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. --646 FXUS66 KSEW 031717 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 1017 AM PDT Mon Jun 3 2024 .SYNOPSIS...First wave in this atmospheric river event moving into the Cascades early this morning. Upper level trough over the area this morning moving east by afternoon. Increasing low level onshore flow this morning with convergence zone near East Entrance to the Strait of Juan de Fuca. Second wave arriving later tonight with the wave moving through Tuesday. Upper level ridge building over Western Washington Wednesday through Friday. Ridge shifting east Saturday with a weak upper level trough Sunday. && .UPDATE...-- Changed Discussion --Convergence showers across Snohomish/Skagit counties are weakening (there were rainfall rates of up to an inch an hour this morning). A wind advisory was issued late tonight into Tuesday morning for all lowland areas. There are increasing probabilities that we will see wind gusts exceeding 40 mph in several areas. See the full discussion below for further details. HPR-- End Changed Discussion --&& .SHORT TERM /TODAY THROUGH WEDNESDAY/...Satellite imagery shows first wave of this atmospheric river event moving into the Cascades early this morning with rain ending behind the wave. Temperatures at 3 am/10z were mostly in the mid 50s. First wave in atmospheric river event will be east of the area later this morning. Fast moving upper level trough behind the wave moving through Western Washington this morning keeping showers in the forecast. There was a lightning strike offshore earlier this morning. Cloud top temperatures showing no signs of cooling on the satellite imagery and the trough will move through quickly so have left the mention of thunderstorms out of the forecast. Convergence zone developing near the East Entrance to the Strait later this morning with increasing low level onshore flow behind the trough. Breezy southerly winds will peak midday then slowly ease this afternoon. The convergence zone looks to stay in place for most of the day extending eastward into the Cascades. Not much change in temperatures with highs near 60. Rain out ahead of the second wave in this atmospheric river event arriving along the coast this evening with the rain spreading inland overnight. This wave is not as juicy as the first one with PWAT values peaking near 1.0 inches for a few hours. The first wave had PWAT values as high as 1.4 inches. Lows tonight in the 50s. Second wave moving through Western Washington late Tuesday making for another wet June day. Rainfall amounts with this feature forecasted to be from 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 inch in the Cascades. Snow levels will still be elevated, at least 6000 feet for most of the event so the precipitation will fall mainly as rain in the mountains. Showers behind the second wave drying up pretty fast Tuesday night as the weather pattern over the area begins to make a quick transition to drier and warmer. With less cloud cover by Wednesday morning lows will drop into the 40s. Upper level ridge building over Western Washington Wednesday clearing skies out and warming daytime temperatures. 500 mb heights in the 570 dms by late Wednesday afternoon. Highs getting back to near normal, mid 60s to lower 70s. .LONG TERM /THURSDAY THROUGH SUNDAY/...The idea of a blocking upper level pattern setting up over the Eastern Pacific this weekend only lasted a model run or two. Models in good agreement that the upper level ridge will continue to build Thursday and Friday with 500 mb heights in the lower to mid 580 dms Friday afternoon. Low level flow never really turns offshore and 850 mb winds do not turn easterly for any significant length of time. The lack of offshore flow will keep temperatures from getting too warm with highs Thursday in the mid 60s to mid 70s and Friday in the 70s to lower 80s. Models also in good agreement with the upper level ridge axis shifting into Eastern Washington Saturday and a weak upper level trough moving through Western Washington Sunday. With the trough will mention a slight chance of showers in the Cascades. For the lowlands highs cooling from the 70s and lower 80s Saturday to the mid 60s to mid 70s Sunday. Felton && .AVIATION...-- Changed Discussion --Mainly MVFR with post-frontal showers continuing to stream inland this morning. Conditions look to remain more widespread MVFR through much of the morning and afternoon, though could see some slight improvement towards VFR for interior terminals near 00Z. However, temporary reductions to IFR and even LIFR conditions cannot be ruled out in any heavier shower activity in the vicinity of any area terminals. Southerly surface winds look to remain breezy through much of the day, with gusts up to 30-35 kt possible into the evening before a stronger front brings gustier winds and more widespread rain, which will reach the coast between 00z-03z. KSEA...Primarily MVFR conditions will persist in steady rain through the morning hours, however could see temporary reductions to IFR in heavier showers though the day. A brief rebound to VFR will be possible by late afternoon, before ceilings look to lower back towards MVFR tonight as another front approaches. Southerly winds look to remain breezy, with gusts to 30 kt expected at times through the day. 14/15-- End Changed Discussion --&& .MARINE...-- Changed Discussion --A strong frontal system continues to push inland this morning, maintaining gusty winds to most area waters. The current small craft advisories for the Coastal Waters, Puget Sound, and the Eastern Strait of Juan de Fuca remain in good shape and continue to cover current conditions as the front progresses eastward. Multiple rounds of SCA strength westerlies look likely over the next 24-36 hours, with brief lulls in between, so can expect additional small craft issuance or extensions at times for the Strait through Tuesday. In addition to the breezy winds, seas across the coastal waters have remained rather steep this morning, and generally persist at 8 to 9 feet at 8 seconds. Seas will then build towards 10-13 feet over the coastal waters throughout the day. Another strong front will move across the region on Tuesday. Guidance continues to suggest that the winds with this system will be stronger, with more widespread gales possible, so have issued a Gale Watch for the Coastal Waters, the eastern Strait, and the Northern Inland Waters through Tuesday morning. Winds will gradually ease through the afternoon and evening hours. 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 then 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 12-15 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-- End Changed Discussion --&& .HYDROLOGY...-- Changed Discussion --Rainfall amounts with the first wave of this atmospheric river event were as follows, 1 to 2 inches along the coast, 1.5 to 3 inches in the Olympics, 0.50 inches to an inch in the north half of the interior with 0.75 inches to 1.5 inches in the southern half of the interior and 1.5 to 2.5 inches in the Cascades. Rivers are rising this morning with a few rivers like the Snoqualmie at Carnation and the Skokomish near Potlatch forecast to crest above 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. Felton/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-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 8 PM PDT this evening for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca. Gale Watch from late tonight through Tuesday morning for East Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters Including The San Juan Islands. Small Craft Advisory until 2 AM PDT Tuesday for Northern Inland Waters Including The San Juan Islands. Small Craft Advisory until 11 AM PDT Tuesday for Admiralty Inlet. Small Craft Advisory until 5 AM PDT Tuesday for Puget Sound and Hood Canal. 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. Gale Watch from this evening through late tonight 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 --&& $$