Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
502 FXUS66 KSEW 221742 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 942 AM PST Fri Nov 22 2024 .SYNOPSIS...An upper-low continues to churn off the PNW coast through the start of next week with active weather. A strengthening surface low (not as intense as the one Tuesday) will brush across the region today with widespread precipitation and gusty winds. Conditions will settle towards the middle of next week as guidance hints at the return higher heights. && .UPDATE...The east winds in the Cascade Foothills/eastside suburbs and Western Whatcom County have diminished below wind advisory criteria - have ended the advisory early. The focus turns to increasingly gusty southerly winds this afternoon for much of the region. The advisory continues for the Pacific Coast, and the advisory has now been expanded to include western Whatcom, Admiralty Inlet area, San Juan County and Western Skagit County from noon until 4 am Saturday (gusts up to 50 mph). Areas not under any wind advisories will still see gusty southerly winds this afternoon, but only at 35 to 40 mph. Showers also continue for areas east of Puget Sound. Isolated thunderstorms have popped up over the coastal waters, and there is the potential for a couple of them moving along the coast late this morning and afternoon. HPR && .SHORT TERM /TODAY THROUGH SUNDAY/...A sub 990 mb surface low is deepening over the NE PAC. It`s spreading precipitation ahead of an occluded front from south to north across the region as it parallels the PNW coastline. Here locally, we`ll see rain persist through the early morning hours before breaking into showers by midday. Can`t rule out a slight chance (15%) of thunderstorms, primarily along the coast this afternoon. Accompanying rainfall, a tightening pressure gradient will bring another round of gusty winds as a Wind Advisory is in effect for the coast, western Whatcom, and Cascade foothills adjacent to gaps. Gusts upwards of 45 to 55 mph are in the forecast. HREF guidance is hinting at a 40% chance for easterly gap wind gusts nearing 60 mph for a few hours this morning as well. Although not the most likely scenario it is within the realm of possibility. Wrap-around showers are to remain in the forecast tonight as the low center gradually ushers away towards Vancouver Island. Overnight lows are to bottom into the 40s. Additionally, a high surf advisory will be in effect Friday for waves of 20 to 24 feet. Showers are to remain in the weekend forecast (with snow showers for the mountains) due in part to the upper-low churning offshore. Again, can`t rule out a rumble of thunder or two occuring over the coastal waters/WA coastline. Temperatures are to remain fairly seasonal with highs near 50 F and overnight lows in the 40s. .LONG TERM /MONDAY THROUGH THURSDAY/...Models continue to hint at the upper level low moving inland by Tuesday. With the low expected to depart off and eastward, it appears the wet weather will be replaced with drier weather come midweek as ridging builds offshore allowing dry northerly flow into the PNW, just in time for the Thanksgiving holiday. && .AVIATION...Southerly flow aloft with strong low pressure off the coast, turning more southwesterly this evening as said low shifts northward. Surface winds remain easterly for some locations however a shift to more southerly direction underway at the time of this writing /927 AM PST/ and should see this become the dominant direction for most of W WA by this afternoon. Speeds remain generally 10 to 15 kts with gusts up to 25 kts still possible. During transition from east to southerly, speeds may ease briefly /an hour or two/ before speeding up again to aforementioned values. Mixed cigs due to combination of frontal passage and post-frontal showers. VFR conditions mainly along the Sound, but also present at HQM. Locations in and near showers likely to see cigs dip into MVFR or IFR conditions at least through early afternoon. Gradual improvement expected throughout the day with widespread low-end VFR conditions expected in the early afternoon. Some additional slight improvement possible through the remainder of the afternoon and early evening, but abundant low-level moisture will allow cigs to fall this evening and tonight. While most locations should still remain VFR, locations more prone to lower cigs will likely see conditions erode down into MVFR to IFR tonight and into early Saturday morning. Instability over the coastal waters may allow for a slight chance for thunderstorms this afternoon along the coast, but little to no expectation for impacts to coastal terminals. KSEA...VFR conditions in place and likely to remain that way for the TAF period, although showers may allow for brief periods of low-end VFR to high-end MVFR cigs. Some improvement possible throughout the day and into the evening, however plenty of low-level moisture will result in lower cigs overnight and into early Saturday morning. Although lower...cigs expected to remain just above or right at VFR thresholds. Light southerly winds will increase in speed by 19Z with speeds generally 10-15 kts and gusts up to 25 kts for much of the afternoon and early evening. Wind speeds will gradually lower tonight down to 5-10 kts after 03Z, but will remain southerly. 18 && .MARINE...A deep surface low will track north off the coast today with storm force winds over the coastal waters and seas building over 20 ft. Easterly gales through the Strait of Juan de Fuca turning more southeasterly this afternoon. Winds will ease and seas will subside this weekend as the low weakens over the offshore waters. 33/18 && .HYDROLOGY...The Skokomish River will stay in action today, before climbing up into minor flood stage tonight. For the remainder of the rivers no flooding is expected at this time. Lower snow levels into the weekend in the Cascades will limit runoff and reduce any flooding chances for rivers flowing off the Cascades. Precipitation for the remainder of the period will come in bursts. This combined with snow levels remaining relatively low will keep rivers in their banks. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...Wind Advisory until 4 AM PST Saturday for Admiralty Inlet Area- San Juan County-Western Skagit County-Western Whatcom County. Flood Watch through late tonight for Hood Canal Area-Lower Chehalis Valley Area-Olympics. High Surf Advisory until 10 PM PST this evening for Central Coast-North Coast. Wind Advisory until 4 AM PST Saturday for Central Coast-North Coast. PZ...Small Craft Advisory until 4 AM PST Saturday for Admiralty Inlet- Grays Harbor Bar-Puget Sound and Hood Canal. Gale Warning until 4 AM PST Saturday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters Including The San Juan Islands-West Entrance U.S. Waters Strait Of Juan De Fuca. Storm Warning until 4 AM PST Saturday 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. && $$