130 PM PST WED JAN 23 2008 WEATHER SYNOPSIS FOR WEDNESDAY AND THURSDAY A weakening northeasterly flow around a positively tilted upper ridge over southern BC is moving over the Northwest early Wednesday afternoon. This is producing generally dry and continued cool to cold weather in most areas, with very cold temperatures dominating lower elevations along the Cascade east slopes where some early morning readings reached 10 deg F below zero. Continuing past Washington and northern Oregon to the south, the upper level flow moves southwestward offshore around a deepening upper low just west of San Francisco, with several disturbances rotating around that low spreading moderate to heavy precipitation across much of California. As the east-west oriented upper ridge moves southward over the area Wednesday afternoon, this should maintain mostly fair skies over most Northwest locations, along with relatively light winds and slight warming, mainly at mid and upper elevations in the southern Washington Cascades, the Mt Hood area and the Olympics. Following the retreating upper ridge which should move east of the area late Wednesday and early Thursday, a narrow upper trough is expected to slide southward just off the Washington coast while slowly strengthening. Although much of the associated precipitation should remain offshore on Thursday, circulation around the low should still spread briefly increasing mid and high level moisture over most areas on Thursday along with a chance of a few flurries in the Olympics Thursday morning and some brief light snow in the southern Washington Cascades and Mt Hood area Thursday afternoon and evening. However, only a very slight increase in winds is expected with freezing levels remaining very low. As the disturbance sinks southward into the currently preferred trough position off the California coast, slow clearing should spread southward overnight with light showers ending in the south by early Friday. WEATHER FORECAST FOR WEDNESDAY AND THURSDAY * OLYMPICS- Wednesday afternoon: a few high clouds at times, otherwise mostly fair and a little warmer Wednesday night: increasing high clouds Thursday morning: increasing mid and high clouds with a chance of a few flurries late morning and mid-day Thursday afternoon: clouds decreasing and flurries ending with partial clearing Thursday night: clearing trend becoming mostly fair and cold early Friday * WASHINGTON CASCADES NEAR AND WEST OF THE CREST- Wednesday afternoon: a few high clouds at times, otherwise mostly fair and a little warmer, especially higher terrain in the south Wednesday night: increasing high clouds Thursday morning: increasing mid and high clouds spreading southward Thursday afternoon: variable mid and high clouds north and central to mostly cloudy south with a chance of light showers from about Mt Rainier southward Thursday night: clearing trend north and central with decreasing clouds and flurries ending in the south * CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Wednesday afternoon: a few high clouds at times, otherwise mostly fair and continued cool Wednesday night: increasing high clouds Thursday morning: increasing mid and high clouds spreading southward Thursday afternoon: variable mid and high clouds north of Mt Rainier with some filtered sunshine; otherwise mostly cloudy south of Mt Rainier with a chance of light showers in the south Thursday night: clearing trend north and central with decreasing clouds and flurries ending in the south * EAST SLOPES WASHINGTON CASCADES- Wednesday afternoon: a few high clouds at times, otherwise mostly fair and continued cold lower terrain with slight warming higher terrain, especially south Wednesday night: cold with increasing high clouds Thursday morning: variable mid and high clouds spreading southward Thursday afternoon: variable mid and high clouds north of Mt Rainier to partly cloudy south of Mt Rainier with a chance of light showers in the south Thursday night: clearing trend north and central with decreasing clouds and flurries ending in the south * MT HOOD AREA- Wednesday afternoon: a few high clouds at times, otherwise mostly fair and a little warmer, especially higher terrain Wednesday night: variable high clouds, otherwise mostly fair