textproduct: Seattle/Tacoma

SYNOPSIS

Upper level low off the coast near 130W will move south ending up off the Central California coast Tuesday. Southwesterly flow aloft over the area Wednesday. Front dissipating over Western Washington Thursday with the trailing upper level trough moving through Thursday night into Friday. Lots of uncertainty in the weekend forecast with a few model solutions showing a strong front moving into the area.

SHORT TERM /TODAY THROUGH WEDNESDAY/

Satellite imagery shows high clouds over Western Washington this morning with an upper level low along 130W west of Hoquiam. Temperatures at 3 AM/10Z in the 40s and lower 50s.

Upper level low moving south today with southwesterly flow aloft keeping high clouds over the area. There are some temperature dew point spreads near 0 early this morning so even with the cloud cover patchy fog possible until mid morning. Highs in the upper 50s to mid 60s.

Upper level low continuing to move south tonight and Tuesday ending up off the Central California coast. As the low moves farther away high cloud cover will thin out overnight into Tuesday. Thinner cloud cover overnight plus light surface gradients will lead to more fog coverage Tuesday morning. The layer will be shallow enough to dissipate by noon. Lows tonight mostly in the mid 30s to mid 40s with local lows near freezing over the Southwest Interior and near the Hood Canal. Highs Tuesday in the upper 50s to mid 60s.

Upper level low well to the south with a developing upper level trough well to the north Tuesday night and Wednesday leaving mostly clear skies over Western Washington. Low level flow turning offshore but not strong enough to prevent areas of fog from developing early Wednesday morning. What fog that does form will dissipate by midday. Lows in the 30s and lower 40s. Highs in the lower to mid 60s. Felton

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

Extended models in good agreement early on with a weakening front dissipating over the area Thursday for a chance of showers. Trailing upper level trough moving through Thursday night into early Friday with surface high pressure building into the area for a dry Friday.

Confidence in the forecast for the weekend pretty low at this point. Model run to run consistency terrible with solutions all over the place for a developing system off the coast. Previous run had a few windy solutions for Saturday into Sunday with rain. Some of the ECMWF ensembles still pointing at a windy coast and Northwest Interior scenario. GFS solutions much weaker with the operational run about 20 mb weaker with the surface low associated with the front versus the ECMWF. With all the uncertainty weekend forecast a broadbrush chance of rain/rain likely. Do not have any impactful winds in this forecast package. Pretty confident the weekend forecast is going to change a few times before Friday.

Highs in the mid to upper 50s though the period with lows in the 30s and lower 40s. Felton

AVIATION

Southwesterly flow aloft is expected today as an upper trough digs southward offshore. Flow aloft then turn more variable into early Tuesday. Mid to high level clouds this morning is limiting areal coverage of low clouds and fog with the exception of more fog prone locations in the Southwest Interior, some river valleys, and extreme southern Puget Sound for the potential of IFR/LIFR conditions. Impacted terminals expected to improve by 18z for widespread VFR conditions. Winds will shift more southerly Monday morning then transition back northerly in the evening. More widespread low clouds/fog a possibility late tonight into Tuesday morning.

KSEA...Confidence leans toward VFR conditions continuing today. Mid- high clouds overhead should limit fog development this morning but can't rule out fog activity near the vicinity. Surface winds light this morning. Winds will shift more southerly by the afternoon, before transitioning northwesterly after 19Z-21Z at 5-8 kt and remaining into the evening.

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MARINE

A low pressure system passing southward well offshore will keep winds northerly or weakly offshore for today. Weak high pressure will remain across the waters into the middle of the week for a period of benign conditions. A larger swell train near 10-12 feet generated by active weather well offshore is expected to reach the coastal waters around Thursday along with an increase in onshore flow. A front may reach the waters toward the end of the week but much uncertainly exists in regards to current track and intensity.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...None.