215 PM PST SAT MAR 01 2008 WEATHER SYNOPSIS FOR SATURDAY AND SUNDAY A moderate frontal system brought increasing winds, lowering freezing levels and about 3-12 inches of new snow to most areas near and west of the Cascade crest at lowering freezing levels mid-late Friday afternoon and night, with the closely following upper trough producing another 3-5 inches reported in several areas Saturday morning and mid- day. A weak secondary upper and surface trough moving southeastward over the region Saturday afternoon should combine with daytime heating of the unstable atmosphere and increasing onshore flow to bring another surge in showers or isolated thundershowers mid-late Saturday afternoon. This should also help to set up a relatively weak and brief Puget Sound convergence. The convergence should begin near Stevens Pass early-mid Saturday afternoon and slowly shift southward toward Snoqualmie Pass later Saturday afternoon and evening. As upper winds turn more northwesterly and slowly dry, gradually decreasing showers and winds are expected, with the convergence slowly dissipating near or just south of Snoqualmie Pass later Saturday night. Transitory upper ridging should result in some brief clearing Sunday morning, but increasing mid and high clouds should spill over the offshore ridge Sunday afternoon and evening as a weak warm front passes by mainly across southern BC. While some light showers are also possible with the increased clouds Sunday night, most shower activity should be very light and confined to the Olympics and northern Washington Cascades. As the ridge passes over and to the east of the area overnight Sunday, some brief warming aloft is also likely mainly in the south. WEATHER FORECAST FOR SATURDAY AND SUNDAY * OLYMPICS- Saturday afternoon: moderate snow showers or thundershowers, heaviest west slopes Saturday night: moderate snow showers decreasing and becoming light showers Sunday morning: scattered light showers ending becoming partly sunny Sunday afternoon: increasing mid and high clouds Sunday night: mostly cloudy with light rain or snow showers developing * WASHINGTON CASCADES NEAR AND WEST OF THE CREST- * CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Saturday afternoon: moderate snow showers or thundershowers slightly increasing, heaviest southern Cascades and near Stevens Pass early afternoon with weak convergence; convergence shifting southward toward Snoqualmie Pass late afternoon Saturday evening: moderate snow showers except locally moderate to heavy near Snoqualmie Pass in convergence Saturday night: moderate showers gradually decreasing and becoming light early Sunday Sunday morning: scattered light showers ending becoming partly sunny Sunday afternoon: increasing mid and high clouds north with variable high clouds south and central Sunday night: mostly cloudy north and partly cloudy south with light rain or snow showers developing in the north * EAST SLOPES WASHINGTON CASCADES- Saturday afternoon: moderate snow showers or thundershowers, heaviest central Cascades and mainly higher terrain near the crest Saturday night: light to moderate snow showers higher terrain decreasing and becoming scattered light showers Sunday morning: partly to mostly sunny Sunday afternoon: increasing mid and high clouds north with variable high clouds south and central Sunday night: mostly cloudy north and partly cloudy south with light rain or snow showers developing higher terrain north * MT HOOD AREA- Saturday afternoon: moderate to heavy snow showers or thundershowers Saturday night: moderate snow showers decreasing and becoming light showers Sunday morning: scattered light showers ending becoming partly to mostly sunny Sunday afternoon: increasing high clouds Sunday night: variable high clouds SNOW LEVELS-CASCADE MTNS 2000 ft N and S Saturday afternoon, locally lower in