1230 PM PST TUE DEC 25 2007 WEATHER SYNOPSIS FOR CHRISTMAS AND WEDNESDAY An active cool westerly flow continues over the northeast Pacific Ocean. This should continue to carry fronts to the Northwest every couple days through the weekend. Therefore more significant snowfall accumulation is expected in the Olympics and Cascades. The next front rapidly approached over the Northwest coastal waters Christmas morning. This front is moving into the Olympics Christmas midday and should cross the Cascades Christmas afternoon. This should cause increasing snow with low snow levels. Offshore surface flow may slightly delay snow in the passes Christmas midday. Cool orographic west flow and an unstable air mass should result in significant snow showers at all locations near and west of the Cascade crest Christmas evening and night. The cool orographic west flow and unstable air mass should continue into Wednesday morning. Convergence effects should enhance the snow showers in the north and Central Cascades Wednesday morning. A brief short wave ridge and temporary surface high pressure should help snow showers to decrease and end Wednesday afternoon and evening. The MM5 model prolongs the showers however on Wednesday in the south at Mt Hood. WEATHER FORECAST FOR MONDAY AND CHRISTMAS DAY * OLYMPICS- Christmas midday: Increasing moderate snow. Christmas afternoon and evening: Moderate to heavy snow showers. Wednesday morning: Light to moderate snow showers heaviest west Olympics. Wednesday afternoon and evening: Light snow showers decreasing and ending. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST- * CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Christmas midday: Increasing light snow. Christmas afternoon: Increasing moderate snow. Christmas evening and night: Moderate to heavy snow showers. Wednesday morning: Light to moderate snow showers heaviest north and central Cascades in convergence. Wednesday afternoon and evening: Light snow showers decreasing and ending. * EAST SLOPES WASHINGTON CASCADES- Christmas midday: Increasing clouds. Christmas afternoon: Increasing light to moderate snow. Christmas evening and night: Light to moderate snow showers especially higher elevations. Wednesday morning: Light snow showers heaviest higher elevations. Wednesday afternoon and evening: Light snow showers ending. * MT HOOD AREA- Christmas midday: Increasing light snow. Christmas afternoon: Increasing moderate snow. Christmas evening and night: Moderate to heavy snow showers. Wednesday: Moderate snow showers. Wednesday evening: Light snow showers decreasing and ending. SNOW LEVELS-CASCADE MTNS 1000 ft N, 1500 ft S Christmas Day and night 500 ft N, 1000 ft S Wed and Wed night SNOW LEVELS-OLYMPIC MTNS 1500 ft Christmas Day and night 1000 ft Wed and Wed 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 WED THU * HURRICANE RIDGE .75 .25-.5 * MT BAKER .75-1 .5 * WASHINGTON PASS .5 .25-.5 * STEVENS PASS .75 .5 * SNOQUALMIE PASS .75 .5 * MISSION RIDGE .25 LT .25 * CRYSTAL MTN .5-.75 .25-.5 * PARADISE .75-1 .25-.5 * WHITE PASS .5-.75 .25-.5 * MT HOOD .75-1 .5-.75 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS E 0-10 Tue morn and midday W 10-20 Tue aft W 15-25 Tue night and Wed morn W 5-15 Wed aft and eve * FREE WINDS AT 5000 FT SW 20-30 Tue late morn and midday SW 25-35 Tue aft W 25-35 Tue eve to Wed morn strongest south part W 15-25 Wed aft and eve strongest south part * FREE WINDS AT 9000 FT SW 30-40 Tue late morn and midday SW 35-50 Tue aft W 30-40 Tue eve to Wed morn strongest south part W 25-35 Wed aft and eve strongest south part EXTENDED WEATHER SYNOPSIS FOR THURSDAY THROUGH SATURDAY The cool westerly flow should carry another front across the Olympics and Cascades Thursday. This should cause increasing snow Thursday. More orographic snow showers should be seen Thursday night and into Friday morning. A brief shortwave ridge and weak surface high pressure should cause snow showers to become light or to end Friday afternoon and evening. The cool west flow is indicated to carry yet another front across the Olympics and Cascades on Saturday. Once again this should cause increasing snow Saturday and orographic snow showers Saturday afternoon and night. EXTENDED FORECAST FOR THURSDAY THROUGH SATURDAY Thursday: Increasing light to moderate snow in the morning becoming moderate to heavy midday and afternoon. Thursday night: Moderate to heavy orographic snow showers. Friday morning: Light to moderate orographic snow showers. Friday afternoon and night: Light snow showers. Saturday: Increasing moderate to heavy snow. Saturday night: Moderate to heavy orographic snow showers. * SNOW LEVELS 5-1500 ft N and S Thu 5-1500 ft N, 1-2000 ft S Fri 5-1500 ft N, 2-4000 ft S Sat