Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000 FXUS66 KSEW 172229 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 329 PM PDT Sun Jun 17 2018 .SYNOPSIS...An upper level ridge will build offshore with an upper level low remaining well east of the area through Monday. The upper level ridge will shift inland on Tuesday then shift east later Wednesday. High temperatures will be well above normal through Wednesday. A weak upper level trough will move through the area on Thursday inducing a push of marine air into the interior, cooling highs back down to near normal. A weaker upper level ridge will build into the area next weekend. && .SHORT TERM...
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A few cells have developed over the central and southern Cascades, drifting SW, with isolated thunderstorms possible this evening. These cells will diminish after sunset tonight. A strong upper level ridge will continue to build offshore through Monday for dry, northerly flow over Western Washington. Expect plenty of sunshine with above normal temperatures. Highs will be mostly in the low to mid 80s with 70s near the water. Overnight lows will be around 55-60. Some mid level moisture from a low over ID may clip the central and Southern Cascades for a chance of showers and thunderstorms Monday afternoon/evening, but confidence is low. The GFS is showing an onshore push Monday night which may bring low level stratus clouds into the interior Tuesday morning. The stratus deck will be shallow and will burn back to the coast Tuesday afternoon. A few showers may develop over the mountains where heating and instability is the greatest. Isolated thunderstorms are possible, especially in the Cascades. Wednesday will be the warmest day of the stretch as the trough axis moves inland. Temperatures in the interior will reach the mid to upper 80s with a few low 90s possible, close to daily records. Expect cooler conditions along the coast with onshore flow. Isolated thunderstorms are a possibility again in the Cascades. 33 .LONG TERM...An strong onshore push will develop Wednesday night and Thursday, bringing cooler marine air inland. This will knock temperatures down into the mid 60s to 70s. There is a chance of showers Thursday afternoon, mainly across the northern half of the CWA with a passing trough. We may also see showers in the north sound with a Puget Sound Convergence Zone. An upper level ridge will cross the area Friday and Saturday for more dry weather. Temperatures will be close to normal with onshore flow. A dry cold front may cross the region next Sunday for increasing onshore flow. 33
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&& .AVIATION...
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Wrn WA will lie between an upper level ridge centered offshore and an upper level low over the Great Basin thru tonight. This will keep the flow aloft nly. The air mass will be slightly unstable thru this evening for a risk of isold tstms over the central Cascades. The low level flow will remain nly. There will be patchy fog (VSBYs 4-6SM) on the coast late tonight; otherwise, expect VFR conditions. KSEA...VFR. Northerly winds of 10-15 knots will become light and variable. Winds tomorrow will be lighter and more westerly.
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&& .MARINE...
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Northerly flow will become onshore or southerly Monday afternoon and then briefly strengthen Monday night. The combination of a near +3.0 mb pressure gradient across the Strait of Juan de Fuca and about a 15-degree difference in temperatures between the coast and the interior may be enough to cause a brief period of gale force westerlies over the central Strait of Juan de Fuca Monday evening. Therefore, a Gale Watch was issued for this area. Anticipate generally weak onshore flow Tuesday and Wednesday. Westerly or onshore flow will strengthen Thursday for a higher threat of gale force winds over parts of the Strait of Juan de Fuca.
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&& .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$ www.weather.gov/seattle

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