textproduct: Portland

SYNOPSIS

A strengthening ridge will keep temperatures on an upward trend through the first half of the week. Inland areas will climb into the upper 80s to maybe 90 today and Monday, then see the hottest conditions Tuesday and Wednesday when many valleys rise into the upper 80s to mid 90s. Dry weather will persist, and heat-related impacts will become a growing concern across the interior lowlands before temperatures ease slightly late week.

DISCUSSION...Now through Saturday

The forecast pattern early this morning remains dominated by building high pressure over the western U.S., with the core of the ridge centered near the Great Basin and extended northwest into the Pacific Northwest. This setup will continue to favor a warming and drying trend across southwest Washington and northwest Oregon through at east midweek. Even though weak onshore flow near the surface persists, especially closer to the coast, it will only modestly slow the warming rather than stop it. As a result, temperatures will continue to rise each day inland, while coastal communities stay cooler but still trend a bit warmer as well.

Today will mark another step upward in temperatures, with most interior lowland locations reaching the upper 80s to maybe 90 degrees by the late afternoon. The warmest temperatures should occur in the typically hotter valleys, while the coast remains in the mid 60s to mid 70s under continued marine influence. Higher terrain will also warm efficiently today, with many mountain and foothill locations rising into the upper 70s and 80s.

The hottest stretch of the forecast appears to be Monday through Wednesday as the ridge reaches maximum strength. Confidence remains fairly high that Monday will bring widespread upper 80s to lower 90s across the interior lowlands. After that, the forecast becomes a bit less certain for Tuesday and Wednesday. Much of that uncertainty is tied to moisture and cloud trends over the eastern Pacific, including a low off the California coast and the potential for remnant tropical moisture to become entrained into the broader pattern. If that moisture spreads north, even subtle increases in cloud cover could have a noticeable effect on high temperatures. Ensemble guidance and cluster analysis continue to show this uncertainty by carrying a broader range of possible outcomes in the middle of the week. With that said, recent cluster analysis looks to have trended a bit more drier compared to previous runs.

Even with those details still being worked out, confidence remains high in the broader message: Tuesday and Wednesday are still favored to be the hottest days for much of the interior. Probabilities remain supportive of widespread 90-degree highs across inland valleys, with the best chances occurring Tuesday and Wednesday. Some of the warmest locations also have a reasonable shot at reaching the mid 90s, especially if cloud cover remains limited. With multiple days of above normal heat and only limited overnight cooling, expect at least Moderate HeatRisk across most if not all of the interior lowlands. The Portland/Vancouver metro now appears increasingly likely to reach Major HeatRisk on Tuesday, with a few additional areas also possibly reaching that risk if the warmer end of the forecast verifies.

By Thursday/Friday, guidance still points towards a modest weakening of the ridge as a broader trough begins to influence the Pacific Northwest and nudges the heat eastward. That should allow temperatures to edge downward a few degrees late in the week, though temperatures may still run somewhat above average for late July. Dry weather is expected to continue through much of the period, though there is a low-confidence potential for a shortwave trough to rotate eastward along a broader trough, bringing a chance of light rain Friday into Saturday. ~12

AVIATION

Currently VFR inland and a mix of MVFR/IFR CIGs along the coast as of 11Z Sun. Coastal terminals will continue to see these MVFR/IFR CIGs until 17-19Z Sun as marine stratus continues to push into the coast (70-90% chance of MVFR CIGs, 30-50% chance of IFR CIGs). Conditions will improve to VFR thereafter and persist until around 03-05Z Mon. Coastal terminal conditions will then deteriorate back to MVFR/IFR CIGs and remain so through the end of the TAF period (50-70% chance of MVFR CIGs, 30-50% chance of IFR CIGs). As for inland terminals, expect VFR conditions through the TAF period, with a 15-25% chance of MVFR CIGs between 12-17Z Sun (highest chance at KTTD due to the potential of stratus backbuilding off the Cascade foothills). Otherwise, expect light north to northwest winds early this morning to build to 7-12 kt with gusts up to 15-20 kt inland and 10-15 kt with gusts up to 25 kt at the coast by midday Sunday.

KPDX AND APPROACHES...VFR conditions favored throughout the period, with just a 15-25% chance of MVFR CIGs between 12-17Z Sun. Light northwest winds build to 5-10 kt by midday Sunday. ~12

MARINE

A typical summertime pattern will continue through early next week with persistent north to northwest winds over the coastal waters. Winds will be strongest during the afternoon and evening hours each day, especially today for the waters south of Cape Falcon. Expect wind gusts up to 25 kt over the central and southern waters today, with seas becoming steep due to a fresh northwest swell around 6-7 ft at 7-8 seconds. By this afternoon, these gusty winds and steep seas will expand into the waters north of Cape Falcon. Between the increasing winds and steepening seas, conditions will become hazardous to small craft. As such, Small Craft Advisories are in effect for the waters south of Cape Falcon through this morning, then for all the waters this afternoon through early Monday morning.

Winds decrease below 20 kts early Monday morning, with seas becoming less steep through the day as the swell decreases. Benign conditions expected Tuesday into late next week. ~12

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 2 PM this afternoon to 5 AM PDT Monday for PZZ251-271.

Small Craft Advisory until 5 AM PDT Monday for PZZ252-253-272- 273.