textproduct: Seattle/Tacoma

SYNOPSIS

An upper level trough will continue to make its way across the area this morning, bringing chances of showers and isolated thunderstorms primarily to the mountains and the northern tier of western Washington. Upper level ridging will build into the Pacific Northwest on Monday and Tuesday for warmer and drier conditions. Another upper level low will approach the area around midweek, bringing increasing onshore flow and cooler conditions to western Washington the second half of the week.

SHORT TERM /TODAY THROUGH TUESDAY/

An upper level trough will continue to make its way inland across the area early this morning. Meanwhile, a surface trough currently extends along the interior of British Columbia, through Vancouver, and down along the Washington coast. A cluster of showers and thunderstorms associated with this feature have remained rather vigorous to the north of the border over the past couple of hours, with latest radar trends showing shower and thunderstorm activity slowly starting to drift southeastward early this morning. Thunderstorms have generally continued to weaken as they drift closer to Washington, however will need to continue to keep an eye on trends through the remainder of the overnight hours as latest hi-res guidance does hint at the possibility of a few storms drifting into portions of the San Juans, Whatcom, and Skagit counties through the early morning hours. Otherwise, expect shower and thunderstorm activity to primarily become confined to the Cascades by this afternoon and to gradually wane throughout the day as the upper level trough pushes off to the east and ridging starts to build in from the west. Widespread cloud cover across the area will take a bit longer to scatter today, helping to keep temperatures slightly cooler and primarily in the low to mid 70s across the interior and in the mid 60s along the coast.

Upper level ridging will then build into the Pacific Northwest on Monday, with the ridge axis shifting eastward over the Intermountain West by Tuesday. This will bring a warming and drying trend to western Washington the first part of the week, with Tuesday expected to be the warmest day across western Washington. Afternoon high temperatures will climb into the 80s across the interior lowlands and into the low 90s across the Cascade valleys by Tuesday, reintroducing Moderate HeatRisk to portions of these areas. Surface flow will also transition to northerly and then offshore at times, which may allow for some smoke transport from ongoing wildfires across British Columbia and eastern Washington to make its way back into western Washington at times through the early part of the week.

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

Ensemble guidance remains in decent agreement with an upper level low approaching the Pacific Northwest on Wednesday. This would bring the return of onshore flow and cooler conditions to western Washington the second half of the week. Chances of precipitation will also increase Wednesday and Thursday, though overall amounts look to remain light at this time. Will need to keep an eye on any thunder potential for the area, though probabilities at this time remain at around 10 percent or less. Temperatures will generally trend near to slightly cooler than normal the second half of the week, with afternoon highs topping out in the low to mid 70s across the interior and mid 60s along the coast. Ensemble guidance suggests the upper level trough will remain an influence across the area heading into next weekend, which would continue to promote onshore flow and near to slightly below temperatures across western Washington.

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AVIATION

Upper level trough moving east of the area this morning. Flow aloft becoming northwesterly behind the trough. Upper level ridge building in tonight with flow aloft becoming westerly. Low level onshore flow today becoming northerly late tonight into Monday with thermally induced surface trough along the coast.

VFR ceilings inland with IFR or LIFR ceilings along the coast. MVFR ceilings developing over the interior 14z-16z. Ceilings over the interior improving to VFR around 21z.

Showers with embedded thunderstorms from about NAS Whidbey northward until 18z.

KSEA...VFR ceilings early this morning. MVFR ceilings developing around 15z continuing to around 20z. VFR ceilings middle of the afternoon onward with clouds scattering out this evening. Southwest wind 4 to 8 knots becoming northwesterly 00z-03z. Felton

MARINE

High pressure rebuilding over the coastal waters today will remain through Tuesday. Thermally induced surface trough along the coast Monday will dissipate Monday night. A weak frontal system will move across the waters Wednesday night. High pressure rebuilds over the area Thursday.

Small craft advisory westerlies in the Central and Eastern Strait of Juan de Fuca Tuesday night otherwise winds 20 knots or less through the period.

Seas remaining in the 3 to5 foot range through the week. Felton

FIRE WEATHER

An upper level trough will pass through the area this morning. While at the surface, a trough currently extends southwestward from British Columbia down along the Washington coast. Showers and isolated thunderstorms will remain possible across the northern tier of the area, primarily across the San Juans and Whatcom and Skagit counties, through the morning hours before waning. While storms have been producing heavy downpours for areas north of the border, storms have also been associated with abundant lightning. Should any storms drift into the area over the next several hours, they will remain capable of producing abundant lightning and gusty, erratic outflow winds - and could have an impact to any ongoing fires across the North Cascades should they make it within the vicinity. Overall chances of thunderstorms will then decrease by the afternoon and evening as the upper trough exits the region.

An upper level ridge will then build into the area Monday and Tuesday, bringing brief periods of low- level offshore flow as a thermal trough builds along the coast and pushes inland overnight into Tuesday. Elevated fire weather conditions are likely across the Cascades on Tuesday with the warm and dry pattern and with relative humidities dipping into the low to mid 20s. Another upper level trough will arrive in the middle of next week, bringing the return of onshore flow- as well as chances for more showers and the potential for thunderstorms. Upper- level troughing then looks to linger into the weekend.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...None.