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Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
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Issued by NWS Seattle/Tacoma, WA
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-- Discussion containing changed information from previous version are highlighted. --000 FXUS66 KSEW 261612 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 912 AM PDT Sun Mar 26 2023 .UPDATE...-- Changed Discussion --No changes needed to the forecast this morning. A shortwave trough in the mid and upper levels will rotate across the area through this evening, providing sufficient lift for both the maintenance of current scattered shower activity and the development of new activity. The development of new activity will also be aided by daytime heating, especially in areas of sunbreaks and combined with continued cold mid level temps will support isolated thunderstorm development. Activity will decrease in coverage into the overnight period, with a deep trough of closed low pressure diving from Haida Gwaii westward well offshore the WA/OR Coasts. Previous discussion below with an updated marine and aviation section. Kovacik-- End Changed Discussion --&& .PREV DISCUSSION...-- Changed Discussion --/issued 340 AM PDT Sun Mar 26 2023/ .SYNOPSIS...Upper level troughing over the region will keep conditions cool and showery today, before conditions dry out on Monday. Overall drier and warmer conditions are expected the first half of the week, with temperatures expected to approach the low 60s by Wednesday. An active pattern returns late in the week as another weather system moves into the region and brings wetter conditions, cooler temperatures, and lowering snow levels.-- End Changed Discussion --&& .SHORT TERM /TODAY THROUGH TUESDAY/...-- Changed Discussion --Upper level troughing persists over western Washington this morning, with latest radar showing shower activity continuing along the coast and coastal waters. Current temperatures as of 2AM/09Z are in the 30s for the majority of the area. Expect morning lows to get down to near freezing in spots, especially south of the Sound along the Chehalis River Valley. Could still see some pockets of a rain/snow mix, or even a brief transition to snow, in heavier shower activity for areas south of Puget Sound through the early morning hours given near freezing temperatures and lowering snow levels overnight. The upper level trough will continue to influence the region today, but is expected to push south and east of the area this evening. Shower activity will continue through the day, increasing in coverage with a vort max situated just along the coast. Temperatures will remain cooler than normal and only look to top out in the mid to upper 40s for the majority of the area. A strong closed low will then drop southward into the region from Haida Gwaii late tonight into Monday morning and looks to continue to track southward, well offshore, throughout the day. Flow will transition to offshore and confidence remains high that the bulk of the moisture associated with this system will remain to the west and south of western Washington, making for a primarily dry day across the region. The only exception would be the Cascades, where upslope flow may spark some shower activity east of the crest that may drift westward. Overall, expect conditions to dry out and for temperatures to rebound into the mid 50s. The closed low will then sink further towards the northern CA coast Monday night into Tuesday. Some wrap-around moisture may brush the southern portion of the forecast area heading into Tuesday, so have kept a mention for a slight chance of POPs for Lewis, Grays Harbor, Thurston, and Pierce counties. That said, however, expect the majority of areas to remain dry and for temperatures to continue to climb a few degrees from Monday`s highs - likely topping out in the upper 50s to near 60. 14 .LONG TERM /WEDNESDAY THROUGH SATURDAY/...Weak upper level ridging looks to nudge into the region on Wednesday as the aforementioned upper low continues to track southward along the CA coast. Wednesday looks to be the nicest day of the week- with ample sunshine and afternoon highs expected to climb into the low to mid 60s for the majority of the area. A shortwave trough then looks to drop down into the region on Thursday, however moisture continues to look limited. Nonetheless, this feature may spark a few showers across the region, with the most favorable spots being along the coast and across any higher terrain. A switch back to wetter and cooler conditions looks likely late in the week as a more organized frontal system approaches the region Friday morning and brings with it more widespread rain, mountain snow, and the return of cooler temperatures. Mountain snow may be heavy at times with snow levels likely dropping below the passes. 14-- End Changed Discussion --&& .AVIATION...-- Changed Discussion --Light flow aloft will increase southerly tonight as an upper low slides south well offshore. Generally a mix of VFR/MVFR this morning with spotty areas of IFR (KPAE and KOLM). Scattered showers and an isolated rumble of thunder will be around today, mainly south of KSEA and along the Olympic Peninsula. Lower cigs will improve to VFR this afternoon. VFR cigs with mid clouds into tonight, will have to further monitor for any potential fog development Monday morning with clear in some areas. Mainly light southerly winds. KSEA...MVFR cigs this morning will improve to VFR late morning into early afternoon (generally between 18z to 20z). Mainly dry this morning with a slight chance of a shower possible this afternoon and evening. A thunderstorm cannot be ruled out as well (after 20z) but the potential is very limited. Light southerly winds today shifting more easterly late tonight. JD-- End Changed Discussion --&& .MARINE...-- Changed Discussion --Generally light southerly winds through tonight. A surface low will slide southward across the Offshore Waters on Monday and move towards the California coast later on Tuesday. Offshore flow will increase during this period, beginning Monday afternoon and continuing into Tuesday evening before tapering off. Small Craft Advisory level winds are likely for most waters during this period with the strongest winds likely across the outer Coastal Waters and through the Strait of Juan de Fuca. Winds will shift more northerly on Wednesday. Seas of 5 to 8 feet today will subside to 3 to 5 feet tonight into Monday. Southerly swell will then build 6 to 8 feet Tuesday into Tuesday night. JD-- End Changed Discussion --&& .HYDROLOGY...No river flooding expected in the next 7 days. && .SEW WATCHES/WARNINGS/ADVISORIES...-- Changed Discussion --WA...None. PZ...None.-- End Changed Discussion --&& $$
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