215 PM PST FRI JAN 11 2008 WEATHER SYNOPSIS FOR FRIDAY AND SATURDAY A moderate to strong secondary upper trough moved through the Cascades early to mid Friday morning, helping to maintain moderate to heavy snowfall at slowly and slightly lowering freezing levels. Following the upper trough which exited to the east of the Cascades later Friday morning and mid-day, decreasing moderate showers have begun to occur in most areas. As briefly and weakly building ridging builds offshore Friday afternoon and moves over the area Friday evening, this should result in further decreasing showers and winds along with further brief cooling mid-late Friday afternoon and evening. However, the break should almost be unnoticeable, with increasing light rain or snow ahead of the next slightly splitting moderate frontal system expected to move into the Olympics Friday night and into the Cascades late Friday night and early Saturday morning. This should be accompanied by increasing winds and brief and limited warming aloft along with a return to briefly cooler easterly surface flow across the Cascade passes. Moderate rain or snow should develop in most location Saturday morning before the front moves east of the area mid-day when pass winds should shift to briefly warmer westerly. Following the front, the weak to moderate upper trough should move over the area early Saturday afternoon bringing a brief increase in moderate showers. Gradually decreasing light to moderate showers are expected later Saturday afternoon and evening as a flat ridge begins to build offshore, pressure gradients relax and the upper level flow slowly dries. WEATHER FORECAST FOR SATURDAY AND SUNDAY * OLYMPICS- Light to occasionally moderate showers decreasing and becoming light Friday afternoon with some partial clearing. Increasing clouds Friday night with light rain or snow redeveloping. Light to moderate rain or snow increasing Saturday morning and becoming moderate, heaviest south and southwest slopes. Moderate rain or snow decreasing and becoming more late Saturday morning. Light to moderate showers Saturday afternoon decreasing later Saturday afternoon and night with some partial clearing. Further brief clearing trend early Sunday * WASHINGTON CASCADES NEAR AND WEST OF THE CREST- Moderate showers decreasing Friday afternoon and becoming light showers with some partial clearing. Partly cloudy Friday evening, but increasing clouds overnight with light rain or snow redeveloping later Friday night and early Saturday. Light to moderate rain or snow increasing and becoming moderate Saturday morning. Rain or snow decreasing and becoming more showery mid-day. Moderate showers early Saturday afternoon, decreasing later Saturday afternoon with some partial clearing. Light showers decreasing and becoming scattered Saturday night with further partial clearing. * CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Moderate showers further decreasing Friday afternoon and becoming light showers mid-late afternoon with some partial clearing. Partly cloudy Friday evening, but increasing clouds overnight with light snow redeveloping later Friday night and early Saturday. Light to moderate snow increasing and becoming moderate Saturday morning. Snow becoming mixed with rain and decreasing mid-day. Moderate rain or snow showers early Saturday afternoon, decreasing and becoming mostly light to moderate snow showers later Saturday afternoon with some partial clearing. Light snow showers decreasing and becoming scattered Saturday night with further partial clearing. * EAST SLOPES WASHINGTON CASCADES- Light showers decreasing Friday afternoon and evening with partial clearing. Increasing clouds late Friday night and early Saturday with light snow redeveloping early Saturday. Light to occasionally moderate snow mid- late Saturday morning, decreasing mid-day and becoming light to moderate showers Saturday afternoon. Light showers decreasing later Saturday afternoon with clearing trend Saturday night. * MT HOOD AREA- Moderate showers decreasing Friday afternoon and becoming light showers mid-late afternoon with some partial clearing. Partly cloudy Friday evening, but increasing clouds overnight with light rain or snow redeveloping later Friday night and early Saturday. Light to moderate rain or snow increasing and becoming moderate Saturday morning. Rain or snow decreasing and becoming more showery mid-day. Moderate showers early Saturday afternoon, decreasing later Saturday afternoon with some partial clearing. Light showers decreasing and becoming scattered