1230 PM PST TUE JAN 15 2008 WEATHER SYNOPSIS FOR TUESDAY AND WEDNESDAY Following a strong front and associated upper trough that blasted through the region mid-late Monday and are now in eastern Montana, a generally cool, drier and slowly decreasing northwesterly flow ahead of strong offshore upper ridging produced decreasing showers and gradually diminishing winds in most areas Tuesday morning. This shift toward a drier and cooler northerly flow also weakened a moderate Puget Sound convergence that produced locally heavy snowfall near Stevens Pass overnight, with the convergence slowly shifting southward and dissipating during the morning hours. As the upper flow further dries and turns more northerly Tuesday afternoon and night, this should allow for scattered light showers to end in most areas by later Tuesday afternoon with slow clearing but continued cool conditions spreading southward during the afternoon and evening hours. Although the northerly flow should maintain mostly dry weather in most areas in the southern and central Washington Cascades and Mt Hood area on Wednesday, some mid and upper level moisture associated with a moderate warm front moving over and through the offshore ridge should move southward through the area later Tuesday night and Wednesday while slowly thinning and dissipating. This should result in considerable mid and high clouds in the north along with a chance of a few flurries; further south considerable sunshine is likely through more variable and thin high clouds. While relatively light winds are likely at lower and mid elevations, moderate northerly winds should persist near higher ridgelines in a moderate northerly flow aloft. WEATHER FORECAST FOR TUESDAY AND WEDNESDAY * OLYMPICS- Mostly sunny Tuesday afternoon. Mostly fair Tuesday evening with increasing mid and high clouds later Tuesday night and early Wednesday. Areas of fog lower terrain with considerable mid and high clouds higher elevations Wednesday and Wednesday night with a chance of flurries, mainly north slopes. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST FROM STEVENS PASS NORTHWARD- * CASCADE PASSES FROM STEVENS PASS NORTHWARD, INCLUDING STEVENS PASS- * EAST SLOPES WASHINGTON CASCADES FROM STEVENS PASS NORTHWARD - Scattered light showers mid-day decreasing and becoming mostly sunny Tuesday afternoon. Mostly fair Tuesday evening. Increasing mid and high clouds later Tuesday night and early Wednesday. Areas of fog lower valleys early Wednesday otherwise considerable mid and high clouds higher elevations Wednesday and Wednesday night with a chance of flurries, mainly extreme north. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST SOUTH OF STEVENS PASS, - * CASCADE PASSES SOUTH OF STEVENS PASS, INCLUDING SNOQUALMIE AND WHITE PASSES- * EAST SLOPES WASHINGTON CASCADES SOUTH OF STEVENS PASS - Scattered light snow showers decreasing early-mid afternoon becoming mostly sunny later Tuesday afternoon. Mostly fair Tuesday evening. Increasing high clouds spreading southward later Tuesday night and early Wednesday. Areas of fog lower valleys early Wednesday otherwise considerable filtered sunshine through variable mid and high clouds higher elevations Wednesday and Wednesday night. * MT HOOD AREA- Scattered light snow showers decreasing and becoming partly to mostly sunny later Tuesday afternoon. Mostly fair Tuesday evening. Increasing high clouds spreading southward later Tuesday night and early Wednesday. Areas of fog lower valleys early Wednesday otherwise considerable filtered sunshine through variable mid and high clouds higher elevations Wednesday and Wednesday night. SNOW LEVELS-CASCADE MTNS Sea level N and S Tuesday afternoon FREEZING LEVELS-CASCADE MTNS Sea level N and S Tuesday night and Wednesday morning Sea level N and C, 5000 ft S Wednesday afternoon Sea level N and C, 7000 ft S Wednesday night SNOW LEVELS-OLYMPIC MTNS Sea level Tuesday afternoon FREEZING