200 PM PST WED FEB 20 2008 WEATHER SYNOPSIS FOR WEDNESDAY AND THURSDAY An upper ridge which was over the US west coast has shifted east to the Rocky Mountains. This has allowed 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 continue to be to bring the north parts of these systems through the Northwest in a weaker and slower manner. The very weak north part of a front should move slowly across the Northwest as it dissipates on Wednesday morning. Weak flow and moisture should decrease following this system Wednesday afternoon and evening. The next weakening north part of the next front should approach over the Northwest coastal waters on Thursday. But it should not affect the Olympics and Cascades until at least Thursday night or mainly Friday. A slight increase in winds aloft may be seen by Thursday night. It is hard to discern any significant trend in snow levels Wednesday or Thursday. East winds may bring a little cooling to the Cascade passes Thursday. WEATHER FORECAST FOR WEDNESDAY AND THURSDAY * OLYMPICS- Wednesday afternoon: Decreasing clouds becoming mostly sunny. Wednesday night: Partly or mostly clear. Thursday: Partly or mostly sunny. Thursday night: Increasing clouds. * WASHINGTON CASCADES- * CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Wednesday afternoon: Decreasing clouds becoming mostly sunny. Wednesday night: Partly or mostly clear. Thursday: Partly or mostly sunny north and central and partly cloudy south. Thursday night: Increasing clouds mainly south part. Slightly cooler at lower elevations in the passes Thursday and Thursday night. * MT HOOD AREA- Wednesday afternoon: Decreasing clouds becoming mostly sunny. Wednesday night: Partly or mostly clear. Thursday: Partly cloudy. Thursday night: Increasing clouds and slight chance of light rain or snow by Friday morning. SNOW LEVELS-CASCADE MTNS 3500 ft N, 4500 ft S Wed and Thu slightly lower night and morning hours slightly higher afternoon hours, also near the surface Cascade passes and east slopes night and morning hours. SNOW LEVELS-OLYMPIC MTNS 4000 ft Wed and Thu slightly lower night and morning hours slightly higher afternoon hours. 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 THU FRI * HURRICANE RIDGE 0 LT .10 * MT BAKER 0 LT .10 * WASHINGTON PASS 0 LT .10 * STEVENS PASS 0 LT .10 * SNOQUALMIE PASS 0 LT .10 * MISSION RIDGE 0 0 * CRYSTAL MTN 0 LT .10 * PARADISE 0 LT .10 * WHITE PASS 0 LT .10 * MT HOOD 0 LT .10 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS Light variable Wed E 5-15 Thu * FREE WINDS AT 5000 FT SE-W 5-15 Wed aft and eve S 10-20 Thu S-SE 10-20 Thu night strongest south part * FREE WINDS AT 9000 FT S-SW 10-20 Wed aft and eve S 15-25 Thu S 20-30 Thu night strongest south part EXTENDED WEATHER SYNOPSIS FOR FRIDAY THROUGH SUNDAY A weak upper trough and weak north part of the next front should move over the Northwest on Friday. This should bring a better chance of light rain or snow showers to the Olympics and Cascades at slightly lower snow levels. A shortwave ridge and weak surface high pressure should be seen over the Northwest on Saturday. This should cause a day of mostly fair weather. A surface low pressure system in the split flow should approach the Oregon coast on Sunday. Moisture is indicated to rotate out of this system and affect mainly the south Cascades on Sunday. EXTENDED FORECAST FOR FRIDAY THROUGH SUNDAY Friday: Light rain or snow showers mainly near and west of crest. Saturday: Partly cloudy. Increasing clouds south part Saturday night. Sunday: Cloudy with light rain or snow mainly south part. * SNOW LEVELS 15-2500 ft N, 25-3500 ft S Fri and Sat 25-3500 ft N, 35-4500 ft S Sun slightly lower night and morning hours slightly higher afternoon hours Friday to Sunday