Key parameters definitions

  • Written by Administrator

THis forecast viewer is based on well known and highly regarded RASP (Regional Atmospheric Soaring Prediction)   maps, developed by Dr John W. Glendening for soaring pilots. There is a selection of the most popular parameters. Generally the model is recommended to view for changes more then for absolute prediction. Relative predictions are more reliable then absolute prediction. It's meant relative in time,relative in space and relative to the model topography.

   (THermal Updraft Velocity)  This prediction is intended to forecast the upward velocity of air within the thermal and will never be negative - so the glider descent rate while thermalling must be subtracted to give the expected variometer reading. It has been established  theoretically and experimentally. Physically it depends upon the amount of heat entering into the atmosphere at the ground and the thermal hight as an important factor because a rising thermal bubble will achieve a higher velocity if it accelerates for a longer time. Boundary level depth and surface heating are predicted by numerical model.

    Star rating - Foot Launchers: Based on "Thermalling Height" (hglider). An adjustment for 10 m height wind speed, CuPotential is between 500 and 5000 (indicates small puffy Cu) and 0.5 deducted if CuPotential is < 0 (blue conditions). The Rating is then modified by the Buoyancy-Shear Ratio (bsratio): -0.9 @ 0; 0 @ 3; +0.9 @ 6 (this will be inappropriate in regions with stronger thermals). Finally, the result is spatially filtered to remove noise.

    The speed and direction of the wind at 10m above the ground.  Speed is depicted by different colors and direction by streamlines.  This parameter is obtained directly from WRF model output and not from a BLIPMAP (Boundary Layer Information Prediction MAP) computation.

     No distinction is made between low, middle, or high level clouds.  This parameter is obtained directly from model output and not from a BLIPMAP computation.

   Cloudbase where Cu potential is bigger then 0. This plot is a combination of the value of the 'Cumulus Potential for non-extensive puffy cloud' (LCL - which indicates areas where cloud may form) and the 'Lifted Condensation Level' (the level to which humid air must rise to form cloud). It thus depicts the Cumulus Cloudbase at locations where cumulus may form and so alleviates the need to look at both Cumulus Potential and Cumulus Cloudbase plots. Note that the threshold Cumulus Potential should be empirically determined for your site, which has not been done for the UK: it is assumed to approximate to the theoretical value of zero.  For locations where the actual threshold is greater than zero, as is often the case, this depiction will over-estimate the extent of the cumulus region.

   This depicts the Overcast Development (OD) Cloudbase only at locations where the OD Potential parameter is positive.  This single plot can be used, instead of needing to look at both the OD Potential and OD Cloudbase plots, if the threshold OD Potential empirically determined for your site approximately equals the theoretical value of zero.


    Soundings graphs on the right side of the page. To clear the selection,  click in any empty map area.

 For more  detailed interpretation of the all RASP parameters click here or here