100 PM PST THU NOV 29 2007 WEATHER SYNOPSIS FOR THURSDAY AND FRIDAY An upper level disturbance continues to move southward Thursday afternoon and is mainly affecting the Mt Hood area and extreme southern Washington Cascades where light to occasionally moderate snowfall is being received along with moderate northwest ridgetop winds. Only minor and very light sow showers remain in the wake of the feature over most of the west and east slopes of the Cascades and the Olympics Thursday afternoon. A cool northerly flow aloft is directing these generally weak disturbances through the area. As the feature slowly moves southward later Thursday evening, precipitation and winds should slowly decrease over the Mt Hood area. A relative break in the action is expected Friday with continued cold temperatures in a weak northerly flow aloft. A few light snow showers may linger in the south under very weak flow. The next disturbance is expected to develop off Vancouver Island Friday night and begin affecting the forecast area later Saturday. This system should produce light snow at cold temperatures Saturday afternoon as it moves southward. WEATHER FORECAST FOR THURSDAY AND FRIDAY * OLYMPICS- Thursday afternoon and night: Mostly cloudy with possible light snow showers. Friday and Friday night: Mostly cloudy with a chance of light snow showers. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST NORTH OF MT RAINIER- * CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Thursday afternoon and night: Mostly cloudy with possible light snow showers. Friday and Friday night: Mostly cloudy with a slight chance of light snow showers. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST MT RAINIER SOUTHWARD- Thursday afternoon and night: Cloudy with decreasing light snow showers. Friday morning: Mostly cloudy with occasional light snow showers. Friday afternoon and night: Mostly cloudy with a chance of light snow showers. * EAST SLOPES WASHINGTON CASCADES- Thursday afternoon and night: Mostly cloudy with possible light snow showers. Friday and Friday night: Mostly cloudy with a slight chance of light snow showers. * MT HOOD AREA- Thursday afternoon and evening: Light to occasionally moderate snow showers. Thursday night: Decreasing light snow showers. Friday morning: Mostly cloudy with occasional light snow showers. Friday afternoon and night: Mostly cloudy with a chance of light snow showers. SNOW LEVELS-CASCADE MTNS 500 ft N, 1500 ft C, 2000 ft S Thursday afternoon and night Near sea level N and C, 1000 ft S Friday and Friday night SNOW LEVELS-OLYMPIC MTNS Near sea level Thursday night through Friday 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 FRI SAT * HURRICANE RIDGE LT .10 LT .10 * MT BAKER LT .10 LT .10 * WASHINGTON PASS LT .10 LT .10 * STEVENS PASS LT .10 LT .10 * SNOQUALMIE PASS LT .10 LT .10 * MISSION RIDGE LT .10 LT .10 * CRYSTAL MTN .25 LT .10 * PARADISE .25-.5 LT .10 * WHITE PASS .25-.5 LT .10 * MT HOOD .5-.75 LT .10 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS E 5-10 Thursday aft through Friday night * FREE WINDS AT 5000 FT SE 5-15 N, WNW 20-30 S Thursday afternoon SE 5-15 N, WNW 10-20 S Thursday evening and night SE 5-15 Friday morning and aft SW 5-15 Friday night * FREE WINDS AT 9000 FT N-NW 5-15 N, NW 20-30 S Thursday afternoon N 5-15 N, NW 10-20 S Thursday evening W 5-15 Friday and Friday night EXTENDED WEATHER SYNOPSIS FOR SATURDAY THROUGH MONDAY A cool north to northwest flow should persist over the Northwest Saturday. A developing disturbance is expected to form off Vancouver Island Saturday and bring increasing generally light to moderate precipitation over the mountain areas beginning Saturday afternoon and increase through Sunday morning. Freezing levels should remain low through Sunday morning. Winds should begin increasing and becoming strong Saturday evening and increasing further through early Sunday. A major change in the weather pattern is expected Sunday through Monday. A strong southwest flow is expected to undercut the northerly branch that has been persistent recently. This should usher in a strong frontal boundary later Sunday through Monday. Heavy precipitation, rapidly and substantially rising freezing levels are expected later Sunday into Monday. Current model runs also indicate extremely windy conditions should develop over the region Sunday night and Monday as well. Free level winds are forecast to be from 70 to 90kts at near the 5000 ft. elevation and near 100 kts near 7000 ft. EXTENDED FORECAST FOR SATURDAY THROUGH MONDAY Saturday: Cloudy with light snow developing in the afternoon. Saturday night: Light snow. Sunday morning: Light to occasionally moderate snow Sunday afternoon and night: Increasing moderate to heavy rain or snow with rapidly rising snow levels. Monday and Monday night: heavy rain or snow and very windy with further rising freezing levels. * SNOW LEVELS Near sea level N and C, 1000 ft S Sat Near sea level N and C, 2000 ft S Sun morn 2500 ft N, 3500 ft C, 7000 ft S Sun aft 4500 ft N, 5000 ft C, 8000 ft S Sun night 6000 ft N, 7000 ft C, 9000 ft S Mon and Mon night