textproduct: Seattle/Tacoma

SYNOPSIS

Surface high pressure plus dry northwesterly flow aloft giving Western Washington a sunny day today. The flow aloft will turn more westerly tonight with some high clouds moving over the area. Next system arriving Wednesday with the front moving through later in the day. Cool upper level low following Thursday. Weak high pressure building Thursday night will remain over the area into the weekend.

SHORT TERM /TODAY THROUGH WEDNESDAY/

Satellite imagery shows skies have already cleared over the northern portion of the area with mostly high clouds over the southern portion. Patchy fog/freezing fog forming over the Southwest Interior. Convergence zone over King and Pierce counties last night has dissipated with no precipitation echoes on the doppler radar. Temperatures at 2 am/09z were in the lower to mid 30s.

Skies will continue to clear out this morning with a sunny day in store for Western Washington. Patchy fog over the Southwest Interior will dissipate later this morning. Even with the sunshine the air mass aloft is cool so highs only near 50.

Flow aloft turning west southwesterly tonight. This will push some high clouds into Western Washington. Question is will the cloud cover be thick enough to prevent temperatures from falling below freezing. For the most part yes with just the colder locations like the Southwest Interior dropping just below freezing. Lows mostly in the 30s.

Another dry day Tuesday with high clouds. The change in the flow aloft will warm the air mass a bit with highs a few degrees warmer than today, in the lower to mid 50s.

Next system dropping out of the Gulf of Alaska Tuesday night already negatively tilted by 12z Wednesday. This will slow down the eastward movement of the front. With the front well offshore just chance pops overnight. Lows in the upper 30s to mid 40s.

Front continuing to slow down Wednesday. Front reaching the coast late in the afternoon. Rain spreading over the area in the morning continuing through afternoon. Snow levels around 3000 feet with snow in all the passes except maybe Snoqualmie. The slower arrival of the front will keep new snow amounts in the Cascades in the 2 to 4 inch range. Higher amounts on Mount Rainier. Breezy day for the coast and Northwest Interior with winds increasing in the morning. Highs near 50. Felton

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

Models remaining pretty consistent bringing the front through Wednesday evening. This is when the heaviest snow will fall in the Cascades. Low end advisory amounts still possible.

Cool upper level low trailing the front moving through Thursday keeping showers and low snow levels in the forecast. Weak upper level ridge building Thursday night. Showers coming to an end.

Weak upper level ridge remaining over the area through Saturday. Some differences in the models showing up with a weak system moving by to the north Saturday night into Sunday. The operational GFS is much stronger with this feature versus the ECMWF. Ensemble solutions favoring the ECMWF at the moment so will stay with a dry forecast. Confidence not real high on the Sunday forecast.

Highs in the lower to mid 50s Thursday warming to the mid 50s to lower 60s for the weekend. Lows in the mid 30s to lower 40s.

AVIATION

Westerly flow continues to prevail across western Washington today. Skies have become mostly clear across much of the area with some lingering cirrus over the southern half of the area. With mostly light winds across the area, this has allowed for low clouds and fog to begin to develop across the area. OLM and PWT are already in LIFR, with other area terminals beginning to show fog and low stratus in the vicinity. Areas of fog and low stratus will continue to develop across the area this morning. Conditions will improve from around 17-19Z as winds develop and the sun burns the fog/clouds away. Afterwards, VFR conditions will prevail through the remainder of the period with mostly clear skies. High clouds will begin to fill back in after 06Z Tue.

Light to calm winds will increase to 6 to 12 kt, northerly, late this morning. Winds peak this afternoon before slowly easing tonight into early Tuesday.

KSEA...VFR conditions early this morning with scattered low clouds. Expect low clouds to continue to fill in with low-MVFR to potentially IFR conditions by 15Z. Limitations in visibility in patchy fog cannot be ruled out this morning, as well. Conditions should improve after 18-19Z as winds pick up and the sun burns off the fog. VFR conditions then prevail through the day with mostly clear skies. High clouds fill back in after 06Z Tue. N winds increase to 8-12 kt this afternoon, then slowly easing tonight.

MARINE

High pressure will continue to filter in across the area this morning. Elevated winds will continue early this morning in the Strait of Georgia and around the northern San Juans early, but those winds will continue to taper off this morning. Otherwise, light winds will prevail across the area waters through Tuesday. A low pressure system will approach the area early Wednesday with increasing southerly winds. The trend continues with slightly weaker winds then previously forecast. Small Craft Advisory winds remain likely (60-90%) across most all the area waters, with only a 15-30% chance of seeing gale force winds across the coastal waters and the East Strait of Juan de Fuca. Winds will peak Wednesday afternoon as the front passes across the waters before decreasing Wednesday evening as the system tracks away to the southeast. Broad high pressure will rebuild back across the area Thursday through the end of the week, keeping winds light.

Seas will remain 3-5 ft through Tuesday. Seas then look to rise up to 8-10 ft on Wednesday as the system moves through. Seas remain elevated into Thursday before decreasing once again Friday into the weekend.

62

HYDROLOGY

No river flooding in the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 5 AM PDT early this morning for Northern Inland Waters Including The San Juan Islands.