textproduct: Seattle/Tacoma

SYNOPSIS

Strong high pressure will build under a ridge across western Washington early this week. Temperatures will increase going into Monday and Tuesday, with highs into the 80s and 90s for many in the interior. Moderate HeatRisk will remain a concern for those spending significant time outside. Additionally, dry air with a weak offshore and thermal trough pattern will lead to elevated fire concerns for grassy and shrubby areas that are dry. The second half of the week is significantly cooler with the first chance of precipitable moisture in a couple weeks, with breezy conditions at times.

SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/

Western WA remains quite dry this afternoon, with the surface pattern remaining quite neutral in between lower pressure to the east, and higher pressure to the west. A few high clouds on satellite are moving east across the interior, with some clouds rolling south from B.C., and a large area of stratus offshore. Highs today remain in the upper 70s to low 80s in the interior (but may come in a few degrees cooler due to the high clouds). The coast will stay in the 60s. Lows tonight drop into the low to mid 50s.

An upper level ridge offshore will begin to move inland tomorrow and Tuesday, with the thermal trough setting up in the interior (rather than the coastline). As heights build with more sinking motion provided by the higher pressure, temperatures will warm quite a bit going into Monday and Tuesday, with Tuesday being the warmest day this week. There remains a heat advisory across a majority of the lowlands (including Cascade valleys, islands, and all but the immediate Washington/Pacific Coast and mountains). This goes into effect 11 am Monday and expires for at 11 PM Tuesday night (except for Puget Sound which goes through 11 PM Wednesday night). Temperatures will be quite warm (especially on Tuesday), with widespread highs into the upper 80s and low 90s. HeatRisk is moderate for much of the interior, and a couple isolated pockets of major HeatRisk can't be ruled out for portions of Puget Sound/Seattle metro (although the major likelihood remains at 20-30%). Overnight lows will increase into the upper 50s, with low 60s in the Seattle area. Those spending time outdoors next few days should take breaks in the shade, or in an air conditioned room when possible, stay hydrated, and wear sun-screen and loose fitting clothing to minimize the potential for heat-related illness.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Beginning Tuesday night into Wednesday, the onshore gradients are expected to increase significantly as the ridge moves inland, which should increase cloud coverage significantly going into Wednesday. There remains some model disagreements into how warm it will be exactly going into Wednesday (especially given the timing of the onshore push), but the message of moderate HeatRisk continuing into Wednesday for Puget Sound remains (especially given the overnight lows are the warmest this morning). Thus the heat advisory will continue for now into Wednesday, but there remains a descent spread into the temperatures for the first onshore push (and some limitations of the models handling the first push).

As the ridge flattens and move east, ensembles bring in a cooler pattern as the flow transitions to zonal, and eventually a trough pattern going into Friday for the region as a low drops down from the Gulf of Alaska. Highs will cool into the 60s and 70s for much of the interior, and an increase of moisture from the trough/Pacific will lead to the first chance of rain/showers in a couple of weeks. The wettest day appears to be Friday with at least a 10-15% chance of thunder with this activity.

Winds will become breezy at times in this part of the forecast. The southwest interior/Strait of Juan de Fuca areas will see the winds first Wednesday, as well as the immediate ridge areas of the Cascades. Friday and Satuday's front may result in more widespread winds for the interior. While winds gusting over 20-25 mph appear likely, probabilities for over 30 mph remains low.

HPR

AVIATION

VFR conditions remain in place over W WA this evening with mostly clear skies over the area. Current satellite shows marine stratus holding steady over the coast with limited incursion onto land. Stratus having more success moving eastward through the Strait, but no impacts to land, including terminals. Any additional eastward progress will be limited, with only HQM expected to dip down into MVFR to IFR conditions overnight...although CLM may need to be monitored should stratus over the waters of the Strait start to spillover onto land.

Terrain driven winds resulting in a variety of directions depending on the terminal, although speeds generally falling into the 4-8 kts range. Winds will continue to ease tonight with many terminals becoming light and variable around midnight tonight. Widespread northerly winds ranging 5-10 kts expected to resume by Monday afternoon, with some variances to the northwest or northeast depending on location. HQM will be the exception, although speeds will be similar, direction is likely to be more westerly.

18

KSEA...VFR expected through the TAF period. Winds stubbornly remaining westerly but still expected to shift northerly by 06Z tonight and remain there into Monday. Speeds overnight generally 4-8 kts, picking up by 18Z to 8-12 kts with occasional gusts up to 20 kts possible. Speeds ease Monday evening with a slight shift to the northeast Monday night.

18

MARINE

High pressure will increase offshore early this week as an upper level ridge moves inland. The immediate coastline and coastal waters will likely continue to see north/northwest winds due to the thermal trough setting up closer into the interior. The remaining inland areas will see a mix of light northwest to northeast winds with the pattern through Tuesday night. Onshore will return Tuesday night, with a trough also dropping down with a front by late week. The next best chance of winds over 20 kt will come late Tuesday in the outer coastal waters, with a strong push likely in the Strait of Juan de Fuca Wednesday into Thursday (30-50% chance of gale gusts with this push). The late week front will have the potential to produce widespread winds across most waters with gusts over 20 kt.

Seas 4-6 ft through the end of the week, the 7-9 ft seas with short periods of 7-8 seconds with the frontal system late this week.

HPR

FIRE WEATHER

High pressure will increase inland under a ridge early this week. This ridge combined with a thermal trough setting up inland in the interior will result in a few days of elevated fire conditions via warm, dry, and conditional unstable air across the region. The offshore flow in the interior/Cascades will result in humidity values dropping into the twenties, and even the teens going into Monday, Tuesday, and potentially Wednesday. Fuels are approaching critical levels, but the main concern remains dry grasses or shrubs, or dead piles of fuels where brush fires may be able to start (as seen the past couple days). Onshore flow will return late Tuesday night and make it inland on Wednesday with improved moisture, and the first chance of wetting rain in a couple of weeks for much of the region.

HPR

SEW WATCHES/WARNINGS/ADVISORIES

WA...Heat Advisory from 11 AM Monday to 11 PM PDT Tuesday for Eastern Strait of Juan de Fuca-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-Lower Chehalis River Valley-Lowlands of Lewis and Southern Thurston 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- Southern Hood Canal-Willapa and Black Hills.

Heat Advisory from 11 AM Monday to 11 PM PDT Wednesday for City of Seattle-Downtown Everett / Marysville Area- Eastern Kitsap County-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-Lowlands of Pierce and Southern King Counties-Shoreline / Lynnwood / South Everett Area.

PZ...None.