2 PM PST FRI JAN 04 2008 WEATHER SYNOPSIS FOR FRIDAY AND SATURDAY The early winter of 2008 continues to be dominated by a moist and intermittently strong south to southwesterly flow around a deep upper low about 400 miles west of the central Oregon coast. While strongest associated flow, driven by a 200 knot jetstream, is being increasingly directed toward California, slightly weaker northern parts of associated frontal systems keep rotating northeastward over the Northwest. Warm overrunning from the most recent frontal system moved onshore over Oregon and southwest Washington early Friday, with the following cold front quickly sweeping over the area mid-late Friday morning and mid-day. This brought increasing moderate snowfall in most areas, heaviest near the southern volcanoes and along the Cascade east slopes where the southeasterly flow produced enhanced lift of the moist air mass. The front also produced strong winds...southerly near higher ridges and easterly across the Cascade passes. While there has been some brief warming aloft, the cold easterly surface flow across the Cascades has maintained all precipitation there as snow, with any rain primarily confined to lower elevations along the west slopes of the Cascades and Olympics. The primarily southerly flow aloft has also resulted in generally less precipitation near the Cascade passes. Following the frontal passage several upper disturbances rotating out of the parent upper low should move over the region later Friday afternoon through much of Saturday. Currently, substantial shower activity along the coast has organized into a developing comma cloud band just moving onshore in southwest Washington and northern Oregon. As this moves northeastward later Friday afternoon and evening, enhanced showers are likely with the associated surface trough bringing a pass wind shift to strengthening westerly Friday evening. With several more upper level disturbances expected to move over the region later Friday night and Saturday in a moderate to strong west to southwesterly flow, this should maintain periods of moderate to occasionally heavy orographic snowfall at low and lowering freezing levels for much of the day. By late in the day, the heaviest precipitation should slowly shift southward into south- central Oregon. This should allow for gradually decreasing showers and winds in most areas late Saturday afternoon and night. WEATHER FORECAST FOR FRIDAY AND SATURDAY * OLYMPICS- Windy with moderate rain or snow decreasing and becoming more showery Friday afternoon. Moderate showers slightly increasing later Friday afternoon and night. Periods of moderate snow or snow showers Saturday, heaviest west and southwest slopes, along with a chance of thundershowers. Moderate snow or snow showers decreasing Saturday night. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST- Windy with moderate to occasionally heavy rain or snow decreasing and becoming more showery early-mid afternoon. Moderate showers increasing and becoming moderate to occasionally heavy snow or snow showers Friday night. Periods of moderate to occasionally heavy snow on Saturday with chance isolated thundershowers. Moderate snow or snow showers gradually decreasing Saturday night. * CASCADE PASSES, INCLUDING STEVENS, SNOQUALMIE AND WHITE PASSES- Windy with light to moderate snow decreasing and becoming more showery early-mid afternoon. Moderate showers increasing and becoming moderate snow or snow showers Friday night. Periods of moderate to occasionally heavy snow or snow showers Saturday with chance isolated thundershowers. Moderate snow or snow showers gradually decreasing Saturday night. * EAST SLOPES WASHINGTON CASCADES- Windy with moderate snow decreasing and becoming more showery mid-late afternoon. Light to moderate showers increasing and becoming moderate snow or snow showers Friday night. Periods of light to moderate snow showers Saturday, heaviest higher terrain near the crest. Showers gradually decreasing Saturday night. * MT HOOD AREA- Windy with moderate snow briefly decreasing early Friday afternoon. Moderate snow showers increasing later Friday afternoon and night. Periods