textproduct: Portland

SYNOPSIS

Persistent onshore flow will continue to yield dry and seasonable weather through this weekend. Daytime highs trend warmer early next week as high pressure builds over the Great Basin. After the middle of next week, uncertainty increases in the exact forecast, but a warming and drying trend is expected.

DISCUSSION...Today through Wednesday

Minimal changes in the overall synoptic pattern through the remainder of the week. A broad, upper level trough will continue to push south and east through British Columbia, while a broad area of high pressure remains anchored over the Great Basin. This synoptic set-up is resulting in zonal flow aloft and onshore flow at the surface. This pattern will help to maintain near normal daytime highs across the forecast area as well as slightly cooler than normal, overnight lows.

As the start of next week approaches, another upper level trough or closed low, looks to dive southward out of the Gulf of Alaska and move into British Columbia. Which will result in the upper level flow pattern becoming southwesterly. In addition to the Alaskan system, the Great Basin high will also re-build. This general pattern change will result in a slight warming trend starting Sunday and continuing through the middle of the week. Expect high temperatures through the first half of next week to reach the mid to upper 80s inland and mid 60s to near 70 degrees along the coast, while overnight lows similarly push a few degrees warmer into the mid 50s across the region. This combination of temperatures continues to support widespread Minor HeatRisk across the majority of the region with isolated areas of Moderate HeatRisk in the Portland/Vancouver metro and through the Columbia Gorge, especially on Tuesday.

There remains a broad region from Salem north through the Lower Cowlitz Valley and east along the I-84 corridor through the Gorge where there is a 20-50% chance of Moderate HeatRisk on both Monday and Tuesday if forecast temperatures trend warmer, with the highest likelihood in the Lower Tualatin Valley (Beaverton, Tigard, Tualatin) and neighboring portions of Multnomah and Clackamas Counties (Portland, Wilsonville). Chances for Major HeatRisk are 10% or less across the region. Uncertainty in the temperature forecast increases beyond Wednesday as consensus is relatively low in the long-term evolution of the strong upper ridge. Nonetheless, chances for rain remain minimal through the period. /42-36

AVIATION

Generally VFR through the entire TAF period for inland locations. Coastal terminals will likely experience intermittent MVFR/IFR conditions through 18Z Thursday marine stratus slowly develops along the coast. Along the coast there is a 20-30% chance for MVFR conditions to develop along with a 10-20% chance of IFR conditions developing, higher near KAST. If lowered flight conditions develop, expect improvement towards VFR after 18Z Thursday. However,guidance suggests the potential of MVFR/IFR conditions to return to the coast around 03Z-05Z Friday. North to northwest winds through the TAF period, 5-10 kt with afternoon gusts up to 20 kt possible at inland terminals from 00Z-06Z Friday and 7-15 kt with afternoon gusts up to 25 kt possible at coastal terminals from 18Z Thursday through 04Z Friday.

KPDX AND APPROACHES...VFR through the TAF period. Northwest winds around 5-10 kt with gusts up to 20 kt from 00Z-06Z Friday. /42

MARINE

North to northwest winds across all waters through the weekend. Winds generally remain around 15 kt or less, though pressure gradients are expected to tighten this afternoon and evening which will result in a 10-20% chance of gusts up to 25 kt for locations south of Cape Foulweather. There is also a 5-15% chance for gusts up to 22 kt for locations south of Cape Falcon for the same time period. 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. /42

PQR WATCHES/WARNINGS/ADVISORIES

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