215 PM PST FRI FEB 01 2008 WEATHER SYNOPSIS FOR FRIDAY AND SATURDAY A broad and moderate to strong upper lies over the Cascades early Friday afternoon, with strongest associated flow over Oregon. However, moderate westerly flow combined with considerable instability showers in the trough helped maintain moderate to occasionally heavy snow or snow showers at continued relatively low snow levels in most areas near and west of the Cascade crest Friday morning with generally lighter snowfall along the Cascade east slopes. As the trough moves further east Friday afternoon, this should for slightly and briefly decreasing showers in most areas; however, moderate to occasionally heavy showers should continue in a weak Puget Sound convergence near Stevens and Snoqualmie Passes through much of the afternoon before gradually weakening and dissipating Friday evening. Also, satellite pictures indicate an enhanced shower band moving onshore currently. This should move into the southern Cascades later Friday afternoon and the north-central Cascades Friday evening, bringing another surge of snowfall. While another brief and slight decrease in showers should follow this band for a few hours overnight, any respite should be very brief, especially in the southern Washington Cascades and Mt Hood area which should be hardest hit by the next incoming Pacific storm system late Friday night and Saturday. The next front and associated moderate upper trough are expected to initially head toward Oregon overnight and into early Saturday morning; however a second strongly developing front and upper trough should follow closely behind the first, with its circulation gradually lifting moisture from the first front northward over the area Saturday morning into early afternoon. This should result in increasing light to moderate snow spreading northward Saturday morning, with light snow north, moderate snow central and heavy snow south Saturday afternoon. Highly variable winds should accompany these disturbances, with lighter south to southeasterly winds in the north shifting to strengthening. As the second upper and surface disturbances move mostly south and east of the region late Saturday into early Sunday, decreasing showers should spread southward, with moderate snow changing to more showery precipitation in the south Sunday morning. WEATHER FORECAST FOR FRIDAY AND SATURDAY * OLYMPICS- Friday afternoon: moderate to occasionally heavy snow showers gradually decreasing Friday night: showers slightly increasing late Friday afternoon and evening, decreasing and becoming light to occasionally moderate Friday night Saturday morning: light snow showers increasing later Saturday morning Saturday afternoon: light to occasionally moderate snow Saturday afternoon and evening, heaviest south and southeast slopes Saturday night: light to moderate snow decreasing later Saturday night and becoming light showers early Sunday. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST- Friday afternoon: moderate to occasionally heavy snow showers slightly decreasing Friday afternoon, increasing late afternoon south and Friday evening north Friday night: showers decreasing and becoming light to occasionally moderate Saturday morning: light snow showers early Saturday, with light to moderate snow redeveloping in the south Mid-day Saturday: light to moderate snow increasing in the south and spreading northward later Saturday morning and early afternoon Saturday afternoon: showers increasing and becoming light to occasionally moderate snow north, moderate snow central and moderate to heavy south Saturday afternoon and evening. Saturday night: light to moderate snow decreasing in the north and central later Saturday night, but moderate snow continuing in the south. * CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Friday afternoon and evening: moderate to occasionally heavy snow showers Friday afternoon, heaviest near Stevens Pass in convergence. Moderate to occasionally heavy showers briefly increasing late afternoon south and Friday evening north. Friday night: showers decreasing and becoming light to occasionally moderate Friday night except moderate showers central Cascades. Saturday morning: light snow showers early Saturday, with light to moderate snow redeveloping from about White Pass southward. Mid-day Saturday: light to moderate snow increasing in the south and spreading northward later Saturday morning and early afternoon Saturday afternoon: snow becoming light to occasionally moderate north, moderate central and moderate to heavy south Saturday afternoon and evening Saturday night: light to moderate snow decreasing in the north and central later Saturday night, but moderate snow continuing in the south into early Sunday * EAST SLOPES