Question about blipmaps

[Spam]

Alright here's a question about top of useable lift for the blipmaps.

If the thermal tops are 7,000
and the cloudbases are 5,000
and the top of useable lift is 4,000

Does this mean that when you get to 4,000 you will have risen to the
top and can only circle around in zero sink there?

[Tony Condon]

At 18:22 24 August 2009, Spam wrote:
>Alright here's a question about top of useable lift for the blipmaps.
>
>If the thermal tops are 7,000
>and the cloudbases are 5,000
>and the top of useable lift is 4,000
>
>Does this mean that when you get to 4,000 you will have risen to the
>top and can only circle around in zero sink there?
>
>
>

by top of useable lift do you mean the hcrit parameter?

if so then that is supposedly approximately the alititude where you will
no longer be able to climb. be careful though, the NAM and RUC forecasts
(at least around here) are often a bit optimistic on the temperature and
dew points, which skews the forecast vs. reality. remember that the
forecast temperature, dew point, sun heating, and everything else has to
line up in order for the lift forecast to be valid as well.


-Tony Condon
Cherokee II N373Y

[[email protected][_2_]]

On Aug 24, 2:45*pm, Tony Condon > wrote:
> At 18:22 24 August 2009, Spam wrote:
>
> >Alright here's a question about top of useable lift for the blipmaps.
>
> >If the thermal tops are 7,000
> >and the cloudbases are 5,000
> >and the top of useable lift is 4,000
>
> >Does this mean that when you get to 4,000 you will have risen to the
> >top and can only circle around in zero sink there?
> Cherokee II N373Y

My experience is that the "top of useable lift" is conservative; I
find the NAM "Height of the Boundary Layer" to more accurately predict
how high the "best" thermals will go. This from extensive soaring in
Arizona and Illinois. YMMV, of course ;^)

Kirk
66

[BT]

remember that "thermal tops" is where the thermal either hits an inversion
layer or "the lifted air mass" has cooled to the actual temperature. The
difference between "expected lapse rate temperature" and "actual measured
temperature" becomes zero

for gliders to effectively be able to climb, they need a "thermal index" or
difference in temperatures between actual and expected lapse rate of
about -3. Considering the std lapse rate of about 2.5C per 1000ft, that
works out.

There may still be some lift at 4000ft, most gliders have a "sink rate" of
about 1.2 to 1.7knts (120fpm) and if the lifting air mass has slowed or
reached about the same... then yes.. you may have reached "zero sink".

The other posted responses cover what they use in the forecast to best
determine the "lift band"

BT

"Spam" > wrote in message
...
> Alright here's a question about top of useable lift for the blipmaps.
>
> If the thermal tops are 7,000
> and the cloudbases are 5,000
> and the top of useable lift is 4,000
>
> Does this mean that when you get to 4,000 you will have risen to the
> top and can only circle around in zero sink there?
>
>