[MAMS] More on conditions this morning

[Rich Griffiths]

I beg to differ on one point.

The old saw is technically correct.  The flow is not a valley-wide 
sinking, but cold air flow down valley sides to the bottom is common.  
It's called katabatic flow or katabatic wind.  Some tests may have 
failed to measure it, but countless others have.

... Rich   W2RG

On 10/04/2012 11:11 AM, Dr. Gerald N. Johnson wrote:
> 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
>>
>>
>>      
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