[MAMS] More on conditions this morning

[Dr. Gerald N. Johnson]

Cold front shoving under warm air to make an inversion? It cooled a lot 
here overnight. Then when the surface air cools to the dewpoint, its a 
hint of calm and clear so there's much radiant cooling at the surface 
that doesn't get mixed with air above the surface making a temperature 
inversion. The old saw about cold air sinking into valleys is 
technically incorrect. Valleys cool by radiation and when its really 
calm there's not enough circulation to move cold air to the valleys or 
to mix warmer air flowing over the hills to mix warmer air with that in 
the valleys. I have software that monitors satellite observed 
temperatures trying to use cold cloud temperature to tell clouds from 
bare earth and snow to discriminate radar precip echoes from AP. It 
compares to surface observations and some times the surface temperature 
the satellites see is more than 10 degrees colder than the 2m altitude 
dewpoint observation. Radiant cooling is stronger than most weather 
types realize. Valley cooling requires dead calm, and the standard 
anemometer stops about 3 mph. But some tests for air moving using an 
anemometer made to work under 1 mph didn't detect air moving into a 
valley. And its been observed that a line of trees can prevent that air 
motion from getting to a road, making frost on a road that was hard to 
predict because it was a local condition.

73, Jerry, K0CQ

On 10/4/2012 7:08 AM, Dave Sublette wrote:
> I forgot to add that Hepburn did not appear to predict the conditions
> that were observed this morning. Hepburn only calls for "marginal"
> enhancement, the lowest level.
>
> However, when I checked the weather conditions this morning I found the
> local conditions to be temperature equaling dewpoint, which resulted in
> 100% humidity.    Bob's conditions showed a dewpoint of two degrees
> lower than ambient temperature and a relative humidity of 93%.  Bob and
> I then concluded that this was the cause of the enhancement.
>
> I don't claim to be any sort of expert on microwave conditions.  One of
> the reasons that I post these comments is that, perhaps someone who does
> know more about it than I do can chime in and I can learn something.
>
> 73,
>
> Dave, K4TO
>
>