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20030826: freezing level using PTDISP

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  • Subject: 20030826: freezing level using PTDISP
  • Date: Tue, 26 Aug 2003 19:05:02 -0600
>From:  "Travis Martin" <address@hidden>
>Organization:  Weathernews Americas Inc.
>Keywords:  200308262341.h7QNfULd005256 McIDAS PTDISP

Travis,

>Has anyone been able to do sub-selects with PTDISP commands.

Yes.

>...example.
>I want to find the lowest level in feet where the temperature is below
>32F. I use the following command, but it doesn't pick the lowest level.
>I also strip the last three digits from the altitude.

>SFCDISP RTPTSRC/UPPERMAND SELECT='T[F] -100 32' PARAM='FLEV=(P1/100)'
>P1=Z[FT] FORMAT=I3 MAP=USA COLOR=7

Presumably, you mean PTDISP, not SFCDISP.

>It would be nice if adding a MIN in front of the Z[FT} parameter would
>get the minimum level, but doesn't seem to do it.
>Any ideas?

I tried your same command with slightly more constraints in the SELect
clause, and it seemed to work with no problems:

ERASE
PTDISP RTPTSRC/UPPERMAND SELECT='T[F] -100 32 ; TIME 12 ; DAY 238' 
PARAM='FLEV=(P1/100)' P1=Z[FT] FORMAT=I3 MAP=USA COLOR=7

A spot check of the values plotted using PTLIST shows that they _are_
the lowest levels:

PTLIST RTPTSRC/UPPERMAND PARAM=IDN Z[FT] SEL='T[F] -100 32 ; TIME 12 ; DAY 238; 
CO US' LSIZE=6 COLOR=7 NUM=9999

I further checked this for a couple of stations with PTLIST that had no
temperature selection.  For instance:

PTLIST RTPTSRC/UPPERMAND PAR=IDN T[F] Z[FT] SEL='IDN 72672; TIME 12; DAY 238' 
NUM=ALL
PTLIST RTPTSRC/UPPERMAND PAR=IDN T[F] Z[FT] SEL='IDN 72645; TIME 12; DAY 238' 
NUM=ALL
PTLIST RTPTSRC/UPPERMAND PAR=IDN T[F] Z[FT] SEL='IDN 70026; TIME 12; DAY 238' 
NUM=ALL

It  makes sense to me that the value plotted is at the lowest level since
the data is stored from the ground up in the upper air MD file created
by XCD, so it will be the first found for each station.

Are you seeing something different?  Am I missing something?

>Thanks,

>Travis Martin
>Software Engineer
>Weathernews Americas Inc.
>149 New Montgomery St.
>San Francisco, CA  94105
>415-848-5261 (Office)
>415-310-5719 (Mobile)
>415-848-5201 (Fax)

Tom

>From address@hidden Wed Aug 27 08:34:54 2003

Thanks Tom, and yes I meant PTDISP (sorry).  The altitudes looked a bit
higher than they should be...also much less deviation than I would
expect across the country.  Upon comparing them with the analysis put
out by NOAA <http://weather.noaa.gov/pub/fax/QYSA00.TIF>  on the same
day at 12Z, it was indeed different.  They could be using different
data, I'm not sure.  I'll repeat your process and attempt to confirm the
data. Thanks Again.

Travis Martin
Weathernews Americas Inc.