Thermal Index Reports

To get a consistently reliable idea of the day's soaring conditions, one can make use of: upper-air data, measured twice daily at hundreds of weather stations all over North America: current surface conditions, at most an hour or two old, from thousands of locations; and forecasts based on weather models running on National Weather Service supercomputers, oriented toward a variety of timespans.

GBSC's home page provides multi-part "TI Reports" for two New England glider ports (Sterling, MA, and Franconia, NH), comprised of:

• a thermal index table and graph
• an NWS regional weather synopsis
• the Weather Observation report from the closest large airport
• a Terminal Aerodrome Forecast for that airport

The Thermal Index section is based on upper-air data measured at 12 UTC (8 am EDT), and 18-hour Aviation Model daily maximum temperature forecasts generated at 00 UTC. The TI Reports are produced every morning as soon as upper-air data is available, typically around 1230 UTC.

Over the years, the most reliable thermal predictions available for Sterling have been found to be generated by using upper-air data from RAOB balloons launched at Albany NY at 12 UTC. The forecast is most accurate when the mid-level winds are from the northwest. It tends to be accurate for conditions around noon at Sterling when those winds are at about 20 knots; forecast accuracy tends to peak earlier or later in the day if the mid-level winds are stronger or weaker respectively.

The forecast high temperature for a region is a crucial element in Thermal Index computation; it directly influences calculation of trigger altitudes and cloud bases. The forecast for the town of Fitchburg, less than 10 miles from Sterling and - very important - at the same altitude, is used when available, with Concord NH as a backup.

For Franconia, upper-air data from Maniwaki, Quebec is the best that is reliably available. It is combined with the forecast high temperature for Whitefield, NH, with Burlington VT as a backup. Maniwaki is quite far upwind, so prediction accuracy is more sensitive to mid-level wind direction, and tends to peak at 3 pm when the mid-level wind is 20 knots; the peak's timing varies with wind strength as with Sterling.

Today's Reports:
     Sterling      Franconia

Archived Reports:
The Thermal Forecast Archive contains an archive of most days' forecasts, starting in early 1996 for Sterling, and Sept 1999 for Franconia. Older data is in gzip'd tar format.

More information:
TI Program - Kevin Ford and Gary Helmstetter's "white paper" about the program that produces the Thermal Index section of the Reports.
Annotated TI Report - explains the contents of a sample report in complete detail.

Boundary Layer Information Prediction Maps

Dr. Glendening's Boundary Layer Information Prediction Maps use weather forecast model data - as opposed to physical upper-air data measured from balloons - to make detailed forecasts about soaring conditions, both near-term and farther into the future. These are presented in a graphically sophisticated form called "BLIPmaps". Here is a link to the New England BLIPmaps.