Eric Greenwell wrote:
Unless you fly where you have homogenous weather over a broad area for
most of the day, it's hard to imagine a single number is worth anything.
From our airport (Richland, Washington, USA), the homogenous area is
maybe a 10 mile radius circle. With the usual cloudbase, that's only 30%
of a final glide. Beyond that, picking the right direction to go
determines the quality of the flight, and not the weather around the
airport.
And then there is the problem of different pilots in different gliders:
a beginning XC pilot flying a Ka-6 will have different criteria than an
experienced XC pilot in an ASW 27.

So, we have weather that change with time and location, and pilots that
differ greatly in what is worthwhile rigging for. My suggestion: if you
are going to stay close to home, look at the Blipspot (mini or
otherwise) for your airport; if you want to go a long distance, spend
the 5-10 minutes it takes to digest the Blipmaps. Hey, you are looking
for a five hour flight, the drive time to the airport, plus rigging and
derigging, so what's 10 minutes figuring out when and where to go?



Exactly. So, what a forecaster does to add value is to take all of
these various factors into account to provide an analysis of the
weather and its potential to support cross country flight in your area.
Maybe I didn't give a clear explanation of the background and intent.


- We're fortunate to have a number of tools available to the general
soaring public that didn't exist just a few years ago. Various
forecast soundings, satellite data, etc. are all easily available over
the Web. Add to that interpretive sites such as Dr. Jack's, and one
has a fighting chance of predicting the good days... IF one takes the
time to consider all of the elements that affect XC soaring (a big IF).


- However, the average glider pilot still has a pretty hard time
interpreting even the simplest data. For instance, I can't tell you
how many times people I know have just looked at a RUC Blipmap
forecasting 500fpm lift and figured "it's a great day." They don't
know that it's a moment in time (18Z typically), whether it will be
blue or not, if there is OD potential, etc. etc. Yeah, Dr. Jack gives
you the info you need to do this, but most people can't put it all
together. And, this doesn't even begin to address the issue of
conflict across models and picking the best one (ever looked at the NAM
vs. GFS vs. NGM 24 hours out from a complex frontal passage?)

- The concept of the Soaring Composite Index (SCI as I'm calling it)
is for a human forecaster to interpret all of the available data and
come up with a score for the day. This score is subject to all of the
constraints you listed above (and more), so of course "your mileage may
vary."

- In terms of the assumptions, I do address the fact that the SCI will
be a) site specific (ie. somebody who knows your operating area will
have to do the interpretation) and b) it uses a benchmark of a
"competent pilot flying a Standard Cirrus" (so a Nimbus driver or a
1-26 driver will have to adjust accordingly) and c) the conditions in
any one quadrant may be significantly better or worse.

- In a practical sense, the SCI is really for those poor working
stiffs like myself who can only afford to take a very limited number of
"emergency days off" ("calling in soar" as one of the old-timers in our
club used to say). For me, I will only drop everything for an SCI of 4
or 5 (maybe a 3 if I haven't flown for a month).

- Really the only thing the SCI does is to try to put some rigor
around the statement that "it's going to be a really good day."

Anyway, Jack Harrison is doing the same thing in the UK with what seem
to be very positive results, so I thought I'd try something in Region 2
and see how it goes...

Erik Mann
LS8-18 (P3)