Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000 FXUS66 KSEW 271630 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 930 AM PDT Mon Mar 27 2023 .UPDATE...
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No changes to the current forecast this morning. A quiet but chilly start to the new workweek. A strong sfc cyclone will rapidly intensify today as it merges with another low offshore the OR and CA Coast. This will increase the pressure gradient over W WA through the day today, with the flow becoming offshore and breezy. A wind advisory is still set to take a effect late this evening over the East Puget Sound lowlands. Increasing upslope flow on the E side of the Cascades still carries the potential to spark a few showers this afternoon and evening, however, coverage appears less impressive as compared to previous forecasts. An overall dry day is in store for the local area, with high temperatures rebounding into the mid and possibly upper 50s. Previous discussion included below with an updated marine and aviation section. Kovacik
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&& .PREV DISCUSSION...
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/issued 359 AM PDT Mon Mar 27 2023/ .SYNOPSIS...A warming and drying trend will commence today and persist through midweek as offshore flow develops across western Washington and a low offshore tracks southward towards California. Upper level ridging will nudge into the region Wednesday in its wake. A return to cooler and wetter conditions is then expected the latter half of the week and into the weekend as a seasonally strong frontal system moves into the region.
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&& .SHORT TERM /TODAY THROUGH WEDNESDAY/...Radar early this morning shows some light shower activity persisting over the coastal waters and along portions of the Strait of Juan de Fuca and the San Juan Islands. Overall, expect showers to wind down over the next couple of hours. Temperatures early this morning are rather chilly out there, currently ranging in the upper 20s to the upper 30s across the majority of the forecast area. Areas of fog have also started to develop across portions of the south Sound overnight with clear skies and ample moisture still present in the low levels. A robust upper level low, will sink southward into the region from British Columbia today, remaining well offshore. Its associated surface low will merge with another low tracking towards southern OR. This will act to strengthen the surface low - and aid in the intensification of the upper level low through the day as well. The bulk of the moisture will primarily remain well to the west of the area today as the low continues to sink south. All in all, expect a primarily dry day for the majority of western Washington with low level flow transitioning to offshore and mid- level cloud cover streaming overhead. Have kept a mention of POPs in the Cascades, however- where upslope flow east of the crest may spark some shower activity in the afternoon that drifts on over to the west side. Temperatures will climb a few degrees today, with afternoon highs expected to be in the low to mid 50s. As the closed low sinks further southward towards the southern OR/northern CA coast tonight into Tuesday, some wrap- around moisture looks like it will start to make its way northward and move into the southern fringes of the forecast area. Thus, have maintained rain chances in the forecast, mainly for Lewis, Grays Harbor, Thurston, Mason, and Pierce counties. Strengthening offshore flow tonight will lead to locally windy conditions across the Cascade gaps overnight and through Tuesday afternoon, mainly for areas like Enumclaw and North Bend - where gusts to 45-50 mph will be possible at times. Have issued a wind advisory for the Puget Sound lowlands with this forecast package as a result. Temperatures on Tuesday will climb a few degrees from Monday`s highs - topping out in the upper 50s to near 60 across the area. The upper level low will then continue to move south along the CA coast on Wednesday, pulling its remaining moisture out of the area and allowing for upper level ridging to nudge into the region from the west. Wednesday is still trending as the sunniest and warmest day of week, with afternoon highs expected to climb into the upper 50s to low 60s across the area. 14 .LONG TERM /THURSDAY THROUGH SUNDAY/...A switch back to wetter and cooler conditions is on tap in the extended period with an upper level shortwave looking to brush the region on Thursday. Although moisture continues to look rather limited, this feature has the potential to bring a few showers to the region- mainly along the coast and across the mountains. A more organized frontal system then looks to approach the region on Friday, bringing with it more widespread rain for the lowlands, mountain snow, and cooler temperatures headed into the weekend. Snow levels look to drop back down below pass level with periods of heavy mountain snow possible. This may create some travel impacts across the passes should current forecast trends hold. Thus, those planning cross- Cascade travel this weekend will want to make sure to stay updated to the latest regarding the forecast over the next few days. 14 && .AVIATION...
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An upper-level low will dig southward offshore through Tuesday, promoting intensification of a strong surface low. This will lead to the development of an easterly flow pattern over the region through Tuesday. Patchy IFR in fog dissipating this morning, then VFR with areas of high level moisture. Low level easterly winds increasing tonight...especially near gaps in terrain. KSEA...VFR conditions with building high clouds. Surface winds N/NE 7 to 12 knots knots...turning E/NE tonight with gusts of 20 knots possible...especially around daybreak Tuesday. 27
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&& .MARINE...Light southerly winds will begin to turn offshore through the day as a surface low rapidly intensifies well offshore and slides southward into Tuesday. Small Craft Advisories will go into effect this afternoon for the offshore waters then expand over the coastal waters this evening. Fraser Outflow winds will lead to strong gusts over the Northern Inland Waters into the Strait of Juan de Fuca tonight through Tuesday night. Winds look to remain below gale criteria with the stronger winds being closer to the surface low well offshore then to our south as the low dives southward. Winds will gradually ease into Tuesday night as the remaining SCAs expire for the Strait and Northern Inland Waters. Seas will increase in part with the offshore winds but look to remain below 10 feet through Tuesday. A weak surface trough will move across the area Thursday followed by a stronger frontal system into Friday, both of which look to bring another round of Small Craft Advisories to the area waters. Davis && .HYDROLOGY...No river flooding expected in the next 7 days. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...Wind Advisory from 11 PM this evening to 5 PM PDT Tuesday for East Puget Sound Lowlands. PZ...Small Craft Advisory from 8 PM this evening to 8 PM PDT Tuesday for Central U.S. Waters Strait Of Juan De Fuca-West Entrance U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory from 11 PM this evening to 5 AM PDT Wednesday for Northern Inland Waters Including The San Juan Islands. Small Craft Advisory from 8 PM this evening to 2 PM PDT Tuesday for 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 2 PM this afternoon to 2 PM PDT Tuesday 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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