####018009251#### WWUS86 KSEW 171440 SABNW MOUNTAIN WEATHER FORECAST FOR THE OLYMPICS WASHINGTON CASCADES AND MT HOOD AREA NORTHWEST WEATHER AND AVALANCHE CENTER SEATTLE WASHINGTON 630 AM PST SAT JAN 17 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-ORZ011-181700- && WEATHER SYNOPSIS FOR SATURDAY AND SUNDAY The upper ridge is big, bigger than most Stretching from LA to the Canadian coast. It brought change from rain, a welcome diversion Along with much warmth above a strong inversion. Proceeding down to the pass, you hit the temp wall An almost solid feeling, as if you might fall. Warm and melt above, moist and cold below Make challenging conditions in near surface snow. Crusts of fear in places, breakable nearby Turns may be tough, making equipment fly. Hoar frost at night mostly dies during the day Except shaded north faces where it lingers to play. At least some slopes have corn, that feels quite nice Just avoid steeper terrain that transition to ice. Only minor changes ahead from this most stable flow With snow stability varying from moderate to low. An unseasonably strong upper level ridge...more common during mid-summer than mid-winter...with a center just off the northern Oregon coast should slowly move northward along the Washington coast Saturday and move slowly eastward across southern BC on Sunday. Associated weak northerly flow Saturday morning should slowly transition toward slightly increasing east and southeasterly flow by Sunday as this upper ridge migration occurs. However, little else is expected to change this weekend with very warm and generally clear conditions expected in most mid and upper elevation locations above a continuing cool and relatively moist layer at lower elevations near and east of the Cascade crest. This strong temperature and moisture inversion, with some mountain top locations over 20 degrees warmer than base sensors along with humidity differences well over 50%, should persist or slightly intensify through Sunday as gradually increasing east to southeasterly winds lift the widespread layer of cold and cloudy low level air that covers much of the Columbia River Basin. && WEATHER FORECAST FOR SATURDAY AND SUNDAY *OLYMPICS- Saturday and Sunday: cool with areas of low clouds and fog persisting below about 1000-1500 feet Sunday, otherwise mostly fair and unseasonably warm mid and upper elevations *WASHINGTON CASCADES NEAR AND WEST OF THE CREST- Saturday and Sunday: cool with areas of low clouds and fog below about 1000-1500 feet through Sunday, otherwise mostly fair and unseasonably warm mid and upper elevations *CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Saturday and Sunday: cool with areas of low clouds or fog below about 3500 to 4000 feet east approaches and over the passes through Sunday; otherwise mostly fair and unseasonably warm mid and upper elevations *EAST SLOPES WASHINGTON CASCADES- Saturday and Sunday: cool and cloudy below about 3500 to 4000 feet; otherwise mostly fair and unseasonably warm mid and upper elevations *MT HOOD AREA- Saturday and Sunday: cool and cloudy below about 3 to 4000 feet east slopes and some areas of fog or low clouds lower terrain west slopes; otherwise mostly fair and unseasonably warm mid and upper elevations && FREEZING LEVELS-CASCADE MTNS 12,500 ft N and S Saturday morning 13,000 ft N and S Saturday afternoon 13,500 ft N, 13,000 ft S Saturday night and Sunday morning 13,000 ft N and S Sunday afternoon and evening 12,500 ft N and S late Sunday night or early Monday FREEZING LEVELS-OLYMPIC MTNS 13,500 ft Saturday and Sunday 13,000 ft Sunday night 12,500 ft early Monday 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 SUN MON *HURRICANE RIDGE0 0 *MT BAKER 0 0 *WASHINGTON PASS0 0 *STEVENS PASS 0 0 *SNOQUALMIE PASS0 0 *MISSION RIDGE 0 0 *CRYSTAL MTN 0 0 *PARADISE 0 0 *WHITE PASS 0 0 *MT HOOD 0 0 && WINDS IN MILES PER HOUR (MPH) *CASCADE PASS LEVEL WINDS E 15-25 with higher gusts Saturday and Saturday night E 15-30 Sunday morning E 10-20 with occasional higher gusts Sunday afternoon E 5-15 with occasional higher gusts Sunday night *FREE WINDS AT 5000 FT E-SE 5-15 Cascades, N 5-15 Olympics Saturday morning E-SE 10-15 N, 15-25 S Saturday afternoon and night SE 10-20 N, 15-30 S Sunday morning S-SE 10-20 N, 15-25 C and Olympics, 15-30 S Sunday afternoon S 10-20 Cascades, 15-25 Olympics Sunday night *FREE WINDS AT 9000 FT N 10-20 Cascades, 15-25 Olympics Saturday morning N-NE 10-20 mid-day NE 10-20 N and S Saturday afternoon E 10-20 N, SE 10-20 S and 15-25 Olympics Saturday night SE 10-20 N, 15-25 S and Olympics Sunday morning S 10-20 N, 15-25 C and Olympics and 20-40 S mid-day S 15-30 N and S Sunday afternoon S 15-30 N, 20-40 S Sunday night && EXTENDED WEATHER SYNOPSIS FOR MONDAY THROUGH WEDNESDAY As the center of the very strong upper ridge that has dominated NW weather for the past several days slides slowly southward in Idaho Monday and into eastern Utah and western Wyoming late Monday, the dominant upper flow over the Northwest should transition from easterly to southerly. However, incoming storm activity in the eastern Pacific should continue to be affected by the slowly weakening upper ridge through mid-week, with storms splitting and weakening about 2-400 miles offshore. This should maintain generally fair but slightly cooling weather at most mid and upper elevations mountain locations Monday into Tuesday morning, with a very slow lowering in freezing levels and temperatures aloft expected. Also, slowly decreasing easterly surface winds should allow for some moderation of the recently strong temperature and moisture inversion near the Cascade passes and along the Cascade east slopes. By mid-late Tuesday, a weak to moderate upper trough breaking into the retreating ridge should move mainly across central BC. This should bring further decreasing easterly surface winds and some increase in mid and high clouds. As the disturbance and upper trough move east of the region on Wednesday, variable mid and high clouds Wednesday morning should decrease mid-late Wednesday along with further lowering freezing levels. However, mid and upper elevation winds should remain quite light. Extended forecast models show considerable differences in the longer range solutions to the gradual breakdown of the recently dominant west coast ridge, although all agree that some transition toward a gradually wetter flow appears likely later Friday and Saturday. EXTENDED FORECAST FOR MONDAY THROUGH WEDNESDAY Monday and Monday night: continued cool with areas of low clouds or fog persisting lower terrain west of the crest and below about 3000 feet Cascade east slopes; otherwise mostly fair and continued warm Tuesday and Tuesday night: continued cool with areas of low clouds or fog persisting lower terrain west of the crest and below about 2- 000 feet Cascade east slopes; otherwise mostly fair Tuesday morning with increasing mid and high clouds Tuesday afternoon and night Wednesday and Wednesday night: cooler with variable mid and high clouds slowly decreasing mid-day and considerable filtered sunshine mid-late Wednesday; variable high clouds Wednesday night *FREEZING LEVELS 11-13,000 ft N and S Monday 8-10,000 ft N and S Tuesday 5-7000 ft N, 7-9000 ft S early Wednesday 4-6000 ft N, 6-8000 ft S late Wednesday...except freezing levels remaining near the surface Cascade passes and lower terrain east slopes Monday through early Tuesday, with slowly moderating temperatures likely later Tuesday and Wednesday 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. Moore/Northwest Weather and Avalanche Center $$