Area Forecast Discussion

SYNOPSIS

Dry weather will persist this weekend into next week as an upper level ridge builds over a thermal trough this weekend. Temperatures remain on track to increase over the weekend into early next week into the 80s and 90s across the region, with much of the lowlands seeing moderate HeatRisk and a few isolated areas of major HeatRisk. The dry and unstable airmass will also produce elevated fire weather concerns. Onshore flow returns Monday night into Tuesday, with breezy winds bringing in cooler air.

SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/

Satellite continues to show clear skies with cumulus clouds near the Olympics this afternoon.

Upper level pattern remains the same, continuing to show that ridge beginning to set up over Western Washington on Friday, bringing max temperatures between 70 and 75 degrees along with it. On Saturday, expect localized moderate HeatRisk, with temperatures between 75 and 85 degrees at the hottest point of the day.

Cloud cover will continue to be minimal over the Western Washington region. Widespread cloud coverage has located off the coast, with low clouds forming during the mornings over the Cascade and Olympic Mountains, eventually dissipating as the weekend days drag on.

HPR/NW

LONG TERM /SUNDAY THROUGH THURSDAY/

The upper level ridge will continue to build over the thermal trough Sunday into Monday, which will produce an offshore pattern where temperatures will climb, and relative humidities will decrease. See fire weather discussion below for details on elevated fire weather concerns. The other concern is heat, with high temperatures remaining on track to peak Sunday into Monday. Given the persistent forecast in high confidence for widespread moderate HeatRisk Sunday/Monday, and pockets of isolated major HeatRisk in the Seattle metro and south/southwest interior, a heat advisory was issued, which will go into effect at 11 AM Sunday through 5 AM Tuesday. The warmest period will be from Sunday into Monday night. High temperatures will reach from the mid 80s into the upper 90s, with the warmest temperatures in the south sound/southwest interior. Overnight temperatures in the upper 50s/low to mid 60s also may not allow for homes to cool off substantially overnight from daytime heat. Additionally, water temperatures during this heat event remain chilly, with most lakes and rivers hovering in the 50s and 60s. Even with the warm air temperatures, the cold waters can result in cold shock for prolonged time spent in the water. Take precautions if spending time near the water, or if spending time outdoors early next week.

The pattern remains on track to shift towards an onshore pattern late Monday night into Tuesday, as ensembles have the ridge weaken and shift eastward. Onshore flow will increase as early as Monday night, persisting into Tuesday and through the week. There will be a few breezy areas, particularly the southwest interior, the Strait of Juan de Fuca coast, and along the Cascade Crest, where there is potential for winds up to 25-35 mph Tuesday into Wednesday morning. The onshore winds will be slow to bring temperatures down initially, with highs in the interior Tuesday still ranging from the mid 70s into the mid 80s. The immediate Pacific Coast will see the first of the relief from the heat, with the spread of cooler air moving further inland on Wednesday and Thursday, with highs in the interior dropping into the 70s. Moisture remains virtually nonexistent during the period, although overnight diurnal pushes will bring in some cloud coverage. The chance of showers remains slim, with only a 20% chance of them in the Cascades and Olympics Wednesday and Thursday.

HPR

AVIATION

Northwest flow aloft remains with a transient zonal flow over the region. TAF sites remain VFR going through the evening, with winds this afternoon switching to the northwest around 5-10 kt. A few gusts up to 20 kt are likely around the Strait of Juan de Fuca. Probability for low ceilings tonight remain highest along the Pacific Coast, and the Cascades, with a 50-70% chance of MVFR, and a 40-60% chance of IFR. Some patchy fog can't be ruled out either in these areas. The timeframe for low ceiling development is from 12Z to just before 18Z, before clearing to VFR. Winds overnight/Friday shift to the northeast around 5 kt or less, then back to the northwest 5-10 kt.

KSEA...VFR likely to persist through the TAF period. Winds NW this afternoon 5-10 kt, switching to the northeast 5 kt or less overnight, then back to the north/northwest 5-10 kt Friday afternoon.

HPR

MARINE

High pressure will build over the coastal waters through the end of the week. This will keep the pattern onshore for the next couple of days, with a push expected to produce winds up to 25 kt in the Strait of Juan de Fuca this afternoon/evening. A small craft advisory continues for central and east sections through tonight. The ridge axis will move close to the coast over the weekend, with a thermal trough also building up the coast. This will result in periods of offshore flow to northerly flow from Saturday through Monday. The likelihood of winds exceeding 20 kt during this period remain low, but the outer coastal waters may see north winds approach 20 kt Friday afternoon, and Puget Sound waters approach 15 kt Saturday afternoon. The ridge will weaken and move east, and onshore flow will return Monday night through midweek. There is potential for winds exceeding 20 kt in the coastal waters late Monday through midweek, as well as a potential for gale gusts in the Strait of Juan de Fuca Tuesday.

Seas through Monday will hover around 4-6 ft, and increase to 6-8 ft through midweek, with potential for seas 8-11 ft in the outer coastal waters next week.

HPR

FIRE WEATHER

An upper level ridge offshore will move to the coastline Saturday through Monday. A thermal trough will build under the ridge, creating a dry, warm, and unstable airmass across the region. While recent rains helped fuels from reaching critical red flag criteria going into the weekend, elevated fire concerns will remain for dry grassy/shrubby areas, as well as piles of dead fuels. Highs in the 80s to 90s, combined with northeast winds coming down the Cascades/Olympics, will result in relative humidity values as low as 15-20%, particularly in the south interior, and in valleys of the Cascades where temperatures will be hottest. A few gusts up to 20 mph in the central interior and the Cascade crest from the north/northeast will be possible over the weekend during the morning/afternoon periods. While relative humidities will improve with the return of onshore flow Tuesday, winds will become particularly gusty, with portions of the coast/mountains/south interior seeing west to northwest winds gusting up to 25 to 35 mph.

HPR

SEW WATCHES / WARNINGS / ADVISORIES

WA...Heat Advisory from 11 AM Sunday to 5 AM PDT Tuesday for City of Seattle-Downtown Everett / Marysville Area-Eastern Kitsap County-Eastern Strait of Juan de Fuca-Eastside- Foothills and Valleys of Central King County-Foothills and Valleys of Pierce and Southern King Counties- Foothills and Valleys of Snohomish and Northern King Counties-Foothills and Valleys of Thurston and Lewis Counties-Foothills and Valleys of the North Cascades- Foothills of the Western and Southern Olympic Peninsula- Island County-Lake Crescent Area Including US 101-Lower Chehalis River Valley-Lowlands of Lewis and Southern Thurston Counties-Lowlands of Pierce and Southern King Counties-Lowlands of Western Skagit and Northwestern Snohomish Counties-Lowlands of Western Whatcom County- Middle Chehalis River Valley-Northern Hood Canal-Olympia and Southern Puget Sound-Port Townsend Area-San Juan County-Shoreline / Lynnwood / South Everett Area-Southern Hood Canal-Willapa and Black Hills.

PZ...Small Craft Advisory until 1 AM PDT Friday for Central U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 1 AM PDT Friday for East Entrance U.S. Waters Strait Of Juan De Fuca.