of moderate to occasionally heavy snow or snow showers Saturday with chance isolated thundershowers. Moderate snow or snow showers gradually decreasing Saturday night. SNOW LEVELS-CASCADE MTNS 4000 ft N and C, 4500 ft S early Friday afternoon 3000 ft N, 3500 ft C, 4000 ft S later Friday afternoon 3000 ft N and C, 2500 ft S Friday night 1500 ft N, 2000 ft S Saturday morning 1000 ft N, 1500 ft S Saturday afternoon 500 ft N, 1000 ft S Saturday night, except snow levels at the surface Cascade passes and east slopes Friday, rising to near free air levels Friday evening SNOW LEVELS-OLYMPIC MTNS 3000 ft Friday afternoon and evening 2000 ft later Friday night 1500 ft Saturday morning 1000 ft Saturday afternoon 500 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 .5-.75 .5 * MT BAKER .75 .75 * WASHINGTON PASS .25-.5 .25-.5 * STEVENS PASS .5 .5-.75 * SNOQUALMIE PASS .5 .5-.75 * MISSION RIDGE .5-.75 LT .25 * CRYSTAL MTN .5-.75 .5-.75 * PARADISE .75-1 .75 * WHITE PASS .5-.75 .5 * MT HOOD .5-.75 .75 WINDS IN MILES PER HOUR (MPH) * CASCADE PASS LEVEL WINDS E 10-20 with higher gusts Friday afternoon E 5-10 early Friday evening W 10-15 late Friday evening W 15-25 with higher gusts Friday night and Saturday morning W 10-15 with occasional higher gusts Saturday afternoon W 5-15 Saturday night, decreasing further late * FREE WINDS AT 5000 FT S 30-45 N, 40-60 S Friday afternoon SW 25-40 N, 30-50 S and Olympics Friday night and Saturday morning SW 20-40 Cascades, 30-45 Olympics late Saturday morning SW 15-30 Cascades, 20-35 Olympics Saturday afternoon SW 10-20 Cascades, 15-25 Olympics Saturday night * FREE WINDS AT 9000 FT S-SW 30-50 N, 50-70 S Friday afternoon SW 40-60 N and S Friday night W-SW 30-50 Saturday morning W-SW 30-45 Saturday afternoon W-SW 20-40 Saturday night EXTENDED WEATHER SYNOPSIS FOR SUNDAY THROUGH TUESDAY After brief and weak upper ridging, the final upper trough in the current series should move weakly over the region late Sunday afternoon and night. This should produce increasing light to moderate snow in the Oregon Cascades to about Mt Hood, but only light snow in the extreme southern Washington Cascades and continued light snow showers further north. Slightly stronger but still brief upper ridging is then expected to move over the area on Monday, bringing further decreasing light snow or snow showers and some brief clearing. However, the drought should be very brief with yet another strong frontal system and strong upper low expected to move across the region late Monday and through early Wednesday. This should bring increasing light snow to the Olympics and Mt Hood area Monday night, with moderate to heavy snow spreading to the region Tuesday morning along with brief and limited warming and increasingly strong winds. Moderate to occasionally heavy snow should decrease and become more showery later Tuesday, but a strong westerly flow and several associated upper troughs should produce moderate to heavy orographic snowfall along with west slopes of the Olympics and in most areas near and west of the Cascade crest late Tuesday through mid-late Wednesday, with locally heavy accumulations likely. EXTENDED FORECAST FOR SUNDAY THROUGH TUESDAY Light snow or snow showers decreasing Sunday morning with partial clearing mid-day and Sunday afternoon. Increasing light to occasionally moderate snow Mt Hood area later Sunday, otherwise, light snow showers slightly increasing north and central Cascades and Olympics. Showers or light snow decreasing Monday. Increasing clouds with light to moderate snow redeveloping Olympics and Mt Hood area late Monday night, increasing and spreading to the remainder of the Cascades early Tuesday. Moderate to heavy snow Tuesday. Moderate to heavy snow or snow showers later Tuesday through Wednesday morning with heavy accumulations likely. * SNOW LEVELS Sea level to 1000 ft N, 500-1500 ft S Sunday and Monday Sea level to 1000 ft N, 1000-3000 ft S early Tuesday 1-3000 ft N, 2-4000 ft S mid-day Tuesday 1-2000 ft N and S late Tuesday, except snow levels at the surface Cascade east slopes and passes Monday night and Tuesday morning, rising to near free air levels mid-day Tuesday