"Jim" wrote in message ...
I came across Dr Jack's BLIPMAP forecast page
http://www.drjack.net/BLIPMAP/NE/index.html

Probably a lot of good information if you know how to use it (and some very
pretty maps), but also not exactly intuitive and slightly overwhelming.

Anybody find good use of this material, and in an orderly process how do you
proceed to a practical forecast of what may happen thermal wise today at
your gliderport?

I started to respond privately since there has been extensive
discussion on RAS about blipmap. But then, when I did a google search
within RAS on "blipmap", so much came up about contributing, etc. that
I decided to post this to the site, knowing full well that many will
find this already known. But, I decided that minor inconvenience was
worth getting new people like Jim conversant in blipmaps.

Blipmap has proven to be the most useful thermal forecast tool most of
us (all of us?) have ever used. Compared to Reno FSS' soaring
forecast, which gives a single number for updraft strength and top,
blipmap shows where to find the lift. And, it's more accurate than
anything else I've seen. Early on, when Reno FSS' soaring forecast was
predicting 1500 fpm to 18k, and blipmap was predicting a poor day, I
had trouble getting over 10k out of Minden. Chalk up one for blipmap.
And many others have posted similar experience.

Blipmap is based on a 20 km square grid, so what you're seeing is an
average over each 20 km square. Hence, most of us have found that the
predicted updraft strength, while theoretically a gross figure, tends
to match our actual net climb rates (i.e., after subtracting our sink
rate). Similarly, while the boundary layer top predicts the very top
of the thermals, not the usable top, we have again found that this
tends to match the actual top of our climbs fairly well.

In addition to updraft strength and boundary layer top, I tend to look
at cumulus cloudbase (to determine if I can get to the tops of the
thermals and whether they will be blue or marked by cu's),
overdevelopment potential (numbers greater than 0 and esp greater than
1 indicate OD potential), wind speed in the boundary layer (preferably
under 10 or 15 kts), and B/S ratio if windspeed is significant (B/S =
buoyancy to shear ratio must be greater than 5 to prevent broken up
thermals), and BL max up/down. The last map shows areas of
convergence. Since this is in .01 kts, anything less than 50 (1/2 kt
updraft) produces little effect. Between 50 and 100 is likely to
produce good cloud streets along the convergence line (esp if
cloudbase is close to BL top), and anything over 100 means drop
everything and go for it.

These maps are available starting sometime between 6 PM and 8 PM (Cal
time) the night before and are updated throughout the night, so it's
good to double check in the morning and see if it's changed.

They are also available at different times of the day, but mostly 10
AM, 1 PM and 4 PM PST (talking as a mostly CA/NV soaring pilot) or
11AM, 2 PM and 5 PM PDT during the summer. These different times give
a good indication whether to start early or late.

As a final note, I should mention that Blipmap is available free of
charge, but is supported by donations to Dr. Jack. Until recently, not
only was he putting in unbelievable amounts of time, but also paying
for the web hosting and any other expenses. I strongly encourage you
to make an annual contribution to keep this great soaring tool alive
and well. And, when commenting on blipmap, please keep in mind the
volunteer nature of it's existence. Complaining about a missing
feature is not the way to make Jack and the other volunteers feel
appreciated -- or to keep blipmap alive. I've got my own list of
additions I'd love to see, but am grateful for how far blipmap has
taken us. On the days when the server is down, I feel almost lost
without it. And, many days that I wasn't planning to fly, but blipmap
encouraged me by a great forecast, have paid off handsomely. It's not
perfect, but it's a quantum improvement over what existed before.

Hope this helps.

Martin