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

Relatively weak west to northwest flow aloft today as a broad upper level trough persists over the region. Onshore flow in the lower levels has pushed marine stratus to the coast and into parts of southwest Washington and the northern Willamette Valley, reaching as far south as KUAO. IFR to lower-end MVFR CIGs are expected to persist at coastal terminals through 19-21z this afternoon, while inland MVFR stratus should scatter out by 18-20z. Predominately VFR conditions are then expected to remain for inland terminals through much of the TAF period, as there is currently just a 10-20% chance for stratus to redevelop tomorrow morning. Coastal locations are more likely to see marine stratus push back onshore after 04-08z Thursday with around a 30-40% chance of IFR conditions developing.

Northwest winds are expected to increase this afternoon to around 10-15 kt, while gusts up to 25 kt will be possible along the central Oregon coast.

KPDX AND APPROACHES...MVFR stratus is expected to improve toward VFR around 18-20z as clouds scatter out this afternoon. Northwest winds are also expected to increase to around 10-12 kt with gusts up to 20 kt possible between 00-06z Thu. /DH

MARINE

High pressure will maintain north to northwesterly winds across the coastal waters through the week. Winds generally remain around 15 kt or less, though pressure gradients are expected to tighten later this afternoon and evening producing gusts up to 25 kt near the central Oregon coast. Thus, have issued a Small Craft Advisory for the coastal waters south of Cape Foulweather between 3 PM today and 2 AM tonight. Isolated gusts up to 20-22 kt will also be possible south of Cape Falcon.

Conditions ease slightly on Thursday, and moreso on Friday, as a weak front approaches the waters. Seas are expected to remain around 4 to 6 ft as relatively benign conditions persist through the remainder of the week and into the weekend. /DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 3 PM this afternoon to 2 AM PDT Thursday for PZZ253-273.