MOUNTAIN WEATHER FORECAST FOR THE OLYMPICS WASHINGTON CASCADES AND MT HOOD AREA NORTHWEST WEATHER AND AVALANCHE CENTER SEATTLE WASHINGTON 145 PM PST THU FEB 05 2009 NWAC Program administered by: USDA-Forest Service with cooperative funding and support from: Washington State Department of Transportation National Weather Service National Park Service Washington State Parks and Recreation Commission Pacific Northwest Ski Area Association Friends of the Avalanche Center and other private organizations. This forecast is prepared primarily for federal, state and private snow safety programs in Washington and Northern Oregon. WAZ513-518-519-019-042-501-502-ORZ011-061700- && WEATHER SYNOPSIS FOR THURSDAY AND FRIDAY Blocking ridge, block no more, Let westerly flow through the door. Unfortunately this is wishful thinking, As troughs to our south are sinking. Splits and closed California lows, Are currently the biggest woes. The Southwest should become quite wet, With floods and mud slides a reasoned bet. Although weak moisture is moving north, Mainly light snow will issue forth. But don’t give up, it’s winter still, And cooling temps will produce a chill. The south and Hood should be the winners, Perhaps they are lacking sinners. But even a little is more than none, And alot of littles can still be fun. The primary circulation along the west coast early Thursday afternoon continues to center around a moderate closed upper low about just off the central California coast. The next incoming upper trough in the central Gulf of Alaska is expected to drop slowly southward Thursday afternoon, gradually merging with and broadening the California upper low later Thursday and Friday. This should keep the main frontal activity and heaviest associated precipitation well to the south of our area for the next several days. However, as the previously closed low opens and translates slowly eastward, increasing moisture from this low should gradually lift northward Thursday afternoon and night. Although precipitation amounts should decrease from south to north, increasing light rain or snow should reach the Mt Hood area early to mid afternoon, the south-central WA Cascades later Thursday afternoon and evening, and the northern WA Cascades Thursday night, with heaviest amounts expected in the south. The generally light precipitation in the north and light to briefly moderate precipitation in the south should be accompanied by slowly lowering freezing levels and a slight increase in winds, primarily in the south. A greatly weakened northern part of the incoming split trough should move over the region Friday morning. Combined with relatively weak westerly flow at all levels, again slightly stronger in the south, this should maintain light to occasionally moderate showers at further lowering freezing levels. However, gradually drier northerly flow preceding weak and briefly building upper ridging offshore mid-late Friday should result in decreasing light showers Friday afternoon with a slow clearing trend spreading southward Friday night. && WEATHER FORECAST FOR THURSDAY AND FRIDAY * OLYMPICS- Thursday afternoon: cooler and cloudy with light rain or snow developing late afternoon or early evening Thursday night: cool with occasional light rain or snow Friday morning: cooler with light to occasionally moderate snow showers decreasing late Friday afternoon: light snow showers ending with partial clearing Friday night: slow clearing trend * WASHINGTON CASCADES NEAR AND WEST OF THE CREST FROM SNOQUALMIE PASS NORTHWARD- Thursday afternoon: cooler and cloudy with light rain or snow spreading northward late afternoon and evening Thursday night: cool with occasional light rain or snow, heaviest south Friday morning: cooler with light to occasionally moderate snow showers Friday afternoon: light snow showers decreasing with partial clearing Friday night: scattered light showers ending with slow clearing trend * CASCADE PASSES FROM SNOQUALMIE PASS NORTHWARD, INCLUDING SNOQUALMIE AND STEVENS PASSES- Thursday afternoon: cooler and cloudy with light snow spreading northward late afternoon and evening Thursday night: cool with occasional light snow north and light snow or mixed rain and snow south Friday morning: cooler with light to occasionally moderate snow showers Friday afternoon: light snow showers decreasing with partial clearing Friday night: scattered light showers ending with slow clearing trend * WASHINGTON CASCADES NEAR AND WEST OF THE CREST SOUTH OF SNOQUALMIE PASS- * CASCADE PASSES SOUTH OF SNOQUALMIE PASS, INCLUDING WHITE PASS- Thursday afternoon: cooler and cloudy with light snow developing mid-late afternoon Thursday night: cool with light to occasionally moderate rain or snow Friday morning: cooler with light to moderate snow showers Friday afternoon: light snow showers decreasing with partial clearing Friday night: scattered light showers ending with slow clearing trend