Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
865 FXUS66 KSEW 191629 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 929 AM PDT Thu Sep 19 2024 .SYNOPSIS...Weak high pressure holds over the region through Thursday with morning clouds but afternoon sunshine. Expect a return to a wetter pattern Friday and again late in the weekend as the next disturbance crosses the region. && .SHORT TERM /TODAY THROUGH SATURDAY/...Forecast remains on track with some lingering low clouds across parts of the area. These will gradually scatter through the morning with increasing sun this afternoon for most of the area. No updates this morning, and the previous short/long term sections follow. 12 Western WA remains under the influence of onshore flow for slightly cooler weather today - highs tracking a degree or two below average. There is a disturbance rolling through southern B.C. but we remain dry for the most part (aside from a few light showers in the Cascades). A weak ripple may help generate a few more showers in the interior and Cascades on Friday. The next incoming frontal system pushes into B.C. and stalls as we move into Saturday, keeping western WA mainly dry. The air mass will be a little warmer with temps tracking closer to average. 33 .LONG TERM /SUNDAY THROUGH WEDNESDAY/...Wetter weather is ahead as we move into later Sunday and Monday, especially for the coast and mountains with a steady stream of moisture over the region. Ensemble guidance is backing off on total rainfall amounts in the interior (Seattle south) with a 25-50% chance of seeing measurable rain. But there`s a good chance of wetting rains at the coast and mountains with 0.25-0.50" ranges. Moving on, we`re on the northern edge of a ridge as it moves inland on Tuesday. This results in a dry and warmer pattern with highs in the 70s again. Then, toward midweek, moist SW flow returns as the ridge moves farther inland. This brings cooler and wetter weather back to western WA with a chance of rain. 33 && .AVIATION...An upper ridge centered well offshore and an upper trough moving into British Columbia today will produce increasing northwesterly flow aloft over Western Washington. Widespread low level moisture remains in place across the area this morning producing a mixed bag of ceilings. Areas of IFR/MVFR ceilings/mist and localized LIFR fog/clouds will continue this morning before lifting to VFR across interior areas 18Z-20Z. Increasing low level onshore flow later today is expected to spread low MVFR stratus across much of the lowlands of Western Washington on Friday morning. Winds will be variable between southwesterly (South Puget Sound) to northwesterly elsewhere at 4 to 8 kt (highest winds towards the coastline and Strait of Juan de Fuca). KSEA...Still on the lookout for possible brief periods of low stratus/fog this morning (but this has only filled in a couple of times - however low stratus to the north of the terminal may sneak in briefly mid morning before mixing/lifting upward). The risk of low clouds/mist will diminish late this morning/afternoon by 19-20Z as clouds scatter out. MVFR ceilings will fill back in as early as 12Z Friday for the morning. Winds will be variably out of the west 4 to 8 kt. 27/HPR && .MARINE...Broad surface ridging will remain centered well offshore into the weekend. Onshore flow will increase tonight into Friday as a system moves by well to our north. Small craft advisories have been posted for the outer coastal waters and the central/east portions of the strait. Surface ridging expands in the coastal and interior waters on Saturday for lighter winds. A series of weak frontal systems will brush the area early in the coming week, but are presently not expected to produce any headlines. 27 && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory from 5 PM this afternoon to 3 AM PDT Friday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory from 11 PM this evening to 5 PM PDT Friday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm. && $$