textproduct: Portland

SYNOPSIS

Persistent onshore flow and varying degrees of morning cloud cover will bring seasonable temperatures July 8-11 along with continued dry weather. Temperatures trend warmer July 12-14 as upper level flow becomes southwesterly upstream of an amplifying upper level ridge over the central U.S.

DISCUSSION...Today through Tuesday

The forecast is highlighted by persistent onshore flow, seasonable temperatures, and continued dry weather across the CWA. Model ensemble guidance is in good agreement for an extended period of near zonal flow aloft from Tuesday night through at least Thursday night. Upper level flow becomes more southwesterly late Friday into the weekend. At the surface, onshore flow is expected to persist. This typical summer-time weather pattern will bring temperatures that are around normal for this time of year. Onshore flow at the surface will also result in varying degrees of morning cloud cover and plenty of afternoon sun. Expect daytime highs in the upper 70s to low 80s for inland valleys with highs in the low 60s to low 70s along the coast and high Cascades through Saturday. As the weekend approaches, model spread for temperatures begins to increase slightly over the weekend for inland valleys, with highs ranging anywhere from the upper 70s to upper 80s, with the coast and Cascades warming in a similar pattern, thus having daytime highs in the upper 60s to upper 70s. The daytime high will be highly dependent on how widespread morning cloud cover is and how early in the day cloud cover is able to scatter out. The current forecast favors more widespread and persistent cloud cover on Saturday when compared to Sunday.

Beyond the weekend, confidence is high temperatures will begin to warm early next week with less cloud cover. This warming trend is in response to increasing 500 mb heights and 850 mb temperatures upstream of an amplifying upper level ridge over the central United States. Since the ridge axis will be located east of the Rocky Mountains and far removed from the Pacific Northwest, extreme heat is not expected with this synoptic pattern. Instead, a more modest warm-up is likely with high temperatures most likely peaking in the mid to upper 80s for inland valleys. Meanwhile, the coast will remain cooler with highs staying in the low 60s to low 70s.

It should be noted that there is a 15-35% chance for highs of 90 degrees or warmer across the Willamette Valley, Portland/Vancouver metro, Columbia River Gorge, and Upper Hood River Valley on Monday and a 20-50% chance for highs of 90 degrees or warmer on Tuesday. Chances for highs above 95 degrees on Monday and Tuesday are around 10-20%, with the highest probability on Tuesday. While this pattern does not favor extreme heat; probabilistic HeatRisk guidance suggests there is a 20-50% chance for Moderate HeatRisk within the Willamette Valley,Portland/Vancouver metro, Columbia River Gorge, and Upper Hood River Valley Monday and Tuesday, with higher probabilities on Tuesday. /42-23

AVIATION

Onshore flow will continue through the TAF period, which will support marine stratus along the coast. Coastal sites are expected to maintain a mixture of IFR to LIFR conditions through at least 16Z-19Z Wednesday. Current observations are showing marine stratus pushing southward along the Columbia River bringing MVFR conditions to KPDX, KVUO and KTTD. Said stratus has a 30-50% chance of also spreading and impacting KUAO, KMMV and KHIO through 18Z-20Z Wednesday. 20-30% chance for MVFR stratus impacting KSLE and KEUG through 20Z Wednesday as well. Any lowered flight conditions that develop within the Willamette Valley should improve to VFR around 19Z-22Z Wednesday and should persist through the remainder of the TAF period. As for coastal locations, conditions should improve towards VFR/MVFR around 19Z-21Z Wednesday, but will return towards IFR/LIFR around 04Z-06Z Thursday.

Northerly winds expected to increase around 18Z-20Z Wednesday to around 10 kt. In addition, gusts are expected to develop for inland and coastal locations. For inland locations, gusts up to 20 kt starting around 19Z-21Z Wednesday through 04Z-06Z Thursday. For coastal locations, gusts up to 25 kt possible starting around 18Z-20Z Wednesday through 03Z-05Z Thursday. Afterwards, northerly winds will continue but less than 10 kt for the remainder of the TAF period.

KPDX AND APPROACHES...Current MVFR conditions will improve towards VFR starting around 17Z-19Z Wednesday. Northerly winds expected to increase around 18Z-20Z Wednesday to around 10 kt with gusts up to 20 kt starting around 19Z Wednesday through around 04Z Thursday. /42

MARINE

Broad troughing over the eastern Pacific will help to maintain north to northwest winds, generally 15 kt or less across all waters. Isolated gusts up to 20 kt possible this afternoon and Thursday afternoon for locations south of Cape Foulweather. Seas around 4 to 6 ft. Latest guidance suggests similar conditions continue into Thursday with winds easing slightly on Friday as a weak front approaches the waters. Otherwise, relatively benign conditions expected to persist through the week and into the weekend. /42

PQR WATCHES/WARNINGS/ADVISORIES

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