textproduct: Seattle/Tacoma

SYNOPSIS

Upper level ridging building over the area today and Tuesday will bring warm and dry conditions to western Washington. An upper level low approaching the region midweek will bring the return on onshore flow, cooler temperatures, and chances of precipitation to the area. Upper level troughing will continue to influence the region heading into the weekend, keeping conditions cooler and cloudier across western Washington.

SHORT TERM /TODAY THROUGH WEDNESDAY/

Upper level ridging will build over the Pacific Northwest today, while a thermal trough at the surface builds northward along the Washington coast. The ridge axis will shift inland over the Intermountain West by Tuesday, while the thermal trough at the surface also pushes inland. This pattern will bring a warming and drying trend to western Washington for the start of the week. Morning stratus will scatter quicker today and afternoon highs will climb into the mid 70s to mid 80s across the interior lowlands and into the mid 70s along the coast. A combination of northerly and offshore flow will promote continued drying in the low levels and may allow for some smoke from regional wildfires over British Columbia and eastern Washington to make its way back into the area. Tuesday is still on tap to be the warmest day of the week, with afternoon high temperatures expected to climb into the 80s across the majority of the interior and into the low 90s across the Cascade valleys. This will reintroduce Moderate HeatRisk to the valleys as well as the Everett-Seattle- Tacoma metro areas.

A pattern change is expected around midweek as an upper level low approaches the Pacific Northwest. This will bring the return of onshore flow and cooler conditions to western Washington, as well as reintroduce a few chances of showers to the area. Overall QPF amounts look to remain light at this time, however cannot rule out a few chances (around 10%) for thunderstorm development along the coast as the low swings northeastward towards Vancouver Island and Haida Gwaii and brings southwesterly flow aloft to western Washington. Afternoon highs will generally be 5 to 10 degrees cooler than Tuesday's and look to top out in the upper 70s to near 80 across the interior and in the mid 60s along the coast.

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

Ensemble guidance remains in decent agreement with upper level troughing lingering over the region through the second half of the week. This will help maintain onshore flow across western Washington and chances of light showers at times. Thunderstorms will remain possible on Thursday as the aforementioned upper level low swings through the region, but will primarily be confined to the North Cascades. Temperatures will generally trend to near to slightly below normal, with afternoon highs topping out in the low to mid 70s across the interior and in the low to mid 60s along the coast. Morning lows will generally be in the 50s, but may fall into the 40s by later in the weekend.

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AVIATION

Southwest flow aloft across western Washington with light low level offshore/northeasterly flow. Shallow marine stratus and fog this morning has cleared quickly over the last hour with widespread VFR expected this afternoon and evening. Another round of marine stratus is expected along the coast with valley fog/shallow stratus possible again Tuesday morning. This is expected to be more limited than Monday morning. N/NE winds 5 to knots will increase slightly this afternoon, generally around 8 to 12 knots, easing around 08Z then becoming light southerly around 14-15Z for many locations south of the Strait of Juan de Fuca and Skagit County.

KSEA...VFR conditions through the afternoon and evening hours. North to northeast winds through the afternoon, generally around 8 to 12 knots then becoming light southwesterly around 14/15Z. Stratus and or shallow fog not expected at the terminal into Tuesday morning. Valley fog may be near, developing again to the east again during the early morning. Shift to southwesterly winds may help keep the terminal clear. LAMP guidance still indicating around a 15% chance of ceilings less than 500ft by 13z Tuesday morning, this will be something to keep an eye on overnight.

MARINE

Surface high pressure remains over the coastal waters today and will continue through Tuesday. Could see patchy fog over the waters this morning as marine stratus continues to push onshore, which may limit visibilities at times. Northerly winds will increase over the coastal waters later this afternoon and evening, with latest probabilities suggesting small craft advisory gusts over the majority of the waters. A Small Craft Advisory has been issued, particularly for gusts up to 25 kts. Onshore flow looks to increase over the area Tuesday into Wednesday, with a westerly push down the Strait of Juan de Fuca that likely will warrant headlines.

Coastal seas 4 to 6 feet into Tuesday, with some areas, especially in the outer coastal waters, seeing seas up to 7 feet. Additionally, with period of around 6 seconds, could see choppy seas Monday afternoon and evening. Seas will subside to 3 to 5 feet through much of the week.

Mazurkiewicz

FIRE WEATHER

Warmer and drier conditions are expected across western Washington today and Tuesday as an upper level ridge builds into the region. A thermal trough will also build northward along the coast today, allowing for flow to turn offshore and promoting additional drying in the low levels. Elevated fire weather conditions are likely across the Cascades on Tuesday (the warmest day of the week), with isolated spots expected to approach critical minimum RH thresholds by dipping into the low to mid 20s. A pattern change midweek will bring the return of onshore flow, cooler temperatures, and chances of light precipitation to the area. A 10-20% chance of isolated thunderstorms will be possible, primarily along the coast and North Cascades, Wednesday and Thursday as the upper trough swings northeastward across the region.

Upper level troughing then looks to remain over the area into the weekend and should continue to promote onshore flow, excellent overnight humidity recoveries, and cooler temperatures across western Washington, which in turn will help mitigate fire weather conditions through the weekend.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until midnight PDT tonight for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm- Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm.