2 PM PST THU MAR 06 2008 WEATHER SYNOPSIS FOR THURSDAY AND FRIDAY A moderate but slowly weakening upper ridge lies over the Cascades early Thursday afternoon, resulting in relatively high freezing levels, variable mid and high clouds and slightly increasing ridgetop winds in most areas. Meanwhile a weakening front just offshore early Thursday is continuing to slowly split and move northeastward over western Washington with associated mid and high clouds drifting over the region. As the ridge continues to move eastward later Thursday afternoon, and an associated upper trough moves to the northeast and weakens, the front should continue to stretch, thin and weaken with little more than frontal remnants likely reaching the Cascades late Thursday through early Friday, mainly in the form of increased mid and high clouds with a few virga (higher based showers not reaching the ground) possible. After the recently dominant ridge briefly rebuilds behind the dying front Friday morning and mid-day, a stronger frontal system and associated upper trough should slowly move over the area mid-late Friday afternoon through early Saturday. This should spread lowering freezing levels, slowly increasing winds, and increasing light rain or snow into the Olympics later Friday afternoon, and the Cascades Friday evening, with briefly moderate rain or snow likely Friday night along with moderate winds and significant cooling. WEATHER FORECAST FOR THURSDAY AND FRIDAY * OLYMPICS- Thursday afternoon: increasing mid and high clouds Thursday night: considerable mid and high clouds with some virga or very light showers possible Friday morning: variable mid and high clouds increasing late Friday afternoon: clouds lowering and thickening with light rain or snow developing Friday night: moderate rain or snow decreasing late Friday night to light to moderate showers * WASHINGTON CASCADES NEAR AND WEST OF THE CREST- * CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Thursday afternoon: variable mid and high clouds with considerable filtered sunshine Thursday night: variable mid and high clouds north and variable high clouds south with some virga or very light showers possible north Friday morning: variable mid and high clouds Friday afternoon: gradually increasing clouds with increasing chance few showers or occasional light rain or snow mid-late afternoon, mainly north and central Friday night: light to moderate rain or snow increasing and becoming moderate; moderate rain or snow decreasing and becoming more showery early Saturday * EAST SLOPES WASHINGTON CASCADES- Thursday afternoon: variable mid and high clouds with considerable filtered sunshine Thursday night: variable mid and high clouds north and variable high clouds south with some virga or very light showers possible higher terrain north Friday morning: variable high clouds Friday afternoon: gradually increasing mid and high clouds with chance showers late Friday night: light to moderate rain or snow developing and becoming briefly moderate overnight; moderate rain or snow decreasing and becoming showery early Saturday * MT HOOD AREA- Thursday afternoon: variable mid and high clouds with considerable filtered sunshine Thursday night: variable high clouds Friday morning: variable high clouds with considerable sunshine or filtered sunshine Friday afternoon: gradually increasing mid and high clouds with chance showers late Friday night: light to moderate rain or snow developing and increasing; moderate rain or snow decreasing and becoming more showery early Saturday FREEZING LEVELS-CASCADE MTNS 7000 ft N, 8500 ft S Thursday afternoon 6500 ft N, 8000 ft S Thursday night 5000 ft N, 7500 ft S Friday morning 4500 ft N, 6500 ft S mid-day SNOW LEVELS-CASCADE MTNS 4000 ft N, 5500 ft S Friday afternoon 3500 ft N, 4000 ft S Friday night 2000 ft N and S early Saturday FREEZING LEVELS-OLYMPIC MTNS 7000 ft Thursday afternoon 6000 ft Thursday night and Friday morning 5500 ft mid-day Friday SNOW LEVELS-OLYMPIC MTNS 4500 ft Friday afternoon 3000 ft Friday night 1500 ft early Saturday 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 FRI SAT * HURRICANE RIDGE 0 .25 * MT BAKER 0 .5-.75 * WASHINGTON PASS 0 .25 * STEVENS PASS 0 .25-.5 * SNOQUALMIE PASS 0 .5 * MISSION RIDGE 0 LT .25 * CRYSTAL MTN 0 .25-.5 * PARADISE 0 .5 * WHITE PASS 0 .25-.5 * MT HOOD 0 .25-.5 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS E 0-10 early Thursday afternoon Variable mostly W 0-10 mid-late Thursday afternoon Variable 0-10 Thursday night and Friday morning E 0-10 mid-day Friday W 5-10 Friday afternoon W 10-20 with higher gusts Friday night * FREE WINDS AT 5000 FT S-SE 10-20 N and Olympics, SW 5-15 S Thursday afternoon S-SW 10-15 N, 10-20 S and Olympics Thursday night W-SW 10-15 Cascades, SW 10-20 Olympics Friday morning S-SW 10-15 N, 15-25 S, 25-40 Olympics Friday afternoon SW 20-40 Cascades, 20-35 Olympics Friday night, decreasing late * FREE WINDS AT 9000 FT SW 15-25 Cascades, 15-30 Olympics Thursday afternoon W-SW 15-25 Thursday night W-SW 10-20 N, 15-25 S Friday morning SW 20-40 Cascades, 30-50 Olympics Friday afternoon W 25-40 N, 30-50 S Friday night, decreasing late EXTENDED WEATHER SYNOPSIS FOR SATURDAY THROUGH MONDAY The associated weakening upper trough should move onshore early Saturday morning and combined with a weak to moderate onshore flow and a lingering Puget Sound convergence, this should maintain light to moderate showers at further lowering freezing levels and gradually decreasing but still light to moderate winds. However, rebuilding and moderate offshore ridging should allow for a gradually drier but initially cool northwesterly flow to move over the area mid- day and Saturday afternoon. This should result in decreasing light to moderate showers and some partial clearing mid-day with scattered light showers diminishing and a slow clearing trend spreading southward mid-late Saturday afternoon and night. As the ridge moves slowly eastward Sunday morning, the first of several offshore frontal systems should slowly weaken and move mostly north of the area later Sunday morning and early afternoon. While this should result in some increased mid or high clouds and a chance of some brief light showers later Sunday afternoon, considerable sunshine or filtered sunshine is still likely along with rising freezing levels and slightly increased winds. Variable mid and high clouds should persist Sunday evening until a second and stronger frontal system approaches the coast Sunday night. This stronger front should spread increasing clouds, increasing winds and light rain or snow into the Olympics later Sunday night and early Monday, with increasing light rain or snow reaching the Cascades late Monday morning, and moderate rain or snow likely developing in most areas Monday afternoon and evening. Increasing moderate to strong winds and lowering freezing levels should accompany the front as it moves over the Cascades Monday afternoon and night, with a moderate upper trough and secondary surface trough helping maintain moderate to occasionally heavy showers into Tuesday morning. EXTENDED FORECAST FOR SATURDAY THROUGH MONDAY Saturday morning: light to moderate showers, heaviest central Cascades in convergence Saturday afternoon: decreasing light showers with partial clearing Saturday night: clearing trend becoming mostly fair overnight Sunday morning: few high clouds otherwise considerable sunshine or filtered sunshine Sunday afternoon: variable mid and high clouds increasing with chance few showers late afternoon Sunday night: clouds increasing and lowering in the Olympics with light rain or snow developing early Monday; otherwise, considerable mid and high clouds Cascades Monday morning: light rain or snow developing Olympics, increasing clouds Cascades with light rain or snow developing late morning Monday afternoon: increasing light to moderate rain or snow Monday night: moderate rain or snow becoming moderate to occasionally heavy showers early Tuesday * SNOW LEVELS 1-3000 ft N and S Saturday into early Sunday 3-5000 ft N, 5-7000 ft S mid-day Sunday 5-7000 ft N, 7-9000 ft S late Sunday through Monday morning 4-6000 ft N, 5-7000 ft S Monday afternoon 2-4000 ft N and S Monday night, further lowering early Tuesday