Thursday morning: increasing mid and high clouds late morning Thursday afternoon: mostly cloudy with light snow showers developing Thursday night: decreasing clouds and showers with flurries ending early Friday FREEZING LEVELS-CASCADE MTNS Sea level N and C, 6000 ft S early Wednesday afternoon Sea level N and C, 6500 ft S later Wednesday afternoon Sea level N and C, 5000 ft S Wednesday night SNOW LEVELS-CASCADE MTNS Sea level N and S Thursday and Thursday night, except snow levels remaining at the surface Cascade passes and east slopes through Thursday FREEZING LEVELS-OLYMPIC MTNS 6000 ft Wednesday afternoon 2500 ft Wednesday night, except freezing levels remaining locally near the surface lower valleys Wednesday SNOW LEVELS-OLYMPIC MTNS Sea level Thursday and Thursday 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 THU FRI * HURRICANE RIDGE 0 LT .10 * MT BAKER 0 0 * WASHINGTON PASS 0 0 * STEVENS PASS 0 0 * SNOQUALMIE PASS 0 0 * MISSION RIDGE 0 0 * CRYSTAL MTN 0 0 * PARADISE 0 LT .10 * WHITE PASS 0 LT .10 * MT HOOD 0 LT .25 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS E 5-15 with occasional higher gusts Wednesday afternoon E 10-15 with higher gusts Wednesday night and Thursday morning E 5-15 Thursday afternoon and night * FREE WINDS AT 5000 FT S-SE 5-15 N, 10-15 S Wednesday afternoon through Thursday morning SE 5-15 Thursday afternoon and evening Variable 0-10 later Thursday night and early Friday * FREE WINDS AT 9000 FT W-SW 10-20 N, variable 5-15 S Wednesday afternoon SW 15-30 N, S 10-20 S Wednesday night S-SW 15-25 Thursday morning S 10-20 N, 15-25 S Thursday afternoon Variable 5-15 N, W 5-15 S Thursday night NW 5-15 N, Variable 5-15 S early Friday EXTENDED WEATHER SYNOPSIS FOR FRIDAY THROUGH SUNDAY Briefly rebuilding upper ridging should move very weakly southeastward over the area on Friday, but should still provide some clearing and relatively light winds. Only brief and relatively minor rises in the freezing levels are expected, mainly in the south. As the ridge moves east, a gradually increasing but still cool west to northwesterly flow across the eastern Pacific is expected to allow a series of strengthening disturbances to move over the region mid-late Saturday into early to mid next week. The first such disturbance is expected to spread increasing clouds to the area late Friday, with clouds lowering and light snow developing in most areas later Saturday morning and early- mid afternoon as circulation around the low pulls moisture into the area from the south. More general and increasing light snow should spread southward with the front later Saturday afternoon and night, with periods of moderate snow expected Saturday night through early Sunday at low and lowering freezing levels. The snowfall should be accompanied by generally increasing winds and slowly lowering freezing levels. Light to moderate showers and slightly decreasing winds are expected early-mid Sunday following the first of several upper troughs behind the front; however, slightly increasing showers and winds are expected later Sunday with a secondary upper and surface trough, with heaviest showers likely in the south and in the central Cascades in convergence. Yet another and stronger disturbance is expected to move over the area later Monday and Tuesday. EXTENDED FORECAST FOR FRIDAY THROUGH SUNDAY Friday: Mostly sunny and continued cool, especially north, Cascade east slopes and near the Cascade passes Friday night: increasing high clouds Saturday: increasing clouds and winds with light snow developing later morning Olympics and Saturday afternoon Cascades Saturday night: windy and cool with light to moderate snow Sunday: light to moderate showers decreasing in the morning, slightly increasing mid-late Sunday especially in the south and in the central Cascades in convergence * SNOW LEVELS Sea level N and S early Friday Sea level N and C, 1-2000 ft Olympics, 3-5000 ft S late Friday Sea level to 500 ft N and C, 3-5000 ft S early Saturday Sea level N and C, 1-3000 ft S late Saturday Sea level N and C, 1-2000 ft S early Sunday Sea levels N and S late Sunday, except snow levels remaining at the surface Cascade passes and east slopes Friday and Saturday, rising to near free air levels early Sunday