textproduct: Portland

SYNOPSIS

Hot weather remains the primary concern through Tuesday, though forecast temperatures have trended a bit lower compared to earlier expectations. Inland highs will still reach the 90s through Tuesday, while somewhat cooler overnight lows should offer at least modest relief in some areas. Temperatures begin easing Wednesday, though inland conditions remain above normal, and a low-end thunderstorm threat may develop. A broader shift toward cooler, more unsettled weather is then favored late week into next weekend.

DISCUSSION...Now through Sunday

As of late Monday afternoon, the forecast remains broadly on track, with upper-level ridging still the dominant feature over the Pacific Northwest. A dry and warm air mass remains in place, and after morning coastal stratus mixed out, temperatures rose efficiently through the day inland. Even with a slight downward adjustment to the temperature forecast, readings still climbed well above normal this afternoon, with many interior valley locations reaching the upper 80s to lower 90s.

Heat remains the main forecast concern through Tuesday, although both afternoon highs and overnight lows have trended somewhat lower than earlier forecasts. The more notable change has been on the overnight side, where lows tonight and again Tuesday night now appear more likely to provide somewhat better relief than previously expected. Even so, many inland areas will remain quite warm during the day, with highs still expected to reach the 90s through Tuesday. This will continue to support widespread Moderate HeatRisk across the interior valleys, especially for those sensitive to heat or without effective cooling.

Tuesday still looks hot, even as the overall temperature forecast comes down slightly. Much of the interior valley should again warm into the low to mid 90s, while areas from Salem northward into the Portland/Vancouver metro may still see warmer overnight lows than surrounding locations due to urban heat retention. The Heat Advisory remains in effect through Tuesday evening for the I-5 corridor from Salem to the Cowlitz Valley, along with the Columbia River Gorge and Upper Hood River Valley. Anyone with outdoor plans should continue taking basic heat precautions, including staying hydrated, seeking shade, and limiting strenuous activity during the warmest part of the day.

A transition begins Wednesday as the ridge weakens and marine influence gradually increases. Temperatures will trend lower, but inland highs are still expected to remain above normal, generally in the upper 80s to lower 90s. In addition, SPC has introduced a general thunderstorms risk for Wednesday across the Cascades/foothills. Confidence remains low, but a few thunderstorms cannot be ruled out as the pattern becomes less stable. While some models suggest CAPE values as high as 1200 J/kg and bulk shear around 20 kt, the chance of precipitation is so low that those same models barely suggest enough saturation for thunderstorm development.

The larger-scale pattern change still appears on track for late Thursday into Friday as upper-level troughing movies into the Pacific Northwest. This should bring a more noticeable turn toward cooler and more unsettled conditions, along with increasing changes for rainfall across much of northwest Oregon and southwest Washington. There is also a low chance of thunderstorms lingering into Saturday, particularly across the interior valleys and Cascades/foothills.

Beyond that, ensemble guidance continues to favor generally seasonable to slightly cool conditions heading into next weekend. While the exact timing and coverage of precipitation later this week still carries some uncertainty, confidence is increasing that the prolonged hot and dry pattern will give way to a more typical late-June regime by the end of the week. ~12

AVIATION

Westerly flow aloft with weak upper level ridging will maintain high pressure over the region today. As of 21z, marine stratus remains just along the coast with LIFR CIGs persisting at KONP, while observations at KAST indicate clouds have pulled offshore enough for skc conditions. Expect widespread VFR conditions under mostly clear skies to persist inland through the TAF period. Chances for marine stratus remain high (50-70%) at KONP this evening through Tue morning, while the northern OR coast sees lower chances (20-30%) for IFR stratus after 04z Tue. North to northwest winds increase this afternoon with gusts up to 20 kt possible, except up to 25 kt along the central OR coast.

KPDX AND APPROACHES...VFR expected through the TAF period with mostly clear skies. Northwest winds around 5 kt expected to increase to around 10 kt with gusts up to 18 kt later this afternoon. /DH

MARINE

High pressure offshore will maintain breezy north to northwest winds across the coastal waters through Wednesday. Winds generally expected to remain under 20 kt, though gusts up to 25 kt are possible across the outer waters south of Cape Falcon through tonight. Small Craft Advisories remain in effect for these waters through 5 AM Tuesday. Weakening high pressure will give way to a frontal system approaching the area on Thursday. Winds are expected to back west to southwesterly before the cold front pushes across the coastal waters late Thursday into Friday. Southwest winds are expected to be strongest across the northern inner waters, but only around a 10-20% chance of gusts reaching SCA thresholds through Friday morning. West to northwest winds will persist behind the front later Friday and into the weekend as weak low pressure lingers near Vancouver Island. High pressure gradually builds across the waters late weekend. Seas remain relatively steep and choppy around 5 to 6 ft through Wednesday, subsiding to 4 to 5 ft Thursday into Friday. /DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...Heat Advisory until 11 PM PDT Tuesday for ORZ108>115-119>123.

WA...Heat Advisory until 11 PM PDT Tuesday for WAZ204>210.

PZ...Small Craft Advisory until 5 AM PDT Tuesday for PZZ272-273.