Radar

Mike Rapoport ) wrote:

Fair enough! I assumed that he was talking about airborn radar. It is
interesting how personal experience colors our interpretation of the same
statement!

Someday I hope to be able to interpret as you do.

--
Peter

On Fri, 22 Oct 2004 15:37:18 GMT, Matt Young
wrote:

A question about something that I guess I just didn't get enough info on
during my instrument training. What exactly are you looking for when
looking at a radar image. Are you trying to avoid all returns? Is an
area of just green ok? Any other things in particular to look for?

I fly a PA28-180 equipped with WxWorx Nexrad. My experience has been:

light green = little/no rain (might be virga)
dk green = solid rain, but still not too heavy, certainly ok for IFR
flight
yellow = strong rain. Strong enough that I will only fly through it
if it is a small return.
orange = deviation
red = no way
purple = no way

I have not flown through orange, red, or purple intensities, and do
not intend to do so.

-Nathan

Mike, add special emphasis to the reading of the Z-scale numbers.
The NOAA radar depiction sets their lowest color level (cyan)
at -24 to -28 dBZ when no storms are shown on the presentation,
but when storms are present, the same color is +5 to +10 dBZ.
That's why a casual look at the radar can mislead the unwary
to mistake wet clouds for a rainstorm. The dBZ numbers rule.
---JRC---

"Mike Rapoport" wrote in message =
news
Weather Radar is the same as vision in another part of the spectrum. =
It has=20
certain resolution and can penetrate a certain distance into obscuring =

conditions. The beam reflects off all surfaces (except the stuff =
stealth=20
aircraft are made of presumably). The value of radar is that there is =
a=20
very high corralation between the reflectivity of water droplets and=20
turbulence. Large droplets are formed from vertical motion.and large=20
droplets reflect radar much better than small ones (that is why most =
clouds=20
appear transparent to radar.). More vertical motion larger drops. =
You have=20
undoubtedly experienced the difference in drop sizes from =
thunderstorms vs.=20
stratiform rain. To evaluate a target, you first have to determine =
that you=20
are not looking at a ground return which you do by knowing your =
altitude,=20
beam width and antenna tilt setting. Generally you avoid all radar =
targets=20
containing red (40dbz) returns. You avoid the whole target, not just =
the=20
red part. I usually avoid yellow too. Even green targets are fairly =
bumpy=20
and full of ice at cruise altitudes (above FL180). Green at lower =
altiudes=20
can be smooth. There are various shapes that are associated with hail =
and=20
tornados but most people avoid all thunderstorms. The irregular =
targets are=20
just avoided by a greater distance.
=20
Basically it comes down to the fact that anything that lifts huge =
amounts of=20
water miles into the atmosphere contains a lot of vertical shear and=20
therefore turbulence.
=20
There are several books on the subject, I like Archie Trammels stuff, =
Dave=20
Gwinn's book and Severe Weather Flying by Newton. There was a great =
deal on=20
AvWeb a couple of years ago where you got Trammels video course, =
Severe=20
Weather Flying and Buck's Weather Flying for around $125 along with a=20
discount for his live course.
=20
Mike
MU-2
=20
=20
"Matt Young" wrote in message=20
ink.net...
A question about something that I guess I just didn't get enough info =
on=20
during my instrument training. What exactly are you looking for when=20
looking at a radar image. Are you trying to avoid all returns? Is an =
area=20
of just green ok? Any other things in particular to look for?=20
=20

John R. Copeland ) wrote:

Mike, add special emphasis to the reading of the Z-scale numbers.
The NOAA radar depiction sets their lowest color level (cyan)
at -24 to -28 dBZ when no storms are shown on the presentation,
but when storms are present, the same color is +5 to +10 dBZ.
That's why a casual look at the radar can mislead the unwary
to mistake wet clouds for a rainstorm. The dBZ numbers rule.

I got burned by the sensitivity of the Nexrad display last March. I was
flying down to Wings Field (north of Philly, PA) from central NY when
radar depicted what looked like a line of t-storms approaching mid-PA.

After seeing this on the ADDs weather site, I was going to cancel but
instead decided to call Flight Service for a briefing. It was then that
I learned the red radar returns were from snow, not heavy liquid precip.
The briefer had told me that most likely the radar was more sensitive
than it would have been during the summer, which made the returns look
much stronger than they were.

Had I seen the key, I would have determined this myself.

--
Peter