Saturday night with further partial clearing. SNOW LEVELS-CASCADE MTNS 2500 ft N and C, 3500 ft S Friday afternoon 2000 ft N, 3000 ft C, 4000 ft S Friday night 3500 ft N, 4000 ft C, 4500 ft S Saturday morning 3500 ft N and S mid-day 3000 ft mid-late Saturday afternoon 2500 ft N and S Saturday night, except snow levels lowering to near the surface Cascade passes and east slopes Saturday night, rising to near free air levels late Saturday morning or mid-day SNOW LEVELS-OLYMPIC MTNS 2500 ft Friday afternoon 3500 ft Friday night 4500 ft Saturday morning 3500 ft mid-day 3000 ft Saturday afternoon 2000 ft Saturday 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 SAT SUN * HURRICANE RIDGE .25 .25-.5 * MT BAKER .5-.75 .5 * WASHINGTON PASS .25 .25-.5 * STEVENS PASS .5 .25-.5 * SNOQUALMIE PASS .5 .5 * MISSION RIDGE LT .25 .25 * CRYSTAL MTN .25 .25-.5 * PARADISE .25-.5 .5 * WHITE PASS .25-.5 .25-.5 * MT HOOD .5-.75 .5 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS W 5-10 Friday afternoon E 0-10 Friday night E 5-15 with occasional higher gusts late Friday night and Saturday morning W 5-15 mid-day Saturday W 10-20 Saturday afternoon W 5-15 Saturday night * FREE WINDS AT 5000 FT W-SW 15-25 N, 20-30 S early Friday afternoon S-SW 10-20 N, 15-25 S and Olympics later Friday afternoon S-SW 10-20 Cascades, 20-40 Olympics Friday night S 15-30 Cascades, 30-50 Olympics early Saturday morning SW 25-40 Cascades, 30-50 Olympics late Saturday morning W 15-30 N, 30-45 S Saturday afternoon W 10-20 all areas Saturday night * FREE WINDS AT 9000 FT W 10-20 N, 20-40 C and S Friday afternoon W-SW 10-20 Cascades, 15-25 Olympics Friday night SW 15-30 N, 25-40 S, 30-50 Olympics Saturday morning SW 30-50 Cascades, 25-40 Olympics mid-day W 25-40 N, 30-50 S Saturday afternoon W-SW 20-40 Saturday night EXTENDED WEATHER SYNOPSIS FOR SATURDAY THROUGH MONDAY Briefly building but flat upper ridging should move over the Northwest Sunday. This should initially push a strong frontal system and associated upper trough northward into north-central BC, with partly cloudy skies and considerable filtered sunshine likely in most areas through gradually increasing high clouds. Significant warming is also expected at higher elevations along with an increasingly cool easterly flow across the Cascades passes. As the ridge weakens and moves eastward late Sunday, this should allow the strong surface front to move southeastward and spread increasing light rain or snow into the Olympics overnight, with moderate rain or snow, strong winds and dramatically lowering freezing levels spreading southward over the Cascades Monday morning and early afternoon. With the amount of warming expected combined with the strong easterly surface flow across the Cascade passes, this should also increase the possibility of some freezing rain spreading toward the passes Monday morning. Following a wind shift mid-late morning, significant cooling and moderate to heavy showers are expected mid-day and early afternoon before gradually decreasing later Monday afternoon and night. With extended forecast models continuing to indicate strong and at least briefly blocking upper ridging developing just offshore late Monday through much of next week, this should produce a gradually drier and initially cool northerly flow over the region Tuesday into Wednesday. EXTENDED FORECAST FOR SATURDAY THROUGH MONDAY Increasing light to moderate rain or snow Saturday morning becoming moderate showers mid-day. Light to moderate showers gradually decreasing Saturday afternoon and evening with some partial clearing. Light showers ending Saturday night with clearing trend. Partly cloudy and gradually warmer higher terrain Sunday with considerable sunshine through increasing high clouds. Clouds further increasing later Sunday night and early Monday north and Olympics with increasing moderate rain or snow spreading southward Monday morning along with a chance of freezing rain near the Cascade passes. Rain or snow decreasing and becoming showery mid-day. Much cooler with moderate to heavy showers Monday afternoon. Showers decreasing late Monday and early Tuesday. Partly cloudy with scattered showers decreasing Tuesday. * SNOW LEVELS 1-3000 ft N and S early Sunday 4-6000 ft N, 7-9000 ft S late Sunday 5-7000 ft N, 7-9000 ft S early Monday 2-4000 ft N, 4-6000 ft S mid-day 1-2000 ft N, 1-3000 ft s later Monday Sea level to 1000 ft N and S Tuesday, except snow levels lowering to near the surface Cascade passes and east slopes mid-late Sunday, rising to near free air levels mid-late Monday morning