115 PM PST THU FEB 14 2008 WEATHER SYNOPSIS FOR THURSDAY AND FRIDAY A positively tilted moderate amplitude upper ridge just offshore early Thursday morning moved over south-central BC by late morning and should ease over western Washington and Oregon Thursday afternoon and evening before flattening and weakening to the east of the area Thursday night. An associated dry northerly flow aloft produced mostly dry weather over the forecast area Thursday morning but should also allow gradually increasing high level moisture (from the southern end of a weak, split frontal system passing mostly north of the area) to brush northern Washington Thursday afternoon and night. As a result, increasing mid and high clouds that spread over the Olympics and north- central Cascades Thursday morning should slightly thicken Thursday afternoon and night along with a chance of scattered high based showers or virga. Further south, considerable sunshine is expected through variable high clouds for much of Thursday, and in all areas the weak system remnants should be accompanied by generally rising freezing levels. Following this initial weak impulse to the north, the southern part of a still weak though slightly stronger disturbance should move over southern BC and north- central Washington later Friday morning through Friday evening. This should spread light rain or snow southward to about Snoqualmie Pass by mid-day, with light to occasionally moderate rain or snow likely in the Olympics and northern Washington Cascades Friday afternoon, occasional light rain or snow in the central Cascades and some light showers possibly reaching Mt Rainier and the southern Washington Cascades. In the Mt Hood area, only increased clouds and some widely scattered light showers are expected late Friday afternoon and evening. As the trough moves east of the region Friday night and the upper flow turns more northwesterly and dries, decreasing light showers are likely overnight into early Saturday. WEATHER FORECAST FOR THURSDAY AND FRIDAY * OLYMPICS- Thursday afternoon and night: considerable mid and high clouds with scattered high based showers or virga Friday morning: mostly cloudy with light rain or snow developing Friday afternoon: light rain or snow at times Friday night: decreasing light rain or snow showers * WASHINGTON CASCADES NEAR AND WEST OF THE CREST NORTH OF STEVENS PASS- * CASCADE PASSES NORTH OF STEVENS PASS Thursday afternoon and night: considerable mid and high clouds with scattered high based showers or virga Friday morning: cloudy with light rain or snow developing Friday afternoon: light to occasionally moderate rain or snow Friday night: light rain or snow showers decreasing late * WASHINGTON CASCADES NEAR AND WEST OF THE CREST FROM STEVENS PASS SOUTHWARD TO MT RAINIER- * CASCADE PASSES FROM STEVENS PASS SOUTHWARD TO MT RAINIER, INCLUDING STEVENS AND SNOQUALMIE PASSES- Thursday afternoon: variable mid and high clouds with filtered sunshine Thursday night: variable mid and high clouds Friday morning: increasing clouds with occasional light rain or snow developing late morning Friday afternoon: occasional light rain or snow Friday night: light rain or snow showers decreasing * WASHINGTON CASCADES NEAR AND WEST OF THE CREST FROM MT RAINIER SOUTHWARD- * CASCADE PASSES FROM STEVENS PASS SOUTHWARD TO MT RAINIER, INCLUDING WHITE PASS- Thursday afternoon: variable high clouds otherwise partly to mostly sunny and warmer Thursday night: variable high clouds Friday morning: increasing clouds Friday afternoon: partly to mostly cloudy with light rain or snow showers Friday night: cooler with light rain or snow showers decreasing * EAST SLOPES WASHINGTON CASCADES- Thursday afternoon and night: considerable mid and high clouds north with chance scattered showers higher terrain near the crest; otherwise variable high clouds central and mostly sunny and warmer south Friday morning: increasing clouds with occasional light rain or snow developing late morning Friday afternoon: occasional light rain or snow north with light rain or snow showers developing south Friday night: cooler with light rain or snow showers decreasing * MT HOOD AREA- Thursday afternoon and night: variable high