So it turns out that it's all based on the wet bulb temperature, which you can compute from ambient temp and relative humidity. Wet bulb temp less than 20F is excellent (dry snow), 21-27 is OK (wet snow), and 28-> is no snowmaking. There's a wet bulb temp calculator web page (and a link to a spreadsheet) here:
http://www.the-snowman.com/wetbulb.htmlI wrote a little UNIX shell script that pulls weather info off the National Weather Service XML feed and displays the info along with the snowmaking condition. I'll probably refine it over the next couple days and maybe wrap it in a GUI. It could be a little app that sits on the desktop and keeps tabs on favorite ski areas.
CRaig
Sample Output:
Current Snowshoe Weather
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Report: Last Updated on Jan 8, 11:51 pm EST
Conditions: Overcast
Temperature: 37 F
Rel. Humidity: 79 PERCENT
Wet Bulb: 34.6533 F
Wind: Calm
Gusts: 0 MPH
Wind Chill: Not Applicable F
Snowmaking: NOT POSSIBLE
Current Wintergreen Weather
--------------------------------------------------------------
Report: Last Updated on Jan 9, 12:00 am EST
Conditions: Fair
Temperature: 34 F
Rel. Humidity: 87 PERCENT
Wet Bulb: 32.6206 F
Wind: Calm
Gusts: 0 MPH
Wind Chill: Not Applicable F
Snowmaking: NOT POSSIBLE
Current Sugarbush Weather
--------------------------------------------------------------
Report: Last Updated on Jan 8, 11:51 pm EST
Conditions: Fair
Temperature: 19 F
Rel. Humidity: 92 PERCENT
Wet Bulb: 18.3905 F
Wind: Calm
Gusts: 0 MPH
Wind Chill: Not Applicable F
Snowmaking: EXCELLENT (DRY SNOW)