100 PM PST SUN DEC 2 2007 WEATHER SYNOPSIS FOR SUNDAY AND MONDAY The ridge that has been over the Northwest the past few days has been undercut by a very strong, very moist southwest flow. This should lead to extremely stormy weather in the Olympics and Cascades on Sunday and Monday. The increasing southwest flow will carry an initial frontal system over the Olympics and Cascades on Sunday. This should lead to strongly increasing crest level winds, increasing heavy precipitation and rising snow levels in most areas of the Olympics and Cascades. The most difficult predication might be the possible evolution and timing of the change from snow to freezing rain to rain at the lower Cascade passes. A gradual erosion of cool easterly winds at the lower Cascade passes seems most likely with some freezing rain near the west approaches shifting toward the passes on Sunday. A minor and temporary decrease in precipitation might be seen between systems Sunday evening. A 170 knot southwest jet stream flow is indicated over the Northwest on Monday. A second frontal system of tropical origin is indicated to move over the Northwest. This should cause further increasing extremely strong southwest crest level winds, extremely heavy precipitation at high snow levels on Monday. Further complete erosion of cool easterly winds in the lower Cascade passes is likely by Monday morning, with a change to west winds and rain on Monday. Computer models begin to indicate slightly decreasing flow aloft and slightly decreasing crest level winds, decreasing precipitation and slightly lowering snow levels Monday night. WEATHER FORECAST FOR SATURDAY AND SUNDAY * OLYMPICS- Sunday afternoon and evening: Moderate to heavy rain or snow. Sunday night: Increasing heavy rain or snow. Monday: Very heavy rain or snow. Monday night: Decreasing moderate to heavy rain or snow. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST- Sunday afternoon and evening: Moderate to heavy rain or snow. Sunday night: Increasing heavy rain or snow. Monday: Very heavy rain or snow. Monday night: Decreasing moderate to heavy rain or snow. * CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Sunday afternoon and evening: Moderate to heavy snow with freezing rain west approaches especially Snoqualmie. Sunday night: Increasing heavy rain or snow with freezing rain west approaches especially Snoqualmie. Monday: Heavy rain or snow changing to rain, with areas experiencing freezing rain changing to rain by Monday morning especially Snoqualmie. Monday night: Decreasing moderate to heavy rain or snow. * EAST SLOPES WASHINGTON CASCADES- Sunday afternoon and evening: Moderate snow. Sunday night: Increasing moderate to heavy snow. Monday: Moderate to heavy rain or snow. Monday night: Decreasing moderate rain or snow. * MT HOOD AREA- Sunday and evening: Moderate to heavy snow. Sunday night: Increasing heavy rain or snow. Monday: Very heavy rain or snow. Monday night: Decreasing moderate to heavy rain or snow. SNOW LEVELS-CASCADE MTNS Near sea level N and C, 1000 ft S Sun morn Near sea level N, 2000 ft C and S Sun midday 1000 ft N, 3000 ft C, 4000 ft S Sun aft 4000 ft N, 5000 ft C, 8000 ft S Sun eve 7000 ft N, 8000 ft C, 10000 ft S Mon morn 6000 ft N, 7000 ft C, 8000 ft S Mon aft 5000 ft N, 6000 ft S Tue morn, except near the surface Cascade passes Sunday, then rising to near free air levels Sun night/Mon morning. SNOW LEVELS-OLYMPIC MTNS 1000 ft Sun morn 2000 ft Sun midday 4000 ft Sun aft 5000 ft Sun eve 8000 ft Mon morn 7000 ft Mon aft 5500 ft Tue morn 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 2 3 * MT BAKER 2 4-6 * WASHINGTON PASS 1 1.5-2 * STEVENS PASS 1.5 2 * SNOQUALMIE PASS 2 3 * MISSION RIDGE .75 1-1.5 * CRYSTAL MTN 1.5-2 2-3 * PARADISE 2-3 3-5 * WHITE PASS 1-1.5 2 * MT HOOD 2 3 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS E 5-10 Sun aft E 10-15 Sun eve E 15-20 Mon morn E 5-15 Mon aft W 5-15 Mon eve * FREE WINDS AT 5000 FT SW 40-60 Sun aft SW 50-70 Sun eve SW 60-80 Mon morn SW 50-70 Mon aft SW 50-60 Mon night * FREE WINDS AT 9000 FT SW 70-90 Sun aft SW 80-110 Sun eve SW 100-120 Mon morn SW 90-110 Mon aft SW 70-80 Mon night EXTENDED WEATHER SYNOPSIS FOR TUESDAY THROUGH THURSDAY A decreasing cooler southwest flow should be seen over the Northwest on Tuesday. This should generally bring decreasing light to moderate orographic showers to the Olympics and Cascades. A weak upper ridge should build over the northeast Pacific Ocean with weak flow over the Northwest Wednesday and Thursday. Light orographic showers should end Wednesday. Dry conditions are currently indicated by the US GFS model Thursday. EXTENDED FORECAST FOR TUESDAY THROUGH THURSDAY Decreasing light to moderate orographic rain or snow showers Tuesday. Light showers near and west of the crest ending Wednesday. Partly or mostly cloudy Thursday. * SNOW LEVELS 4-6000 ft N, 5-7000 ft S Tue 15-2500 ft N, 2-4000 ft S Wed 1-2000 ft N, 2-4000 ft S Thu