####018011533#### WWUS86 KSEW 232131 SABNW MOUNTAIN WEATHER FORECAST FOR THE OLYMPICS WASHINGTON CASCADES AND MT HOOD AREA NORTHWEST WEATHER AND AVALANCHE CENTER SEATTLE WASHINGTON 130 PM PST FRI JAN 23 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-ORZ011-241700- && WEATHER SYNOPSIS FOR FRIDAY AND SATURDAY High over low, low over high Doesnt much matter as it looks pretty dry. A weak system moving through later tomorrow Brings further cooling and a few flakes to borrow. Ridging rebuilds on Sunday it seems, Bringing an end to snow covered dreams. Clearing and cold by late in the day, Not much until Tuesday so the models say. So if you like crusts youre in for a treat Though weakening further as they lose more heat. With shallow new or hoar lying over the crust Weather watching shifts from maybe to must. Much of the Northwest lies under a very weak col or area of little flow that lies sandwiched between a developing closed low about 400 miles west of Los Angeles and some remnants of the old dominant ridge that extends to its north into the south-central BC coast. With a weak but gradually increasing offshore surface flow and relatively weak winds aloft, this weather pattern should help to maintain a weak temperature and moisture inversion in most areas Friday, especially near the Cascade passes. However, freezing levels have generally lowered and are producing a more limited inversion than during much of the past week. Also, some thin and patchy mid and high clouds are slowly lifting northward in a weak deformation zone associated with the weak southerly flow around the California low. However, these should mostly dissipate as they spread northward Friday afternoon, being replaced by further cloudiness associated with a newly arriving though very weak disturbance moving though the offshore ridge. As this weak upper disturbance passes through the offshore ridge and slowly moves southward across the region late Friday into early Saturday, and a second trough slightly reinforces the disturbance mid-late Saturday, this should allow increasing mid and high clouds to spread southward over the area late Friday into early Saturday, with further clouds and some light snow or snow showers spreading southward mid-late Saturday. While only very light new snow accumulations are expected, and these mainly in the south, this slowly changing weather pattern should also produce significant cooling from the recent rather mild mid-winter temperatures at mid and higher elevations along with gradually increasing ridgetop winds. && WEATHER FORECAST FOR FRIDAY AND SATURDAY *OLYMPICS- Friday afternoon: mostly sunny with increasing high clouds late Friday night: increasing mid and high clouds Saturday morning: partly cloudy and cooler Saturday afternoon: becoming mostly cloudy with light snow or snow showers developing Saturday night: colder with occasional light snow or light snow showers; light showers, heaviest north slopes, decreasing early Sunday *WASHINGTON CASCADES NEAR AND WEST OF THE CREST- Friday afternoon: variable high clouds spreading northward Friday night: increasing mid and high clouds Saturday morning: partly cloudy and cooler Saturday afternoon: becoming mostly cloudy with light snow or snow showers developing Saturday night: colder with occasional light snow or light snow showers, heaviest south *CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Friday afternoon: cool with clouds and fog persisting lower terrain east slopes and near the passes below about 3000 feet; otherwise variable high clouds spreading northward Friday night: cool with clouds and fog persisting lower terrain; otherwise increasing mid and high clouds Saturday morning: cooler and mostly cloudy lower elevations, otherwise partly cloudy higher elevations Saturday afternoon: becoming mostly cloudy all areas with light snow or snow showers developing Saturday night: occasional light snow or light snow showers, heaviest south *EAST SLOPES WASHINGTON CASCADES- Friday afternoon: cool with clouds and fog persisting lower terrain; otherwise variable high clouds Friday night: cold with clouds and fog persisting lower terrain; otherwise increasing mid and high clouds Saturday morning: cold and mostly cloudy lower elevations, otherwise partly cloudy and cooler higher elevations Saturday afternoon: partly to mostly cloudy all areas with light snow or snow showers developing, mainly higher terrain Saturday night: cold and mostly cloudy with occasional light snow or light snow showers, heaviest south *MT HOOD AREA- Friday afternoon: variable high clouds Friday night: increasing mid and high clouds Saturday morning: partly cloudy and cooler Saturday afternoon: becoming mostly cloudy with light snow or snow showers developing Saturday night: colder with light snow or light snow showers && FREEZING LEVELS-CASCADE