Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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391 FXUS66 KSEW 140937 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 237 AM PDT Tue May 14 2024 .SYNOPSIS...
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A ridge of high pressure will provide dry and warmer conditions for the region through Wednesday. An upper trough dipping southward from British Columbia will produce clouds and cooler temperatures Thursday through Saturday along with a chance for showers across mainly northern portions of the area. Below normal temperatures and somewhat unsettled conditions could persist into the early part of next week.
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&& .SHORT TERM /TODAY THROUGH THURSDAY/...
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An upper ridge centered well to our southwest will build into the area today and Wednesday. This will allow for dry conditions and a modest warming trend. Low level onshore flow will keep temperatures in check with 60s for coastal areas and mid 60s to mid 70s for the interior lowlands. The upper ridge will flatten on Thursday in response to an upper level trough moving onshore over British Columbia. This will act to increase the onshore flow and the end result will be increasing cloud cover and cooler temperatures. Onshore flow becomes relatively strong Thursday afternoon into Thursday night and this will likely initiate a convergence zone over Skagit/Snohomish counties. .LONG TERM /FRIDAY THROUGH MONDAY/...An upper trough axis will be over Western Washington on Friday for another mostly cloudy and cool day. The best chance for showers will be over the mountains and across northern portions of the lowlands. Snow levels will dip to around 5000 feet...something to consider if you`ve got hiking plans in the higher backcountry late this week. For the weekend and beyond, uncertainty is the word for the day to day forecast. Cluster plots show a considerable spread in solutions. Ensemble height anomalies show ridging retrograding well offshore with a mean upper trough position over the Northern Rockies heading into early next week. While not a particularly wet scenario, this does suggest that temperatures will be a little below average and shower chances will linger...especially over the higher terrain. 27
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&& .AVIATION...
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Upper level ridging in the eastern Pacific will keep northwesterly flow aloft over W WA at least into Wednesday. Surface flow this early morning generally light and variable with a few exceptions reporting northerly winds 5-10 kts. Majority of TAF sites should see similar low level winds develop by this afternoon. Widespread VFR conditions this early morning with only UIL reporting MVFR. Inherited forecast suggests MVFR conditions after 12Z for many sites although current models backing away from those solutions. Will likely gear 12Z TAF updates more toward keeping VFR conditions in place, although with some SCT lower clouds possible. Locations more prone to lower cigs, such as HQM, OLM and PWT still seem on track for MVFR to emerge in the early morning before lifting by around 18Z. VFR conditions expected over the entire area this afternoon and evening. KSEA...VFR conditions expected to persist throughout the TAF period, although some SCT020 possible after 12Z. Fair conditions expected after 18Z, with only high clouds to consider. Northerly winds 6-10 kts will persist through about 15Z before turning light and variable. Northerly winds 5-10 kts return by 20Z and persist into early Wednesday morning. 18
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&& .MARINE...
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High pressure will build off the coast throughout this week. North to northwesterly surface winds starting out over the Pacific waters then pushing inland will give rise to SCA concerns throughout the day. Headlines are staggered from west to east and limited to the coastal waters and Strait at this time, although consideration for Strait-adjacent waters may be needed depending on future model solutions. At the very least, headlines with early morning forecast package will cover the next 12-18 hours, allowing for better near-term analysis. Another push down the Strait is possible for Wednesday into Thursday while the coast may see speeds ramp up for late Thursday and all of Friday. Seas will hold around 4 to 6 ft through Friday before increasing 8 to 12 ft from Friday into the weekend. 18
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&& .HYDROLOGY...The daily hydrology discussion has ended until the start of the next rainy season; it will only be updated as needed. && .SEW WATCHES/WARNINGS/ADVISORIES...
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WA...None. PZ...Small Craft Advisory from 2 PM this afternoon to 11 PM PDT this evening for West Entrance U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory from 2 PM this afternoon to 5 AM PDT Wednesday for Central U.S. Waters Strait Of Juan De Fuca- Coastal Waters From Cape Flattery To James Island Out 10 Nm- Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm. Small Craft Advisory from 5 PM this afternoon to 5 AM PDT Wednesday for East Entrance U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory until 5 AM PDT Wednesday 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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