interior valleys and low to mid 60s along the coast each afternoon. Inland intrusions of low marine stratus clouds overnight will largely clear to sunny skies each day, aside from more persistent coastal clouds Friday and a deeper inland intrusion Saturday morning as the trough makes its closest approach. These clouds will help keep Friday and Saturday a few degrees cooler.

By the beginning of next week, a broad upper-level ridge over the Central Plains will amplify, pushing heights aloft upward locally. This will result in warmer temperatures Monday and Tuesday, with afternoon highs most likely in the mid 80s to around 90 degrees within inland valleys and mid 60s to near 70 degrees on the coast. Temperatures look to peak on Tuesday, with the chances to exceed 90 degrees reaching 25-40% along the I-5 corridor from Portland southward. The chances for Moderate HeatRisk reach 25-45%, highest in the lower Tualatin Valley (Beaverton, Tigard, Tualatin) and adjacent portions of Multnomah and Clackamas Counties (Portland, Wilsonville, Canby), while the chances of Major HeatRisk remain less than 5%. While forecast uncertainty increases, the ensemble consensus is that another trough will move into western Canada midweek, pushing temperatures back down a few degrees on Wednesday, resulting in widespread Minor HeatRisk.

Looking slightly beyond the 7-day forecast period, the ensemble consensus suggests the robust inland ridge may retrograde to the west, resulting in increased chances for more hazardous heat toward the end of next week. At this lead time, the chances for Major HeatRisk reach 10-25% from Salem north to the lower Cowlitz Valley and Portland east through the Columbia Gorge from next Thursday into the following weekend. -36

AVIATION

A weak upper level trough digs south towards airspace, turning the flow aloft more southwesterly. Expect VFR conditions to continue through the TAF period for inland terminals, with only a 10-20% chance for MVFR CIGs between 12-17Z Fri. For coastal terminals, expect deteriorated conditions to begin around 07-09Z Fri and continue through the rest of the TAF period. Specifically, between 07-17Z Fri, expect a mix of LIFR/IFR conditions (20-40% chance of LIFR, 30-50% chance of IFR), then gradual improving MVFR conditions thereafter (chances of MVFR decreasing from 70% to 30%). Otherwise, expect west to northwesterly winds 5-10 kt at all terminals, highest during the afternoon. Possible gusts up to 20 kt at a few inland terminals.

KPDX AND APPROACHES...VFR conditions with a 10-20% chance of MVFR CIGs between 12-17Z Fri. Northwesterly winds around 5-10 kt, with gusts up to 20 kt possible during the afternoon. ~12

MARINE

High pressure over the waters today will maintain breezy north to northwest winds through this evening. Gusts up to 20 kt will be possible south of Cape Foulweather. A weak cold front will move across the waters on Friday, ultimately disrupting the high pressure and decreasing winds across the waters. High pressure effetely rebuilds over the coastal waters through the weekend, returning northerly winds later Saturday and increasing pressure gradients on Sunday, returning chances for gusts up to 25 kt. Seas are expected to remain around 4 to 6 ft as relatively benign conditions persist through the weekend and into the start of next week. /DH

PQR WATCHES/WARNINGS/ADVISORIES

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