MOUNTAIN WEATHER FORECAST FOR THE OLYMPICS WASHINGTON CASCADES AND MT HOOD AREA NORTHWEST WEATHER AND AVALANCHE CENTER SEATTLE WASHINGTON 130 PM PST MON FEB 16 2009 NWAC Program administered by: USDA-Forest Service with cooperative funding and support from: Washington State Department of Transportation National Weather Service National Park Service Washington State Parks and Recreation Commission Pacific Northwest Ski Area Association Friends of the Avalanche Center and other private organizations. This forecast is prepared primarily for federal, state and private snow safety programs in Washington and Northern Oregon. WAZ513-518-519-019-042-501-502-ORZ011-171700- && WEATHER SYNOPSIS FOR MONDAY AND TUESDAY A few days ago the pattern had weak low pressure systems moving southeast over the Northwest coastal waters. Now the pattern has become more split and the lows are larger, slower moving, further offshore and tending to move to California. The current large slow moving low pressure system began to move across California on Sunday with a couple of weak circulation centers within the low. A band of moisture moved north out of the low on Sunday and caused light amounts of snow at Mt Hood and in the Olympics and Washington Cascades on both sides of the crest. The remnant of this band is dissipating over the north Cascades on Monday morning. The low should continue to move slowly across California on Monday and Tuesday. A very weak trough over the International border Monday should drift west and mostly dissipate Tuesday. This should cause very weak flow aloft and little change in the air mass over the Northwest. Satellite images Monday afternoon indicate a lot of clouds east of the crest and less to the west. A weaker band of moisture is indicated to move north out of the low and affect the Mt Hood area Monday afternoon and Tuesday with little effect further north. All in all this should cause generally uneventful but cool weather in the Olympics and Cascades Monday and Tuesday. Weak offshore surface pressure gradients may areas of low clouds to linger east of the Cascade crest. && WEATHER FORECAST FOR MONDAY AND TUESDAY * OLYMPICS- Monday afternoon through Tuesday morning: Partly or mostly cloudy with slight chance of light snow showers. Tuesday afternoon and night: Partly cloudy. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST- * STEVENS, SNOQUALMIE AND WHITE PASSES- Monday afternoon through Tuesday morning: Partly or mostly cloudy with slight chance of light snow showers. Tuesday afternoon and night: Partly cloudy. * EAST SLOPES WASHINGTON CASCADES- Monday afternoon through Tuesday morning: Cloudy with chance of light snow showers. Tuesday afternoon and night: Partly or mostly cloudy. * MT HOOD AREA- Monday afternoon through Tuesday morning: Cloudy with chance of light snow showers. Tuesday afternoon and night: Partly or mostly cloudy. && SNOW LEVELS-CASCADE MTNS 2000 ft N, 3000 ft S Mon morn through Tue night except near the surface night and morning hours especially passes and east slopes and slightly higher afternoon hours. SNOW LEVELS-OLYMPIC MTNS 2500 ft Mon morn through Tue night Near sea level Tue morn except near the surface night and morning hours and slightly higher afternoon hours. Cascade Snow/Freezing Levels refer to the northern Washington Cascades (N) through Mt Hood area (S). Central Washington Cascade snow levels (typically near Snoqualmie Pass) are normally midway between indicated N and S levels. Note that surface snow/freezing levels are common near the passes during easterly pass flow and may result in multiple snow/freezing levels. && 24 HOUR FORECAST OF PRECIPITATION IN INCHES OF WATER EQUIVALENT ENDING AT 4AM MON TUE * HURRICANE RIDGE LT .10 LT .10 * MT BAKER LT .10 LT .10 * WASHINGTON PASS LT .10 LT .10 * STEVENS PASS LT .10 LT .10 * SNOQUALMIE PASS LT .10 LT .10 * MISSION RIDGE LT .10 LT .10 * CRYSTAL MTN LT .10 LT .10 * PARADISE LT .10 LT .10 * WHITE PASS LT .10 LT .10 * MT HOOD LT .25 LT .25 && WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS E 5-15 Mon aft E 5-10 Mon eve E 0-10 Tue morn Light variable Tue aft and eve * FREE WINDS AT 5000 FT SE 5-10 Mon aft to Mon eve Light variable Tue morn SW 5-15 Tue aft and eve * FREE WINDS AT 9000 FT S-SW 10-15 Mon aft to Mon eve SW 0-10 Tue morn SW 1-0-20 Tue aft and eve && EXTENDED WEATHER SYNOPSIS FOR WEDNESDAY THROUGH FRIDAY The next large slow moving cut off low pressure system is indicated by the US GFS model to linger further west of California near 140 degrees west the latter half of the week. This is indicated to help an upper ridge and weak surface high pressure to build over the Northwest and west US. This should cause light crest level winds and decreasing cloud cover over the Olympics and Cascades. EXTENDED FORECAST FOR WEDNESDAY THROUGH FRIDAY Wednesday and Wednesday night: Partly cloudy. Thursday through Friday: Partly sunny days and partly clear nights. * FREEZING LEVELS 1-3000 ft N, 2-4000 ft S Wed 2-4000 ft N, 4-6000 ft S The 3-5000 ft N, 5-7000 ft S Fri except lingering near the surface in the Cascade passes and along the lower east slopes night and morning hours. NWAC weather data and forecasts are also available by calling 206-526-6677 for Washington, 503-808-2400 for the Mt Hood area, or by visiting our Web site at www.nwac.us. Ferber/Northwest Weather and Avalanche Center $$