textproduct: Seattle/Tacoma

SYNOPSIS

A warm front will clip the area tonight and Friday for light precipitation. A cold front will stall over western Washington on Sunday. A cold and wet pattern will set up next week for lower snow levels and periods of heavy mountain snow.

SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/

Light rain is beginning to move inland this evening. Otherwise, the forecast remains on track, with no major changes to the forecast this evening.

We remain under onshore flow today with lingering light showers in the interior and Cascades. Rain will increase in coverage overnight and into Friday as a warm front moves in. The warmer air mass will bring higher snow levels around 5,000 ft. We'll sit in the warm sector on Saturday while high pressure nudges inland. Expect highs in the lower to mid 50s with light precipitation (mainly coast and north part). 33

LONG TERM /SUNDAY THROUGH THURSDAY/

A cold front will stall over western WA on Sunday with strong westerly flow aloft. Snow levels will lower below the passes Sunday night with accumulating snow possible at both Stevens and Snoqualmie Pass.

The weather pattern is cold and wet moving through early next week with low snow levels. Strong, moist, westerly flow will pound the mountains with potential for several feet of snow. Rates increase on Wednesday which could make travel over the mountains difficult. Across the lowlands, with low snow levels, there is a rain/snow mix in the forecast Mon-Thu. The low level flow will remain onshore, though, which will help temperatures mostly stay above freezing and thus limit impacts. Snow levels will be rising on Wed and Thu and any snow would mostly affect areas close to the mountains. 33

AVIATION

North to northwesterly flow aloft as upper level ridging builds over the eastern Pacific. Surface winds generally southerly for most terminals, although BFI and PWT are actually showing easterly at the time of this writing. Current speeds mainly 4-8 kts although seeing some occasional winds up to 12 kts at BLI this evening. Overnight, winds will become more uniformly south to southwesterly with speeds increasing to 8-12 kts with some gusts up to 20 possible for most terminals.

Mostly VFR conditions in place over W WA, although starting to see some MVFR emerge along the coast ahead of incoming frontal system. SEA and BFI also reporting MVFR conditions, but this may be more due to a dissipating weak convergence zone to the north. Widespread MVFR conditions will emerge overnight tonight due to aforementioned approaching front...with rain developing by early Friday morning. Precip is associated with a warm front, so current TAFs reflect that with VCSH...however latest PoPs suggest that an upgrade to -SHRA will likely be a better fit and will opt to edit in that direction with the 06Z issuance.

KSEA...MVFR conditions in place as of 04Z /as mentioned above/...and while there may be a short recovery to VFR, given the incoming front will likely opt for conditions to remain MVFR this evening and tonight. Timing for precip start may be a little aggressive as front still no quite yet to the coast. Rainfall and showers however still look good from 10Z on and will alter TAF to reflect this thinking. Reduced visibilities/ceilings are expected with rainfall. IFR conditions expected as cigs sink further in the mid to late morning hours Friday...although increasing winds Friday afternoon may help lift cigs back to MVFR and help improve vis. Southwesterly winds throughout the period with speeds 4-8 kts this evening and tonight, increasing to 8-12 kts overnight and for the remainder of the TAF period. Some gusts up to 20-25 kts will be possible.

18

MARINE

A warm front will swing through area waters tonight into Friday with widespread stratiform precipitation. Reduced visibilities due to heavier rain/mist are likely at times. The flow will continue to remain southwesterly tonight into Friday, with a series of troughs expected to pass through the waters later this weekend into next week. This will largely keep the pattern onshore through the forecast period. The next likelihood of significant winds for small craft will come Sunday into Monday, with the chance of gale force gusts in the Strait of Juan de Fuca. This will keep the pattern active going through next week.

Seas have eased to 6-8 ft, allowing for inherited SCA to expire, and will remain there into the weekend. The next increase comes with the Sunday system, with pushes up to 9-11 ft Sunday into next week.

HPR/18

HYDROLOGY

Heavy precipitation over the Olympics will force rises on the Skokomish River with the potential for flooding mid to late next week. No other river flooding is expected over the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

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