Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000 FXUS66 KSEW 231029 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 229 AM PST Fri Feb 23 2024 .SYNOPSIS...
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High pressure building briefly into the area today with morning fog and dry conditions. The ridge will flatten Saturday for increasing precipitation. A stronger frontal system will move through Sunday into Monday for lowland rain, heavy mountain snow, and breezy winds. A cooler, wetter weather pattern is expected for most of next week.
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&& .SHORT TERM /TODAY THROUGH SUNDAY/...
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Areas of fog developing early this morning across western Washington, particularly near Puget Sound and in the vicinity of San Juan Islands/Whatcom County. Expect fog to continue through this morning for these areas, likely becoming a bit more widespread over the next few hours. Low stratus and fog will clear late morning into midday with mostly sunny skies this afternoon due to brief ridging. The ridge will flatten Friday night into Saturday with a system north of the area. This will increase precipitation potential on Saturday, especially for King County northward, across the Cascades, and over the Olympic Peninsula. Temperatures will also cool a few degrees on Saturday with highs in the upper 40s to low 50s. A stronger frontal system will slide southward across western Washington on Sunday associated with troughing moving southward across British Columbia and into the northern Pacific Northwest by Monday. Steadier lowland rain is expected on Sunday, along with breezy winds. At this time, the best potential for wind gusts exceeding 40 MPH is over Whidbey Island with a stronger westerly push through the Strait of Juan de Fuca later Sunday. Perhaps the most impactful weather on Sunday will be from snow over the Cascades and Olympics. Snow levels ranging from 3000 to 4000 feet Sunday will fall below 1000 feet by later Sunday night. A rain/snow mix will be likely at Snoqualmie Pass on Sunday before snow levels fall quickly late Sunday afternoon into Sunday evening. Snow amounts Sunday through Sunday night will range 1 to 2 feet for the Cascade Passes, with heaviest snowfall amounts over Stevens Pass. For this reason, a Winter Storm Watch has been issued for the Cascades from Sunday morning through Monday. Stratiform precipitation will transition more to convective showers Sunday night into early Monday with colder air aloft. .LONG TERM /MONDAY THROUGH THURSDAY/...Precipitation will continue on Monday, generally in the form of convective showers with at least minimal instability noted due to colder air aloft. Snow levels by early Monday morning will also range 200-700 feet. This will allow for the potential of snow or rain/snow mix into the lowlands. At this time, guidance suggests the area near Snohomish/Skagit Counties as a favored area for convergence Sunday night into Monday morning, leading to perhaps light snowfall accumulations on grassy or elevated surfaces, with a similar outcome for the Cascade Foothills. However, showers elsewhere on Monday may result in a rain/snow mix too. Any snowfall accumulations Monday morning will likely melt quickly by Monday afternoon due to highs in the low to mid 40s. Additional mountain snow is expected Monday as well with periods of showers. Temperatures will be slightly colder Tuesday morning across western Washington. The threat for a rain/snow mix may exist again during this period, although QPF amounts are generally lighter Monday night into early Tuesday. Ensemble guidance suggests the active period continues Tuesday through Thursday with additional weather systems moving into western Washington. Snow levels will slowly rise on Tuesday and further into midweek. Heavier mountain snow will be the theme during midweek with perhaps the most beneficial Cascade/Olympic snow pattern so far this season. If you plan on traveling over the Passes Sunday through next week, continue to monitor the forecast. Temperatures will remain cooler than normal for most of next week across the area. JD
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&& .AVIATION...
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Weak upper-level ridging is building into the region with light west to northwest flow aloft. Mostly clear skies this morning. Hints of fog are beginning to be observed on satellite, with the Southwest Interior (OLM, CLS) and the North Interior (BLI, ORS, NUW, etc.) reporting reduced visibilities. Winds are mostly light to calm this morning and with low dewpoint depressions across the region, only expect fog to proliferate. The most conservative solution would keep the fog in these regions, and develop it through the Kitsap Peninsula (PWT) and into the Strait of Juan de Fuca (CLM). Fog will likely develop over Puget Sound and could push very close to the Seattle terminals. A more aggressive solution would push the fog into to the Seattle terminals, however the shallow nature of it and the remaining light north wind may be a saving grace and keep at least SEA and PAE mostly clear of any fog. Any fog that does develop should scatter out between 16-18Z this morning. Mostly clear skies again during the day today with high clouds filling in this evening. Ceilings are expected to quickly lower late this evening and potentially reach MVFR through Seattle and northward as early as 12Z Saturday. Winds light northerly to calm this morning, becoming somewhat variable after sunrise as winds shift to onshore along the coast and light southerly through the interior. KSEA...VFR conditions this morning. Shallow fog west of the terminal near the Sound this morning already, and could spread closer to the terminal. Best probabilities for reduced visibilities/low stratus at the terminal between 14-17Z this morning. Otherwise VFR with mostly clear skies tomorrow. Clouds fill in this evening with ceilings expected to drop overnight tomorrow to MVFR by the end of the TAF period. Light NNE winds transitioning to light southerly between 00- 03Z Saturday. Southerly winds picking up into the end of the period. LH
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&& .MARINE...
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Surface high pressure is building across the region this morning for rather tranquil conditions to finish off the week. Fog is developing throughout the interior waters this morning, and may become dense at times. Winds will begin to pick up the the Central and East Entrance to the Strait of Juan de Fuca this evening into Saturday as the flow turns onshore, prompting a Small Craft Advisory for the aforementioned areas. A vigorous frontal system will approach the area from the Gulf of Alaska and bring widespread gusty winds across the area waters. Gales most likely through the northern-most coastal waters and the Strait of Juan de Fuca during the day Sunday. Several additional systems will traverse the region next week which will possibly warrant additional headlines. Seas 5 to 7 ft will build on Sunday to around 12 to 16 ft and remain hazardous through Tuesday of next week. LH
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&& .HYDROLOGY...No river flooding is forecast over the next 7 days, but heavy precipitation entering the region next week may contribute to river rises across western Washington. && .SEW WATCHES/WARNINGS/ADVISORIES...
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WA...Winter Storm Watch from late Saturday night through Monday afternoon for West Slopes North Cascades and Passes-West Slopes North Central Cascades and Passes. Winter Storm Watch from Sunday morning through Monday afternoon for West Slopes South Central Cascades and Passes. PZ...Small Craft Advisory from 4 PM this afternoon to 4 PM PST Saturday for Central U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory from 4 PM this afternoon to 4 AM PST Saturday for East Entrance U.S. Waters Strait Of Juan De Fuca.
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&& $$

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