[ RASP UK Forecast (Stratus) ]

Further Information

(Links are to DrJack's Website; The Words are his too!)

Overview These forecasts are intended to help the meteorology-minded pilot better evaluate soaring conditions. The maps are particulalry useful to cross-country soaring pilots, since they allow evaluation of conditions away from the home field. Utilizing the forecasts can require some self-education (though that can't be too hard since over 2000 US pilots actively use BLIPMAPs in the US) as individualized assistance is not provided. At first glance the website can seem intimidating since so many parameters are forecast - but most are "supplemental" forecasts to be used as needed and many users normally look only at the three or four they have found to be most useful, such as the expected lift strength or the maximum (dry) thermalling height or cloud potential/height forecasts, looking at additional parameters only under special conditions. How are these RASP forecasts produced ? My traditional RUC and ETA BLIPMAP forecasts are obtained by post-processing forecast files output from NCEP prognostic models, so horizontal and vertical resolution is determined by that used in those models. Here I am instead running a prognostic model myself, so am able to specify the vertical/horizontal grid (though of course subject to limits of practicality). A WRF (Weather Research and Forecasting) model is being initialized and marched forward in time at 180 second time intervals to produce forecasts at 3 hr increments. Initial and boundary conditions come from the larger-scale models run by NCEP, in this case from the GFS model having a resolution of around 100km. To increase accuracy, forecasts are produced for three different grids: a large-domain coarse-mesh grid (36 km), a 12 km grid nested inside it, and a small-scale fine-mesh 4km grid within that (but only results for the latter two grids are presented). Since the data needed to make such runs is available globally, the forecasts can be made for anywhere in the world. Notes and Caveats
  • One is not supposed to believe all the details of these forecasts, particularly since the smallest-scale structure is constantly changing yet one a few snapshots at different times are shown. Rather, one should be looking for patterns.
  • Forecasts for points close to the boundary will be less accurate than for those located nearer the center of the domain, due to inevitable mis-matchings between the coarse and fine grids. In particular, predictions of max/min BL vertical velocity are very noisy and inaccurate near the boundary (particularly where boundary condition problems exist). To remind users of this, a dotted line marks the "frame" outside of which coarse-fine boundary interaction problems are most prevalent.
  • The "Explicit CloudWater Cloudbase" estimates are based on cloud water predicted from internal model equations and problematical since there is no simple criterion for differentiating "mist" concentrations from "cloud" oncentrations. The criterion presently used is a first guess.
  • The "Cu Potential" and "Sfc. LCL" predictions are based on a simple formula which considers only water vapor at the surface.
  • This model does not ingest as much observational data as do the institutional models such as RUC and ETA, hence some effects are not included.
  • The fact that these forecasts are only a snapshot in time of a fairly noisy field should be particularly emphasized for the 4 km resolution forecasts, as forecasts for, say, 30 minutes before or after would look different. At this point it's difficult to figure how much value they really add anything, but one never knows till one tries.
  • The "Vert. Velocity at 850mb (or 700mb or 500mb)" and "Vert. Velocity Slice at Vert.Vel.Max" parameters attempt to forecast mt. wave events, although strong vertical velocities resulting from deep BL convergence can also be found in the plots. The first parameter gives a plan view of vertical velocity at the 850mb level, a height of roughly 1500 m MSL and thus often above the BL top. The second parameter is a vertical slice taken at a point of maximum vertical velocity (as found at a height of approximately 1500 m AGL within a horizontal box which excludes ane outer edge of the domain; the position of that slice is indicated by a dotted line on the plot of the first parameter (with left-right on the slice always being left-right on the plan view). A label above the plots gives the location and magnitude of the found maximum value. Mt. wave predictions are best made using resultions no larger than 4km, since a coarser grid generally does not resolve the waves accurately.
  • Time loops are provided to illustrate the variability, and hence uncertainty, over a 3 hour period. Unfortunately the color scales are not identical for all maps in the loop, but generally they are roughly comparable.

The Webmaster makes no representations or warranties, expressed or implied, as to the accuracy of the information held herein or its fitness for any purpose whatsoever. In no event will the Webmaster be held liable for any direct, indirect, special incidental or consequential damages arising out of the use of the information held on this server.
BLIPMAP = Boundary Layer Information Prediction MAP - Created by Dr. John W. (Jack) Glendening, Meteorologist