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 Thursday

Seasonable conditions are expected across the region through the weekend. An upper level trough over northern British Columbia will slip farther south today, supporting average temperatures in the uppers 70s to low 80s across the inland valleys and in the low to mid 60s along the coast each afternoon. Marine stratus expected to remain confined to the coast, coast range valleys, and along the lower Columbia River Friday. Coastal locations may see a short period of broken or scattered clouds this afternoon before stratus rebuilds eastward. Stratus is expected to be more widespread tonight into Saturday morning as the trough shifts more overhead. Saturday morning is expected to start out cloudy, eventually dissipating by the afternoon but overall keeping the temperatures cooler.

Expect a shift toward warmer temperatures to start next week as an upper level ridge amplifies over the Central Plains. Temperatures expected to jump into the mid 80s to around 90 degrees on Monday and Tuesday for inland valleys and mid 60s to around 70 degrees along the coast. Tuesday looks like the warmest day next week and has the highest and most widespread probabilities for 90 degrees. Chances are 30-40% along the I-5 corridor and around the Portland metro with lower chances of 15-30% within the Cascade and Coast Range Foothills. There is also a low (5-15%) chance for some locations around the Central Willamette Valley to reach 95 or greater. The chances for Moderate HeatRisk reach 25-50%, 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%.

Confidence begins to drop off by the middle of next week with 500 mb clusters divided on whether the ridge remains the dominant feature or if a trough is able to move into the region. There is a 15-20 degree spread in the 10th-90th percentile high temperatures for Wednesday, ranging from the mid 70s to mid 90s. At this lead time and given the uncertainty, 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 Wednesday through Friday. -19/36

AVIATION

A trough continues to dig southward toward the region, supporting onshore flow and marine stratus along the coast. MVFR/IFR CIGs are expected to persist along the coast into the afternoon with a chance for cloud cover to break up or clear out late this afternoon. Higher chances for VFR conditions around KONP at 70-80% after 20Z and lower chances around KAST at 40-50%. There is also a 40-50% chance for MVFR CIGs in the eastern Portland Metro between 12-18Z. Stratus quickly rebuilds along the coast this evening along with backbuilding toward the lowlands off the Cascade Foothills after 06-09Z Saturday. Expect MVFR or lower CIGs for all terminals for a period Saturday morning.

Light west to northwest winds less than 5 kt through 18Z, then increasing to 6-10 kt for all terminals. Could see a few gusts to around 15-18 kt around the Portland metro after 00Z.

KPDX AND APPROACHES...VFR conditions with a 30-50% chance of MVFR CIGs between 12-18Z. Northwesterly winds around 5 kt, increasing to 7-9 kt after 18z and possible gusts 15-18 kt after 00z Saturday. -19

MARINE

A weak cold front will move across the waters on today, ultimately disrupting the high pressure and decreasing winds across the waters. High pressure rebuilds over the coastal waters through the weekend, returning northerly winds later Saturday and increasing pressure gradients on Sunday. Chances for gusts up to 25 kt return Sunday afternoon, mainly across the central and southern waters out to 30-40 nm. 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. -19/DH

PQR WATCHES/WARNINGS/ADVISORIES

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