230 PM PST THU JAN 10 2008 WEATHER SYNOPSIS FOR THURSDAY AND FRIDAY The almost daily onslaught of snowfall continues early Thursday afternoon with precipitation rates reaching over .2 inches/hour in some locations with well over an inch/hour of snowfall. The most recent strong weather system in a long line of such disturbances to welcome in 2008 tracked over the region late Wednesday night into early Thursday, with the front moving mostly east of the area by mid-late Thursday morning. However, strong westerly flow following the surface front continued periods of heavy orographic snowfall in most areas mid-day and early Thursday afternoon, especially near and west of the Cascade crest, with satellite pictures indicating several strong bands of showers continuing to rotate into the area. Combined with a continued moderate to strong westerly flow, this should maintain periods of moderate to heavy snowfall in most locations through Thursday evening, especially near and west of the Cascade crest. A secondary upper trough should help to renew heavy snowfall later Thursday night and early Friday. As weak upper ridging builds offshore Friday, gradually decreasing westerly flow should result in slowly diminishing showers Friday morning, with scattered light showers briefly ending Friday afternoon along with some partial clearing. However, the break should be almost unnoticeable with a moderate frontal system and associated upper trough expected to move across the region Friday night and Saturday morning. After slightly lowering freezing levels for much of Friday, this next weather system should bring a brief and limited rise in freezing levels and moderate to strong winds. WEATHER FORECAST FOR THURSDAY AND FRIDAY * OLYMPICS- Moderate to heavy showers Thursday afternoon and evening, heaviest west and southwest slopes. Heavy showers later Thursday night and early Friday, gradually decreasing Friday morning and becoming light to moderate later Friday morning. Light showers further decreasing mid-day and Friday afternoon with brief partial clearing. Increasing clouds later Friday afternoon and evening with light rain or snow developing. Moderate rain or snow later Friday night and early Saturday. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST- Periods of moderate to heavy rain or snow Thursday afternoon and night with further heavy snow accumulations likely, especially above about 3500 feet. Moderate to heavy showers gradually decreasing Friday morning and becoming light to moderate late Friday morning. Light showers mostly ending Friday afternoon with partial clearing. Increasing clouds Friday night with light rain or snow redeveloping overnight. Light to moderate rain or snow increasing early Saturday. * CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Periods of moderate to heavy rain or snow Thursday afternoon and evening, slightly increasing overnight with further heavy snow accumulations likely, especially above about 3500 feet. Moderate to heavy showers gradually decreasing Friday morning and becoming mostly light to moderate snow showers late Friday morning. Light snow showers mostly ending Friday afternoon with partial clearing. Increasing clouds Friday night with light snow redeveloping overnight. Light to moderate snow increasing early Saturday. * EAST SLOPES WASHINGTON CASCADES- Moderate to occasionally heavy showers Thursday afternoon and night, mainly higher terrain near the crest. Showers increasing later Thursday night and early Friday, again mainly higher terrain near the crest with light to moderate showers lower terrain. Moderate showers decreasing Friday morning and becoming light with partial clearing. Scattered light showers higher terrain mid-day decreasing Friday afternoon with further brief clearing. Increasing clouds Friday night with light snow redeveloping later Friday night, increasing early Saturday. * MT HOOD AREA- Moderate to heavy rain or snow showers Thursday afternoon increasing slightly overnight and early Friday with heavy accumulations likely. Moderate to heavy showers decreasing Friday morning and becoming light to moderate later Friday morning. Light showers further decreasing Friday afternoon with partial clearing. Increasing clouds Friday night with light snow redeveloping overnight. Light to moderate rain or snow