130 PM PST FRI DEC 14 2007 WEATHER SYNOPSIS FOR FRIDAY AND SATURDAY On the 14th of December, the snow appeared to me Shallow overall with a low to moderate instability. Late on the 14th of Dec, the snowpack seemed to be Ripe with weakness over something old and very crusty. On the 15th of December, the weather gave to me Increasing snow and winds and considerable instability. On the 16th of December, the snow appeared to be Heavily loaded and trending toward high instability. The last several days have produced relatively weak weather systems passing through the region in a generally cool northwesterly flow aloft down the backside of offshore ridging. The most recent disturbance in this series slowly exited the area early Friday morning after bringing up to 6 inches of snowfall late Thursday through early Friday, heaviest in the north-central Washington Cascades. Although the greatly weakened offshore ridge flattened and moved onshore and over the region late Friday morning and early afternoon, significant moisture spilling over and through the ridge has maintained partly to mostly cloudy skies in most areas along with diminishing light snow or light snow showers. As the ridge moves east of the area Friday afternoon, this should allow the warm front from the offshore frontal system to move mainly onshore in southern BC, with the weak southern fringe brushing the Olympics and northern Cascades later Friday afternoon and early evening. This should result in slightly and briefly rising freezing levels and generally increasing winds...southwesterly at higher elevations and cool easterly low level winds near the Cascade passes. The moderate cold front should follow closely Friday night, with increasing light snow reaching the Olympics and northern Cascades Friday evening and more significant and increased light to moderate snow reaching most of the remainder of the region late Friday night and early Saturday. With the front weakening somewhat as it moves southward, this should result in moderate to occasionally heavy snow in the Olympics and Washington Cascades from about Mt Rainier northward, with generally lighter amounts likely in the southern Washington Cascades and Mt Hood area. After frontal passage early-mid Saturday morning, the associated upper trough and moderate westerly flow should help maintain moderate showers in most areas Saturday morning, with a slight decrease likely mid-day before a secondary upper trough helps enhance moderate showers and bring further cooling mid-late Saturday afternoon and evening. Briefly decreasing showers and a slight decrease in winds should follow later Saturday night before increasing moisture and winds from a stronger frontal system move onshore mid-late Sunday morning. WEATHER FORECAST FOR FRIDAY AND SATURDAY * OLYMPICS- Cloudy and slightly warmer with light snow showers briefly decreasing early-mid Friday afternoon. Light rain or snow developing late Friday afternoon and evening, increasing and becoming mostly moderate snow Friday night and early Saturday, heaviest south and southwest slopes. Moderate snow decreasing later Saturday morning and mid- day and becoming light to occasionally moderate showers. Showers increasing Saturday afternoon and evening. Light to moderate showers briefly decreasing later Saturday night. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST- Mostly cloudy with light snow showers decreasing early- mid Friday afternoon along with brief partial clearing, mainly south and central. Light rain or snow developing in the north late Friday afternoon and evening, increasing and spreading southward Friday night. Moderate snow later Friday night and early Saturday, heaviest from about Mt Rainier northward. Snow decreasing and becoming more showery later Saturday morning and mid-day. Light to occasionally moderate snow showers increasing mid-late Saturday afternoon and evening and becoming moderate snow or snow showers. Showers briefly decreasing Saturday night. * CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Cloudy with scattered light snow showers decreasing early-mid Friday afternoon along with some brief partial clearing, mainly south. Light snow developing in the north late Friday afternoon and evening, increasing and spreading southward Friday night. Moderate snow late Friday night and early Saturday, heaviest north and central, with light to occasionally moderate snow in the south. Snow decreasing and becoming more showery later Saturday morning and mid-day. Light to occasionally moderate snow showers increasing mid-late Saturday afternoon and evening and becoming moderate snow or snow showers. Showers briefly decreasing Saturday night. * EAST SLOPES WASHINGTON CASCADES- Partly to mostly cloudy with few flurries Friday afternoon. Occasional light snow developing in the north late Friday afternoon and evening. Light to occasionally moderate snow spreading southward overnight. Light to occasionally moderate snow decreasing and becoming light showers Saturday morning with some