textproduct: Portland

SYNOPSIS

A strengthening ridge will keep temperatures on an upward trend through at least the middle of the week. Inland areas will slowly climb towards the low to mid 90s by Tuesday and Wednesday, with the coast noticeably cooler. Hottest conditions Tuesday and Wednesday. Dry weather will persist, and heat-related impacts will become a growing concern across the interior lowlands before temperatures ease slightly late week.

DISCUSSION...Tonight through Saturday

Minimal change in the overall forecast through at least the middle of the week. High pressure anchored over The Great Basin will slowly build northwestward, which will bring warm and dry conditions for the majority of the CWA. 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. There remains some uncertainty in the forecast as southerly flow will develop through the first half of the week as a series of lows push northward towards the Olympic Peninsula. Also, the southerly flow will push smoke into the region as well.

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, with the coast running around 10-20 degrees F cooler. After that, the forecast uncertainty increase as models and there ensembles are having a challenging time dealing with a series of lows moving northward from the central and southern Pacific for Tuesday and Wednesday. The first low in question is currently centered around 35.53 N/132.06 W, which puts it well west of the central California coast. This low will bring the potential for monsoonal moisture into the region, but models have continued to keep any moisture well east of the Cascades. The more probable impacts would come from whatever remains of TS Elida as it also moves northward and injects remnant tropical moisture into the broader pattern. If that moisture spreads north, even subtle increases in cloud cover could have a noticeable effect on high temperatures. In addition to the potential for cloud cover, southerly flow would also bring smoke/haze from fires in southern OR into the region and that could also result in slightly cooler temperatures than what ensemble guidance is showing. Still, ensemble guidance and cluster analysis continue to show this uncertainty by carrying a broader range of possible outcomes in the middle of the week. However, recent cluster analysis looks to have trended towards the drier solutions when 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. Current deterministic guidance has daytime highs, for inland valleys around 95-97 degrees F. NBM probabilistic guidance is showing a 10-25% chance of daytime highs at or above 100 degrees F on Tuesday and Wednesday.

Given that the region will very likely see multiple days of above normal heat and very limited overnight cooling, most inland areas will experience Moderate HeatRisk. As a result, have issued a Heat Advisory starting Tuesday morning through at least Wednesday evening for The Greater Portland/Vancouver metro area, The Columbia River Gorge (to include Hood River County) and Kelso/Longview, WA. Also, there a 35-60% probability of Major HeatRisk for those two days for the areas discussed above. So, drink plenty of fluids, stay in a cool place during the heat of the day, stay out of the sunshine, and check up on relatives and neighbors.

As Thursday/Friday approaches, guidance still points towards a modest weakening of the ridge as a broader trough begins to influence the Pacific Northwest and nudges the ridge eastward. That should allow temperatures to edge downward a few degrees late in the week, though temperatures may still run slightly above average for late July. Dry weather is expected to continue through much of the period, with no appreciable precipitation in the forecast at this time. -42/12

AVIATION

VFR conditions very likely (>80% chance) to continue throughout the period at inland terminals. While low clouds may again develop, chances for MVFR cigs reach only 20% overnight along the Cascade foothills including at KTTD, and 10% or less elsewhere along the I-5 corridor. Any low clouds will mix out by 15-17z Mon. Winds will remain at or below 5 kt, generally out of the north to northwest.

Along the coast, low marine stratus has already developed, and is likely to remain in place through tonight, with 50-70% chances cigs lower further to LIFR. Restricted vis is also likely to continue at MVFR or worse, with IFR/LIFR vis most likely at KONP. Conditions may briefly improve to MVFR/VFR between 18z Mon and 03z Tue. Winds will remain 5 kt or less tonight, then build to 5-10 kt out of the northwest late Monday morning.

KPDX AND APPROACHES...VFR conditions expected through the period. Low clouds along the Cascade foothills are very likely (90% chance) to remain east of the terminal. Northwest winds ease below 5 kt by 08-09z Mon. -36

MARINE

A typical summertime pattern will continue through early this 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, with seas becoming steep due to a fresh northwest swell around 6-8 ft at 7-8 seconds. Strongest winds and steepest seas will be in the waters south of Cape Falcon. A Small Craft Advisory remains in effect for all the waters through 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. -12/03

PQR WATCHES/WARNINGS/ADVISORIES

OR...Heat Advisory from 10 AM Tuesday to 11 PM PDT Wednesday for ORZ108-109-111-112-115-120>122.

WA...Heat Advisory from 10 AM Tuesday to 11 PM PDT Wednesday for WAZ204>207-209-210.

PZ...Small Craft Advisory until 11 AM PDT Monday for PZZ251>253- 271>273.