increasing early Saturday. SNOW LEVELS-CASCADE MTNS 3500 ft N and S Thursday afternoon and night 3000 ft N, 3500 ft S Friday 2500 ft N, 3500 ft S Friday evening 3500 ft N, 4500 ft S late Friday night and early Saturday, except snow levels lowering to near the surface Friday night SNOW LEVELS-OLYMPIC MTNS 3500 ft Thursday afternoon and night 3000 ft Friday and Friday evening 4500 ft late Friday night and early Saturday 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 .75 .25 * MT BAKER 1.5 .5 * WASHINGTON PASS .75-1 .25 * STEVENS PASS 1-1.5 .25 * SNOQUALMIE PASS 1.5 .25-.5 * MISSION RIDGE .25 LT .25 * CRYSTAL MTN .5-.75 .25-.5 * PARADISE 1 .25-.5 * WHITE PASS 1 .25-.5 * MT HOOD 1.5 .25-.5 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS W 5-15 with higher gusts early Thursday afternoon W 10-20 with higher gusts mid-late Thursday afternoon through early Friday morning W 5-15 later Friday morning and afternoon E 0-10 Friday night, increasing late * FREE WINDS AT 5000 FT W-SW 20-40 N, 30-45 S Thursday afternoon W-SW 20-40 N, 25-40 S Thursday night and early Friday morning W 15-30 N, 20-40 S later Friday morning W 15-25 Cascades, SW 15-25 Olympics Friday afternoon S-SW 15-30 Cascades, 25-40 Olympics Friday night, increasing late * FREE WINDS AT 9000 FT W-SW 25-40 N, 30-50 S Thursday afternoon W-SW 20-40 N, 30-45 S Thursday night W-SW 25-40 N, 30-50 S Friday morning W 15-30 N, 20-40 S mid-day and Friday afternoon W-SW 15-30 N, 20-40 S and Olympics Friday night, increasing late EXTENDED WEATHER SYNOPSIS FOR SATURDAY THROUGH MONDAY Moderate rain or snow, moderate to strong winds and briefly rising freezing levels should accompany a moderate but slightly splitting frontal system moving over the Northwest late Friday night and early-mid Saturday morning. Behind the front, moderate showers with the upper trough should gradually decrease Saturday afternoon and evening ahead of broad flat ridging developing just offshore. This upper ridge should move over the area later Saturday afternoon and evening and should initially help force most energy from a strongly developing weather system into north-central BC early-mid Sunday, with partly to mostly sunny skies briefly gracing the Northwest mountains Sunday morning. However, as the ridge move further east and weekend, this should allow the upper trough to carve slowly to the southeast and bring the still strong southern part of the frontal system over the region late Sunday and Monday. The associated warm front should move primarily across north-central Washington Sunday night with the following cold front spreading more general moderate rain or snow to most areas Monday morning along with a pass wind shift to strong westerly. Moderate to heavy showers should follow with the strong upper trough mid-day and Monday afternoon along with dramatically lowering freezing levels. Extended forecast models are indicating a strong and potentially blocking upper ridge developing just offshore later Monday through Wednesday of next week. Although the associated moderate northerly flow should initially bring low freezing levels and slow clearing to most of the area on Tuesday, as the ridge slowly eases eastward, this should allow for mostly fair and gradually warmer weather toward mid-week, especially at higher elevations. EXTENDED FORECAST FOR SATURDAY THROUGH MONDAY Moderate rain or snow decreasing and becoming more showery mid-day Saturday. Moderate showers decreasing later Saturday. Light showers ending Saturday night with brief clearing trend Sunday with light winds early. Increasing clouds and winds mid-late Sunday with light rain or snow redeveloping Olympics and north-central Cascades late Sunday. Warmer with moderate to heavy rain Monday morning. Cooler with moderate to heavy showers decreasing late Monday. Slow clearing early Tuesday. * SNOW LEVELS 2-4000 ft N, 3-5000 ft S early Saturday 1-3000 ft N, 2-4000 ft S later Saturday 1-3000 ft N, 4-6000 ft S early Sunday 3-5000 ft N, 6-8000 ft S late Sunday 4-6000 ft N, 6-8000 ft S early Monday 1-2000 ft N and S late Monday, except snow levels near the surface Cascade passes and east slopes early Saturday, rising to near free air levels later Saturday morning, lowering to near the surface again mid-late Sunday and rising to near free air levels again mid-late Monday morning