textproduct: Seattle/Tacoma

SYNOPSIS

Upper level low west of Haida Gwaii this morning will slowly move southeast through tonight. Upper level disturbance spinning out of the low moving through Friday. Upper level low moving over Western Washington Saturday moving east Saturday night. Temporary upper level ridge Sunday. Another upper low will move through the first part of next week for more showers and cool temperatures.

SHORT TERM /TODAY THROUGH SATURDAY/

Weak convergence zone activity continues in Snohomish county this morning and will likely dissipate into early this afternoon.

Upper level low moving slowly south off the British Columbia coast tonight. Upper level shortwave spinning out of the low approaching the coast overnight with a chance of showers along the coast and over the Northwest Interior. Lows in the mid 40s to lower 50s.

Shortwave moving through Friday in the afternoon keeping at least a chance of showers in the forecast. Increasing southwesterly flow aloft will create a rain shadow centered near Everett in the morning before it fills in the afternoon. Clouds and showers with highs only near 60.

Upper level low approaching Western Washington Friday night will move inland Saturday keeping showers in the forecast. Convective indices lining up for isolated thunderstorms Saturday. Lifted indexes still in the 0 to -3 range, 500 mb temperatures -25C to -29C, convective temperatures in the mid 50s and CAPE between 300 and 600 J/KG. Lows in the mid 40s to lower 50s. Highs like Friday near 60. While both Friday and Saturday high temperatures are well above record low maximum temperatures for the day this time of year there is only about a 10 percent chance in Seattle of getting a high in the 50s.

Felton

LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/

Low weakens to a trough and exits the area Saturday night. Extended runs showing pretty good run to run consistency with a temporary upper level ridge moving through Sunday for a brief break in the showers. Another cool upper level low dropping down out of the Gulf of Alaska a little slower on the current run with the low not moving inland over Oregon until Tuesday. Still the potential for wrap around moisture Wednesday as the low moves slowly east. At least a chance of showers in the forecast Monday through Wednesday. Temperatures remain below normal with highs in the lower to mid 60s. Lows in the mid 40s to lower 50s.

AVIATION

Westerly flow aloft will become southwesterly tonight as an upper trough situated west of Haida Gwaii pushes a frontal system toward the region. Low level onshore flow continues to generate some convergence over Puget Sound through early this afternoon where areas of MVFR ceilings and isolated showers will linger. VFR is expected for most areas mid-afternoon into this evening. Ceilings will lower to MVFR along the coast late tonight in increasing shower activity associated with an incoming trough. These conditions will spread to interior areas late Friday morning through the remainder of the day.

KSEA...MVFR ceilings will lift to VFR this afternoon as remnant convergence zone activity north of the terminal gradually dissipates. There's a less than 20% chance of MVFR ceilings early Friday with ceilings more likely to lower later in the day as shower activity ramps up with the next frontal system. Surface winds southwesterly 8 to 12 knots will veer northwesterly 5 to 8 knots for a few hours late this afternoon and early evening before backing southerly again overnight and rising to to 9 to 14 knots Friday AM. 27

MARINE

Onshore flow will ease later today as a weak surface ridge shifts inland and a broad surface low drops southward in the offshore and coastal waters. A weak front will cross the waters midday Friday into Friday afternoon. A vertically stacked trough trailing the front will move onshore during the day on Saturday with relatively little impact in terms of wind. A weak surface ridge will cross the waters Saturday night into Sunday before another frontal system reaches the area Sunday night and Monday with potential headlines for the coastal waters. Coastal seas look to remain below 10 feet through the period.

27

FIRE WEATHER

Low level onshore flow today with temperatures near normal. Relative humidity values will stay well above critical thresholds. Cool unsettled weather Friday and Saturday. Thunderstorm chances elevated Saturday afternoon for the entire area. Lightning will be a primary hazard, and depending on the moisture accompanying each thunderstorm, may pose a risk to drier areas of grasses/cured fuels. Preceding cool conditions (and live fuels still growing and in the green up phase) will limit holdover risk as temperatures remain cool early next week. Felton

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory 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.