Update, Sunday, Dec. 16, 5 p.m.: With gusty winds forecast for Puget Sound and heavy snow forecast for the passes, Washington State Department of Transportation maintenance and bridge crews are preparing for heavy snow in the mountain passes and the possibility that high winds on the State route 520 bridge could force temporary closures of the structure.
WSDOT crews spent much of the day fighting snow in the passes and tracking the next storm system as it moves into the state. As of 5 p.m. Sunday, chains were required on Snoqualmie Pass for all vehicles except those with all wheel drive.
Meanwhile the National Weather Service revised its high wind watch to a wind advisory, in effect from 10 p.m. tonight until 4 p.m. Monday, Dec. 17 for most of the Puget Sound, saying winds will rapidly rise late tonight from the southwest at 20 to 35 mph with gusts to 55 mph.
WSDOT said that the forecast calls for up to three feet of snow on Snoqualmie and Stevens passes and very high winds on the Washington Coast, across Whidbey Island, Skagit County as well as gusty winds in Puget Sound.
“While every state highway is important, in Puget Sound this particular wind storm has us paying special attention to the State Route 520 floating bridge because of its vulnerability,” said Dave McCormick, assistant regional administrator for maintenance and operations.
State Route 520 bridge
Bridge crews are dispatched to SR 520 when sustained winds reach 40 miles per hour for one minute which will likely happen in this storm.
“We don’t typically close the bridge to drivers unless sustained winds reach 50 miles per hour for 15 minutes or more which the forecast doesn’t show at this time,” said Archie Allen, WSDOT bridge superintendent. As a precaution, WSDOT will not allow any drawspan openings for boats between 9 p.m. Sunday, Dec. 16 and 10 a.m. Monday, Dec. 17.
The Washington State Patrol or WSDOT maintenance crews may close the bridge if waves are too high or water on the bridge presents a driving hazard. Contractor crews working on the floating bridge have secured all construction materials.
Fall storm reminder
This is the first big fall storm of the season. Drivers could see downed trees or power lines, signal outages and standing water. Drivers are reminded to stay away from downed power lines, treat dark intersections as four-way stops and never drive through standing water. Temperatures may drop in the coming days. Drivers should watch for ice or frost on the roads. Other tips can be found on the WSDOT winter weather page.
Before heading out, check the WSDOT web site for traffic alerts and closures. On the road, passengers can call 511 for information or check the WSDOT twitter feed for the greater Seattle/Bellevue area or the Tacoma area.
Puget Sound Energy reminds residents to be prepared for storm conditions in case of power outages.
--Information from the National Weather Service and WSDOT
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Original story:
Twitter is abuzz with reports of snow Saturday morning, from the Renton Highlands to Maple Valley and Hobart, among other places.
Much of this will turn to rain later this morning, according to the National Weather Service, but it says a Pacific stormfront is on the way that likely will bring heavy rain and mountain snow, and gusting winds Sunday and Monday. the NWS issued the following Special Weather Statement:
High winds...heavy mountain snow...and coastal flooding are possible in western Washington Sunday night and Monday... A strong Pacific storm will impact the region late Sunday through. This system has the potential to produce damaging winds on the coast Sunday night and North interior early Monday. Elsewhere... It will also become windy with gusts to 50 mph possible. Large swells of 20 feet or higher are predicted for Monday...and this could lead to coastal flooding...especially if the large ocean waves occur during the time of astronomical high tide. The mountains could receive another 1 to 3 feet of snow by late in the day Monday from this upcoming system...on top of the 10 to 16 inches being predicted by midday Sunday. Monitor the latest forecasts from the National Weather Service or your local media on this upcoming storm.
The strongest winds (easterly to south easterly) in Enumclaw mostly occur with a deep low pressure approaching Washington State and a strong high pressure in Eastern Washington. In contrast the highest winds in the Puget Sound region (southerly) occur when a deep low pressure moves just north of Puget Sound. In the first case the storng pressure difference across the mountains forces air to flow westward through the valleys. In the second case air is channeled northward up the sound by the mountains on either side. The strong east winds hardly ever reach Puget Sound and the strong southerly winds hardly ever are as strong in Enumclaw. In the coming storm both winds should happen, but maybe not super high wind speeds either location.
http://cliffmass.blogspot.com/2012/12/big-storm-but-worst-south-of-seattle.html