textproduct: Seattle/Tacoma

SYNOPSIS

Upper level trough exiting the Gulf of Alaska today will move by to the west Monday. The trough will continue to move south Tuesday with a weak upper level ridge over the area. Another upper level trough will approach the coast Wednesday. The associated weakening front will move through Western Washington Thursday. Cool upper level trough over the area Friday and Saturday.

SHORT TERM /TODAY THROUGH TUESDAY/

Satellite imagery shows a patch of stratus over Grays Harbor county and fog in the Snohomish River Valley otherwise clear skies over the area. Temperatures at 3 AM/10Z were in the upper 30s to near 50.

Zonal flow aloft becoming southwesterly today as an upper level trough digs south well offshore. At the surface, high pressure will weaken with light northerly flow. Narrow temperature dewpoint spreads early this morning with light gradients so expect more fog to develop especially over the Southwest Interior and near the Puget Sound and Hood Canal. The fog that does form will be gone by late morning. Mostly sunny this afternoon with highs in the mid 50s to lower 60s.

Upper level trough continuing to move south tonight and Monday with the trough axis near 130W Monday afternoon. This is too far west to bring any weather to Western Washington other than some middle and high level clouds. Another round of patchy morning fog in the fog prone places late tonight through mid morning. Lows in the mid 30s to mid 40s. Highs Monday a couple of degrees either side of 60.

Large upper level low developing in the trough Monday night into Tuesday ending up off the Central California coast Tuesday afternoon. Weak upper level ridge over Western Washington with light/split flow aloft. Light surface gradients allowing for a little more fog coverage Tuesday morning. Like most of the foggy mornings this month the fog will be gone before noon. Lows in the mid 30s to mid 40s. Highs in the upper 50s to mid 60s.

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

Extended models in good agreement with the upper level low spinning around off the California coast Tuesday night and Wednesday. Weaker upper level trough moving out of the Gulf of Alaska still well offshore Wednesday. Another sunny day in store with areas of morning fog and local freezing fog. Lows in the 30s to lower 40s. Highs in the lower to mid 60s.

Upper level trough with the associated front still offshore Wednesday night. Front weakening as it moves inland Thursday with just chance pops in the forecast. Lows in the mid 30s to mid 40s. The increase in cloud cover will knock a few degrees off the highs with mid 50s to near 60 in the forecast.

Cool upper level trough hanging over the area Thursday night into Saturday. Very little in the way of dynamics with the trough. Will have to keep a slight chance of showers at times through the period. Snow levels near 4500 feet so chance for some very light snow in the higher elevations. Highs near normal, mid 50s to near 60. Lows in the mid 30s to mid 40s Friday morning and 30s to lower 40s Saturday morning.

Very little in the way of precipitation forecast for the next week. So far in October there has only been 0.08 inches of rain at Seattle-Tacoma airport. There have only been 4 Octobers in the 81 years of the records at Seattle-Tacoma airport with less than an inch of rain, 1987 0.31 inches, 2002 0.67 inches, 1972, 0.72 inches and 1978 0.98 inches. Felton

AVIATION

Westerly flow aloft turning more southwesterly into Monday. Light flow and residual surface moisture is leading to the develop of fog across the area this morning. Areas of IFR/LIFR are expected but any lingering fog should subside by 18z to widespread VFR. Mid to high level cloud coverage will stream overhead Sunday afternoon - evening but can't rule out another round of patchy fog Sunday night into Monday morning. Northerly surface winds Sunday afternoon 5-10 kt.

KSEA...VFR conditions this morning. Can't rule out vicinity fog around the terminal as the morning progress but if manifest it should scatter out by the afternoon (17-18z). A TEMPO group has been introduced into the TAF to highlight this potential. NE surface winds this morning 5-10 kt, shifting to the NW 5-10 kt with gusts to 18-20 kt during the afternoon. Winds will gradually decrease overnight Sunday into Monday.

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MARINE

Surface high pressure will build across the waters today. A low pressure system passing southward well offshore will turn winds northerly or weakly offshore Sunday into Monday. Weak high pressure will remain across the waters into the middle of the coming week for rather quiet conditions. A larger swell train near 10-12 feet generated by active weather well offshore is expected to reach the coastal waters around Thursday. Seas will then subside into the weekend.

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SEW WATCHES/WARNINGS/ADVISORIES

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