130 PM PST FRI JAN 18 2008 WEATHER SYNOPSIS FOR THURSDAY AND FRIDAY A strong large upper level ridge remains over the northeast Pacific Ocean. This should cause north flow aloft over the Northwest on Friday with some low clouds over the west lowlands and some mid or high clouds over the Olympics and north Cascades. A warm air mass in the ridge is helping cause some warmer temperatures at higher sites Friday. A down-slope wind effect may have helped cause warm temperatures at higher elevations on Mt Hood Meadows on Thursday and again Friday. But inversion conditions are causing cooler temperatures at lower sites Friday. A short wave should move over the ridge on Saturday with a surface low pressure system moving from BC Saturday morning to Montana Saturday night. This should cause increasing clouds and possible light snow showers by Saturday early morning in the Olympics and north Cascades. This weather system should spread increasing light to moderate snow showers to the Olympics and Cascades mainly near and west of the crest Saturday. A west-east oriented Arctic front should move south over the Northwest Saturday night. This should cause cooling temperatures and light snow showers to shift from the Olympics and north Cascades to the south Cascades Saturday night with the main showers near and west of the crest. WEATHER FORECAST FOR THURSDAY AND FRIDAY * OLYMPICS- Friday: Partly sunny. Friday night: Increasing clouds with chance of light snow showers early Saturday. Saturday: Increasing light to moderate snow showers. Saturday night: Light snow showers decreasing and ending. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST-CASCADE PASSES INCLUDING STEVENS, SNOQUALMIE, WHITE PASSES- Friday: Partly sunny north and mostly sunny central and south. Friday night: Increasing clouds especially north part with chance of light snow showers Snoqualmie north. Saturday: Increasing light to moderate snow showers. Saturday night: Light snow showers decreasing and ending. * EAST SLOPES WASHINGTON CASCADES- Friday: Sunny. Friday night: Increasing high clouds especially north part. Saturday: Increasing light snow showers. Saturday night: Light snow showers decreasing and ending. * MT HOOD AREA- Friday: Sunny. Friday night: Increasing high clouds. Saturday: Increasing light to moderate snow showers. Saturday night: Decreasing light to moderate snow showers. FREEZING LEVELS-CASCADE MTNS 6000 ft N, 7000 ft S Fri aft 5000 ft N, 6000 ft S Fri eve except remaining at the surface many sites below 4-5000 feet Friday. SNOW LEVELS-CASCADE MTNS 2000 ft N, 3000 ft C, 5000 ft S Sat morn 1000 ft N, 2000 ft S Sat aft and eve FREEZING LEVELS-OLYMPIC MTNS 5000 ft Fri morn 6000 ft Fri aft 5500 ft Fri eve SNOW LEVELS-OLYMPIC MTNS 4000 ft Sat morn 1500 ft Sat aft and eve 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 SAT SUN * HURRICANE RIDGE LT .25 .25-.5 * MT BAKER LT .25 .25-.5 * WASHINGTON PASS LT .10 .25 * STEVENS PASS LT .10 .25-.5 * SNOQUALMIE PASS LT .10 .25-.5 * MISSION RIDGE 0 LT .25 * CRYSTAL MTN 0 .25 * PARADISE 0 .25-.5 * WHITE PASS 0 .25-.5 * MT HOOD 0 .25-.5 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS W 0-10 Fri aft and eve W 5-15 Sat morn W 10-20 Sat aft and eve * FREE WINDS AT 5000 FT NW 10-20 Fri aft NW 15-25 Fri eve W 20-30 strongest south part Sat NW 15-25 strongest south part Sat night * FREE WINDS AT 9000 FT NW 20-30 Fri aft NW 30-40 Fri eve W 30-40 Sat morn W 30-40 Sat aft strongest south part NW 25-35 strongest south part Sat night EXTENDED WEATHER SYNOPSIS FOR SUNDAY THROUGH TUESDAY The strong large upper ridge over the northeast Pacific should become dominant again Sunday through Tuesday. Surface high pressure and a cold Arctic air mass should shift from BC Sunday to the northwest US Monday and Tuesday. This should cause lingering light snow showers over the Olympics and Cascades to end Sunday morning. Mostly sunny days and mostly clear nights should be seen Monday and Tuesday with cold temperatures. Strong northeast crest levels winds are indicated Monday mainly over the south Cascades and Mt Hood area. EXTENDED FORECAST FOR SUNDAY THROUGH TUESDAY Sunday morning: Light snow showers mainly near and west of the crest ending. Sunday afternoon and evening: Partly cloudy. Monday and Tuesday: Mostly sunny days and mostly clear nights. Especially cool and windy south Cascades and Mt Hood. * SNOW LEVELS Near sea level N, 1000 ft S Sun FREEZING LEVELS Near sea level N and S Mon and Tue