Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000 FXUS66 KSEW 251027 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 327 AM PDT Sun Aug 25 2019 .SYNOPSIS...Upper level ridge offshore slowly building today as an upper level trough moves east of the area. The ridge will continue to build, moving inland on Tuesday and remaining in place into next weekend. The ridge will weaken somewhat on Thursday. Low level flow turning offshore later Monday with the strongest offshore flow Tuesday into early Wednesday. Low level flow turning back onshore Thursday. && .SHORT TERM /TODAY THROUGH TUESDAY/...Satellite imagery shows mostly cloudy skies over most of the area at 3 am/10z with a break in the cloud cover from the central coast southeast into Cowlitz county. Temperatures at 3 am were in the mid 50s to lower 60s. Pretty "normal" late August day on tap for Western Washington today. Upper level trough well east of the area this afternoon with weak upper level ridging developing over the area. In the lower levels light onshore flow. Marine layer is shallow and with the low level flow trending toward neutral there will be no reinforcement of the marine layer. End result plenty of afternoon sunshine after the morning cloud cover. Temperatures near normal, mid 60s to mid 70s. Upper level ridge offshore continuing to build and move east tonight into Monday. Surface gradients going northwesterly overnight which does not bode well for morning stratus on Monday for the interior. Temperatures aloft warming and by 00z Tuesday 500 mb heights in the mid 580 dms. Afternoon seabreezes will put a cap on the high temperatures near the water but even with the seabreezes most places a few degrees warmer Monday with highs in the 70s. Lows tonight in the 50s. Upper level ridge moving over Western Washington Monday night into Tuesday with the low level flow turning offshore. Winds aloft in the lower levels also turning offshore but not very strong, 850 mb winds easterly less than 10 knots. Temperatures aloft continuing to warm with 850 mb temps around plus 20C by 00z Wednesday. All this adds up to much warmer temperatures on Tuesday with highs in the 80s even along the coast. Warmest locations will be near 90. .LONG TERM /WEDNESDAY THROUGH SATURDAY/...Extended models in good agreement with upper level ridge over Western Washington and low level offshore flow weakening on Wednesday. Right now it looks like the high temperatures will peak Wednesday for the interior with a little cooling along the coast with the lack of offshore flow allowing afternoon seabreezes to kick in. Highs in the interior from the upper 70 to lower 90s with highs cooling back down into the 70s along the coast. Upper level ridge weakening on Thursday with temperatures aloft cooling and the low level flow going light onshore. Weak surface low off the coast preventing a stronger onshore flow scenario from developing. The weak marine push Thursday will drop high temperatures up to 5 degrees with mid 70s to mid 80s for the interior and lower to mid 70s for the coast. Weak surface low off the coast will continue to put a damper on the low level onshore flow Friday. 00z model runs are much slower with the approach of the next upper level trough next weekend. The slower approach actually pumps the upper level ridge back up a bit over the area. Low level flow remaining weakly onshore Saturday as well. With the lack of any significant low level onshore flow will stay on the warm side of guidance for the high temperatures Friday and Saturday, in the 70s to lower 80s. Will also take the chance of showers out of the forecast for Saturday with the slower approach of the upper level trough. Felton && .AVIATION...Northwesterly flow aloft as an upper level trough departs the Pacific Northwest. Onshore flow at the surface. VFR conditions as of 8Z. Brief period of MVFR ceilings later this morning as marine stratus makes another push inland. Clearing expected by the late morning/early afternoon as upper level ridging begins to build into the area. KSEA...VFR conditions early this morning with mid level clouds. Brief period of MVFR ceilings possible later this morning as marine stratus moves inland before improvement again by this afternoon. NE winds 5-10 kts become southwesterly after 12z. CEO && .MARINE...Onshore flow continues into Monday. A westerly push down the Strait tonight behind a weak front has resulted in small craft advisory winds. Winds will gradually weaken this morning. Another round of small craft advisory winds through the Strait possible this evening but for now have forecast just under criteria and will let day shift monitor trends. Offshore flow returns on Tuesday and will persist through much of the week. CEO && .HYDROLOGY...The daily hydrology discussion has ended until the start of the next rainy season; it will only be updated as needed until then. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory until 5 AM PDT early this morning for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca. && $$ www.weather.gov/seattle

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