MTNS 3000 ft N, 6000 ft C, 7500 ft S Friday afternoon 3000 ft N, 5500 ft C, 7500 ft S Friday night 2500 ft N and C, 6500 ft S Saturday morning...except freezing levels remaining at the surface Cascade passes and east slopes through Saturday morning SNOW LEVELS-CASCADE MTNS 1000 ft N, 1500 ft C, 2500 ft S mid-day 500 ft N, 1500 ft C, 3000 ft S Saturday afternoon 500 ft N and C, 1000 ft S Saturday evening Sea level N and C, 1000 ft S later Saturday night...except snow levels remaining at the surface Cascades passes and east slopes from Snoqualmie Pass northward through Saturday evening, but rising to near free air levels southern Cascades and Mt Hood area Saturday afternoon and night FREEZING LEVELS-OLYMPIC MTNS 6000 ft Friday afternoon 5000 ft Friday night 3000 ft Saturday morning...except freezing levels locally at the surface lower valleys early morning hours SNOW LEVELS-OLYMPIC MTNS 1500 ft mid-day 1000 ft Saturday afternoon and evening 500 ft later Saturday 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 SAT SUN *HURRICANE RIDGEO LT .10 *MT BAKER 0 LT .10 *WASHINGTON PASS0 LT .10 *STEVENS PASS 0 LT .10 *SNOQUALMIE PASS0 LT .10 *MISSION RIDGE 0 LT .10 *CRYSTAL MTN 0 LT .10 *PARADISE 0 LT .25 *WHITE PASS 0 LT .25 *MT HOOD 0 LT .25 && WINDS IN MILES PER HOUR (MPH) *CASCADE PASS LEVEL WINDS E 10-20 Friday afternoon E 5-15 later Friday afternoon and night E 5-15 Saturday morning E 5-15 Saturday afternoon E 10-20 Saturday night *FREE WINDS AT 5000 FT E-SE 10-20 Cascades, SW 5-15 Olympics Friday afternoon S-SE 5-15 Cascades, W 5-10 Olympics Friday night Variable 5-15 Cascades, NW 5-15 Olympics Saturday morning N-NE 10-15 N and Olympics, W-NW 5-15 S Saturday afternoon N-NE 10-20 N and Olympics, W-NW 10-20 S Saturday night *FREE WINDS AT 9000 FT SW 10-15 Friday afternoon W-SW 10-15 N, 5-15 S Friday night W 10-20 Cascades, W-NW 10-20 Olympics Saturday morning NW 15-25 N, 15-30 S and 20-35 Olympics Saturday afternoon N-NW 10-15 N, 15-25 S and 20-35 Olympics Saturday night N 10-20 Cascades, 15-30 Olympics early Sunday && EXTENDED WEATHER SYNOPSIS FOR SUNDAY THROUGH TUESDAY As the very weak upper trough moves further southward in Oregon and into California on Sunday and a briefly colder north to northeasterly flow establishes ahead of rebuilding offshore ridging, associated clouds and light showers should decrease Sunday morning. As strong surface high pressure drops southward to the east of the area, and an increasingly dry northeasterly flow establishes mid-day and Sunday afternoon, this should spread a slow clearing trend southward mid-day into Sunday night along with quite cold overnight temperatures and generally increased east winds. Residual weak ridging and continued northeasterly flow into Monday morning should help maintain mostly fair but cold skies in most areas above some shallow areas of low clouds or fog along the Cascade east slopes. The weakening upper ridge should be progressively flattened and forced eastward by several incoming weather systems later Monday into Tuesday. The southern fringe of the first such disturbance should brush the Olympics and northern WA Cascades Monday afternoon and evening, bringing increased clouds and a chance of some light snow or snow showers in the north, but little more than variable mid or high clouds further south. This should be followed by a second stronger weather disturbance that further flattens the ridge early Tuesday. Clouds and light to moderate precipitation associated with this moderate upper trough and front should increase in the north and Olympics Tuesday morning and spread into the central Cascades by mid-day and the southern Cascades and Mt Hood area Tuesday afternoon and evening. While slight warming and increased winds are also expected, light to moderate snowfall is expected in most areas mid- late Tuesday into early Wednesday. EXTENDED FORECAST FOR SUNDAY THROUGH TUESDAY Sunday morning: decreasing light snow or snow showers, mainly south, with cooling and slow clearing north and central Sunday afternoon and night: clearing trend spreading southward Sunday afternoon becoming mostly fair and cold Sunday night Monday morning: mostly fair and cold Monday afternoon and night: increasing clouds with chance of light snow or snow showers north and Olympics; otherwise variable mid and high clouds south and central Tuesday: increasing clouds with light to moderate snow spreading southward SNOW LEVELS Sea level to 500 ft N, 500 to 1000 ft S Sunday through Monday morning 500 to 1500 ft N, 1-2000 ft S Monday afternoon and night 1-2000 ft N, 1-3000 ft S Tuesday 1-3000 ft N, 2-4000 ft S late Tuesday...except snow levels at the surface Cascade passes and east slopes Sunday through Monday morning, rising to near free air levels later Monday afternoon through Tuesday 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 $$