Sami, you've hit upon the answer to your question, and one thing to keep in
mind is that radar don't know squat about whether the rain is from a
thunderstorm or not, all it sees is the "reflection" of the precip, the
higher the number, the higher the bounce back. Granted, a thunderstorm that
is full of rain and hail will definately produce a higher return.
Additional information about the current conditions vs. forecast conditions
combined with front locations, movement, direction, sigmets, and airmets
should provide you with a more complete picture of what your Data Link is
showing you.

Over the past couple weeks, we've had two totally different low pressure
systems move through Wisconsin. The first contained a leading edge of
thunderstorms, high winds and heavy rain. The last contained high winds,
heavy rain, but no thunderstorms. The echoes for both storms were level 2's
and 3's. The difference between the two storms was the amount of lifting
action available. The first storm occurred during a period of relatively
hot and unstable conditions. The second occurred during cool and more
stable conditions, it was much less violent but the radar returns were the
same.

Jim Burns


"O. Sami Saydjari" wrote in message
...
In googling around a bit, I found the following:

------------------------------------------------------------------------

At: http://www.weatherzone.com.au/misc/g...y.jsp?letter=V

"Video Integrator and Processor, which contours radar reflectivity (in
dBZ) into six VIP levels:
• VIP 1 (Level 1, 18-30 dBZ) - Light precipitation
• VIP 2 (Level 2, 30-38 dBZ) - Light to moderate rain.
• VIP 3 (Level 3, 38-44 dBZ) - Moderate to heavy rain.
• VIP 4 (Level 4, 44-50 dBZ) - Heavy rain
• VIP 5 (Level 5, 50-57 dBZ) - Very heavy rain; hail possible.
• VIP 6 (Level 6, 57 dBZ) - Very heavy rain and hail; large hail
possible."

--------------------------------------------------------------------------
-
At:

http://www.garmin.com/manuals/773_Ga...deAddendum.pdf

Ok, now, from the Nextrad intensity table on page 13 of the Garmin
"400/500 Series garmin Options Displays", I learned:

GREEN means 5-30 dBZ
YELLOW means 30-55 dBZ
RED means 55-75 dBZ

So...
Green is VIP Level 1
Yellow is VIP Levels 2,3,4
Red is VIP levels 5 and 6

The radar appears to come from an aggregation of ground NEXTRAD sites,
that is beamed up via satellite based on user request messages.



O. Sami Saydjari wrote:

As I was coming into Grand Rapids (KGRR) yesterday, the controller
announced that there was a "level 5" return (or perhaps she said "cell")
on final to runway 8, so I was vectored to 35 where there were mostly
"just level 4" stuff. So, forgive my ignorance, but where are these
levels defined? I assume they have to do with what sort of radar return
they get off a cloud and therefore has to do with rain intensity. Does
a level 5 return imply that a thunderstorm is likely to be generating
it?

Also, I have a GDL-49 Satellite Data Link Transceiver linked to my
Garmin 430 display. I understand (and now have seen) that these things
just are not adequate to locate big cells. Rather, they show large
areas of showers. Are these based on satellite imagery, or from
aggregated ground station data or what?

Also, how to the radar levels (1 thru 6?) relate to the colors shown on
a GDL-49 display on a Garmin 430? Does red equal level 5 or level 6? I
think only have red, yellow and green...so it seems there are not
enough colors to show 6 levels.

-Sami, N2057M, Piper Turbo Arrow III