partial clearing lower terrain. Light showers increasing Saturday afternoon, mainly higher terrain near the crest. Light showers decreasing Saturday night. * MT HOOD AREA- Partly to mostly cloudy with light snow showers decreasing Friday afternoon with some partial clearing. Increasing clouds Friday evening with light rain or snow developing later Friday night. Light to occasionally moderate rain or snow early Saturday, decreasing and becoming more showery and mostly snow later Saturday morning and mid-day. Light to occasionally moderate snow showers increasing mid-late Saturday afternoon and evening and becoming moderate snow or snow showers. Showers briefly decreasing Saturday night. SNOW LEVELS-CASCADE MTNS 2500 ft N, 3000 ft C, 4500 ft S Friday afternoon 2500 ft N and C, 3500 ft S Friday night 2000 ft N, 2500 ft C, 3000 ft S Saturday morning 1500 ft N, 2000 ft C, 2500 ft S mid-day and early Saturday afternoon 1500 ft N, 2000 ft S late Saturday afternoon 1500 ft N and S Saturday night, except snow levels near the surface Cascade passes and east slopes Friday afternoon and night, rising to free air levels early Saturday morning SNOW LEVELS-OLYMPIC MTNS 4500 ft Friday afternoon 3000 ft Friday night 2000 ft Saturday and 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 RIDGE .25-.5 .25-.5 * MT BAKER .75 1 * WASHINGTON PASS .25-.5 .25-.5 * STEVENS PASS .5 .5-.75 * SNOQUALMIE PASS .5 .5-.75 * MISSION RIDGE .25 LT .25 * CRYSTAL MTN .5 .25-.5 * PARADISE .5-.75 .75-1 * WHITE PASS .25-.5 .25-.5 * MT HOOD .25 .25 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS E 5-15 early Friday afternoon E 10-20 with occasional higher gusts mid-late Friday afternoon and night W 5-15 early Saturday morning W 10-20 with occasional higher gusts later Saturday morning W 5-15 Saturday afternoon Variable mostly E 0-10 Saturday night, increasing early Sunday * FREE WINDS AT 5000 FT S-SW 10-15 Cascades, 15-25 Olympics early Friday afternoon S-SW 15-30 Cascades, 20-40 Olympics later Friday afternoon S 20-40 Cascades, 40-60 Olympics Friday night W-SW 20-40 Saturday morning W-SW 15-30 N, 20-35 S Saturday afternoon SW 20-40 Saturday night, increasing in the Olympics early Sunday * FREE WINDS AT 9000 FT SW 15-25 Cascades, 20-40 Olympics Friday afternoon SW 30-50 Friday night W-SW 30-50 Saturday morning W 25-40 mid-day W 20-40 Saturday afternoon SW 20-40 N, 15-30 S Saturday night, increasing all areas early Sunday EXTENDED WEATHER SYNOPSIS FOR SUNDAY THROUGH TUESDAY A broad upper trough establishing in the Gulf of Alaska is expected to circulate significant moisture over the area Sunday through Tuesday at relatively low freezing levels. The first associated frontal system should spread increasingly strong winds and a slight and limited rise in freezing levels over the region later Sunday morning and afternoon, with increasing light to moderate snow reaching the Olympics and northern Cascades during the morning, and increasing moderate snow spreading to most areas mid-day and Sunday afternoon as the first of several upper troughs moves across the region. Although moderate to occasionally heavy snow should turn more showery later Sunday night and early Monday ahead of a second strong trough, a moderate to strong orographic flow with the trough should produce moderate to heavy snow or snow showers in most areas Monday morning before decreasing mid-day and early Monday afternoon. A third and strongly splitting upper trough and associated frontal system should spread increasing light to moderate showers to most areas late Monday night and Tuesday morning while maintaining moderate winds and relatively low and lowering freezing levels. However, heaviest frontal precipitation is expected to slide mostly onshore well to the south, mainly over southern Oregon and north-central California. Nevertheless, light to moderate snow should reach most areas later Tuesday morning into early afternoon as the surface and weaker northern part of the split upper trough move onshore. Another weak trough and weather disturbance rotating out of the broad, upper Gulf of Alaska low should bring further light to moderate snow or snow showers to most areas early-mid Wednesday, with another stronger but more significantly splitting disturbance likely favoring heaviest snowfall in the Oregon Cascades mid-late Wednesday, once again at generally low freezing levels. EXTENDED FORECAST FOR SUNDAY THROUGH TUESDAY Light to moderate snow showers increasing early-mid Sunday. Light to moderate snow becoming moderate to occasionally heavy mid-late Sunday. Moderate to heavy snow showers early Monday decreasing mid-day, but increasing again later Monday. Light to moderate snow or snow showers Tuesday morning. Light to moderate showers late Tuesday, increasing early Wednesday. * SNOW LEVELS 1-2000 ft N and S early Sunday 1-3000 ft N, 2-4000 ft S later Sunday 1-2000 ft N and S Monday and Tuesday, except snow levels lowering to near the surface Cascade passes and east slopes Sunday, rising to near free air levels Sunday night