1. GROUP # 3 UPDATED 02/20/2007 Xian Lu Justin Hampton Bryce Harrop Hang Lei

2. 1) TUESDAY MESOSCALE DISCUSSION For Thursday 12Z, upstream of the main trough located just off the coast of California starts to move further inland aided by a jet streak where winds are in access of 145kts. This begins to push the surface cold front as well as the upper level front right against the mountains. Winds are geostrophic out of the west as these winds surge into the mountains, orographic lifting will take place right at the area of interest. This strong convergent boundary will be responsible for heavy snowfall totals along the western side of the mountains. The jet dynamics look favorable for a long lasting snow event as TVL is located in the right entrance region of the jet on Thurs 12Z and has the potential to experience influence from the left exit region of the jet which is streaming down the backside of the trough. Temperatures hover around the freezing level however wet bulb temps are actually below zero indicating that the precip will fall as snow. Liquid precipitation totals re forecasted to reach.75 to 1 inch. Using a conservative snowfall ration of 10:1 accumulations could reach between 7.5in to 10 inches. If jet dynamics stay favorable accumulations could get to 13 inches. The GFS and the NAM are pretty much in agreement with the timing of this system. However the GFS breaks up the trough slightly and does not have as strong of jet influence around 00Z Fri. Due to this fact, the GFS does not drop as much precip in the area. Time will have to play out to see if the jet on the back side of the trough will aid a prolonged precipitation event.

3. 2) TUESDAY PUBLIC FORECAST Winter weather conditions can be expected to start around 10:00pm Feb 20 local time for South Lake Tahoe, CA. And are expected to continue throughout the week. Weather conditions will consist primarily of snow for this region. Accumulation can be seen up to 2 inches falling by Wednesday afternoon. In 48 hours there is a small change that the precipitation will transition into freezing rain. At 48 hours, there is also a slight chance that instead of transition the precipitation will cease entirely.

4. 3) TUESDAY FIGURE 1

5. 4) TUESDAY FIGURE 2

6. 5) TUESDAY FIGURE 3

7. 6) WEDNESDAY MESOSCALE DISCUSSION

8. 7) WEDNESDAY PUBLIC FORECAST

9. 8) WEDNESDAY FIGURE 1

10. 9) WEDNESDAY FIGURE 2

11. 10) WEDNESDAY FIGURE 3

12. 11) NOWCAST AND WARNINGS

13. 12) CRITIQUE (1)

14. 13) CRITIQUE (2)