Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
-- Highlight Changed Discussion --
Issued by NWS Seattle/Tacoma, WA
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --531 FXUS66 KSEW 032241 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 341 PM PDT Mon Jun 3 2024 .SYNOPSIS...-- Changed Discussion --A second atmospheric river event will arrive in western Washington late Monday into Tuesday as a frontal system moves through. Moderate to heavy rainfall remains possible between the lowlands and mountains, and a few thunderstorms are also possible with heavier bands of precipitation. Gusty winds are also expected as the system moves through overnight. High pressure will build in the second half of the week, with temperatures increasing to above average levels.-- End Changed Discussion --&& .SHORT TERM /TONIGHT THROUGH THURSDAY/...-- Changed Discussion --Western Washington remains situated under a strong 300 mb jet core with the max still off the coast. This continues to funnel in plenty of moisture in the region from the remnants of tropical activity in the East Pacific. The shortwave trough from yesterday at the mid levels sits over Idaho/Montana, with the next broad trough/mid level low sitting well off the B.C. shoreline. Cool air remains aloft with temperatures at -18 to -24 degrees celsius. A weak mid-level ridge also sits in between troughs over western Washington this afternoon. This has helped to break out some of the cloud cover seen over the weekend. Behind the first front, popcorn showers have continued in north Puget Sound, and have also now been developing in the Kitsap Peninsula this afternoon. There have been a couple of lightning strikes early in the day, although instability remains limited (50-100 J/kg). Still, there is an isolated thunder chance this afternoon, but the threat remains low. As the next frontal system approaches, southwest flow aloft is expected to tap in additional low/mid level moisture (via the initial warm front). The showers this afternoon are expected to converge into stratiform rain late tonight through Tuesday. The frontal system will occlude as it moves inland. The heaviest of the rain is expected to remain in the mountains, with an additional 1-2 inches of rain likely in the Olympics and Cascades. There remains half an inch to an inch of rain expected along the coast, and for remaining lowland areas (Puget Sound), amounts have decreased overall to around a quarter of an inch to half an inch. Higher amounts are possible (especially if convective banding occurs with the rainfall). See the hydrology section for concerns on the rivers. With the weak ridging that developed in between troughs, gusty winds have been an issue for many across the region. Winds this morning caused several power outages, as well as downing branches and blowing leaves. The wind advisory that went out earlier today will continue through Tuesday morning 11 am PDT. Gusty winds have continued through the afternoon (with occasional gusts closer to 40 mph observed at a few of the observation sites). More widespread winds of 15 to 25 mph (with gusts over 35 to 40 mph) are expected late tonight into Tuesday morning. This is expected to be the windiest time as the system progresses inland. The windiest area is expected to be around Bellingham and western Whatcom County, where there is a 40% chance that wind gusts may exceed 50 mph. Once the system moves out late Tuesday night, the jet stream pattern will shift north, becoming zonal and will eventually build into a ridge over the northern U.S. states and Canada. Skies will clear out significantly on Wednesday and Thursday, with flow weakening significantly aloft (and down at the surface). Temperatures will start to increase from the 50s and 60s Monday through Wednesday, into the low 70s by Thursday. .LONG TERM /FRIDAY THROUGH MONDAY/...Ensemble/deterministic models have a ridge continuing to build over the Pacific coast going into the weekend. This will result in above average temperatures with weak offshore flow. The warmest days are expected to be Friday and Saturday, where high temperatures could pop out in the upper 70s to low 80s. At this time, the heat risk remains minor for all areas expect for the immediate Seattle metro (which has a moderate heat risk on Saturday). The ridge will move out of the region Sunday into Monday, and a weak shortwave trough will bring the next chance of showers into the mountains Sunday and Monday. HPR-- End Changed Discussion --&& .AVIATION...