Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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296 FXUS66 KSEW 161627 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 927 AM PDT Sat Jun 16 2018 .SYNOPSIS...
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A weak upper level low will stall over southern Oregon and northern California this afternoon into tonight with a chance of showers or thunderstorms over the Cascades. High pressure will build offshore Sunday and Monday with ridge shifting inland Tuesday night and Wednesday. High temperatures will warm over the weekend into the first part of next week peaking on Wednesday. Increasing onshore flow will result in cooler temperatures over the interior on Thursday and Friday.
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&& .SHORT TERM...
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An upper level low is spinning over the Pac NW today and will shift south into northern CA and NV tonight. Satellite shows some wrap-around moisture associated with the low, affecting Western WA this morning. Showers will pop up along the Cascades this afternoon with a slight chance of thunderstorms, most likely in the central and southern Cascades. Showers will diminish this evening as the low exits. A strong upper level ridge will build offshore on Sunday then nudge inland early next week for a warming trend. Dry northerly flow will prevail Sunday and Monday with skies mostly clear. The warm air mass will lead to above normal temperatures with highs reaching the mid to upper 80s in the interior, around 10-20 degrees warmer than normal. Along the coast, surface pressure gradients remain onshore with a tight temperature gradient expected. Temperatures along the beaches will be in the 60s to lower 70s with low 80s inland. 33 .LONG TERM...Previous discussion...Extended models in good agreement Tuesday and Wednesday with the upper level ridge offshore shifting inland Tuesday night into Wednesday. Highs both days close to records, in the upper 70s to near 90 for the interior. Slightly cooler temperatures on the coast with an afternoon seabreeze. Surface onshore gradients increasing Wednesday night into Thursday bringing a push of cooler marine air into the interior. GFS is a little stronger with the push, 10 to 15 degrees of cooling, versus the ECMWF, 5 to 10 degrees of cooling. For now have used a model blend for Thursday with highs in the interior in the 70s for the most part. Temperatures continue to cool on Friday with low level onshore flow continuing pushing high temperatures back closer to normal, in the mid 60s to mid 70s. Felton
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&& .AVIATION...
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An upper level ridge centered offshore along with an upper level low over OR will result in nely flow aloft across the area today. The low level flow will remain onshore or nwly. Expect areas of MVFR CIGs over mainly the interior this morning to scatter out later this morning or about midday. The air mass will become unstable over the Cascades this afternoon for a risk of isold tstms. KSEA...VFR conditions will return by 1800 UTC (11 AM PDT), 1900 UTC (noon PDT) at the latest. Visible satellite imagery showed a very well-defined back edge to the cloud deck with clear skies to the west. The back edge should reach the terminal by 1800 UTC. VFR conditions will privily this afternoon thru Sunday morning. Winds will be northerly 10-16 knots, with occasional gusts near 25 knots this afternoon. Winds will gradually diminish this evening.
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&& .MARINE...
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Onshore or northwest flow will persist through this evening. The flow will become light offshore or northerly overnight and then continue through Sunday morning due to a 1020 mb high briefly setting up over British Columbia. Expect a diurnally driven pattern of onshore or northwest flow during the afternoons and evenings Sunday through Tuesday.
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&& .SEW WATCHES/WARNINGS/ADVISORIES...
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WA...None. PZ...Small Craft Advisory until 11 PM PDT this evening for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm- Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm.
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&& $$ www.weather.gov/seattle

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