DrJack's Forecast Method
Dr. John W. (Jack) Glendening, Meteorologist
Below is a outline of how I typically do my own forecasts for my
personal flying. This approach considers just the basics - for
certain conditions an amended approach would be used, or someone
forecasting for a contest or a very long flight might want to spend
more time than I do, etc.. Note that (1) I fly a sailplane,
which biases my forecasting toward sailplane cross-country
(e.g. through my choice of a minimum B/S ratio), (2) clouds are
usually not a factor for my location, so their prediction is not a
large concern in my methodology (in fact I often skip the cloud
forecast parameters), and (3) I normally fly over the higher terrain
near my airport, so am not usually concerned with "flatland"
I look at the "Height of Critical Updraft Strength (Hcrit)" forecast
just after mid-day (solar noon) to see if thermals will take me high enough to
undertake the flight I contemplate - if not, then I need not look at
Caveat: If other parameters could affect the
thermalling height I need -- such as lift from convective clouds or
convergence -- those parameters should also be looked at.
I look at the "COMPOSITE: Thermal Updraft Velocity & Buoyancy/Shear (B/S) Ratio" forecast to see if the
thermals produced will be workable, i.e. a B/S Ratio above 4 and even better above 7 - if not, then I need go no
Caveats: (1) the B/S value below which thermal are not
workable depends upon glider type and pilot experience, (2) If
convective clouds produce significant "cloud suck", then B/S and W*
forecast values are underestimates since they do not include that
cloud effect, (3) I am not much concerned with "Thermal
Updraft Velocity (W*)" per se because it is included in the Hcrit
calculation and because I fly where terrain is significant (i.e. not
under flatland conditions) and know that if I can reach my desired
Hcrit in that terrain then I will be OK.
If clouds might be important then I look at the
"COMPOSITE: Cu Cloudbase for Cu Potential > 0"
forecast to see if clouds might prevent me from reaching my desired
thermalling height - but in addition, the presence of clouds might
produce additional "cloud suck", which is neglected in the computation
of "dry thermal" parameters such as Hcrit and B/S Ratio and W* and so
can alter expectations based on those parameters. If much
cloudiness is indicated, then I might also check out the possibility
of overdevelopment using the "COMPOSITE: OD
Cloudbase for OD Potential > 0" forecast.
I look at the "COMPOSITE: BL Wind Speed and Direction" forecast.
I look at any locally important parameter - since I am flying around
mountains, one such is the "convergence" forecast ("BL Max.Up/Down Motion").
I look at the local weather service forecast for my area, looking for factors
beyond these soaring parameters which their forecasters might highlight, notably
the chance of rain, thunderstorms, etc - such factors are best determined by
experience rather from a simple model output.
(Even better can be the
"Forecast Discussion" which every NWS regional forecast office
provides - while somewhat technical, they provide valuable insight
into what experienced meteorologists think of the current
conditions and forecasts.)
I look at a detailed resolution (1 km) visible satellite photo to see if there
are cloud factors which the models might have missed, such as high cirrus (which
is often missed by model forecasts but which can greatly diminish thermal strengths).
Occasionally I will do a more detailed analysis, e.g. looking at other
parameters, different times, comparison of forecasts from different
models, looking at forecast soundings, etc.
BASIC Thermal Forecast Parameters
Additional helpful information - see "For NEW USERS" and "What NEXT?" sections