WASHINGTON CASCADES- Friday afternoon: moderate showers gradually decreasing Friday afternoon and becoming light, except continued moderate higher terrain central Cascades near convergence Friday night: light to moderate showers late Friday afternoon south and Friday evening north, decreasing briefly later Friday night Saturday morning: snow increasing in the south early Saturday with light to moderate snow redeveloping in the south Saturday morning Mid-day Saturday and Saturday afternoon: snow spreading northward and increasing later Saturday morning and becoming light north, moderate central and moderate to occasionally heavy south Saturday afternoon Saturday night: snow decreasing in the north and central Saturday night with light to moderate snow continuing south. * MT HOOD AREA- Friday afternoon: moderate to heavy snow or snow showers slightly decreasing and becoming moderate mid afternoon, increasing late afternoon. Friday night: Snow increasing overnight Saturday: moderate to heavy snow Saturday Saturday night: moderate to heavy snow Saturday night, decreasing and becoming moderate early Sunday. SNOW LEVELS-CASCADE MTNS 500 ft N, 1000 ft S Friday afternoon through Saturday morning 1500 ft N and S Saturday afternoon 500 ft N, 1000 ft C, 2000 ft S Saturday night, except snow levels lowering to near the surface Cascade passes and east slopes early Saturday, remaining at the surface through early Sunday SNOW LEVELS-OLYMPIC MTNS 1000 ft later Friday morning and afternoon 500 ft Friday night and Saturday 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 .25 LT .25 * MT BAKER .5-.75 LT .25 * WASHINGTON PASS .5 LT .25 * STEVENS PASS .75 .25 * SNOQUALMIE PASS .75 .25-.5 * MISSION RIDGE LT .25 .25-.5 * CRYSTAL MTN .5 .5-.75 * PARADISE .75 .5-.75 * WHITE PASS .5-.75 .75 * MT HOOD 75 1 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS W 5-15 with occasional higher gusts Friday afternoon W 0-10 Friday night E 5-10 Saturday morning E 5-15 with occasional higher gusts mid-day and Saturday afternoon E 5-15 Saturday night * FREE WINDS AT 5000 FT W-SW 15-25 N, 20-35 S Friday afternoon and night SW 10-20 N, 15-25 C, 20-40 S Saturday morning S-SE 10-20 N, 15-25 C and S-SW 25-40 S mid-day SE 15-25 N and C, W 20-40 S Saturday afternoon E 15-25 N and C, S-SW 20-30 S Saturday night, decreasing late * FREE WINDS AT 9000 FT W 15-30 N, 20-40 S Friday afternoon and night W-SW 15-25 N, 20-30 S Saturday morning S-SE 15-25 N and C, W-SW 25-40 S mid-day S 10-20 N, SW 20-40 C, W-SW 30-45 S Saturday afternoon S 10-20 N, 15-25 C, and SW 25-40 S Saturday night, decreasing late EXTENDED WEATHER SYNOPSIS FOR SUNDAY THROUGH TUESDAY Following the most recent series of strong storm systems, a briefly drying northwesterly flow ahead of weak and relatively flat offshore ridging should bring decreasing light showers and some partial clearing to most areas on Sunday, along with briefly diminished winds at continued low freezing levels. However, considerable moisture spilling through and over the ridge should begin to move onshore Sunday night, with a moderate warm front ahead of the next strong Pacific frontal system expected to spread increasing light to moderate snow over most areas Monday along with slowly rising freezing levels and gradually strengthening winds. The first significant warming in some time should allow increasing rain or mixed rain and snow to spread up to the 3 to 4000 ft level later Monday into early Tuesday, with higher elevations receiving increasingly heavy snow and strong winds late Monday into Tuesday morning ahead of and with a very strong frontal system. As the front moves east of the area and the following strong upper trough moves onshore Tuesday afternoon, this should bring significant cooling and gradually shift heaviest snowfall southward into Oregon by late Tuesday. EXTENDED FORECAST FOR SUNDAY THROUGH TUESDAY Light showers north, light to moderate showers central and moderate snow south slowly decreasing early-mid Sunday. Light showers all areas Sunday afternoon with some brief partial clearing and relatively light winds. Winds and light snow gradually increasing overnight becoming light to moderate Monday morning. Gradually warmer with moderate snow increasing mid-late Monday. Very windy with moderate to heavy rain or snow Monday night and early-mid Tuesday. Cooler and windy with moderate to heavy snow Tuesday afternoon. Cool with heaviest snow slowly shifting southward late Tuesday. * SNOW LEVELS Sea level to 1000 ft N, 1-2000 ft S early Sunday Sea level to 500 ft N, 500-1500 ft S late Sunday and early Monday 1-2000 ft N, 1-3000 ft S mid-late Monday 1-3000 ft N, 2-4000 ft C and S later Monday night and early Tuesday 1-2000 ft N and C, 2-4000 ft S mid-day Tuesday 500-1500 ft N, 1-2000 ft S late Tuesday