Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000 FXUS66 KSEW 141044 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 344 AM PDT Thu Jun 14 2018 .SYNOPSIS...
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An upper level trough will remain over the area today keeping at least a slight chance of showers in the forecast. The trough will move southeast tonight and Friday with dry northerly flow aloft developing. A weak upper level low will move south through the area Friday night. The low will stall over southeastern Oregon/northern Nevada over the weekend into next week. Temperatures will warm beginning Sunday with the warming trend continuing into the middle of next week with east or northeasterly flow aloft and low level offshore flow at times.
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&& .SHORT TERM...
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Satellite imagery shows classic convergence zone signature with clear skies over the San Juans and extreme south Puget Sound areas and cloudy skies over most of King and Snohomish counties. Mostly cloudy skies over the remainder of the area early this morning. Doppler radar shows showers continuing in the convergence zone with scattered showers along the coast and isolated showers elsewhere. Temperatures at 3 am/10z were in the upper 40s to mid 50s. Convergence zone slowly dissipating this morning with surface gradients through the Strait and up the Puget sound weakening. For the remainder of the area weak troughiness overhead will keep mostly cloudy skies with a slight chance of showers in the forecast. As the convergence zone weakens the clouds will fill in over the south Puget Sound and north around the San Juans later this morning. A few sunbreaks this afternoon will push high temperatures into the 60s, a couple of degrees below normal for mid June. Trough digging slowly southeast tonight with drying northwesterly flow aloft developing. Air mass still weakly unstable with the daytime heating keeping a slight chance of showers over the Olympics and North Cascades. Plenty of low level moisture remaining over the area tonight and with the low level flow light onshore the moisture will not be going anywhere leaving skies mostly cloudy. Lows will be in the mid 40s to mid 50s. An upper level low will move south through British Columbia on Friday ending up just north of the border by late afternoon. Most of the shower activity with the low will develop in the afternoon with some daytime heating and remain fairly confined to around the low center. This will keep showers north of the area Friday afternoon. The air mass will become slightly unstable over the mountains for a slight chance of showers with the best chances near Mount Baker. Weak low level onshore flow will keep some low level moisture in the area at least in the morning hours. For now will go with partly sunny wording on Friday. Highs will be a little warmer in the 60s and lower 70s. Low moving quickly south through western Washington on Friday night. The low is weak and without any daytime heating to add a little extra pop will keep the chance of showers confined to the mountains Friday night. Lows once again will be in the mid 40s to mid 50s. Drying and warming trend on Saturday with the flow aloft becoming northeasterly after the low passes through and the surface gradients turn northerly. Temperatures aloft warming with 850 mb temperatures rising from plus 6 to 8C 00z Saturday to plus 10 to 14C 00z Sunday. The afternoon northerly breezes will cut a couple of degrees off the high temperatures. In general expect 5 to 10 degrees of warming with highs in the upper 60s and 70s. .LONG TERM...Big question in the extended is where will the upper level low end up. The 00z model runs are a little further south with the low keeping the wrap around moisture south and east of the area through the period. Temperatures aloft warming with model 850 mb temperatures rising to plus 20C or higher by Tuesday and Wednesday. Northwesterly surface gradients continuing on Sunday with a thermally induced surface trough trying to develop along the coast Monday into Tuesday with the trough shifting inland on Wednesday. Have gone ahead and warmed the high temperatures up a few degrees in the extended with 70s to mid 80s on Sunday rising to the mid 70s to near 90 on Tuesday and possibly into Wednesday. Felton
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&& .AVIATION...
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A broad upper trough axis will remain over the Inland Northwest for the next 24 hours, with light to moderate northwest flow aloft over Western Washington. The low-level air mass will be moist and a little unstable, with dry and stable air above about 7000 feet msl. Puget Sound Convergence Zone currently near PAE, with associated showers and cigs below 020. PSCZ will dissipate in the hours after sunrise. Clouds scattering back from cold saltwater bodies this afternoon, banking up against the mountains. KSEA...Familiar rhythm of clouds lifting late this morning, with cigs rising above 020 by 17z (10 am). Continued lifting and partial scattering during the afternoon. Light southerly wind this morning, gradually transitioning through a light westerly seabreeze off Puget Sound this afternoon, then turning northerly around 00z-01z (5-6 pm). Haner
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&& .MARINE...
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Weak high pressure will build over the offshore waters today and weaken tonight, with light onshore flow. Marginal small craft advisory westerlies are likely in the central and eastern Strait of Juan de Fuca this evening. A weak disturbance moving south into the region Friday and Friday night will result in small craft advisory northwest winds over the coastal waters, with small craft advisory west winds again in the central and eastern Strait of Juan de Fuca Friday night. High pressure will remain offshore Saturday through Monday, with a generally weak northwest pressure gradient across the forecast area becoming light on Monday. McDonnal
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&& .CLIMATE...
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The warmest Father`s day on record in Seattle is 88 degrees in 2004. Even to get a high in the 80s on Father`s day is somewhat rare in Seattle with only 9 days in the 80`s in the 73 years of records at Sea-Tac airport. Felton
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&& .SEW WATCHES/WARNINGS/ADVISORIES...
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WA...None. PZ...Small Craft Advisory from 6 PM this evening to midnight PDT tonight for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.
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&& $$ www.weather.gov/seattle

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