LEVELS-OLYMPIC MTNS Sea level Tuesday night and Wednesday morning 6000 ft Wednesday afternoon 7000 ft Wednesday 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 WED THU * HURRICANE RIDGE LT .10 LT .10 * MT BAKER LT .10 LT .10 * WASHINGTON PASS LT .10 LT .10 * STEVENS PASS LT .10 0 * SNOQUALMIE PASS LT .10 0 * MISSION RIDGE LT .10 0 * CRYSTAL MTN LT .10 0 * PARADISE LT .10 0 * WHITE PASS LT .10 0 * MT HOOD LT .25 0 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS W 5-15 with occasional higher gusts mid-day W 5-15 Tuesday afternoon Variable 0-10 Tuesday night and Wednesday morning W 0-10 Wednesday afternoon and night * FREE WINDS AT 5000 FT N-NW 10-20 Cascades, N 15-30 Olympics Tuesday afternoon N 15-25 Cascades, 20-40 Olympics Tuesday night N 15-25 N, 10-20 S Wednesday morning N 15-30 N and Olympics, 10-20 S mid-day N-NW 15-30 Cascades, strongest north, and 20-40 Olympics Wednesday afternoon N-NW 15-30 Cascades, 25-40 Olympics Wednesday night * FREE WINDS AT 9000 FT N-NW 20-40 Cascades, 30-50 Olympics Tuesday afternoon N 20-40 Cascades 30-50 Olympics Tuesday night and Wednesday morning N-NW 25-40 Wednesday afternoon N-NW 30-45 N, 20-40 S Wednesday night EXTENDED WEATHER SYNOPSIS FOR THURSDAY THROUGH SATURDAY The strong upper ridge about 3-4000 miles off the Washington coast early Thursday should move very slowly eastward mid- late Thursday and Friday, with most energy from a weakening but still moderate storm system moving over the top of the ridge and then southeastward along the Rocky Mountains Wednesday through early-mid Thursday. Although variable mid and high moisture from this disturbance should continue to affect the region through Wednesday morning, mainly in the form of mid and high clouds and a chance of flurries in the north, clearing skies are expected mid-late Thursday through early-mid Friday as the disturbance moves further southward well to the east of the region. As the ridge slowly nudges eastward, slowly rising freezing levels are expected along with continue moderate winds near higher ridges and relatively light winds at most lower and mid elevations. However, by mid-late Friday, a moderate upper trough and associated surface front are expected to move through the ridge and start to slowly sink southward along the BC coast later Thursday through early Friday, moving to just north of the area by later Friday. As this disturbance, which is expected to carve out an east-west oriented trough in the otherwise northerly flow aloft, moves southward over the Northwest late Friday into Saturday, lowering clouds, lowering freezing levels and increasing light to moderate snow should spread southward on Saturday. Briefly increased winds should also accompany the disturbance. Behind the disturbance later Saturday, decreasing clouds, showers and winds are expected to spread quickly southward, with more strongly building offshore ridging promising a return to mostly fair but cool weather likely by Sunday into early next week. EXTENDED FORECAST FOR THURSDAY THROUGH SATURDAY Cool with considerable mid and high clouds north and a chance of a flurry early-mid Thursday. Otherwise, slow warming aloft with considerable sunshine through variable high clouds south and central. Clouds decreasing becoming mostly fair and slightly warmer mid-late Thursday through early-mid Friday. Increasing clouds mid-late Friday with increasing winds, rapid cooling and increasing light to moderate snow spreading southward Friday night and early-mid Saturday. Continued cool with decreasing showers and winds spreading southward mid-late Saturday. * FREEZING LEVELS Sea level N and C, 6-8000 ft S and Olympics early Thursday Sea level to 1000 ft N, 1-3000 ft C and 7-9000 ft S and Olympics late Thursday through early Friday Sea level to 1000 ft N, 3-5000 ft C, 7-9000 ft S mid-late Friday * SNOW LEVELS 500 to 1500 ft N, 1-2000 ft C, 1-3000 ft S Saturday 500 to 1500 ft N and S late Saturday