6 AM PST SUN FEB 17 2008 WEATHER SYNOPSIS FOR SUNDAY AND MONDAY A major higher amplitude upper ridge is building about 300 miles off the Washington coast early Sunday with an associated generally dry and significantly warming northerly flow aloft moving over the region. As the ridge moves very slowly eastward toward the coast on Sunday and transits slowly over the Northwest Monday, this should produce mostly fair skies and high freezing levels in most areas along with relatively light winds. However, an increasing offshore flow and associated low level easterly flow across the Cascades should produce generally cooler conditions at lower elevations near the passes both Sunday and Monday. WEATHER FORECAST FOR SUNDAY AND MONDAY * OLYMPICS- Sunday, Sunday night, Monday: few high clouds at times, otherwise mostly fair, warm days with cool, clear nights Monday night: slow cooling with increasing high clouds * WASHINGTON CASCADES NEAR AND WEST OF THE CREST- Sunday, Sunday night, Monday: few high clouds at times, otherwise generally fair, warm days with cool, clear nights Monday night: slow cooling with increasing high clouds * CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Sunday, Sunday night, Monday: few high clouds at times, otherwise mostly fair and warm days higher terrain with cool, clear nights; generally cooler temperatures lower terrain near the passes with moderate east winds developing Monday night: slow cooling higher terrain with increasing high clouds * EAST SLOPES WASHINGTON CASCADES- Sunday, Sunday night, Monday: few high clouds at times, otherwise mostly fair and warm days, especially higher terrain, with cool, clear nights Monday night: increasing high clouds * MT HOOD AREA- Sunday, Sunday night, Monday: few high clouds at times, otherwise mostly fair, warm days with cool, clear nights Monday night: slow cooling with increasing high clouds FREEZING LEVELS-CASCADE MTNS 7500 ft N, 10,500 ft S Sunday morning 10,000 ft N, 11,000 ft S mid-day 11,000 ft N, 11,500 ft S Sunday afternoon through Monday morning 10,500 ft N, 11,000 ft S Monday afternoon 10,000 ft N, 10,500 ft S Monday night, except locally lower near the Cascade passes in cooler easterly surface flow FREEZING LEVELS-OLYMPIC MTNS 10,500 ft Sunday morning 11,000 ft mid-day Sunday through Monday morning 10,500 ft Monday afternoon 10,000 ft Monday 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 M0N TUE * HURRICANE RIDGE 0 0 * MT BAKER 0 0 * WASHINGTON PASS 0 0 * STEVENS PASS 0 0 * SNOQUALMIE PASS 0 0 * MISSION RIDGE 0 0 * CRYSTAL MTN 0 0 * PARADISE 0 0 * WHITE PASS 0 0 * MT HOOD 0 0 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS E 5-15 Sunday morning E 10-15 with occasional higher gusts Sunday afternoon and night E 10-20 Monday and Monday night * FREE WINDS AT 5000 FT E 5-15 N and C, 10-15 S and Olympics Sunday morning SE 5-15 N, 10-20 S and Olympics Sunday afternoon and night S-SE 5-15 N, 10-20 S and Olympics Monday morning S 10-20 Cascades, 15-25 Olympics Monday afternoon S 10-20 Cascades, 15-30 Olympics Monday night * FREE WINDS AT 9000 FT N 20-40 N, 15-30 C, and 10-20 S Sunday morning N 15-30 N, E 10-15 S Sunday afternoon NE 10-15 Cascades, SE 10-15 Olympics Sunday night Variable 5-15 Cascades, S 10-20 Olympics Monday morning S 15-25 Cascades, 20-30 Olympics Monday afternoon S 15-30 Cascades, 20-40 Olympics Monday night EXTENDED WEATHER SYNOPSIS FOR TUESDAY THROUGH THURSDAY The recently blocking upper ridge is expected to slowly move east of the region and give way to a gradually increasing and moistening south to southwesterly flow on Tuesday. While the first disturbance to move into the previous ridge position is expected to be rather weak, a weakening front should still spread increasing and slowly lowering clouds over the area Tuesday morning, with light rain or snow developing in the Olympics and Mt Hood area during the afternoon. Light rain or snow should slightly increase and spread to the remainder of the Cascades later Tuesday afternoon and night, along with slightly strengthening winds and generally lowering freezing levels. While some areas may start precipitation as rain, the cool and relatively dry easterly surface flow across the Cascades should help maintain most precipitation as snow above about 3500 to 4000 feet near the Cascade passes. Following this first frontal passage later Tuesday night or early Wednesday, much of the energy with the following weak upper trough should move into Oregon. However, a moist and unstable southwesterly flow should produce light rain or snow showers in most areas Wednesday morning before decreasing mid-day and Wednesday afternoon with some partial clearing. A slightly stronger front and upper trough should move slowly onshore late Wednesday, with increasing light rain or snow spreading over most areas overnight and early-mid Thursday at continued lowering freezing levels and light to moderate winds. However, the main energy with the following split upper trough should move southeastward toward California mid-late Thursday. This should result in light rain or snow changing to light snow showers mid-late Thursday into early Friday. EXTENDED FORECAST FOR TUESDAY THROUGH THURSDAY Tuesday morning: increasing mid and high clouds, lowering late Tuesday afternoon: light rain or snow developing Olympics and Mt Hood area, spreading northeastward late Tuesday night: light rain or snow decreasing early Wednesday Wednesday morning: light rain or snow showers Wednesday afternoon: light rain or snow showers decreasing with partial clearing Wednesday night: light to occasionally moderate rain or snow spreading to most areas overnight Thursday morning: light to occasionally moderate rain or snow\ Thursday afternoon: light rain or snow decreasing and becoming showery Thursday night: light snow showers * SNOW LEVELS 6-8000 ft N and S early Tuesday 4-6000 ft N and S mid-late Tuesday, except locally lower near the Cascade passes later Tuesday 3-5000 ft N and S Wednesday 2-4000 ft N and S Thursday