000 FXUS66 KSEW 071653 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 852 AM PST Tue Feb 7 2023 .SYNOPSIS...A strong front will cross the region today, bringing lowland rain, mountain snow, and gusty winds across Western Washington. Expect showers to continue early Wednesday with an upper trough crossing the region, but becoming increasingly limited to the mountains through the day. A brief lull lasts into Thursday with high pressure briefly overhead, but another weak front brings renewed moisture Friday. Somewhat drier conditions return over the weekend, but still plenty of showers around. && .SHORT TERM /TODAY THROUGH THURSDAY/...Today`s front is moving into the coastal waters as of this writing. The forecast remains on track. The main thing to monitor will be snowfall totals in the mountain passes with a post-frontal convergence zone expected later this afternoon and tonight. Previous discussion follows with updates to marine and aviation portions. 27 Widespread rain and high elevation snow evident on NWS radar early this morning ahead of the advancing frontal system. Snow levels have risen in response to the warm southerly flow in advance of the front, with the NOAA PSL profiler at Forks indicating a jump from 4000 to near 5500 ft over the last several hours. That said, cooler air will return behind the front as it pushes across the interior portions of the area by late morning or early afternoon today. Meanwhile, gusty southerly winds continue across northern Whidbey Island and north through San Juan and Whatcom counties. Additionally, the strong dynamics and deep moisture content associated with this front are quite evident as it begins to push onshore. Quillayute airport picked up more than a half inch of rain in about 90 minutes already today. These rainfall rates may lead to some minor ponding of water as it pushes inland into the urban areas and some rises on area rivers and streams can be expected. See the hydrology section for more details on this, as well as potential for flooding on the Skokomish River. Behind the front, modest instability may even be sufficient to bring a few flashes of lightning in heavier showers, especially along the coast and inner coastal waters. Strong onshore flow behind the front will likely induce a Puget Sound Convergence Zone by Tuesday evening. This could also bring a few lightning strikes, but more significantly could bring fairly heavy snow. Current winter weather headlines remain unchanged with a Winter Storm Warning on track for the North Cascades/Mt. Baker area and advisory amounts most likely at both Stevens and Snoqualmie passes. Not much change to the forecast with this cycle, but still have the potential for higher end amounts if the convergence zone holds together and sits over either of the passes for an extended period of time. Weak high pressure aloft begins to build over the region late Wednesday through early Thursday, which will bring a brief break in the precipitation for much of the region. However, by late Thursday, some leading rain likely reaches the Olympic Peninsula as a weak front approaches. Temperatures generally hold near seasonal normals for the next few days. Cullen .LONG TERM /FRIDAY THROUGH MONDAY/...Global ensemble guidance continues to favor the development of an upper ridge far enough east (over the Great Basin or east toward the Rockies) that will enable the next frontal system, mentioned above, to spread another round of precipitation across the region on Friday. As heights begin to further rise into the weekend as the upper low tracks south through California and toward the Four Corners region, there`s still some mention of rain/mountain snow chances in the forecast through the weekend. Confidence in the details remains a bit lower as next week begins, with again some potential for insufficient amplification of the ridge to shield the Pacific Northwest from the impact of the next disturbance by Monday. Cullen && .AVIATION...An upper trough and an associated cold front will move through the area today and then shift inland tonight. The flow aloft will be westerly. Southerly flow near the surface ahead of the front this morning will shift to westerly behind the front this afternoon. The air mass will be moist and stable this morning. It will become unstable this afternoon and evening as the upper trough moves through with decreasing low level moisture. A Puget Sound Convergence Zone will likely develop this afternoon and evening over Snohomish County. The convergence zone should shift into the Cascades and fall apart after midnight tonight. KSEA...Low clouds this morning should lift and scatter this afternoon and evening behind a cold front. Gusty southerly winds today will ease later tonight. A Puget Sound Convergence Zone is expected to remain to the north of the terminal this afternoon and evening. 16 && .MARINE...A cold front will push through the area this morning. There will be marginal gale force southerly winds ahead of the front over the north interior waters and small craft advisory strength winds most other waters. Onshore flow behind the front should bring gale force west winds to the Strait this afternoon and evening with small craft advisory westerly winds most other waters. Onshore flow will ease on Wednesday. A second frontal system will move through the area Thursday and Thursday night for another round of small craft advisory strength winds. Onshore flow behind this system Friday and Friday night will ease on Saturday. Combined seas 10 to 13 feet over the Coastal Waters will briefly subside below 10 feet later Wednesday and Wednesday night but then rebuild to 12 to 15 feet on Thursday and remain in that general range Friday and Saturday. 16 && .HYDROLOGY...Expect rises on area rivers today into Wednesday as a round of heavy precipitation moves through the region. Snow levels initially climb to around 4,000 feet, before lowering to 2,500 ft behind the front tonight. The flood watch for Mason County remains in effect, with the Skokomish River expected to rise above flood stage later this morning. Elsewhere, river flooding is not expected through the next week. While the lower snow levels may limit potential impacts for the Bolt Creek Burn Scar area, will need to closely monitor the rainfall rates with this front and especially any convergence zone development later this evening and tonight. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...Wind Advisory until 10 AM PST this morning for Admiralty Inlet Area-San Juan County-Western Skagit County-Western Whatcom County. Flood Watch from 7 AM PST this morning through Wednesday morning for Mason County. Winter Storm Warning until 10 AM PST Wednesday for West Slopes North Cascades and Passes. Winter Weather Advisory until 10 AM PST Wednesday for West Slopes North Central Cascades and Passes-West Slopes South Central Cascades and Passes. PZ...Small Craft Advisory until 6 PM PST Wednesday 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-Grays Harbor Bar-West Entrance U.S. Waters Strait Of Juan De Fuca. Gale Warning from noon today to 1 AM PST Wednesday for Central U.S. Waters Strait Of Juan De Fuca. Gale Warning until 1 AM PST Wednesday for East Entrance U.S. Waters Strait Of Juan De Fuca. Gale Warning until 10 AM PST this morning for Admiralty Inlet- Northern Inland Waters Including The San Juan Islands. Small Craft Advisory from 10 AM this morning to 1 PM PST Wednesday for Northern Inland Waters Including The San Juan Islands. Small Craft Advisory until 4 AM PST Wednesday for Puget Sound and Hood Canal. && $$
NWS SEW Office Area Forecast Discussion
Discussion Script by Ken True at Saratoga Weather - WFO Script by SE Lincoln Weather