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Old Jan 04, 2008, 11:13 PM
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Thermals over frozen lakes

Since water under frozen lakes is warmer than air on typical winter days, is it likely that such lakes commonly cause thermals in winter?

I know that lakes are generally considered poor for lift in the warm months, but in winter wouldn't the heat differential be reversed; when the water is commonly warmer than the air. I've heard that lakes can be ripe with lift at the end of the day if the air temp. drops and the lake gives up its heat. Such a phenomenon would seem to support winter lakes as thermal "radiators."

I know snow is a good insulator, but it would seem that the relative heat from all that water is transferred somewhere as the lake's upper layer turns to thicker and thicker ice. Is it likely turned into thermals as long as the air temp. is below 32 degrees (even with snow cover)?

Would open water in winter enhance the effect?

I find frozen lakes are tempting as vast open flying areas, but have not tried them. Have you?

Thanks,
Bob
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Old Jan 05, 2008, 12:08 AM
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Jo Jo should be able to tell everyone.

Tim
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Old Jan 05, 2008, 12:47 AM
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Here's a reference that's right on topic:
http://ams.allenpress.com/perlserv/?....0.CO%3B2&ct=1

It may be a little technical, but it does indicate there's such a thing as "snow breeze", and a snow breeze suggests thermal activity over the lake.

If you have access to aviation weather for the area, you can find the forecast for surface winds. On days when winds are predicted to be calm or very light, you might try contacting people living in different areas along the shore to see if there's a snow breeze that's different from the general wind direction for the area.

Your idea certainly sounds like it might work.

Roger
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Old Jan 05, 2008, 05:52 AM
May the Wind Always be Good
Webster, Minnesota
Joined Feb 2007
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Winter Lift

Yes there is lift in the winter... have done many over 15min flights in the winter ..Been there and done that ...from the cold of Minnesota....
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Old Jan 05, 2008, 07:01 AM
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Marietta, GA
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It's all relative. When the air temp is 20 degrees, the sun still heats the earth, which warms the air above it, and that air is going to rise. Thermal activity doesn't shut down because we're a bit cold!
..a
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Old Jan 05, 2008, 11:11 AM
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I know that thermals don't shut down in winter climes. A friend who flies free flight hand launched gliders told me caught his strongest thermal during a heavy snow fall. But, I'm wondering if lakes in winter (both frozen and unfrozen) actually "produce" thermals due to their being warm relative to the air. Rogers reference is indeed "right on topic." So I guess I'm really wondering, is the phenomenon actually frequent, pronounced, and useable for soaring, or just too weak to be significant. And what I'm really really wondering is what other's experiences may indicate about this. I'll try it myself sometime, but thought perhaps others could save me the trouble of, say, combining soaring with ice fishing.
Bob
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Old Jan 05, 2008, 12:15 PM
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Jyvaskyla, Finland
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During the darkest winter we have about 4-5 hours of decent daylight. Not much to talk about direct sunlight generating temperature differences. I am happy if I can see which way may plane is oriented

My experience is that winter lift is mostly related to low clouds or waves. I mean during December-January... In March it is totally different ball game. Direct sunlight is heating up the forests and buildings. Frozen lakes make very clear temperature differences with them. Spotting thermals from the treeline is easy but if you are low down, the air is often very rough and difficult to work.

If you have experienced real winter, you will appreciate the warm summer days
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Old Jan 05, 2008, 01:43 PM
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Frozen snow covered ground, frozen lakes, both develop thermals, as has been noted.
So I vote, Yes, it's likely!
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Old Jan 05, 2008, 07:18 PM
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Cold air and warm pods make OK lift.
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Old Jan 05, 2008, 07:33 PM
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Blissfield, Michigan
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Really never tried soaring in winter. For sure the colder the thicker the air so you can fly slower. You know soaring clubs just plain shut down in the winter months - why? If there was any good thermal activity in winter in the North they wouldn't shut down. I am fairly good flying RC gliders and finding thermals. SOOOO next Summer I'm going for my glider (full scale) pilots license. All of you glider folks should consider doing the same since it's MUCH cheaper than a regular power pilots license and full scale gliding is the ultimate BLAST. Jim PM me for a link to our full scale club.
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Old Jan 05, 2008, 08:06 PM
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This thread is very interesting, but making me cold just reading it!
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Old Jan 06, 2008, 04:31 AM
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Jyvaskyla, Finland
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Quote:
Originally Posted by dephela
Frozen snow covered ground, frozen lakes, both develop thermals, as has been noted.
So I vote, Yes, it's likely!
Yes but as tried to explain, it is not that simple. One more thing to note, in cold and clear winter days air is very dry. It does not develop clouds. Also low level thermal activity is very weak and any wind destroys thermals quickly.

In the mids of winter, cloudy warmer days, temperature close to 0c, thermals are much stronger. When cloud base is close to towing height, you can easily work the cloud bottoms and edges. Just head towards the darkest cloud, you see...

The different opinions maybe also partly due to geographical differences. Thanks to warm golf-stream, we live really north here in Scandinavia. Take a map and compare Europe and America! It is not that cold over here, but as I said, we get very little sunshine. Today at 12 am. the sun was barely over treeline!

My friends in US: to understand how weak the winter sun shine is over here, you should go spend your winter holidays in Alaska or northern parts of Canada and try thermalling over there
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Old Jan 06, 2008, 12:43 PM
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Northern lights

Quote:
...to understand how weak the winter sun shine is over here, you should go spend your winter holidays in Alaska or northern parts of Canada...
I’ll take your word for it. However, at mid-summer, it would be interesting to thermal at mid-night. Regis
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Old Jan 06, 2008, 01:04 PM
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It is conceivable that a frozen lake might generate some thermal lift if the air is very cold. However, if that lake is covered with snow (as will often be the case), then the heat of the water/ice system will be insulated from the air – and thermals will not be likely. The same might be the case if the ice gets very thick.

But if anybody out there would have a feel for this sort of thing, it would be Tuomo. If he hasn’t gotten an indication that frozen-lake thermals are happening, then they probably aren’t strong enough to be of any use. Given the lack of sun-driven thermals in central, snow-covered Finland during the winter, a strong frozen-lake “thermal machine” would have been noticed.

And I have experienced a couple of weeks of winter in Tuomo’s home town of Jyvaskyla, and I’d say that thermal lift would indeed be very difficult to come by during the winter. There, a winter’s day is really a sunrise that transitions directly into a sunset. Here in the interior of North America at a much more southerly 39.5 N, the mean January temperature is not a great deal warmer than Jyvaskyla but the sun does indeed produce decent winter thermals at times, even with significant snow cover. For that reason any frozen lake effect would be difficult to detect around here.

FF
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Old Jan 07, 2008, 08:47 PM
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I was coming in from an afternoon of XC skiing on a 3' snow pack a couple of weeks ago. The late afternoon sun was striking a S slope and above it I watched 5 hawks enter a thermal and slowly rise to specs in the sky.
Our glider club (full size) sometimes launches off a pond in the winter using a winch, which now needs it's motor rebuilt, with some good results. Essentially you're starting with a save with a low launch like that. Trick is to land the glider back at the end of the tow line or it's a long slog to push/pull it to the next launch.
-Peter
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