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Williams. Westerly flow indicates Lower Launch, while SW flow indicates Upper Launch provided velocities between 9K and 12K don't exceed 20 knots - and even then you might expect compression on Upper Launch.
Because the Divide acts like a big dam with regard to air mass movement, you can get an idea of upslope, downslope, etc. Look at morning and afternoon data - strong winds in the morning, forecast to decrease in the afternoon, can mean good late day flying mid-summer, but likely blown out midday. Lighter morning winds forecast to increase to strong later indicate the opposite conditions. These data are from a computer model, so you can think plus or minus a couple hours at best with regard to time when things actually occur.
In addition, the winds aloft model data is updated at 10am mountain time. If you get to the flying site and actual winds do not fit the early forecast, you
can call Flight Services (1-800-WX-BRIEF) and ask a briefer for updated winds aloft - just be nice and identify yourself as a hang glider pilot and give your name and general location (i.e., Summit County). If you're in the mountains and concerned about strong winds, ask if there are any pilot reports from near the area you're in - if there are reports of moderate to severe turbulence between 12K and 18K, your concerns are probably well
founded.
The Colorado Forecast for smaller zones discussions is at http://weather.noaa.gov/pd/coframes.html. Lynda stumbled onto this cool web site - one can compare smaller scale forecasts around a flying site of interest. We've found it useful to determine what the forecasters are thinking with regard to OD and other smaller scale weather in the mountains.
The forecast discussion link on the RMHGA site is helpful - when they say high winds, they are generally right. Plus, you get some insight into "...if this happens, then we expect this. But, if this hap
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