1 PM PST SAT FEB 23 2008 WEATHER SYNOPSIS FOR SATURDAY AND SUNDAY A weak upper low between Seattle and Vancouver Island mid- day Saturday is expected to slowly slide eastward across northern Washington and southern BC Saturday afternoon while continuing to weaken. A very weak south to southwesterly flow associated with the low should maintain relatively low freezing levels and partly to mostly sunny skies except for some widely scattered light showers developing later Saturday afternoon. Meanwhile further to the south, a powerful storm system rotating out of a deep upper low moving eastward about 300 miles west of San Francisco should spread increasingly heavy rain or snow to much of California Saturday afternoon through much of Sunday as several upper level disturbances follow the strong front and maintain periods of moderate to heavy shower activity. While most of this strong storm energy should remain well to the south, some weakened storm remnants should slowly drift northward through Oregon Saturday in a slightly increased south- southeasterly flow aloft. This should allow increasing clouds and light precipitation to reach the Mt Hood area late Saturday and Saturday night and south-central Washington by early Sunday. Further north the effects should be more limited with only scattered light showers expected to reach most mountain terrain north of Snoqualmie Pass. As the trough to the south moves east mid-late Sunday, and moderate to strong upper riding rebuilds offshore, gradually decreasing clouds and showers are likely with slowly clearing skies expected in most areas Sunday night into early Monday. WEATHER FORECAST FOR SATURDAY AND SUNDAY * OLYMPICS- Saturday afternoon: partly to mostly sunny; chance scattered light showers late Saturday night: partly cloudy overnight with clouds increasing early Sunday Sunday morning: partly to mostly cloudy with scattered light showers Sunday afternoon: clouds and showers decreasing Sunday night: slow clearing * WASHINGTON CASCADES NEAR AND WEST OF THE CREST- Saturday afternoon: partly to mostly sunny; chance widely scattered light showers late Saturday night: partly cloudy north with gradually increasing clouds south Sunday morning: partly cloudy north with occasional light rain or snow south spreading slowly northward Sunday afternoon: clouds and showers slowly decreasing Sunday night: partly cloudy with scattered light showers early then slow clearing trend * CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Saturday afternoon: partly to mostly sunny; chance widely scattered light showers late Saturday night: partly cloudy north with gradually increasing clouds south Sunday morning: partly cloudy north with occasional light snow south spreading slowly northward to about Snoqualmie Pass Sunday afternoon: clouds and light showers slowly decreasing Sunday night: partly cloudy with scattered light showers early then slow clearing trend * EAST SLOPES WASHINGTON CASCADES- Saturday afternoon: partly to mostly sunny; chance widely scattered light showers late Saturday night: partly cloudy north with gradually increasing clouds south Sunday morning: partly cloudy north with occasional light snow south spreading slowly northward to about Snoqualmie Pass Sunday afternoon: clouds and light showers slowly decreasing Sunday night: partly cloudy with scattered light showers early then slow clearing trend * MT HOOD AREA- Saturday afternoon: partly to mostly sunny; chance widely scattered light showers late Saturday night: increasing clouds with occasional light rain or snow developing overnight Sunday morning: occasional light rain or snow decreasing Sunday afternoon: clouds and light showers slowly decreasing Sunday night: partly cloudy with scattered light showers early then slow clearing trend SNOW LEVELS-CASCADE MTNS 3500 ft N and C, 3000 ft S Saturday afternoon and evening 2000 ft N, 2500 ft S later Saturday night and Sunday morning 2500 ft N, 2000 ft S mid-day Sunday 3500 ft N, 2500 ft S Sunday afternoon 2500 ft N and S Sunday night...except snow levels lowering to near the surface Cascade passes Saturday night and Sunday morning, rising to near free air levels Sunday afternoon SNOW LEVELS-OLYMPIC MTNS 2500 ft Saturday afternoon 3000 ft Saturday night 2000 ft Sunday morning 3500 ft Sunday afternoon and 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 LT .10 LT .10 * MT BAKER LT .10 0 * WASHINGTON PASS LT .10 0 * STEVENS PASS LT .10 LT .10 * SNOQUALMIE PASS LT .10 LT .25 * MISSION RIDGE LT .10 LT .25 * CRYSTAL MTN LT .25 LT .25 * PARADISE LT .25 LT .25 * WHITE PASS LT .25 LT .25 * MT HOOD LT .25 LT .10 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS Variable 0-10 Saturday afternoon E 5-15 with occasional higher gusts Saturday night and Sunday E 0-10 late Sunday * FREE WINDS AT 5000 FT E-SE 10-15 N, 15-25 S Saturday afternoon E-SE 10-20 N, 15-25 C, 20-40 S Saturday night E-SE 10-15 N, 15-25 C, 20-30 S Sunday morning E 5-15 N, 10-15 C and S mid-day Sunday E 5-15 Sunday afternoon Variable 0-10 Sunday night * FREE WINDS AT 9000 FT S-SE 10-20 N, 15-25 S Saturday afternoon SE 10-20 N, 15-30 C, 20-35 S Saturday night SE 10-20 N, SW 10-20 S Sunday morning E 10-20 N, S-SW 10-15 S mid-day Sunday E 5-15 N, Variable 5-15 C, W 5-15 S Sunday afternoon NE 5-15 N, Variable 5-15 C, W 10-20 S Sunday night EXTENDED WEATHER SYNOPSIS FOR MONDAY THROUGH WEDNESDAY Building upper level riding offshore late Sunday should approach the coast mid-day Monday and slowly amplify as it moves over the region later Monday and Tuesday. An associated drier and warmer flow should produce mostly fair and warmer skies over much of the region Monday and Tuesday except for some increase in high clouds mid-late Tuesday. A weak front and associated weak upper trough should move over the area Wednesday, bringing increasing light rain or snow and briefly and slightly lowering freezing levels. However, the moderate to strong upper ridge should rebuild behind this disturbance and bring decreasing clouds and showers late Wednesday into early Thursday. EXTENDED FORECAST FOR MONDAY THROUGH WEDNESDAY Monday morning through Tuesday morning: decreasing clouds early becoming mostly fair and warmer Tuesday afternoon: considerable sun or filtered sun though variable and gradually increasing high clouds Tuesday night: increasing clouds Wednesday: light rain or snow Olympics spreading to the Cascades later morning and afternoon with only minor precipitation amounts likely Wednesday night: decreasing clouds and light showers * FREEZING LEVELS 3-5000 ft N and S early Monday 4-6000 ft N, 5-7000 ft S later Monday 4-6000 ft N, 6-8000 ft S early-mid Tuesday 5-7000 ft N, 8-10,000 ft S late Tuesday * SNOW LEVELS 4-6000 ft N, 6-8000 ft S early Wednesday 2-4000 ft N, 5-7000 ft S late Wednesday...except snow levels locally lower near the Cascade passes in a weak to moderate easterly flow Tuesday, rising to near free air levels early-mid Wednesday