230 PM PST SAT FEB 02 2008 WEATHER SYNOPSIS FOR SATURDAY AND SUNDAY A broad upper trough covers much of the western US coastal waters early Saturday afternoon with several imbedded short waves moving east-southeastward in the flow around the offshore upper low. This flow is currently sending the main storm energy across Oregon and north-central California. The first such weather disturbance spread increasingly heavy precipitation into Oregon and northern California Saturday morning, with a second and stronger upper disturbance helping to lift moisture from the first disturbance slowly northward mid-late Saturday morning and afternoon. This weather situation should maintain relatively low freezing levels while spreading increasing light to occasionally moderate snow northward through the area through Saturday afternoon, with heaviest precipitation expected in the southern Washington Cascades and Mt Hood area. Following this disturbance, the second upper trough and associated front should dig even further southward along the coast, with most of the associated precipitation expected across extreme southern Oregon and much of California on Sunday. Meanwhile further north, a weak northern part of the trough should help maintain some light showers in the northern Washington Cascades and light to moderate snow in the south through Saturday night. However, with a gradually drier north to northwesterly flow developing behind the trough passage for much of Sunday, decreasing showers and slow clearing should spread southward over the region, along with slowly increasing northerly winds aloft and continued low freezing levels. WEATHER FORECAST FOR SATURDAY AND SUNDAY * OLYMPICS- Saturday afternoon: light to moderate snow showers developing, heaviest south and southeast slopes Saturday night: light to moderate showers decreasing late Sunday morning: light snow showers mainly north slopes, decreasing late morning Sunday afternoon: light showers becoming scattered with partial clearing Sunday night: partly cloudy * WASHINGTON CASCADES NEAR AND WEST OF THE CREST NORTH OF MT RAINIER- * CASCADE PASSES NORTH OF MT RAINIER, INCLUDING STEVENS AND SNOQUALMIE PASSES- * EAST SLOPES WASHINGTON CASCADES NORTH OF MT RAINIER - Saturday afternoon: light to moderate snow showers developing north with light to moderate snow south Saturday night: light to moderate showers north and light to moderate snow south decreasing late Sunday morning: light snow or snow showers decreasing with slow clearing spreading southward late morning and mid-day Sunday afternoon: light showers becoming scattered with partial clearing Sunday night: partly cloudy * WASHINGTON CASCADES NEAR AND WEST OF THE CREST FROM MT RAINIER SOUTHWARD- * CASCADE PASSES FROM MT RAINIER SOUTHWARD, INCLUDING WHITE PASS- * EAST SLOPES WASHINGTON CASCADES FROM MT RAINIER SOUTHWARD- Saturday afternoon: light to moderate snow, heaviest extreme south Saturday night: light to moderate snow decreasing late Sunday morning: light to moderate snow showers decreasing late morning Sunday afternoon: light showers becoming scattered with partial clearing Sunday night: partly cloudy * MT HOOD AREA- Saturday afternoon and night: moderate to heavy snow decreasing late Sunday morning: moderate snow decreasing and becoming light to moderate showers late morning Sunday afternoon: light showers decreasing with partial clearing Sunday night: partly cloudy SNOW LEVELS-CASCADE MTNS 500 ft N, 1500 ft S Saturday afternoon Sea level N, 500 ft C, 1000 ft S Saturday night and Sunday morning Sea level N, 500 ft S Sunday afternoon and night SNOW LEVELS-OLYMPIC MTNS 500 ft Saturday afternoon Sea level Saturday night and Sunday 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 LT .25 LT .10 * MT BAKER LT .25 LT .10 * WASHINGTON PASS LT .25 LT .10 * STEVENS PASS .25 LT .10 * SNOQUALMIE PASS .25 LT .10 * MISSION RIDGE .25 LT .10 * CRYSTAL MTN .25-.5 LT .10 * PARADISE .25-.5 LT .10 * WHITE PASS .5-.75 LT .25 * MT HOOD 1 LT .25 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS E 5-15 with occasional higher gusts Saturday afternoon and night E 5-10 Sunday morning W 0-10 Sunday afternoon Variable 0-10 Sunday night * FREE WINDS AT 5000 FT SE 10-15 N, 15-30 C and Olympics and SW 20-40 S Saturday afternoon E 10-15 N, 10-20 C and Olympics and S 15-25 S Saturday night E 5-15 N, 10-15 C, N 10-10 Olympics, W-SW 10-20 S Sunday morning N-NW 10-20 N, 15-25 S Sunday afternoon W 10-20 N, N-NW 15-30 S and Olympics Sunday night * FREE WINDS AT 9000 FT S 10-20 N, 15-25 C, W-SW 30-45 S, and Variable 5-15 Olympics Saturday afternoon SE 10-15 N, 10-20 C, W-SW 20-40 S and NE 10-20 Olympics Saturday night Variable 5-15 N and C, W 10-20 S and N 10-20 Olympics Sunday morning N-NW 10-20 N, C and Olympics and 15-25 S mid-day N-NW 15-25 Sunday afternoon, strongest south N-NW 20-40 Sunday night EXTENDED WEATHER SYNOPSIS FOR MONDAY THROUGH WEDNESDAY After a flat and weak upper ridge brings a brief break from the recent substantial weather events mid-late Sunday through early Monday, residual moisture from an old upper disturbance passing weakly mostly north of the areas should spread through the ridge and onshore mid-late Monday morning and mid-day, with light snow developing in the Olympics during the morning and the Cascades by mid-day. This should be closely followed by moisture ahead of a warm front slowly moves toward the area Monday afternoon and night. As a result, occasional light snow or light snow showers Monday morning should be followed by slowly increasing light snow later Monday afternoon and evening, with snow becoming moderate in the north later Monday night and early Tuesday along with gradually increasing ridgetop winds. Although slow and limited warming is anticipated with the warm front, a cool easterly flow should protect the passes from the warming along which should be relatively minor. Increasing moderate to heavy rain or snow is expected with the following strong cold front Tuesday morning along with dramatically lowering freezing levels and strong winds. An associated strong upper trough should maintain moderate to heavy showers Tuesday afternoon before slowly decreasing late Tuesday. However, extended forecast models indicate that the Northwest should come under the increasing influence of a strengthening jetstream Wednesday through Friday, as two branches of the westerlies flow around a blocking pattern south of the Aleutians and merge 6-800 miles offshore. Initially this very strong westerly flow should produce increasingly heavy snowfall at relatively low freezing levels and strong winds Wednesday. However, as the southern branch of westerlies slowly gains strength, a flat ridge should slowly lift northward. This should result in continued very strong westerly flow with copious precipitation and very slow warming Thursday and Friday. EXTENDED FORECAST FOR MONDAY THROUGH WEDNESDAY Monday morning: increasing clouds with light snow showers developing Monday afternoon: occasional light snow slowly increasing late, mainly north Monday night: slight warming with light to occasionally moderate snow north and light snow south increasing early Tuesday Tuesday morning: windy with moderate to heavy rain or snow Tuesday afternoon and night: cooler with moderate to heavy snow showers decreasing early Wednesday Wednesday morning: light to moderate showers increasing mid- day Wednesday afternoon and night: increasing winds with moderate to heavy snow and very slow warming late * SNOW LEVELS Sea level to 1000 ft N, 500-1500 ft S Monday morning 500 to 1500 ft N, 1-3000 ft S Monday afternoon and night 1-3000 ft N, 2-4000 ft C and S early Tuesday 1-3000 ft N and S mid-late Tuesday 500-1500 ft N, 1-2000 ft S Wednesday 1-2000 ft N, 2-4000 ft S late Wednesday