FOX44 - Burlington / Plattsburgh News, Weather & Sports12.18.11 The Lake Effect

12.18.11 The Lake Effect

On Sunday morning this was the beautiful picture looking southwest across Lake Champlain from Burlington:

All that gray area pictured above the open water is cloud.  That cloud formed from colder air over the warmer water of Lake Champlain. Temperatures Sunday morning were rising from 7 degrees and into the lower 10s as this picture was saved.  I didn't make it down to the lake to see this, but I believe that it was probably 'steaming' over the lake where a light rising mist could be seen on the top layer of the water.

So here was the set up as of Saturday afternoon.  The Lake temperature was 40 degrees.  At the Burlington International Airport the temperature was 19 degrees.  Higher up in the atmosphere the temperature dropped to 10, 3, and -4 degrees. 

This is called an unstable environment.  The atmosphere likes to be in a stable state, which is

WARM AIR

over

COLD AIR

But we had the opposite set up.  Cold air over warm air is unstable and clouds like to form in that environment.  Overall I guess you could say our atmosphere is unstable because temperatures generally drop off the higher in altitude.  That's why we usually see clouds out there! 

Here's a cross diagram (by yours truly) of Lake Champlain's lake effect this weekend:

This is considered VERY unstable.  From the surface of Lake Champlain to 2,200 feet, the temperature dropped 30 degrees.  The "environmental rate" which we use to diagnose stability, is 10 C per 1 kilometer.  Breaking that down to Fahrenheit and feet, it's about 18 F every 3,274 feet.  Compare that to 30F in 2,100 feet!  That's very unstable.

So here's what happens next:

If there is enough moisture, a cloud will form.  Clouds like to rise when the temperature (watch the green line) drops off quickly with height.  That's what we had Saturday.  A quick drop off in the lowest atmosphere, then a more gradual drop off higher up.  In this scenario the cloud will continue to grow until it reaches its equilibrium level, or when it matches the surrounding air temperature.  As long as the cloud is warmer, it will keep rising.  But when it matches its surroundings, it stops.

So we had a cloud thickness Saturday of probably a few thousand feet.  It was just enough (with a northwesterly flow) to give the eastern Champlain Valley a few light snow showers (1.2" fell at the BTV airport).  It doesn't only happen over the Great Lakes, but here in Burlington/Plattsburgh too!

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