130 PM PST SUN DEC 23 2007 WEATHER SYNOPSIS FOR SUNDAY AND MONDAY An active pattern over the northeast Pacific Ocean should continue to carry fronts across the Northwest the next several days. This should bring continued snow accumulations to the Olympics and Cascades. Increasing strong southwest flow aloft over the Northwest should carry a very strong front to the Olympics and Cascades Sunday afternoon. This will cause increasing strong crest level winds, heavy precipitation, and warming temperatures. Very heavy rain is being recorded by the NWAC weather station at Paradise Sunday midday. A change from snow to rain may come most rapidly at the Cascade passes when the front moves past and the wind shifts Sunday afternoon. Some freezing rain is also reported Sunday midday as the air mass change begins to take place at Snoqualmie. An upper trough and much cooler unstable air mass should follow the front across the Northwest Sunday night and into Monday morning. This should help cause a period of strong orographic showers in the Olympics and Cascades with cooling temperatures. Convergence should enhance these showers near Stevens and Snoqualmie by Monday morning. An upper shortwave ridge, drier more stable air mass, and surface high pressure should move to over the Northwest Monday afternoon to Tuesday morning. This should cause light snow showers to mostly end during that period. WEATHER FORECAST FOR SUNDAY AND MONDAY * OLYMPICS- Sunday midday and afternoon: Increasing moderate to heavy rain or snow. Sunday night and Monday morning: Moderate to heavy rain or snow showers with lowering snow levels. Monday afternoon: Decreasing light to moderate snow showers. Monday night: Decreasing light snow showers. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST- * CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Sunday midday and afternoon: Increasing moderate to heavy rain or snow with freezing rain possible midday mainly Snoqualmie and a change to rain in the passes in the afternoon. Sunday night and Monday morning: Moderate to heavy rain or snow showers with lowering snow levels likely heaviest by morning near Stevens and Snoqualmie in convergence. Monday afternoon: Decreasing light to moderate snow showers. Monday night: Decreasing light snow showers. * EAST SLOPES WASHINGTON CASCADES- Sunday morning: Increasing light snow. Sunday midday and afternoon: Increasing moderate rain or snow with rising snow levels. Sunday night and Monday morning: Moderate rain or snow showers with lowering snow levels likely heaviest by morning central Cascades. Monday afternoon: Decreasing light snow showers. Monday night: Partly or mostly cloudy. * MT HOOD AREA- Sunday morning: Increasing light to moderate rain or snow with rising snow levels. Sunday midday and afternoon: Increasing moderate to heavy rain or snow. Sunday night and Monday morning: Moderate to heavy rain or snow showers with lowering snow levels. Monday afternoon: Decreasing light to moderate snow showers. Monday night: Decreasing light snow showers. SNOW LEVELS-CASCADE MTNS 3000 ft N, 5000 ft C, 8000 ft S Sun midday, remaining at the surface passes and east slopes 4000 ft N, 5000 ft C, 8000 ft S Sun aft, rising to free air levels passes and east slopes Lowering Sun night 1000 ft N, 1500 ft S Mon and Mon night SNOW LEVELS-OLYMPIC MTNS 6000 ft Sun midday 3000 ft Sun aft Lowering Sun night 1500 ft Mon and Mon 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 MON TUE * HURRICANE RIDGE 1-1.5 .25-.5 * MT BAKER 1.5 .5 * WASHINGTON PASS 1 .5 * STEVENS PASS 1.5 .5-.75 * SNOQUALMIE PASS 1.5 .5-.75 * MISSION RIDGE .5 .25 * CRYSTAL MTN 1-1.5 .25-.5 * PARADISE 2-3 .5 * WHITE PASS 1.5 .5 * MT HOOD 1.5-2 .5 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS E 5-10 Sun midday W 10-20 Sun aft W 15-25 Sun night and Mon morn W 10-20 Mon aft W 5-10 Mon eve * FREE WINDS AT 5000 FT SW 30-40 Sun midday SW 40-50 Sun aft W 30-40 Sun night and Mon morn WNW 20-30 Mon aft and eve * FREE WINDS AT 9000 FT SW 50-60 Sun midday SW 60-70 Sun aft W 40-50 Sun night and Mon morn WNW 40-50 Mon aft and eve EXTENDED WEATHER SYNOPSIS FOR TUESDAY THROUGH THURSDAY Increasing southwest flow should carry a moderate front to the Northwest on Tuesday afternoon. This should cause increasing light to moderate snow Tuesday midday and afternoon. An upper trough should follow and cause snow showers Tuesday night and Wednesday morning. A shortwave ridge and weak surface high pressure should cause a relative break Wednesday afternoon to Thursday morning. Another moderate or strong front is indicated for Thursday afternoon. This should bring another round of increasing snow Thursday midday and afternoon. Orographic snow showers should follow the front at continued low snow levels Thursday night. At this time it looks like the active pattern is going to continue through the end of the month which should make December 2007 a memorable month! EXTENDED FORECAST FOR TUESDAY THROUGH THURSDAY Tuesday: Increasing light to moderate snow. Tuesday night to Wednesday morning: Light to moderate snow showers. Wednesday afternoon and evening: Mostly cloudy with some light snow showers possible near and west of the crest. Thursday: Increasing moderate to heavy snow. Thursday night: Moderate to heavy snow showers. * SNOW LEVELS 5-1500 ft N and S Tue through Thu