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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 272211 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 311 PM PDT Mon Mar 27 2023 .SYNOPSIS...-- Changed Discussion --Warmer and drier weather will persist through mid week as a strong storm system tracks to the south. A trend back towards cooler and wetter weather will then return the latter half of the week and through the weekend as an upper level trough brings the next chance for widespread rain and a cold front ushers in cooler air.-- End Changed Discussion --&& .SHORT TERM /TONIGHT THROUGH THURSDAY/...-- Changed Discussion --The large scale pattern this afternoon features a strong area of closed low pressure centered near 135W and 45N well offshore the WA/OR Coast. Downstream from this feature exists a weak ridge of high pressure over the Intermountain West with another broad closed low near Hudson Bay. Meanwhile, upstream, a ridge of high pressure extends from the NE Pacific into the Gulf of Alaska with troughing over the Bering Sea. Near the surface, low pressure corresponds well to the strong Pacific low initially mentioned, with a stronger cyclone located to its south with which it is beginning to merge with (and will soon significantly intensify). Downstream from this significant feature exists high pressure over much of the west, with a few weak boundaries over the Plains/Midwest/Southeast. It`s a quiet weather day across W WA today as weak high pressure influences the low levels and the upper closed low over the Pacific remains displaced well to the west. Abundant sunshine along with the gradual development of offshore flow has allowed temperatures to rebound into the 50s. For the rest of today, mid and high level cloud cover will increase, with increasing offshore flow/downslope winds off the Cascades as the pressure gradient tightens between low pressure offshore and higher pressure inland. Conditions will become windy late this evening and overnight tonight in the Cascade gaps and East Puget Sound lowlands (where a wind advisory will remain in place). Isolated power outages and downed trees will be possible in these areas. Elsewhere, winds will become breezier. The strong upper level low and associated strong surface cyclone will begin to drift towards the N CA Coast on Tuesday, with easterly/downslope flow peaking across the area into the morning hours. High clouds will begin to break up over the area, yielding a period of sunny skies, mostly from southern Puget Sound northward. Moisture and cloud cover will advect northward from the low through the day, resulting in increasing cloud cover and even some areas of light rain scraping Grays Harbor, Lewis, Thurston and potentially Pierce Counties. High temperatures generally around 60 in the lowlands but may top off a few degrees cooler in the counties just mentioned where rain and more persistent cloud cover are expected. The upper level low and its sfc reflection will begin to weaken and sink further south into Wednesday, with wrap around moisture still expected to linger across Lewis and Pierce Counties, particularly the southern Cascades. A ridge of upper level high pressure will begin to build briefly into the area from north to south on Wednesday, with enough subsidence from it along with high pressure at the sfc to yield an overall sunny and warm day, with highs reaching the low 60s. Cloud cover is likely to start to increase the second half of the day as a weak trough approaches from the north. This weak trough will slide across the area on Thursday, but with a largely continental trajectory, expect minimal moisture with it. There still could be sufficient lift with it to help generate a few showers along the coast and higher terrain. Cooler weather will follow with it with high temperatures a good 5 degrees cooler in the mid 50s. This will then give way to much more active and cooler weather in the long term period. Kovacik .LONG TERM /FRIDAY THROUGH MONDAY/...On Friday, an area of low pressure will deepen over the Gulf of Alaska, with a shortwave ejecting out of its southern periphery towards the Pacific Northwest. This system will carry a surface frontal boundary with it, bringing the next chance for organized widespread lowland rain and heavy mountain snow to the area. Rain looks to arrive around the Coast Friday afternoon and evening and quickly spread inland through the overnight period into early Saturday. The system will give way to scattered showers across the area through the day Saturday and with cooler mid level temperatures, could support convection. Showery and cooler weather looks to continue through the rest of the weekend and into early next week as upper troughing remains in place. High temps for the lowlands trend back to the upper 40s/near 50 for highs while lows dip into the low-mid 30s. Snow levels hover around 1000ft so not expecting a rain/snow mix potential for the lowlands at this time, but widespread mountain snow showers could be heavy at times. Kovacik-- End Changed Discussion --&& .AVIATION...-- Changed Discussion --A broad upper trough continues to shift southward over the offshore waters with south to southeast flow aloft becoming easterly on Tuesday. The air mass is dry and generally stable. High and mid level clouds will increase later tonight across the southern part of the area. Mainly VFR conditions expected into Tuesday with a few showers possible KHQM-KOLM southward after 12Z Tuesday. Low level offshore flow increases tonight and Tuesday with gusty E/NE surface winds expected...especially near gaps in terrain. KSEA...VFR conditions continuing with high and mid level clouds increasing overnight. Surface winds northerly 7 to 12 knots shifting E/NE overnight with gusts of 20 to 25 knots possible by daybreak Tuesday. 27-- End Changed Discussion --&& .MARINE...-- Changed Discussion --A rapidly deepening surface low around 300 nautical miles west of North Bend Oregon this afternoon will continue to deepen this evening over the Oregon offshore waters while a surface ridge strengthens over interior British Columbia. The combination of these will lead to strengthening low level offshore flow into Tuesday with small craft advisory winds for the coastal waters and portions of the inland waters. Winds could approach gale force near and adjacent to the west entrance to the strait early Tuesday. Winds will gradually ease Tuesday night into Wednesday as the offshore low weakens and shifts into the Northern California offshore waters. Quieter conditions are expected to prevail Wednesday and Thursday before another frontal system arrives from the Gulf of Alaska on Friday. Coastal seas expected to remain below 10 feet for the most part. However, the strengthening system to our south will generate an increasing S/SW oriented swell on Tuesday. 27-- End Changed Discussion --&& .HYDROLOGY...-- Changed Discussion --No river flooding expected the next 7 days.-- End Changed Discussion --&& .SEW WATCHES/WARNINGS/ADVISORIES...-- Changed Discussion --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 until 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.-- End Changed Discussion --&& $$
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