Precip types based on return

[[email protected]]

If you look at the radar plots at NOAA's site here

http://radar.weather.gov/radar_lite.php?product=NCR&loop=no&rid=cxx

there is no prediction for precip type, just the value of reflectivity
is given.

At Intellicast here,

http://www.intellicast.com/IcastPage/LoadPage.aspx?loc=kbml&seg=LocalWeather&prodgrp=RadarImagery&product=Radar&prodnav=none

they go further and predict the precip type. My question, does
Intellicast use some temperature input to allow them to differentiate
between precip types?

It just seems to me that reflectivity alone cannot determine precip
type accurately. For example, heavy snow and light rain could have
the same reflectivity, I'd expect, yet Intellicast clearly has a
distinction between the two.

Ideas? Stan

[Jim Macklin]

Weather radar results, unlike reflections from a metal
surface, are determined by a resonance with a water
molecule. Frozen water is a crystal and the return is of a
lesser and different character, at least that is what I
remember Capt. David Gwinn telling me.



> wrote in message
...
| If you look at the radar plots at NOAA's site here
|
|
http://radar.weather.gov/radar_lite.php?product=NCR&loop=no&rid=cxx
|
| there is no prediction for precip type, just the value of
reflectivity
| is given.
|
| At Intellicast here,
|
|
http://www.intellicast.com/IcastPage/LoadPage.aspx?loc=kbml&seg=LocalWeather&prodgrp=RadarImagery&product=Radar&prodnav=none
|
| they go further and predict the precip type. My question,
does
| Intellicast use some temperature input to allow them to
differentiate
| between precip types?
|
| It just seems to me that reflectivity alone cannot
determine precip
| type accurately. For example, heavy snow and light rain
could have
| the same reflectivity, I'd expect, yet Intellicast clearly
has a
| distinction between the two.
|
| Ideas? Stan

[John R. Copeland]

The captain was partially correct.
Resonance is not a factor, but electrical conductivity of the
frozen crystal is much lower than conductivity of liquid water.
Hence, water reflects radar much better than ice.
(There's a whole lot of Maxwell's Equations and boundary-value
conditions involved in that "hence", but this isn't the place for that. :-)

"Jim Macklin" > wrote in message ...
> Weather radar results, unlike reflections from a metal
> surface, are determined by a resonance with a water
> molecule. Frozen water is a crystal and the return is of a
> lesser and different character, at least that is what I
> remember Capt. David Gwinn telling me.
>
>

[Stan Prevost[_1_]]

I believe it is dielectric constant, not electrical conductivity.


"John R. Copeland" > wrote in message
...
The captain was partially correct.
Resonance is not a factor, but electrical conductivity of the
frozen crystal is much lower than conductivity of liquid water.
Hence, water reflects radar much better than ice.
(There's a whole lot of Maxwell's Equations and boundary-value
conditions involved in that "hence", but this isn't the place for that. :-)

"Jim Macklin" > wrote in message
...
> Weather radar results, unlike reflections from a metal
> surface, are determined by a resonance with a water
> molecule. Frozen water is a crystal and the return is of a
> lesser and different character, at least that is what I
> remember Capt. David Gwinn telling me.
>
>

[[email protected]]

On Mon, 15 Jan 2007 21:45:35 -0500, "John R. Copeland"
> wrote:

>Resonance is not a factor, but electrical conductivity of the
>frozen crystal is much lower than conductivity of liquid water.
>Hence, water reflects radar much better than ice.

Can there be more than that?

Back to my question, heavy snow and light rain, the two can have the
same "electrical conductivity". Especially if the temperature is near
zero and there's some liquid water present in the snow. We're talking
"light" rain here too.

Yet WSI makes a distinct differentiation here. While NOAA doesn't on
their adds weather site.

Further WSI has a category for "mixed" precip. If they are only using
the power of the radar return, how can they determine that there's
some snow mixed in with the much more powerful return from rain?

Stan

[Dave Butler]

Stan Prevost wrote:
> I believe it is dielectric constant, not electrical conductivity.

Two sides of the same coin.

[Jose]

> If they are only using
> the power of the radar return, how can they determine that there's
> some snow mixed in with the much more powerful return from rain?

Just a WAG, but maybe it's spectrally different? Snow reflects more of
one frequency, rain more of another?

Jose
--
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