130 PM PST SUN JAN 6 2008 WEATHER SYNOPSIS FOR SUNDAY AND MONDAY A series of low pressure systems moving across the northeast Pacific Ocean should maintain active weather here in the Northwest through the coming week. A large upper trough should move into the western US on Sunday with the main flow over California. Showers and a cool unstable air mass should be seen in the north part of the trough over the Northwest. Satellite images and radar indicate that a band of these showers will cross the Olympics and Cascades early Sunday, followed by another Sunday late morning or midday, followed by another Sunday afternoon or evening. The southerly component to the upper flow and weak surface flow suggest that the volcanic peaks will be favored for the snow showers Sunday. A temporary upper ridge and a drier more stable air mass should cross the Northwest on Monday, with temporary surface high pressure building east of the Cascade crest. This should cause showers to mostly end Monday morning followed by mostly cloudy conditions near and west of the crest Monday afternoon. Increasing flow aloft and increasing moisture should start to move into the Northwest as the next strong front approaches Monday night. WEATHER FORECAST FOR SATURDAY AND SUNDAY * OLYMPICS- Sunday: Periods of light to moderate snow showers. Sunday night: Light snow showers decreasing and ending. Monday: Mostly cloudy. Monday night: Increasing light to moderate snow. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST- * CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Sunday: Periods of light to moderate snow showers heaviest on the volcanic peaks. Sunday night: Light snow showers decreasing and ending. Monday: Mostly cloudy. Monday night: Increasing light to moderate snow. * EAST SLOPES WASHINGTON CASCADES- Sunday: Periods of light snow showers. Sunday night: Light snow showers mainly higher elevations decreasing and ending. Monday: Partly cloudy. Monday night: Increasing light snow. * MT HOOD AREA- Sunday: Periods of light to moderate snow showers. Sunday night: Light snow showers decreasing and ending. Monday: Mostly cloudy. Monday night: Increasing light to moderate snow. SNOW LEVELS-CASCADE MTNS Near sea level N, 1000 ft S Sun and Mon SNOW LEVELS-OLYMPIC MTNS Near sea level Sun and Mon 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 .25-.5 .25-.5 * MT BAKER .5 .5 * WASHINGTON PASS .25 .25-.5 * STEVENS PASS .25 .25-.5 * SNOQUALMIE PASS .25 .25-.5 * MISSION RIDGE LT .25 LT .25 * CRYSTAL MTN .25 .25-.5 * PARADISE .25-.5 .5 * WHITE PASS .25 .25-.5 * MT HOOD .25-.5 .5 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS Light variable Sun W 0-10 Sun night Light variable Mon E 10-20 Mon night * FREE WINDS AT 5000 FT SW 15-25 Sun SW 10-20 Sun night and Mon SW 30-50 Mon night * FREE WINDS AT 9000 FT SW 20-30 Sun SW 15-25 Sun night and Mon SW 40-60 Mon night EXTENDED WEATHER SYNOPSIS FOR TUESDAY THROUGH THURSDAY Increasing flow and the next strong front is indicated to move into the Northwest Tuesday morning. This should cause increasing winds and increasing snow in the Olympics and Cascades. The front should cross the Cascades Tuesday midday. This should be followed by moderate to heavy orographic snow showers through Tuesday evening. Another temporary shortwave ridge aloft and surface ridge of high pressure should cross the Northwest on Wednesday. This should cause another relative break in the active pattern. Increasing flow and yet another front is indicated to move into the Northwest Wednesday night and Thursday morning. This should cause another period of increasing winds and snow Wednesday night and Thursday morning. Models indicate that snow showers following this system will be heavier in the south Cascades later Thursday. EXTENDED FORECAST FOR TUESDAY THROUGH THURSDAY Tuesday: Moderate to heavy snow especially near and west of the crest. Tuesday afternoon and evening: Moderate to heavy snow showers mainly near and west of the crest. Wednesday: Light to moderate snow showers mainly near and west of the crest in the morning decreasing and ending midday. Wednesday night and Thursday morning: Increasing moderate to heavy snow. Thursday afternoon and night: Light to moderate snow showers north and moderate to heavy snow showers south. * SNOW LEVELS 500-1000 ft N, 15-2500 ft S Tue...near the surface Cascades passes and east slopes in the morning, free air levels in the afternoon 500-1000 ft N, 1-2000 ft S Wed 5-1500 ft N, 2-4000 ft S Thu...near the surface Cascades passes and east slopes in the morning, free air levels in the afternoon