Major Winter Storm to impact Western Washington 17 January 2012 National Weather Service Seattle/Tacoma
Current Warnings Winter Storm Warning for all of Western Washington, except: Northwest interior Extreme SW Washington Avalanche Warning for the mountains High going to Extreme tomorrow Main points regarding forecast: Widespread major impact Higher confidence always a few surprises
Overview Today (lull?) Cold westerly flow with gradually decreasing snow showers (locally mixed with rain near the water); locally heavy near PSCZ Falling temperatures to freezing or below Snow continuing in the mountains Much colder air will begin to impact northwest interior; increasing wind Whatcom County (15-25 mph) late afternoon Impacts 1-3 inches higher hills with heavier amounts near Puget Sound Convergence Zone some accumulation on roads Heavy to moderate mountain snow with increasing avalanche danger
Radar
Satellite Imagery
This evening Shower activity stops Surface winds become northerly Temperatures remaining below freezing most areas Increasing outflow western Whatcom and San Juan counties Impacts Icing of roads Bitterly cold wind chill western Whatcom County and San Juans with some blowing and drifting snow Freezing spray northern inland waters
Overview Wednesday Pacific storm moves into western Washington and briefly stalls before sliding east Snow increasing and spreading from South to North early morning hours Widespread and significant snow Possible transition to rain or freezing rain Olympia south Extreme outflow with gusts to 50 mph Whatcom and San Juan Counties Uncertainty associated with: How far north heavy snow will spread? When, where, and IF there will be a transition to rain or freezing rain?
Snow totals for Wednesday Mountains Cascades 1 to 4 feet inches Olympics 10 to 18 inches Light Snow & Wind 20-30 mph, Gusts to 50 mph Snow 2-5 Mtn. Snow 12-24 Lowlands Metro areas (Tacoma- Seattle-Everett) 5-10 inches Strait 5-10 inches Snow 2-5 ` Mtn. Snow 10-18 Heavy Snow 5-10 Coast 2 5 north 6 14 central North Interior 2 5 (Windy blowing and drifting) SW Interior 6 14 inches and freezing rain threat (1/4 inches) Heavy Snow 6-14 Some potential for ice accumulation midday Wednesday Mtn. Snow 24-48
Snow Timing for Wednesday
Storm Impacts Wednesday Transportation major Interstates will be hazardous Secondary roads treacherous to impassable Extreme wind chill temperatures (around 0 F) with blowing and drifting snow -- Whatcom and San Juan counties Aviation hazards likely resulting in flight delays and cancellations Mountains Extreme conditions; closures for avalanche control Marine areas Gale force winds most waters and freezing spray northern inland waters Power Power outages from downed lines Snow loading on structures
Wednesday evening Snow tapering off and ending except far south Temperatures from upper teens to mid 30s Outflow gradually weakening
THURSDAY Thursday and Friday Another system, but weaker, moves into southwest Washington with increasing snow (several inches) south sound; freezing rain threat Temperatures remaining in the 30s (except 20s northwest interior) FRIDAY Warming begins Increasing rain late and into Saturday Small stream and urban flooding risk Clean drains of snow and ice! Avalanche danger continues
Summary comments Every indication that this will be a major storm with widespread impacts Discretionary activities are discouraged There are remaining uncertainties Rain/freezing rain; snow amounts Stay tuned for latest adjustments Slides will be emailed shortly We will be holding another call tomorrow
Resources weather.gov/seattle/ NWS Seattle web site Area Forecast Discussions (Text and new Graphical) Doppler weather radar and satellite imagery loops Latest forecasts and warning statements nwac.us Northwest Weather and Avalanche Center wsdot.wa.gov Washington State Dept. of Transportation
Questions? Thank you for attending Will email this slide set shortly Online briefing Tomorrow