On Wednesday, December 20, 2017 at 9:42:19 AM UTC-5, wrote:
Yes thanks for a great post! I find it interesting that the "dry" river beds, and the "wet" cattle tanks out west seem to produce great thermals. I have always attributed that to a "low" area allowing the heat bubble to pool to a larger size before being ripped off due to the wind. The late 1V, Carl Herold, always commented that you cant get good thermal days without a good 10-15 mph of wind to keep them releasing.

CH

Wet places that produce thermals are the bane of meteorologist/sailplane pilots. They can drive you nuts. When I flew out west I felt I really understood the soaring boundary layer ... there was rarely anything going on that I couldn't confidently explain.

Starting to fly in the Northeast, flying from Saratoga (5B2) there's all kinds of WTF! stuff. We have some "persistent mysteries" about house thermals within 2 miles of the field.

One REALLY important thing to remember though is that all the really good soaring days happen after a cold front booms through. This is particularly true in the non-desert parts of the country -- basically the only time you can get even "decent" conditions for long flights.

After a cold front a lot of the heat isn't solar (particularly around us) .... it's stored heat in the surface. A good cold front (at jet-stream latitudes) can easily give you -30 °F drop in surface air temperatures (and a nicely near-adiabatic lapse rate) ... and the stored heat available from that can give you a lot of lift.

We have uncommon fall days in the NE that no western pilot "gets" -- days when the skies are gelid overcast at 10,000 ft, a bitter cold wind at the surface, and shockingly good lift ... 8 - 10 kts (that's really good lift out here). All of that is being driven by the extracted surface heat stored up through the previous warm-sector passage.

And in those conditions ... shallow water bodies are often great. Water has high heat capacity AND a little wind-stress can stir it, so the heat can be "mined" out of the top meter or so much more quickly than this heat could conduct up (soil has poor thermal conductivity).

What may be counterintuitive until you think about it is that this works best when the temperature is cold, near freezing. Under those conditions the Bowen ratio will be favorable -- little water can evaporate -- sensible heat flux is maximized.

Flying downwind of the Adirondacks also produces bafflingly complex "wave" phenomena and a great many cases where thermal & wave systems coexist, and also conditions where one can climb in clear air up alongside convective clouds. A lot of this is very hard to explain classically.

My take on some of this is that it is not wave really, instead it is convergence due to the Mohawk/Hudson drainage convergence ... but without a lot of data I can't get, hard to know.

But as Dr. Suess said: “From there to here, from here to there, funny things are everywhere!”