Weather Tutorial

RAOB Soaring Data: Texas A&M University obtains weather data from the National Weather Service via a service provided by Alden Electronics. Twice a day, at 0Z and 12Z, at about 150 locations in North America, weather balloons are sent up to gather data on temperature, pressure, dewpoint, wind speed and wind direction. The data is usually available on the computer within an hour after the observation. The 12Z sounding is particularly useful in the United States for forecasting soaring conditions.

K Index Stability Contour: This is a contour plot of K index with a contour interval of 4. The KI field shows instability in the atmosphere as it relates to the development of air mass thunderstorms. It is based on the 850 to 500 mb lapse rate plus 850 mb dewpoint minus the 700 mb dewpoint depression. Strong Springtime thunderstorms often require dry air at mid levels to cap the convection. On the other hand, summer air mass thunderstorms need a very moist atmosphere at mid levels to prevent evaporation through entrainment. Where KIs are greater than 35, air mass thunderstorms are likely. the higher the number, the higher the probability. Values < 10 indicate areas of stable weather where skies are generally clear.

Lifted Index Stability Contour This is a contour plot of lifted index with a contour interval of 2 degrees Celsius. The LI field shows instability in the atmosphere by lifting a parcel of air from the surface to 500 mb and comparing its temperature to that of the environment. Where LIs are less than 0, thunderstorms are possible. The lower the number, the more unstable the atmosphere is and as a result, the stronger the thunderstorms could become. Values of -4 or lower indicate areas where severe thunderstorms are possible. Values > 10 indicate areas of stable weather where skies are generally clear.