230 PM PDT THU DEC 06 2007 WEATHER SYNOPSIS FOR THURSDAY AND FRIDAY Although a closing upper low just off the south-central Oregon coast is expected to continue tracking to the south- southeast Thursday afternoon and night, associated weak bands of moisture rotating to the east and northeast of the low have produced occasional light snow in most areas of the south-central Washington Cascades and Mt Hood area. Further weak bands of moisture rotating around the low are expected to reach as far north as Stevens Pass Thursday afternoon before the low moves further to the southeast and the moisture retreats southward and diminishes. As the upper low reaches the Oregon-California border late Thursday afternoon and a drier northerly flow spreads southward ahead of moderate to strongly building offshore ridging, slow clearing should spread southward late Thursday into early Friday, with scattered light showers in the northern Oregon Cascades expected to end Friday morning. A weak east-west oriented upper trough in the otherwise dry and cool northerly flow aloft is expected to mainly slide southward offshore mid-late Friday into early Saturday. While models indicate this weak feature should have minimal impact on most of Washington, it is expected to slightly deepen as it moves southward along the coast, with some light showers possibly developing over the northern Oregon Cascades later Friday night and early Saturday along with some increase in higher ridgetop winds, mainly in the Olympics. Otherwise most areas should experience partly to mostly sunny weather on Friday with generally low freezing levels and relatively light winds. WEATHER FORECAST FOR THURSDAY AND FRIDAY * OLYMPICS- Partly to mostly cloudy Thursday morning with a chance of light snow, mainly south and southwest slopes. Light showers decreasing Thursday afternoon becoming partly cloudy later Thursday afternoon and evening. Clearing trend overnight becoming mostly sunny and cool Friday. Mostly fair Friday night. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST AND CASCADE PASSES NORTH OF STEVENS PASS- Mostly sunny north and partly cloudy south early Thursday afternoon. Mostly sunny and cool later Thursday afternoon. Mostly fair and cool Thursday night. Mostly fair Friday and Friday night. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST AND CASCADE PASSES FROM STEVENS PASS SOUTHWARD- Partly to mostly cloudy north and cloudy south early Thursday afternoon with occasional light snow or flurries north and light to occasionally moderate snow south. Snow decreasing mid-late Thursday afternoon north and Thursday afternoon south, becoming partly cloudy later Thursday afternoon north and later Thursday night south. Partly to mostly sunny Friday. Clouds increasing south Friday night otherwise partly cloudy. * EAST SLOPES WASHINGTON CASCADES- Mostly sunny north, partly to mostly cloudy central and mostly cloudy south early Thursday afternoon with light showers or flurries central and light to occasionally moderate snow south. Clouds and showers decreasing Thursday afternoon central and Thursday evening south. Clearing trend Thursday night becoming mostly fair early Friday. Mostly sunny Friday. Increasing clouds south late Friday. * MT HOOD AREA- Light snow decreasing late Thursday afternoon and evening with some partial clearing. Partly cloudy with light showers decreasing Thursday night. Partly cloudy with scattered light showers decreasing Friday morning. Partly sunny Friday afternoon, but increasing clouds late Friday with chance few showers Friday night. SNOW LEVELS-CASCADE MTNS 1000 ft N, 2000 ft C, 3500 ft S Thursday afternoon 500 ft N, 1500 ft C, 3000 ft S Thursday night 500 ft N, 1000 ft C, 2500 ft S Friday 500 ft N, 1000 ft C, 2000 ft S late Friday, except snow levels lowering to near the surface Cascade passes and east slopes Thursday afternoon, remaining at the surface N and C through Friday night, but rising to near free air levels south part Thursday night SNOW LEVELS-OLYMPIC MTNS 1500 ft Thursday afternoon 1000 ft Thursday night 500 ft Friday morning 1000 ft Friday afternoon 500 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 0 0 * MT BAKER 0 0 * WASHINGTON PASS 0 0 * STEVENS PASS LT .10 0 * SNOQUALMIE PASS LT .25 0 * MISSION RIDGE LT .25 0 * CRYSTAL MTN LT .25 LT .10 * PARADISE LT .25 LT .10 * WHITE PASS LT .25 LT .10 * MT HOOD .25-.5 LT .10 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS E 0-10 early Thursday afternoon E 5-15 later Thursday afternoon E 5-15 N and C and W 0-10 S Thursday night and Friday * FREE WINDS AT 5000 FT E-NE 5-15 N and C, NW 5-15 S, N 5-15 Olympics Thursday afternoon N 5-15 Thursday night N 5-15 Cascades, 10-20 Olympics Friday morning NE 10-20 N, NW 5-15 S Friday afternoon and evening NE 10-20 N and C, N 5-15 S later Friday night * FREE WINDS AT 9000 FT Variable 0-10 N and C, W 5-15 S Thursday afternoon and night N 5-15 Cascades, 10-20 Olympics Friday morning N-NW 10-20 Cascades, 20-40 Olympics Friday afternoon NE 10-20 N, NW 15-25 S and 25-40 Olympics Friday night EXTENDED WEATHER SYNOPSIS FOR SATURDAY THROUGH MONDAY Following a weak upper trough passage late Friday, a moderate to strong upper ridge should once again rebuild just offshore Saturday into early Sunday with an associated generally dry northerly flow aloft along the backside of the ridge moving over the region. This ridge should be temporarily flattened by a moderate short wave trough moving mostly by to the north of the area on Sunday. However, some clouds and light snow or snow showers should briefly transit the area later Sunday morning and afternoon, mainly in the north, before the front shears apart over the region. The recent ridge should rebuild behind the weak and split trough, with a drier northerly flow bringing a return to generally dry, cool weather late Sunday and Monday. If the past few model runs are accurate, at this point no significant weather systems appear likely until mid-late next week. EXTENDED FORECAST FOR SATURDAY THROUGH MONDAY Mostly fair north and central early Saturday, with decreasing clouds and slow clearing trend south. Mostly fair mid-late Saturday with a few high clouds at times. Mostly fair early Sunday. Increasing clouds Olympics and north Cascades mid-day Sunday becoming partly to mostly cloudy north and partly cloudy south mid-late Sunday with a chance of a few showers or a little light snow, mainly in the north and Olympics. Decreasing clouds and showers late Sunday. Mostly fair and cool most areas Monday. * SNOW LEVELS 500 to 1500 ft N, 1-2000 ft S Saturday and Sunday 500 to 1500 ft N, 1-3000 ft S late Sunday 1-2000 ft N, 1-3000 ft S Monday, except snow levels locally near the surface Cascade passes and east slopes later Saturday through Monday