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/

Satellite imagery shows cool upper level low centered near Vancouver Island early this morning. Wave clouds over and to the east of the Cascades good indication of some decent winds aloft. Camp Muir at 10,000 feet on Mount Rainier reporting 49 mph with gusts to 66 mph. Showers rotating around the low over much of Western Washington at 3 AM/10Z. Temperatures were in the 40s.

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. Heaviest snowfall occurring early this morning. Paradise on Mount Rainier reported 2 inches of new snow between midnight and 1 AM ( thanks to our friends at the Northwest Avalanche Center for the data ). New snow amounts today will be heaviest around Mount Rainier, up to 6 inches. 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

Northwesterly flow this morning shifting more westerly to southwesterly by this evening. Surface winds will remain south to southwesterly throughout the TAF period, although speeds will start from breezy with some occasional gusts to settling down into the 5- 10 kt range this afternoon and evening.

Widespread rainfall this morning resulting in lower cigs with widespread MVFR to IFR conditions at most terminals. However, some terminals such as HQM, OLM and CLM are reporting VFR conditions as of 2 AM PDT. That said, locations under rainfall will likely remain under the lower cigs while those that see precip move on do have the potential to improve up a category or two. Ultimately, given how widespread precip is, would plan for MVFR or lower conditions until mid to late morning before conditions begin to improve back to VFR by this afternoon. Once VFR conditions are met, will likely remain there for the remainder of the TAF period, with an exception possibly being OLM due to their fog-prone nature.

KSEA...MVFR conditions in place and with precip still upstream from the terminal, would expect MVFR to linger into the late morning hours. Should start to see improvement to VFR conditions by 21Z this afternoon, even though lingering showers will be a possibility. Breezy winds mainly in the 8-12 kt range with occasional gusts up to 20 kt in place for much of the morning, but as per above discussion, should see speeds ease this afternoon to 5-10 kts. Direction is expected to remain south to southwesterly throughout the TAF period.

18

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.

18

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...Small Craft Advisory until 5 AM PDT early this morning 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.