Marine Weather and Tide Forecast for SeaTac, WA

SYNOPSIS
Mostly dry and cool conditions will start off the week as high pressure builds overhead. Unsettled weather will return mid-week and beyond as troughing brings additional chances of precipitation.

SHORT TERM /TONIGHT THROUGH THURSDAY/
Showers will continue to pivot southeastward throughout the afternoon and evening today as the upper level trough exits western Washington and high pressure builds inland. Conditions will dry out on Monday, with northerly flow allowing for temperatures to cool off a few degrees. The lowlands will see highs in the mid 40s alongside some afternoon sun breaks, with slightly warmer temperatures along the coast and Cascade foothills. Temperatures will cool even further heading into Monday night as northerly flow aloft amplifies, bringing low temperatures Tuesday morning near or below the freezing mark for most areas.

High resolution forecast models are picking up on the potential for very light shower and virga activity on Tuesday along the periphery of the high pressure ridge that will continue to amplify along the Pacific coast mid-week. This will likely produce little more than a few sprinkles across western Washington in any showers that develop. Otherwise, Tuesday will provide a cloudy and mostly dry day with continued below-normal temperatures.

The upper trough axis will shift inland on Wednesday, which may once again stir up light shower activity across western Washington ahead of the next incoming system. Operational models continue to lessen the chance for measurable precipitation during the day Wednesday, which may result in another round of sprinkles and virga showers.

LONG TERM /FRIDAY THROUGH MONDAY/
A shortwave trough is on track to pass over the region on Thursday, bringing in another round of widespread lowland rain and mountain snow. With snow levels between 3000-4000 ft, the higher mountain passes will likely see light snow accumulations. Shower activity is favored to continue over higher terrain into Friday as the lowlands dry out, with up to a tenth of an inch of rainfall for the lowlands and up to half an inch of liquid currently forecast over the mountains.

Ensembles continue to highlight potential for a more potent storm system entering the region next weekend, though uncertainty remains over the exact track and intensity of this system. A chance of precipitation is maintained in the forecast through next weekend with near-normal temperatures and breezy winds.

15

AVIATION
An upper ridge will begin to build into the region for north to northwesterly flow aloft. Light surface flow will turn northerly on Monday as surface high pressure builds over the southern interior of British Columbia. A mix of VFR and MVFR ceilings with diminishing shower activity will lower to MVFR with pockets of IFR overnight into Monday morning. Ceilings will lift back to VFR Monday afternoon.

KSEA...VFR cigs presently, with light southerly flow. While VFR cigs are likely to persist, there could be a SCT layer of 1000 ft into Monday morning. An IFR window is possible after 12Z through 17Z for low stratus, with early afternoon scattering. Northerly winds will resume around 20Z and be 5 kt or less.

Kristell/27

MARINE
Surface high pressure will rebuild across the waters today tonight. The ridge will remain over the waters into Wednesday. Another front will reach the area late Wednesday into Thursday. Small craft advisories remain up through tonight for the coastal waters and the west entrance to the strait for seas of 10 to 15 feet. These will subside Monday morning to less than 10 feet.
Seas build back over 10 feet with the next front expected around midweek. 27

HYDROLOGY
Incoming precipitation during the latter half of the week will likely cause rises to area rivers, but is not expected to cause any river flooding at this time.

15

SEW WATCHES/WARNINGS/ADVISORIES
WA...None.
PZ...Small Craft Advisory until 6 AM PST Monday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm- Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm-Grays Harbor Bar-West Entrance U.S.
Waters Strait Of Juan De Fuca.