heavier showers 1500 ft N, 2000 ft S Saturday night 1500 ft N and S Sunday morning 1000 ft N, 1500 ft S mid-day 1500 ft N, 3000 ft S Sunday afternoon 2000 ft N, 3000 ft C, 7000 ft S Sunday night SNOW LEVELS-OLYMPIC MTNS 2000 ft Saturday afternoon 1500 ft Saturday night 1000 ft Sunday morning 1500 ft mid-day 2000 ft Sunday afternoon 3000 ft Sunday 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 SUN MON * HURRICANE RIDGE .25 LT .10 * MT BAKER .5 LT .10 * WASHINGTON PASS .25-.5 LT .10 * STEVENS PASS .25-.5 LT .10 * SNOQUALMIE PASS .5 LT .10 * MISSION RIDGE LT .25 0 * CRYSTAL MTN .25-.5 LT .10 * PARADISE .5-.75 LT .10 * WHITE PASS .5-.75 LT .10 * MT HOOD .5-.75 LT .10 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS W 10-20 with higher gusts Saturday afternoon and evening W 5-15 later Saturday night W 5-10 Sunday morning W 0-10 Sunday afternoon Variable 0-10 Sunday night * FREE WINDS AT 5000 FT W 15-25 N, 15-30 S early Saturday afternoon W-NW 15-25 mid-late Saturday afternoon W-NW 10-20 N, 15-25 S and NW 15-30 Olympics Saturday night W-NW 10-20 Sunday morning W 5-15 mid-day W-SW 10-15 N, 5-15 S Sunday afternoon W-SW 10-20 N, 5-15 S, 15-30 Olympics Sunday night * FREE WINDS AT 9000 FT W-NW 15-30 Saturday afternoon NW 20-30 N, 15-30 S Saturday night NW 15-30 N, 15-25 S Sunday morning W-NW 15-25 N, 10-20 S mid-day W-NW 20-30 N and Olympics, 15-25 S Sunday afternoon W 25-40 N and Olympics, W-NW 15-25 S Sunday night, increasing early Monday EXTENDED WEATHER SYNOPSIS FOR MONDAY THROUGH WEDNESDAY Lowering clouds, substantial cooling, strengthening winds and increasing light rain or snow should spread southward mid-late Monday morning and early afternoon as the brief ridge retreats eastward and a moderate frontal system pushes southeastward across the region. The front should be followed by a moderate to strong upper trough Monday afternoon and a secondary upper disturbance late Saturday afternoon and evening. Combined with a strong onshore flow at the surface, this should result in briefly moderate to heavy orographic snowfall and strong winds later Monday afternoon and evening with a Puget Sound convergence likely enhancing snowfall in the central Cascades. As upper winds turn more northerly overnight and slowly dry ahead of more strongly building offshore ridging, gradually decreasing showers are likely by early Tuesday. A drier northerly flow should produce slow clearing Tuesday morning, with partly to mostly sunny skies, diminishing winds, and low freezing levels expected Tuesday afternoon and evening. As the strong upper ridge edges slowly eastward toward the coast later Tuesday night and Wednesday, associated dry northerly winds should produce mostly fair skies and gradual warming. With the upper ridge moving slowly over the Northwest on Thursday, mostly fair and increasingly warm weather should persist, along with relatively light winds. EXTENDED FORECAST FOR MONDAY THROUGH WEDNESDAY Monday morning: increasing clouds with light to moderate rain or snow spreading southward Monday afternoon: moderate rain or snow decreasing and becoming showery; moderate to heavy showers late Monday night: moderate to heavy showers decreasing and becoming light showers early Tuesday Tuesday morning: scattered light showers ending becoming partly sunny and cool Tuesday afternoon: partly to mostly sunny but continued cool Tuesday night: mostly fair Wednesday: mostly fair and warmer with light winds * SNOW LEVELS 2-3000 ft N, 3-5000 ft C, 6-8000 ft S early Monday morning 1-3000 ft N and C, 2-4000 ft S late Monday morning and afternoon 1-3000 ft N and S Monday night * FREEZING LEVELS 1500-2500 ft N, 2-4000 ft S Tuesday 500-1500 ft N, 1-2000 ft S Tuesday night and early Wednesday 3-5000 ft N, 5-7000 ft S mid-day Wednesday 5-7000 ft N, 6-8000 ft S Wednesday afternoon 7-9000 ft N, 8-10,000 ft S Wednesday night