-- Changed Discussion --Mainly VFR to MVFR with post-frontal showers and breezy southwest winds 10-20 kt with gusts to 35 kt. IFR conditions possible in heavier shower activity in the vicinity of area terminals, and a lightning strike or two cannot be ruled out this afternoon. A strong cold front will cross the region later this evening, bringing in more widespread rain and stronger winds after 03z with gusts to 40-45 kt. Ceilings will lower to MVFR/IFR in heavier showers and low stratus before improving in the afternoon as precipitation slowly tapers off. KSEA...Low-end VFR conditions will continue through the afternoon with scattered shower activity. South to south winds will taper off through roughly 05z, then increase by 09z/10z as the front crosses. A round of heavier rain will come through with the front, lowering ceilings for a few hours below 2k feet. Winds will pick up to 20 kt sustained and 30-35 kt gusts through the morning with continued showers before easing throughout the afternoon. 15-- End Changed Discussion --&& .MARINE...-- Changed Discussion --Winds remain elevated this afternoon behind a strong frontal passage, with seas building towards 10-13 feet over the coastal waters. Another strong front will move across the region later tonight and into Tuesday morning, bringing in even stronger winds. SCAs will be upgraded to Gale Warnings overnight as winds continue to increase, especially offshore and through the Strait of Georgia and into the east entrance of the Strait of Juan de Fuca and Admiralty Inlet. SCAs will continue across the Puget Sound and through the western and central Strait of Juan de Fuca. Seas over the coastal waters will remain above 10 ft and will remain rather steep through Tuesday, so it is likely Small Craft Advisories for the coastal waters will continue despite winds easing. High pressure will build across the coastal waters on Wednesday and persist into late week for an overall less active weather pattern. Seas, however, look to build towards 12-14 ft over the coastal waters on Wednesday, so it is likely headlines will continue. Seas then look to subside below 10 ft again late in the week, but breezy northerlies developing over the coastal waters may maintain steeper seas through the second half of the week. 14/15-- End Changed Discussion --&& .HYDROLOGY...-- Changed Discussion --Rivers are rising although at a slower pace this afternoon with a few rivers like the Snoqualmie at Carnation and the Skokomish near Potlatch forecast to crest near action stage. Forecasted rainfall amounts with the second wave of this atmospheric river event later tonight through Tuesday are for an additional 0.50 to 1 inch along the coast, 1.0 to 1.5 inches in the Olympics, 0.25 to 0.50 inches for the interior and 0.50 to 1 inches in the Cascades. Rivers will continue to rise through Tuesday but this break in the action today along with the lower future rainfall forecast will help lower forecast crest values Tuesday into Wednesday. The Flood Watch will remain in place to account for additional swells on the rivers, as well as overland and small stream flooding on account of some drains being clogged with tree debris due to overnight wind speeds. Kristell-- End Changed Discussion --&& .SEW WATCHES/WARNINGS/ADVISORIES...-- Changed Discussion --WA...Wind Advisory until 11 AM PDT Tuesday for Admiralty Inlet Area- Bellevue and Vicinity-Bremerton and Vicinity-Central Coast- East Puget Sound Lowlands-Eastern Strait of Juan de Fuca- Everett and Vicinity-Hood Canal Area-Lower Chehalis Valley Area-North Coast-San Juan County-Seattle and Vicinity- Southwest Interior-Tacoma Area-Western Skagit County- Western Strait of Juan De Fuca-Western Whatcom County. Flood Watch through Wednesday morning for Bellevue and Vicinity- East Puget Sound Lowlands-Everett and Vicinity-Hood Canal Area-Lower Chehalis Valley Area-Olympics-Seattle and Vicinity-Southwest Interior-Tacoma Area-West Slopes North Cascades and Passes-West Slopes North Central Cascades and Passes-West Slopes South Central Cascades and Passes- Western Skagit County. PZ...Small Craft Advisory until 5 PM PDT this afternoon for Grays Harbor Bar. Small Craft Advisory until 5 PM PDT Tuesday for Central U.S. Waters Strait Of Juan De Fuca-Puget Sound and Hood Canal- West Entrance U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory until 8 PM PDT this evening for Admiralty Inlet-East Entrance U.S. Waters Strait Of Juan De Fuca- Northern Inland Waters Including The San Juan Islands. Gale Warning from 8 PM this evening to 5 PM PDT Tuesday for Admiralty Inlet-East Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters Including The San Juan Islands. 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 Cape Flattery To James Island Out 10 Nm- Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm. Small Craft Advisory from 8 AM to 5 PM PDT Tuesday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm- Coastal Waters From Cape Flattery To James Island Out 10 Nm- Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm. Gale Warning from 11 PM this evening to 8 AM PDT Tuesday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm.-- End Changed Discussion --&& $$