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20000117: Gempak MOS wsym possible?

>From: Peter Schmid <address@hidden>
>Organization: .
>Keywords: 200001071745.KAA18910

>Chiz,
>
>With the demise of WXP 4.8 and the current
>status of WXP 5...we have just about
>completely eliminated the use of wxp
>scripts. 
>
>One of the last things we are working on is
>the MOS plots that we create.  They are just about
>finished but it would be nice to have the
>"present" weather symbol (like in real time
>surface obs) made for the MOS data.  WXP was
>able to do this based on calculations of QPF,
>obstruction to Visibility and POP06 as near
>as I can tell by looking at some of the beta
>code I have.
>
>I started poking around Gempak and quickly saw 
>that this would not be real straight forward.
>
>Is there any chance of getting this done so we
>can remove wxp completely?
>
>Thanks,
>
>Pete.
>

Pete,

Since you are talking about creating a derived parameter- eg, something
not in the original data- this would probably not be something that should 
be done at the decoder end (dcnmos), though that is probably the easiest
place to hanle the data since it is already available. The most logical
place would either be to create a PT subroutine for gemlib and then
provide the function to $GEMTBP/parms/pcconv.tbl- or to compute it
separately in a little program and write the data back out to
the gempak file.

You can compute your own heuristic- of course, debatable as to what
formulation you use, to compute a WTHR number for display as
a symbol.

If you have a formulation, we can look at it.
My guess is you would threshold PP06 for rain and QP06
for ., .., or ..., and TS06 for thunderstorms. OVIS for
fog etc. The questionable part would be what thresholds to impose-
eg 30% TS06 to use the thunderstorm symbol instead of rain?

Anyhow, we should be able to satisfy your needs. It would help
to have references though- eg some sort of paper that the end user
could refer to to understand how that heuristic decides on the weather.

Steve Chiswell
Unidata User Support