clouds otherwise mostly sunny and warmer Friday morning: increasing clouds later morning hours Friday afternoon: partly to mostly cloudy with scattered light rain or snow showers developing Friday night: clouds and scattered light rain or snow showers decreasing SNOW LEVELS-CASCADE MTNS 2000 ft N and C, 7500 ft S Thursday afternoon 2000 ft N, 6500 ft C, 7500 ft S Thursday night 6500 ft N, 7000 ft C, 8000 ft S Friday morning 4500 ft N, 6000 ft C, 8000 ft S mid-day Friday 3000 ft N, 4500 ft C, 7000 ft S Friday afternoon 3000 ft N and C, 5000 ft S Friday night SNOW LEVELS-OLYMPIC MTNS 6500 ft Thursday afternoon 7000 ft Thursday night and Friday morning 6000 ft mid-day 4000 ft Friday afternoon 3000 ft Friday 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 FRI SAT * HURRICANE RIDGE LT .10 .25 * MT BAKER LT .10 .25-.5 * WASHINGTON PASS LT .10 LT .25 * STEVENS PASS 0 LT .25 * SNOQUALMIE PASS 0 LT .25 * MISSION RIDGE 0 LT .10 * CRYSTAL MTN 0 LT .25 * PARADISE 0 LT .25 * WHITE PASS 0 LT .10 * MT HOOD 0 LT .10 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS W 5-10 Thursday afternoon Variable 0-10 Thursday night and early Friday morning W 5-10 later Friday morning W 5-15 Friday afternoon and night * FREE WINDS AT 5000 FT NW 15-25 N, 10-15 S Thursday afternoon NW 15-25 N, 10-20 S Thursday night W-NW 15-25 N, variable 5-15 S Friday morning W 20-35 N, 15-25 C, 10-20 S Friday afternoon W 10-20 N, 15-25 S and N 15-25 Olympics Friday night * FREE WINDS AT 9000 FT N-NW 25-40 Thursday afternoon NW 20-40 N, 15-30 S Thursday night W-NW 20-40 N, N-NW 15-25 C and S Friday morning W-SW 20-40 N, 15-25 C, 10-20 S mid-day Friday W-SW 25-40 N and C, 20-30 S Friday afternoon NW 20-40 N, W 30-45 S Friday night, decreasing late EXTENDED WEATHER SYNOPSIS FOR SATURDAY THROUGH MONDAY Increasingly dry northerly flow ahead of strongly rebuilding upper ridging about 600 miles offshore early Saturday should allow for widely scattered light showers to end Saturday morning with a clearing trend likely in most areas by mid- day. As the ridge moves toward the NW coast Saturday afternoon and evening, and slowly transits the coast into western Washington overnight and Sunday, this should produce mostly fair skies with relatively light ridgetop winds and substantially rising freezing levels. However, an increasing low level easterly flow is expected to develop across the Cascades Sunday and this should help limit the amount of warming near the Cascade passes. The strong upper ridge should slowly slide eastward on late Sunday through early Monday, reaching eastern Washington Monday morning and Idaho by Monday afternoon. Initially this should maintain relatively high freezing levels, light ridgetop winds and mostly fair skies over the region into Monday morning. However, by mid-late Monday, increasing mid and high clouds are likely to spread over the area ahead of a gradually deepening and relatively broad upper trough slowly moving eastward in the Gulf of Alaska. This should also maintain or increase the generally cooler easterly surface flow through the Cascade passes, with some low clouds or fog possible near the passes. Extended forecast models indicate that a gradual return to cooler and more stormy weather is likely Tuesday through much of the remainder of next week, so enjoy this brief mid-winter weather break. EXTENDED FORECAST FOR SATURDAY THROUGH MONDAY Saturday morning: decreasing clouds and light showers with a clearing trend Saturday afternoon and night: mostly fair and warmer Sunday, Sunday night, Monday morning: few high clouds otherwise mostly fair and warm higher terrain; partly cloudy and cooler near the Cascade passes with increasing east winds Monday afternoon: variable high clouds increasing Monday night: becoming windy with increasing mid and high clouds * FREEZING LEVELS 1-3000 ft N, 2-4000 ft C, 6-8000 ft S Saturday 1-3000 ft N, 4-6000 ft C, 7-9000 ft S late Saturday 6-8000 ft N, 7-9000 ft C, 9-11,000 ft S Sunday morning 8-10,000 ft N and C, 9-11,000 ft S Sunday afternoon through Monday morning 5-7000 ft N, 6-8000 ft C, 7-9000 ft S Monday afternoon and night, except locally cooler near the Cascade passes Sunday and Monday in a moderate easterly flow