1 PM PST TUE JAN 22 2008 WEATHER SYNOPSIS FOR TUESDAY AND WEDNESDAY The upper level flow situation affecting the Northwest early Tuesday morning centers around a moderate to strong upper ridge in the eastern Pacific that is becoming increasingly positively tilted and leaning into north-central BC early Tuesday afternoon. This ridge is forcing the main storm track northward into Alaska, eastward across the Yukon, and then southward just east of the Rockies into the Midwest US. Meanwhile, the upper ridge to the north-northwest of Washington is also producing an associated weaker, dry and relatively cold northeasterly flow across the area into a deepening upper low just west of San Francisco, Ca. Associated flow around this southern low is producing light to moderate precipitation in south-central California with strongest associated winds over the Northwest slowly decreasing and moving southward. Over the next 24-48 hours, several upper level disturbances are expected to slowly weaken and force the ridge south and eastward with the ridge moving over south-central BC by late Tuesday and into southern BC and northern Washington on Wednesday. Initially, this should maintain mostly fair skies Tuesday and Wednesday while also producing further slowly diminishing east to northeasterly winds at mid and upper levels and slight warming aloft, mainly in the Olympics and in the southern Washington Cascades and Mt Hood area. However, a weak to moderate easterly surface pressure gradient should maintain light to moderate and continued relatively cold easterly winds through the Cascade passes. WEATHER FORECAST FOR TUESDAY AND WEDNESDAY * OLYMPICS- Tuesday afternoon: mostly fair and cool Tuesday night: fair and cold Wednesday: mostly fair and slightly warmer Wednesday night: increasing clouds late with light snow showers developing early Thursday * WASHINGTON CASCADES NEAR AND WEST OF THE CREST- * CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Tuesday afternoon: mostly fair and continued cold Tuesday night: fair and cold Wednesday: mostly fair and a little warmer, especially south, but continued cool to cold in the passes Wednesday night: increasing high clouds north, otherwise continued mostly fair * EAST SLOPES WASHINGTON CASCADES- Tuesday afternoon: mostly fair and continued cold Tuesday night: fair and cold Wednesday: mostly fair and a little warmer, especially higher terrain south, but continued cool to cold in lower elevations and near the passes Wednesday night: increasing high clouds north, otherwise continued mostly fair and cold, especially lower terrain * MT HOOD AREA- Tuesday afternoon: mostly fair and continued cold Tuesday night: fair and cold Wednesday: mostly fair and warmer higher terrain, but continued cool lower elevations Wednesday night: few high clouds otherwise continued mostly fair FREEZING LEVELS-CASCADE MTNS Sea level N and S Tuesday afternoon through Wednesday morning Sea level N and C, 6500 ft S Wednesday afternoon and night, except remaining at the surface lower terrain Cascade east slopes and passes through Wednesday night FREEZING LEVELS-OLYMPIC MTNS 1000 ft Tuesday afternoon 5000 ft Tuesday night and Wednesday morning 2000 ft Wednesday afternoon Sea level Wednesday night, except remaining near sea level lower valleys Tuesday and Wednesday, especially east and north slopes 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 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 0 * WHITE PASS 0 0 * MT HOOD 0 0 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS E 5-15 with occasional higher gusts Tuesday afternoon E 10-15 Tuesday night and Wednesday morning E 5-15 Wednesday afternoon E 10-15 Wednesday night * FREE WINDS AT 5000 FT E-SE 5-15 N, SE 10-20 S Tuesday afternoon SE 5-15 N, 15-25 S Tuesday night S 5-15 N, SE 1015 S Wednesday morning S 5-15 Cascades, W 5-15 Olympics Wednesday afternoon SW 10-20 N, S 5-15 S Wednesday night * FREE WINDS AT 9000 FT NE 10-20 N, E 10-15 S Tuesday afternoon NE 5-15 N, E 5-15 S Tuesday night NW 5-15 N, E 5-15 S Wednesday morning W 15-20 N, E 0-10 S Wednesday afternoon W-SW 20-40 N, 15-30 C, 10-20 S Wednesday night EXTENDED WEATHER SYNOPSIS FOR THURSDAY THROUGH SATURDAY While all longer range forecast models agree that the recent blocking ridge should move eastward and allow a moderate frontal system and associated short wave trough to slide southward along the southern BC coast toward the Northwest late Wednesday, a large amount of variability exists as to the track of this disturbance as it moves southward over the western US. The most recent run of the primary longer range US forecast model, the GFS, indicates that the associated surface and upper level low should move southward just off the Washington coast Thursday and move into Oregon by early Friday. With this revised solution, this weather system should brush the Olympics and Mt Hood area with light snow, but produce only increased clouds and some light showers or flurries in most of the remainder of the Cascades, with freezing levels continuing near sea level. In any case, relatively minor amounts of snowfall are likely in all areas. Most other forecast models indicate a southerly track of the front and upper low slightly further to the west, with only the Olympics and Mt Hood area being brushed by the disturbance as it passes mostly offshore and then more strongly affecting south-central Oregon and north-central California. Following this disturbance, the upper ridge should briefly rebuild over southern BC and sag southward over the area on Friday. This should produce decreasing clouds and light showers early Friday, with a brief clearing trend developing on Friday. There appears to be more consensus in the longer range models for the weekend, when a moderate to strong and relatively broad, cool upper trough is expected to force the ridge eastward and take up residence just offshore. Several moderate weather systems rotating out of this deep trough should move over the area Saturday and Sunday, producing periods of moderate to occasionally heavy snow at very low freezing levels and generally increased winds Saturday, with a secondary upper and surface disturbance producing light to moderate snow mid-late Sunday, heaviest in the south. EXTENDED FORECAST FOR THURSDAY THROUGH SATURDAY Thursday morning: increasing clouds and light snow spreading slowly southward, primarily affecting the Olympics and Mt Hood area with mainly light snow showers or a few flurries for most of the Washington Cascades. Mid-late Thursday: light showers decreasing from the north Early-mid Friday: decreasing clouds with showers or flurries ending Mid-late Friday: clearing trend Friday night: increasing clouds with light to moderate snow developing Olympics and north Cascades overnight Saturday: light to moderate snow developing and increasing * SNOW LEVELS Sea level N and S Thursday through Saturday