textproduct: Seattle/Tacoma

SYNOPSIS

Upper level low near Vancouver Island this morning will not move much in the next couple of days ending up off the Washington coast Friday. The low will weaken to a trough Saturday and move inland Saturday night. Upper level ridge building offshore Sunday will move over Western Washington Monday and Tuesday.

SHORT TERM /TODAY THROUGH FRIDAY/

Upper level low not moving much today. Showers will continue to spin around the low and move into Western Washington. This afternoon 500 mb temperatures near -30C, convective temperatures in the mid 50s, lifted indexes near 0 and lapse rates around 7.5 C/KM. All this adds up to a chance of thunderstorms late in the afternoon. Snow levels in the 3000 to 3500 foot range, with most of the heaviest snowfall already have occurred early this morning. Snow amounts this afternoon will be heaviest around Mount Rainier, up to 6 inches, elsewhere, just a couple more inches of new snow elsewhere in the Cascades. Winter Weather Advisory will remain up until 5 pm this afternoon. Cool day in the lowlands with the clouds and showers. Highs in the lower to mid 50s.

Little change in the pattern tonight into Thursday. Upper level low drifts slowly south and west ending up west of KUIL by 00z Friday. Showers continuing to rotate around the low moving into Western Washington. The low does weaken a touch with the winds aloft easing. This will weaken the orographics in the mountains so even though the shower activity will continue new snow amounts will decrease. Light additional accumulations in the forecast. Lows tonight in the mid 30s to lower 40s. Highs Thursday again in the lower to mid 50s.

Low drifting south Thursday night and Friday with the flow aloft becoming southwesterly. This is another negative for much in the way of accumulating new snow in the mountains even as snow levels remain in the 3000 to 3500 foot range. For the lowlands a continuation of a chance of showers/showers likely forecast. Lows in the mid 30s to lower 40s. Highs in the lower to mid 50s. Felton

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/

Models in pretty good agreement with the low weakening and continuing to drift south Friday night into Saturday. Flow aloft becoming southerly and with the jet moving inland to the south pops becoming confined to the western half of the area by Saturday afternoon. Low weakens to an upper level trough and moves inland Saturday night. Upper level ridge building off the coast Sunday moving over Western Washington Sunday night and Monday. The ridge will weaken a little Tuesday. Still a few ensemble solutions with a warm front sneaking over the ridge nicking the coast Sunday night and Monday so will have slight chance pops for the north coast. With the ridge aloft and the low level flow turning light offshore the potential for fog exists both Monday and Tuesday morning. Some of the ensemble solutions indicating the ridge will be a little dirty with high cloud cover getting into the area. With this in mind have only gone for patchy or areas of fog both mornings. Highs mostly in the mid 50s. Lows in the mid 30s to lower 40s Saturday and Sunday cooling to the upper 20s and 30s Monday and Tuesday. Felton

AVIATION

An upper low remains over the region with widespread rain showers across the area today and tonight. As a result, prevailing conditions are highly variable with IFR conditions under heavier showers and VFR conditions elsewhere. Southerly surface winds continue, with gusts to 20 kt through the morning. Confidence in wind speeds is a bit lower into the afternoon, but around a 50% chance of stronger gusts continuing into early evening. Otherwise, will be monitoring around a 15% chance for an isolated thunderstorm this afternoon and evening, but likelihood remains too low for TAF inclusion at this time. A convergence zone may maintain more robust shower activity and lower flight conditions near/south of KPAE but north of KBFI this evening. Otherwise, little change with shower activity through the period with increasing stratus potential overnight for most of the area.

KSEA...VFR conditions expected to prevail with gusty southerly winds through the evening. Showers remain around the terminal area and could bring a brief lowering if these move over the terminal. Otherwise, winds easing overnight with showers decreasing the the potential for MVFR ceilings increasing by 12z through the morning Thursday.

MARINE

Northwesterly winds along the outer coastal waters will linger into early this morning, but will ease after 5 AM PDT this morning. Same for seas. As such, timing on inherited headlines looks good and will run its course unaltered.

Following suit, winds will also ease across the inland waters as the accompanying surface low drops into the area and tracks southward along the coastal waters. As it does so, this will allow for flow to turn back offshore, with offshore flow persisting the second part of the week.

Seas easing throughout the day, ranging 7 to 10 ft early this morning favoring 6 to 9 ft by noon today. 5 to 7 ft waves are expected by tonight and remain there into Thursday. Further subsiding of seas is expected, with 4 to 6 ft expected by the weekend.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...Winter Weather Advisory until 5 PM PDT this afternoon for Cascades of Pierce and Lewis Counties-Cascades of Snohomish and Northern King Counties-Cascades of Southern King County-Cascades of Whatcom and Skagit Counties.

PZ...None.