130 PM PST TUE FEB 19 2008 WEATHER SYNOPSIS FOR TUESDAY AND WEDNESDAY An upper ridge which has been over the US west coast should shift east the next couple days. This should allow a split flow pattern to develop over the US west coast. The split pattern should persist through the coming weekend. This means that the stronger flow and main parts of weather systems will generally move into California. Computer model trends are apparently to bring the north parts of these systems through the Northwest in a weaker and slower manner. The weak north part of a front should move across the Northwest on Tuesday evening to Wednesday morning. This weak system should initially affect the Olympics and south Cascades. Weak flow and moisture should decrease following this system Wednesday afternoon and evening. This system should help cause cooling Tuesday and Wednesday. Offshore surface flow should help maintain moderate inversion conditions and cooler temperatures in the Cascades passes and along the lower Cascade east slopes. WEATHER FORECAST FOR TUESDAY AND WEDNESDAY * OLYMPICS- Tuesday afternoon: Increasing mid and high clouds. Tuesday evening to Wednesday morning: Cloudy with chance of light rain or snow. Wednesday afternoon and night: Decreasing clouds becoming partly cloudy. * WASHINGTON CASCADES- * CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Tuesday afternoon: Sunny. Tuesday evening: Increasing mid and high clouds initially south. Tuesday night to Wednesday morning: Cloudy with chance of light rain or snow initially south part. Wednesday afternoon and night: Decreasing clouds becoming partly cloudy. Cooler at lower elevations in the passes Tuesday and Wednesday. * MT HOOD AREA- Tuesday afternoon: Increasing high clouds. Tuesday evening to Wednesday morning: Cloudy with chance of light rain or snow. Wednesday afternoon and night: Decreasing clouds becoming partly cloudy. FREEZING LEVELS-CASCADE MTNS 7,000 ft N and S Tuesday aft SNOW LEVELS-CASCADE MTNS 6000 ft N and S Tue eve 4000 ft N and S Wed morn through eve except near the surface Cascade passes Tue and Wed especially night and morning hours FREEZING LEVELS-OLYMPIC MTNS 7000 ft Tuesday aft SNOW LEVELS-OLYMPIC MTNS 6000 ft Tuesday eve 4000 ft Wed morn through eve 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 LT .10 LT .10 * MT BAKER LT .10 LT .10 * WASHINGTON PASS LT .10 LT .10 * STEVENS PASS LT .10 LT .10 * SNOQUALMIE PASS LT .10 LT .10 * MISSION RIDGE LT .10 LT .10 * CRYSTAL MTN LT .10 LT .10 * PARADISE LT .10 LT .10 * WHITE PASS LT .10 LT .10 * MT HOOD LT .25 LT .10 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS E 10-20 Tue aft and Tue eve E 5-10 Wed and Wed eve * FREE WINDS AT 5000 FT S 10-20 Olympics, S 5-15 Cascades Tue aft and eve SW 5-15 Wed and Wed eve all areas * FREE WINDS AT 9000 FT S 15-25 Olympics, S 10-20 Cascades Tue aft and eve SW 5-15 all areas Wed morn SW 10-20 all areas Wed aft and eve EXTENDED WEATHER SYNOPSIS FOR THURSDAY THROUGH SATURDAY The next system in the split flow is indicated to move over the Northwest Thursday afternoon and night. This should cause a period of light precipitation especially in the Olympics or south Cascades. Weak flow and moisture should decrease again on Friday. A stronger low pressure system is indicated to approach California later Saturday. This should cause some clouds and possible light precipitation to spread to mainly the south Cascades. EXTENDED FORECAST FOR THURSDAY THROUGH SATURDAY Thursday morning: Partly cloudy. Thursday afternoon and night: Increasing clouds and light snow initially Olympics and south Cascades. Friday: Light snow showers ending becoming partly cloudy. Saturday: Partly cloudy with chance of light snow in the afternoon and evening initially south Cascades. * SNOW LEVELS 2-3000 ft N, 3-4000 ft S Thu and Fri 15-2500 ft N, 25-3500 ft S Sat except near the surface Cascade passes Thu to Sat especially night and morning hours