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Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
679 FXUS66 KSEW 301101 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 401 AM PDT Sun Jun 30 2024 .SYNOPSIS...Weak upper level trough over Western Washington today with a convergence zone over mainly Snohomish county. Trough moves east tonight and convergence zone dissipates Monday morning. Upper level ridge building offshore Monday will slowly move east for the remainder of the week ending up near Western Washington by late in the week. && .SHORT TERM /TODAY THROUGH TUESDAY/...Satellite imagery shows cloudy skies over Western Washington early this morning. Doppler radar indicating showers over the Central and Northern Cascades as well as over Whatcom county. With the cloud cover temperatures were on the mild side at 3 am/10z, in the upper 50s to mid 60s. Weak upper level trough over Western Washington today. Convergence zone developing over Snohomish county this morning with the convergence zone continuing into the afternoon hours. Main story today will be the cloud cover. With the weak trough will have a slight chance of showers for most of the lowlands in the morning. By afternoon showers chances becoming confined to the convergence zone and the Cascades. Air mass unstable enough over the North Cascades for a slight chance of a thunderstorm this afternoon. Highs today in the mid 60s along the coast and upper 60s to mid 70s inland. Upper level trough moving east tonight but the weak convergence zone will remain intact into the early morning hours. Showers chances pretty much confined to the convergence zone into early Monday morning. Some clearing early but with increasing low level onshore flow cloud cover increasing again overnight. Lows in the 50s. Upper level ridge building offshore Monday. Weak shortwave rippling down the back side of the ridge nicking the Northern portion of the Cascades keeping a chance of showers in the forecast for that location. For the remainder of the area morning clouds will give way to afternoon sunshine. Highs in the mid 60s coast and upper 60s to mid 70s inland. Upper level ridge slowly starting to move east Monday night into Tuesday. Low level onshore flow continuing through Tuesday keeping the late night and morning clouds with afternoon sunshine forecast going through Tuesday. With the onshore flow highs Tuesday will be similar to Monday, mid 60s coast and upper 60s to mid 70s inland. Lows Tuesday morning in the 50s. .LONG TERM /WEDNESDAY THROUGH SATURDAY/...Extended models in good agreement with the upper level ridge continuing to move east Wednesday. The ECMWF brings the ridge over Western Washington Thursday with the ridge remaining over the area into Saturday. The GFS keeps the ridge offshore Thursday through Saturday. Both models do not turn the low level flow offshore going to more flat gradients beginning Thursday. Slow warming trend through the period with highs Wednesday in the mid 60s along the coast and 70s inland warming to the mid 70s to lower 80s along the coast and upper 70s to near 90 inland Saturday. Ensembles show a big spread in the solutions for the high temperature Saturday. Model blend puts highs in the mid 70s along the coast and mid 70s to upper 80s inland. Ensemble means off both the GFS and ECMWF were a few degrees warmer then the blend. Given the possible HeatRisk issues have gone with the warmer ensemble mean highs for Saturday. Felton && .AVIATION...A weak upper level trough remains over the region today with west to northwest flow aloft. The air mass is moist with widespread IFR and low MVFR ceilings this morning. Ceilings are expected to gradually lift by afternoon with most areas returning to VFR near or after 22Z. Areas of MVFR will redevelop by early Monday A.M. KSEA...IFR or occasional LIFR ceilings are expected to linger through mid-morning before gradually lifting to VFR 20Z-22Z. Surface winds S/SW 5 to 10 knots becoming light and variable late this evening. 27 && .MARINE...Broad surface ridging will rebuild over the coastal and offshore waters through Monday with lower pressure continuing east of the Cascades. This will lead to an increase in onshore flow with small craft advisory westerlies likely in the central/east strait this evening. A somewhat stronger onshore gradient will lead to the potential for a few hours of gales in the strait Monday evening. Thermally induced low pressure is expected to expand northward across the interior midweek onward. This will lead to lighter winds across interior waters, but will likely produce small craft advisory strength N/NW winds for portions of the coastal waters at times Tuesday through late week as a more typical summer synoptic pattern takes hold. 27 && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory from 5 PM this afternoon to 3 AM PDT Monday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca. Gale Watch from Monday afternoon through late Monday night for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca. && $$