Explanation of “Soaring Weather Forecast” sheet 22 June 2004 Data: The weather information used in preparing the sheet comes from www.weather.unisys.com, www.rap.ucar.edu/weather, rams.atmos.colostate.edu/realtime and from analyses using a RAOB program (www.raob.com) with data from www.arl.noaa.gov/ready/cmet.html or www-frd.fsl.noaa.gov/mab/soundings/java/. Definitions: Forecast winds/temperatures: The KFt/km(MSL) column lists the heights above mean seal-level, eg. 02/0.6 means 2000 feet or 600 m MSL. The Deg/Kt column lists the direction the wind will blow from in degrees true and the speed is given in knots. The C column is the predicted air temperature and dew point in degrees Centigrade. Trigger temperature: The temperature the surface air must reach for soarable thermals to 2500 feet above ground level. Time: The time the trigger temperature is expected to be reached. Surface winds: The expected surface winds at the time of trigger temperature. Maximum temperature: The expected maximum surface air temperature. Time: The time the maximum air temperature is expected to be reached. Maximum altitude: The maximum height AGL thermals are expected to reach at the time of the maximum air temperature. “K” Index: A function of the 850, 700 and 500 mb temperatures and dew points that measures thunderstorm potential: <25, weak; 25 to 35, moderate; >35, strong. Showalter Index: A function of 850 mb temperature and dew point and 500 mb temperature that measures thunderstorm potential: >4, weak; 4 to -4, moderate, <-4, strong. Soaring Index: Estimated average climb rates. “TI” @850 mb: A measure of the difference between the 850 mb air temperature and parcel temperature rising dry-adiabatically from the expected maximum surface air temperature: >0, sailplanes will not reach 850 mb level (about 5200 feet MSL); -3, good chance of reaching 850 mb; -8 to –10, strong lift at 850 mb level and excellent soaring. Lifted Index: The LI is a modification to the Showalter Index that measures thunderstorm potential: > -3, weak; -3 to -5, moderate; < -5, strong. Cotton Soaring Index: Surface temperatures are forecast at grid points using solar radiation received at the surface, infrared radiation from the surface, sensible and latent heat fluxes into the air and heat diffusion into soil. The CSI is calculated using forecast surface temperatures and a difference between forecast air temperature 1600 m above ground level and the temperature of an adiabatically lifted parcel to that level. Look for negative values of CSI. The more negative the better for good thermals. CAUTION - CSI does not tell you if clouds will over develop. You must look at rainfall predictions for that. Maximum altitudes and climb rates: The values are valid for the middle of the row or the column. The climb rates are based on an average of the Russell Pearson and Mario Piccagli empirical algorithms, hence, they are for the climb rates of the sailplane not the thermal.