an article by Rebekah Sherwin, a hang glider pilot.
Published in the March 2012 edition of Skywings,
the magazine of the British Hang Gliding and Paragliding Association (BHPA),
it is reproduced with permission of the author.
Webcasts on using RASP,
including an excellent introduction to Soundings.
Done by some Paraglider people, they are hosted by Judith Mole.
Many Thanks to you all.
Weatherjack's excellent Tutorials are still available.
Some papers by Jean Oberson, a RASP maintainer in Switzerland.
Note there are functional differences from RASP-UK
Tephigrams - What you need to know.
From the Black Mountains Gliding Club Ground School, by Gordon Dennis
Notes and Caveats:
- One is not supposed to believe all the details of these
forecasts, particularly since the smallest-scale structure is
changing yet only 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 are problematical
there is no simple criterion for differentiating "mist" concentrations
from "cloud" concentrations. The criterion presently used is a
- 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 2 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 til
- The "Vert. Velocity at 850mb (or 700mb or 500mb)" and
"Vert. Velocity Slice" 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 Cross Section parameter (available as a pop-up) is a vertical slice taken
parallel to the wind direction at the 850mb level
A label above the plots gives the
location and direction of the slice. Mt. wave
predictions are best made using resultions no larger than 4km, since a
coarser grid generally does not resolve the waves accurately.