215 PM PST THU JAN 31 2008 WEATHER SYNOPSIS FOR THURSDAY AND FRIDAY Very strong and moist westerly flow behind an early frontal passage is maintaining moderate to occasionally heavy snow showers along the west slope areas and over the volcanoes Thursday afternoon. The strongest flow and therefore the heaviest precipitation remain over the Mt Hood area. Freezing levels should continue to gradually lower behind the earlier frontal passage and should trend further downward through Thursday night. Strong and very moist west flow should continue through Thursday night and early Friday before gradually decreasing later Friday and Friday night. This should maintain the moderate to occasionally heavy precipitation along the west slope areas through early Friday. The west flow becomes slightly northwesterly Thursday night through Friday morning and should allow a strong convergence zone to form and carry into the Cascades. This should cause locally enhanced precipitation, mainly affecting the Stevens Pass areas Thursday night likely shifting southward to Snoqualmie Pass by early Friday. A brief decrease in flow and precipitation is expected later Friday afternoon and night ahead of another approaching low pressure system offshore. WEATHER FORECAST FOR THURSDAY AND FRIDAY * OLYMPICS- Thursday aft and night: Moderate to heavy snow showers, heaviest along the west slope areas. Friday morning: Moderate to heavy snow showers gradually decreasing. Friday afternoon and evening: Light to moderate snow showers. Friday night: Cloudy with occasional light snow showers. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST- CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Thursday aft: Moderate to occasionally heavy snow showers. Thursday night: Moderate to heavy snow showers, heaviest Stevens Pass to Snoqualmie Pass in convergence. Friday morning: Moderate to heavy snow showers, heaviest Stevens Pass to Snoqualmie Pass in convergence. Friday afternoon and evening: Light to moderate snow showers. Friday night: Cloudy with occasional light snow showers. * EAST SLOPES WASHINGTON CASCADES- Thursday aft and night: Light to moderate snow showers, heaviest higher elevations nearer the crest. Friday: Light snow showers especially higher elevations. Friday afternoon and night: becoming partly cloudy with occasional light snow showers. * MT HOOD AREA- Thursday afternoon and night: Moderate to heavy snow showers. Friday morning: Moderate to heavy snow showers. Friday afternoon and night: gradually decreasing light to moderate snow showers. SNOW LEVELS-CASCADE MTNS 1000 ft N, 2000 ft S Thur aft 500 ft N, 1000 ft S Thur night through Fri night SNOW LEVELS-OLYMPIC MTNS 1500 ft Thur aft 1000 ft Thur night through Fri night 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 FRI SAT * HURRICANE RIDGE .5-.75 .25 * MT BAKER .75 .5 * WASHINGTON PASS .5 .25 * STEVENS PASS 1 .25-.5 * SNOQUALMIE PASS 1-1.5 .5 * MISSION RIDGE .25 LT .25 * CRYSTAL MTN .5 .25 * PARADISE .75 .5 * WHITE PASS .75 .25-.5 * MT HOOD 1.5 .5 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS W 10-20 Thur aft through Fri aft W 0-10 Fri night * FREE WINDS AT 5000 FT W-SW 10-20 N, W-SW 20-30 C, W 35-50 S Thu aft and eve SW 5-15 N, W-SW 25-35 C, W 30-40 S Thursday night and Fri morn W 20-30 Fri aft W 10-20 N and C, W 20-30 S Fri night * FREE WINDS AT 9000 FT W 20-30 N, W 30-50 S Thu aft and eve W-SW 10-20 N, W 25-35 C, W 35-45 S Thur night and Fri morn W 15-25 N, W 30-40 S Fri aft W 15-25 N, 25-50 S Fri night EXTENDED WEATHER SYNOPSIS FOR SATURDAY THROUGH MONDAY A surface low pressure system is expected to approach the region from the northwest Saturday. This should spread increasing moisture over the area later Saturday. The surface low should track towards the Columbia River mouth by Saturday evening. This should spread increasing moderate to heavy precipitation at rising freezing levels to the Mt Hood area and eventually to the central Washington Cascades and east slopes late Saturday and Saturday night. Current models indicate that only light precipitation may reach the north Washington Cascades from this system late Saturday. Strong northwest flow should develop in the wake of this low pressure system Sunday and Monday. This should allow for cool and gradually drying conditions. Showers should persist Sunday and end overnight Sunday and become partly cloudy Monday. Another approaching frontal system should spread increasing precipitation across the region by early Tuesday. EXTENDED FORECAST FOR SATURDAY THROUGH MONDAY Saturday morning: Mostly cloudy with occasional light snow, mainly south. Saturday afternoon to Sunday morning: Increasing moderate to heavy snow Mt Hood area and east slopes Washington Cascades in the south to central part. Otherwise light to moderate snow in the Olympics and remainder of the Washington Cascades with less snow towards the north Washington Cascades. Sunday afternoon and night: Decreasing light snow showers heaviest near and west of the crest. Monday: Partly cloudy with mainly high clouds. Increasing clouds Monday night. * SNOW LEVELS Near sea level-1000 ft N, 15-2500 ft S Sat and Sun Near sea level-1000 ft N, 1-2000 ft S Sat and Sun