spreading southward * EAST SLOPES WASHINGTON CASCADES- Thursday afternoon: cooler and cloudy with occasional light snow or rain developing in the south mid-late afternoon, spreading slowly northward Thursday evening Thursday night: cool with occasional light snow north and light to occasionally moderate snow or mixed rain and snow south Friday morning: cooler with light to moderate snow showers, mainly higher terrain near the crest Friday afternoon: light snow showers higher terrain decreasing with partial clearing Friday night: scattered light showers ending with slow clearing trend spreading southward * MT HOOD AREA- Thursday afternoon: cooler with light rain or snow developing mid-afternoon, slowly increasing late afternoon and evening Thursday night: cool with light to moderate snow Friday morning: cooler with light to moderate snow showers Friday afternoon: light snow showers decreasing with partial clearing Friday night: scattered light showers ending with slow clearing trend late && SNOW LEVELS-CASCADE MTNS 6000 ft N, 7000 ft C and S early Thursday afternoon 5500 ft N and S later Thursday afternoon 4000 ft N, 4500 ft S Thursday night 3000 ft N, 4000 ft S Friday morning 2500 ft N, 3500 ft S mid-day 2500 ft N and S Friday afternoon 2000 ft N and S Friday night…except snow levels locally near the surface Cascade passes and lower terrain east slopes Thursday, rising gradually to free air levels Thursday night and early Friday SNOW LEVELS-OLYMPIC MTNS 5000 ft Thursday afternoon 4000 ft Thursday night 3000 ft Friday morning 2000 ft Friday afternoon 3000 ft 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 .25 LT .25 * MT BAKER LT .25 .25 * WASHINGTON PASS LT .25 LT .25 * STEVENS PASS LT .25 LT .25 * SNOQUALMIE PASS .25 LT .25 * MISSION RIDGE LT .25 LT .25 * CRYSTAL MTN .25 .25 * PARADISE .25 .25 * WHITE PASS .25 .25 * MT HOOD .5 .5 && WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS E 5-15 Thursday afternoon E 0-10 Thursday night Variable 0-10 late Thursday night or early Friday W 0-10 mid-late Friday morning W 5-15 Friday afternoon and night * FREE WINDS AT 5000 FT S 10-15 Cascades, S-SW 10-20 Olympics Thursday afternoon SW 10-15 N, 10-20 S and Olympics Thursday night W 10-15 N, 10-20 C and Olympics, 15-30 S Friday morning W 5-15 N, 10-20 S and N-NW 15-25 Olympics mid-day and early afternoon N 10-15 N and C, N-NW 15-25 S and Olympics later Friday afternoon N 10-20 N and S Friday night * FREE WINDS AT 9000 FT S-SW 10-20 N, 15-25 S Thursday afternoon SW 10-20 N and C, 20-40 S Thursday night W 15-25 N and C, 20-40 S Friday morning W 10-15 N and C, 15-30 S and N 10-20 Olympics mid-day N 10-20 N and C, W 10-20 S and N 20-40 Olympics Friday afternoon N 15-30 N and Olympics, N-NE 10-20 C and S Friday night && EXTENDED WEATHER SYNOPSIS FOR SATURDAY THROUGH MONDAY Following a relatively weak upper ridge and surface high that should result in briefly clearing skies Saturday morning, increasing high clouds and brief warming should spread over the region during the afternoon ahead of a moderate though slowly splitting offshore upper low and associated frontal system. As the first trough and front move over the region later Saturday night and Sunday morning, increasing winds and lowering freezing levels should accompany increasing light to briefly moderate rain or snow. However, the second and stronger trough and associated surface disturbance are expected to quickly drop southward along the coast Sunday afternoon through Monday morning, with a much weaker northern extension of the stronger southern trough expected to move over the area mid- late Monday. This should produce decreasing light showers Sunday afternoon, with some light showers or occasional light rain or snow slowly spreading northward on Monday at continued low freezing levels and generally light winds. EXTENDED FORECAST FOR SATURDAY THROUGH MONDAY Saturday morning: mostly sunny and cool Saturday afternoon: slight warming with increasing high clouds Saturday night: clouds lowering with light rain or snow developing in the Olympics and light showers Cascades Sunday morning: cooler with light to occasionally moderate snow Sunday afternoon: light showers decreasing Sunday night: light rain or snow Olympics and light showers Cascades Monday morning: light snow developing south slowly spreading northward Monday afternoon and night: light snow showers gradually decreasing with some partial clearing * SNOW LEVELS 1-3000 ft N and S Saturday morning 2-4000 ft N, 4-6000 ft S Saturday afternoon and evening 1-3000 ft N, 2-4000 ft S later Saturday night and Sunday morning 1-3000 ft N and S Sunday afternoon 500 to 1500 ft N, 1-2000 ft S Sunday night and Monday 500-1500 ft N and S late Monday NWAC weather data and forecasts are also available by calling 206-526-6677 for Washington, 503-808-2400 for the Mt Hood area, or by visiting our Web site at www.nwac.us. Moore/Northwest Weather and Avalanche Center $$