textproduct: Seattle/Tacoma

SYNOPSIS

Upper level low moving inland south of the area this morning. Air mass behind the low remaining unstable enough to keep showers in the forecast into Thursday morning. Weakening front moving through Thursday night with an upper level trough following the front Friday. Unsettled weather continuing into Saturday. Upper level ridge centered offshore Sunday through Tuesday with a weak system trying to move over the top of the ridge Monday.

SHORT TERM /TODAY THROUGH FRIDAY/

Satellite imagery shows cloudy skies over Western Washington early this morning with an upper level low near Coos Bay/North Bend Oregon. Doppler radar indicating precipitation from the Puget Sound eastward and along the central coast. Mild early morning with the rain and cloud cover keeping temperatures in the 50s. Seattle-Tacoma airport did get 0.01 inches of rain Tuesday breaking a 13 day dry streak. It was only the 12th day with measurable rain in Seattle since the first full day of spring ( March 21st ). The normal number of rain days during this time frame is 25.

Upper level low will weaken and move east today leaving an upper level trough over Western Washington. Showers continuing this morning decreasing this afternoon. The rain, cooling of the air mass and weakening of the upper level trough has and will continue to decrease the instablilty over the area. Enough to keep thunderstorms out of the forecast. The clouds and rain will also not allow for much daytime heating with highs a couple of degrees either side of 60.

Upper level trough east of the area tonight with showers becoming isolated overnight. Convergence zone over Snohomish county in the evening will move into the Cascades before midnight. Lows in the mid 40s to lower 50s.

Thursday morning looks dry with the trough well to the east and the next approaching system still offshore. Front approaching the coast and weakening by the end of the afternoon. Rain chances spreading inland in the afternoon. Westerly flow aloft will rain shadow the Central Puget Sound. Another cool day with highs in the mid 50s to lower 60s.

Front falling apart as it moves through Western Washington Thursday night. Rain along the coast and over the Northwest Interior with just a chance for rain elsewhere. Not much in the way of cold air behind the front early Friday morning leading to just a chance of post frontal showers in the lowlands and showers likely in the Cascades. Lows in the 40s.

Fast moving upper level trough moving into Western Washington Friday for another round of showers. Trough becoming negatively tilted Friday afternoon as it moves inland. Instablilty indexes not too impressive but enough to have a slight chance of thunderstorms in the afternoon for most of the area. Friday looks to be the coolest day in the next week with highs only in the mid 50s, normal for the latter part of March. Felton

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/

Upper level trough remaining over Western Washington Friday night into Saturday keeping at least a chance of showers in the forecast. Could see a convergence zone move through the Puget Sound area late Saturday afternoon into Saturday evening as the trough drifts east.

Upper level ridge building offshore extending into Southern British Columbia Sunday with the ridge remaining in place through Tuesday. A weak system will try and move over the top of the ridge into Western Washington Monday or Monday night.

Slow warming trend with highs in the mid 50s to lower 60s Saturday, upper 50s to mid 60s Sunday and in the 60s Monday and Tuesday.

AVIATION

Southerly flow aloft early this morning as an upper level trough begins to pass through the area. Wind speeds are expected to pick up again to around 10-15 kts later this morning with gusts up to 20 kts for the remainder of the morning and gusts increasing to up to 25 kts after 18Z. These increased winds are expected to remain in place throughout the afternoon and evening before easing slightly back down into the 8-12 kt range by midnight tonight.

Widespread VFR conditions in place with some localized MVFR conditions in lower prone areas. While cigs are expected to lower area- wide as the aforementioned trough moves through, rainfall will be more widespread late this morning and this afternoon, majority of sites should still drop down into MVFR during this time frame. On the back side of this feature, however, recovery should be quick with VFR conditions returning this evening. This may only be short-lived, especially for those terminals more prone to lower cigs, as low-level moisture should nurture the re- emergence of MVFR cigs by late tonight and into Thursday morning. The development of a PSCZ this evening may hasten this lowering at PAE, as well as keep showers going longer than surrounding terminals.

KSEA...VFR conditions, with southwesterly winds persisting between 7- 12 kt. Gusts to 20-25 kt expected to emerge early this afternoon as wind speeds increase to 10-15 kt by 20Z. Ceilings will lower to MVFR later this morning as general shower activity increases. Showers will decrease this evening, although a PSCZ looks to develop and linger into tonight. This feature looks to largely stay to the north of the terminal at this time.

18/Mazurkiewicz

MARINE

Persistent onshore flow will allow for increased speeds in the Strait this morning, and will initially start off at Small Craft Advisory strength, before increasing to Gale Force Strength. Latest guidance suggests a 60-70% chance of gusts up to 35 to 40 kts, and with more frequently of these stronger gusts, have issued a Gale Warning for the Central and Eastern Strait starting this afternoon. At the tail end of this headline, looks like there might be some spillover into the Northern Inland Waters, and as such they will be included in a Small Craft Advisory later this afternoon to its conclusion tonight.

Otherwise, seas building over the coastal waters with a mix of a longer period and shorter period wave groups will bring confused seas that may be more hazardous than the wave heights (5-7 ft) would otherwise suggest. Latest model runs, while still supporting this prospect, still do not lend much in the way of confidence or of a widespread occurrence. As such, will keep coastal waters without headline with the morning forecast issuance. Otherwise, onshore flow continues through the Strait of Juan de Fuca later this week with northerly winds over the coastal waters. Another round of building seas to 8-9 ft over the coastal waters around Saturday from a distant disturbance.

18/Mazurkiewicz

HYDROLOGY

The daily hydrology discussion has ended until the start of the next rainy season; it will only be updated during this time as needed.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 1 PM PDT this afternoon for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Gale Warning until 11 PM PDT this evening for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 11 PM PDT this evening for Northern Inland Waters Including The San Juan Islands.