Marine Weather and Tide Forecast for SeaTac, WA

SYNOPSIS
Strong upper level ridge centered offshore through Wednesday.
The ridge will weaken Thursday allowing a weather system to move over the top of the ridge into Western Washington late in the week.

SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/
Satellite imagery shows clear skies over almost all of Western Washington.
Stubborn patch of fog still in place near the Lewis/Cowlitz county line. Low level offshore flow pushing temperatures in to the upper 40s to mid 50s at 2 pm/22z.

High amplitude upper level ridge offshore through Tuesday. Cross Cascade gradients near -10 mb and Olympia to Bellingham gradient around -2 mb. Models have been too weak with both of these variables. This will keep fog at a minimum Sunday morning with just wind sheltered valleys and the usual locations in the Southwest Interior seeing fog in the early morning hours. Wide range of low temperatures with the wind sheltered areas dropping into the 20s while locations with exposure to the winds staying in the mid 30s.

What little fog that does form Sunday morning will be gone by noon. Under sunny skies with offshore flow highs will be above normal, in the upper 40s to mid 50s. Warmest locations in the lowlands Cascade foothills and along the coast. It will also be in the 50s in the mountains ( it is currently 53 degrees at Paradise on Mount Rainier and 55 degrees at 5000 feet on Mount Baker ).

Little change in the forecast Sunday night through Monday night with the upper level ridge remaining in place offshore and low level offshore/northerly flow over the interior.

Could see a little more fog/low stratus coverage Tuesday with the models indicating the offshore and northerly gradients starting to weaken. With more cloud cover high temperatures a couple of degrees cooler, mostly in the 40s. Felton

LONG TERM /WEDNESDAY THROUGH SATURDAY/
Models showing good consistency breaking down the ridge offshore Wednesday and Thursday. The question is how much cool air will be in place when a weak system moves into the area from the northwest and what will the timing be of this system. Some model solutions have the 1000-850 mb thickness values near 1300 meters Friday morning bringing up the possibility of a rain/snow mix. Surface low solutions moving the low inland over Southwest Washington. This could pull some cool air down from British Columbia Friday afternoon. Model bias is to usually over emphasize the cold air out this far out. Ensemble solutions showing a lot of uncertainty in the timing of the system after the ridge so for now broad brush chance pops from Thursday night through Saturday. Felton

AVIATION
High pressure will remain in place through the TAF period, resulting in mostly VFR conditions outside of morning fog and low stratus.
Winds remain N/NE 5-12 kt this evening and will decrease overnight.
Another temperature inversion tonight/Sunday morning keeps a medium (30-50%) chance of IFR/LIFR fog reforming just past sunset through Sunday morning for most western Washington terminals. Spots that keep a breeze likely will see lower stratus instead of fog. Burnoff to VFR may take longer Sunday morning into the afternoon, especially as winds remain light.

KSEA...VFR through tonight, with N/NE winds 5-10 kt, decreasing to 5- 8 kt after 06Z. There's a 30-50% chance of IFR/LIFR conditions developing over the terminal between 12-21Z Sunday in low stratus and patchy fog, with VFR conditions returning by Sunday afternoon.

HPR/15

MARINE
A high pressure ridge pattern will remain offshore through the weekend into much of next week. Flow will be offshore/northerly at times, with no major wind concerns for the next several days. The high pressure ridge will break down midweek with a system passing through towards the end of the week. Will continue to monitor this system for possible wind concerns.

Seas will hold at 4-6 ft through Thursday, increasing to 6-8 ft Friday/Saturday next week.

HPR/15

HYDROLOGY
No river flooding in the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES
WA...None.
PZ...None.