Seattle, WA 98199 Weather

Synopsis

Upper level trough offshore today and tonight will move inland Thursday with not much moisture associated with the trough. Temporary ridge over the area Friday. Lots of uncertainty in the weekend forecast with a chance of a system moving through Western Washington. Trailing upper level low could still be around Monday before an upper level ridge builds Monday night and Tuesday.

Short Term

Satellite imagery shows fog in the Snoqualmie and Snohomish river valleys with some low clouds and fog near the water in Whatcom, Skagit and Snohomish county. Mostly clear skies over the remainder of the area. Temperatures at 3 AM/10Z were in the mid 30s to mid 40s.

Low level offshore flow this morning will not be strong enough to prevent a little more fog and low clouds from forming near the Puget Sound in the next couple of hours. The layer will be shallow with sunny skies across the area by mid morning. The offshore flow will add a couple of degrees to the highs with most places in the 60s. Not expecting any records but this time of year highs in the upper 60s can be records. The forecast high of 65 in Seattle would be the 10th warmest October 21st in 82 years of records.

Low level flow turning light tonight and remaining light into Thursday. Upper level trough offshore reaching the coast late Thursday increasing the cloud cover over the area Thursday afternoon but not producing any shower activity. Lows tonight in the mid 30s to mid 40s. Cooler Thursday with highs in the mid 50s to lower 60s.

Upper level trough moving through Thursday night perhaps giving the Cascades a shower or two. Mostly cloudy skies in the evening thinning out a little overnight. Lows in the lower 30s to lower 40s.

Weak temporary upper level ridge moving through Friday for another dry day. Light onshore flow in the lower levels with morning low clouds becoming at least partly sunny in the afternoon. Highs in the mid 50s to lower 60s. Felton

Long Term

Upper level ridge weakening and moving east Friday night. Models continuing to have trouble coming to a consistent solution for the weekend. The ensembles favor a weak system moving through later Saturday into Sunday morning. Ensemble mean pops are slowly getting lower in the last three runs with now just chance pops for everywhere but the north coast. Upper level low associated with the front hanging around later Sunday into Sunday night keeping chance/slight chance pops in the forecast. There is better consensus with an upper level ridge building Monday or Monday night for a dry Tuesday. Highs in the 50s through the period. If the ridge does build later Monday good chance we see some lows in the 20s Tuesday morning. Felton

As we head into the last third of October here are some current October rainfall totals in the west. You don't see this very often. Seattle 0.08 inches, Los Angeles 0.23 inches, San Diego 1.04 inches, Palm Springs 1.17 inches, Las Vegas 1.19 inches, Phoenix 0.42 inches. Felton

Aviation

An upper level low continues to spin off CA with dry and stable conditions across western WA. The flow aloft remains southwesterly. Light and variable winds in place for all terminals this early morning except for HQM, where easterly winds ranging 5-10 kts are expected to remain in place into at least late morning/early afternoon. Widespread north to northwesterly winds expected by noon today although speeds expected to generally remain less than 5 or 6 kts for the remainder of the TAF period. HQM may start the afternoon ranging 4-8 kts but winds there will also ease to around 5 kts by this evening.

Low stratus and fog in the interior this morning for IFR to LIFR conditions. Low clouds will scatter by 18-20Z time frame. VFR conditions return for the remainder of the TAF period.

KSEA...Shallow/patchy fog this morning with VFR returning by 18-20z. Light and variable winds this morning before becoming more NW this afternoon with speeds around 5 kt. Winds will shift northerly this evening while speeds remain the same.

33/18