textproduct: Seattle/Tacoma

SYNOPSIS

Showers will continue across the area into Tuesday as a series of disturbances makes its way across the region. Drier conditions are expected late Tuesday into Wednesday as a ridge of high pressure briefly moves over western Washington. Rain chances increase again late Wednesday into Thursday as another system approaches and splits across the area. Additional weak systems may brush the region over the weekend, with more significant precipitation expected to impact the area by early next week.

SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/

The latest forecast remains on track with no updates this evening. Latest radar shows showers continuing to lift northward across the area this evening in association with a stalled frontal system draped across the region. Expect showery conditions to continue across western Washington into Tuesday as an upper level disturbance makes its way across the area this evening. This disturbance could bring a period of heavier precipitation for the northern tier of the area tonight. While not expecting much in the way of impacts, a period of mountain snow is expected for the Cascades into Tuesday as snow levels dip from 6500 ft to 3000-3500 ft by early Tuesday. This may bring a few inches of snow to areas like Rainy Pass in the North Cascades and could even bring around an inch to lower passes like Stevens and Snoqualmie by Tuesday morning.

Another upper level disturbance will move across the area on Tuesday, but generally expect showers to taper across western Washington throughout the day as the moisture decreases. The system will exit the region by Tuesday night, allowing for upper level ridging to build back into the region in its wake. Drier conditions are expected Tuesday night and Wednesday as a result. Clearing skies Tuesday night will increase the potential for fog development overnight into Wednesday with light winds and ample moisture remaining in the low levels. Wednesday will remain dry across the region, but expect an increase in high cloud cover throughout the day as the next system approaches.

LONG TERM /THURSDAY THROUGH MONDAY/

Precipitation chances start to increase again by Thursday as a weak, splitting system approaches the area. Overall rainfall amounts look to remain rather light at this time, with showers mainly expected to move in along the coast and Olympic Peninsula and largely remain west of Puget Sound. Additional, wetter systems may move into the area over the weekend for another round of lowland rain and mountain snow.

Ensemble guidance then remains rather split in solutions heading into early next week, with latest cluster analyses showing roughly 45 percent of the ensemble members highlighting a cooler period for western Washington with shortwave troughing situated over the region, while roughly 35 percent of the members highlight a warmer period with some amplitude of ridging over the Pacific Northwest. Should the colder solution take hold, could see more significant snow for the mountains and the mountain passes by early next week.

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AVIATION

Mostly MVFR to IFR this evening as showers continue to shift northeastward along an exiting frontal system. Southwest flow aloft will continue to transition to west to northwesterly as a weak upper trough moves onshore. Light surface flow and plentiful low level moisture will contribute to the development of widespread IFR or low MVFR stratus tonight into Tuesday morning, with some pockets of LIFR low stratus. Conditions are favored to remain deteriorated into the afternoon Tuesday, with potential for some terminals to briefly break out to low-end VFR ceilings Tuesday evening before returning to MVFR/IFR in continued low clouds and isolated showers.

KSEA...Limited improvement this evening as ceilings bounce between low-end VFR and MVFR. Ceilings are expected to deteriorate once again tonight with high potential for MVFR/IFR conditions overnight into Tuesday morning. Forecast models maintain a 50% chance of ceilings below 2000 ft for much of the TAF period into the early afternoon Tuesday. Ceilings are favored to briefly lift to low- end VFR Tuesday evening before falling to MVFR/IFR once again Tuesday night. Confidence is much lower for visibilities, with a low chance (10% to 15%) of fog developing Tuesday morning at the terminal bringing vis below 6 miles. Southerly winds generally 4 to 7 kt will veer northerly by Tuesday evening.

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MARINE

A broad surface ridge will rebuild over the coastal and offshore waters through Tuesday. The ridge will then shift east of the Cascades on Wednesday as a splitting front approaches the outer coastal waters. This will turn the flow east to southeasterly midweek. Broad surface ridging rebuilds late in the week before another weak front approaches the waters over the weekend.

Coastal seas will dip below 10 feet on Tuesday and Wednesday before another larger swell train arrives Thursday into the weekend.

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HYDROLOGY

No flooding is expected through the week ahead. Stronger weather systems moving into the region next weekend and into early next week could bring periods of heavier rain and will be the next time frame to watch with respect to hydrologic concerns.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 10 PM PST this evening for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm- Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm.