245 PM PST MON DEC 24 2007 WEATHER SYNOPSIS FOR MONDAY AND CHRISTMAS DAY The Pacific Northwest continues to be the recipient of the strong westerly flow across the north Pacific. This puts the Northwest directly in the path of regular and strong frontal systems crossing at the rate of about every one to two days. This pattern is expected to continue into the weekend. Showers have decreased Monday afternoon behind the strong frontal passage that moved across the Olympics and Cascades late Sunday becoming scattered over most Cascade and Olympic locations. Stronger moist westerly flow is maintaining moderate snow showers over the Mt Hood Monday afternoon. The flow should diminish further Monday evening to allow for decreasing showers as a brief upper ridge builds offshore. A transitory upper ridge is expected to maintain a break in precipitation Christmas Eve and into Christmas morning providing light winds partial clearing and continued cool temperatures. The next in the series of storms should begin affecting the region later Christmas morning and early afternoon. A strong westerly jet stream of about 130 kts off the Washington and Oregon coast should strengthen the front as it approaches the area later in the day. This should cause increasing strong winds and moderate to heavy precipitation during the afternoon and evening hours. The front should move across the Cascades during the evening followed by a period of moderate west to northwest crest level flow. This should maintain showers along the typical west slope areas through Monday night at low freezing levels. WEATHER FORECAST FOR MONDAY AND CHRISTMAS DAY * OLYMPICS- Monday afternoon and night: Decreasing light snow showers with partial clearing at times. Christmas morning: Mostly high clouds with light winds and cool. Christmas Day: Increasing light snow late morning becoming moderate to heavy afternoon and evening. Christmas night: Snow changing to light snow showers and gradually decreasing. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST- * CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Monday afternoon: Scattered light snow showers. Christmas Eve: Decreasing light snow showers with partial clearing. Christmas morning: Mostly high clouds with light winds and cool. Christmas Day: Increasing clouds with light snow developing late morning becoming moderate to heavy afternoon and evening. Christmas night: Snow changing to light to moderate snow showers gradually decreasing. * EAST SLOPES WASHINGTON CASCADES- Monday afternoon and night: Decreasing light snow showers with partial clearing at times. Christmas morning early: Mostly high clouds with light winds and cool. Christmas Day: Increasing light snow midday becoming moderate to briefly heavy late afternoon and evening. Christmas night: Snow changing to light snow showers and gradually decreasing. * MT HOOD AREA- Monday afternoon: Light to moderate snow showers. Monday and night: Decreasing light snow showers with partial clearing at times. Christmas morning early: Mostly high clouds with light winds and cool. Christmas Day: Increasing light snow early afternoon becoming moderate to heavy late afternoon and evening. Christmas night: Snow changing to light snow showers and gradually decreasing. SNOW LEVELS-CASCADE MTNS 1000 ft N, 1500 ft S Mon aft and Mon night 1500 ft N, 2000 ft S Christmas Day 500 ft N, 1000 ft S Christmas night SNOW LEVELS-OLYMPIC MTNS 1000 ft Mon aft and Mon night 1500 ft Christmas Day 500 ft Christmas 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 TUE WED * HURRICANE RIDGE LT .25 .25-.5 * MT BAKER .25 1 * WASHINGTON PASS LT .25 .5 * STEVENS PASS .25-.5 .75 * SNOQUALMIE PASS .25-.5 .75 * MISSION RIDGE LT .25 .25-.5 * CRYSTAL MTN .25 .5-.75 * PARADISE .5 .75-1 * WHITE PASS .25 .5-.75 * MT HOOD .75 .75 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS W 10-20 Mon aft W 5-10 Mon night and early Tue E 0-10 Tue aft W 10-20 Tue night * FREE WINDS AT 5000 FT W-NW 20-30 Mon aft and eve NW 5-15 Mon night SW 5-15 Tue morn S-SW 25-35 Tue late morning and midday SW 30-50 Tue aft and eve W 15-30 Tue night * FREE WINDS AT 9000 FT N-NW 25-35 Mon aft and eve W 15-30 Tue early morn SW 35-50 Tue late morn and midday W-SW 35-50 Tue aft and night EXTENDED WEATHER SYNOPSIS FOR WEDNESDAY THROUGH FRIDAY Strong westerly flow should continue Wednesday behind a previous frontal passage to maintain showers at low freezing levels along most west slope areas. A strong northwest jet stream offshore should drive freezing levels lower to about sea level by Wednesday with continued showers. A brief ridge of high pressure should allow for decreasing showers late Wednesday and early Thursday ahead of another vigorous frontal system and surface low pressure expected to develop offshore. This system should spread increasing snow over the area during the day Thursday. The strong front should pass Thursday evening bringing strong winds and a period of heavy precipitation. Orographic showers are expected Thursday night into Friday along the west slope areas at low snow levels. Yet another low pressure center is expected to move directly across western Washington Friday afternoon for another round of moderate to heavy precipitation at continued low freezing levels along with strong winds. EXTENDED FORECAST FOR WEDNESDAY THROUGH FRIDAY Wednesday morning: Light to moderate snow showers. Wednesday afternoon and evening: Decreasing light snow showers mainly near and west of the crest, otherwise partial clearing. Thursday: Light snow developing early and increasing becoming moderate to heavy snow late. Thursday night: Moderate to heavy snow showers. Friday: Light to moderate snow showers, heaviest west slopes Cascades. Friday afternoon and night: Increasing moderate to heavy snow and windy. * SNOW LEVELS 5-1500 ft N and S Tue through Thu