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20010905: pressure tendency

Dorothy,

If you have the WMO code from table 200, and the pressure change in tenths
of millibars, then this is generally what is reported as P03D
(See the Appendix A in the user guide) in weather bulletins as
"appp". The "a" character is the value 0-8 from table 200, and "ppp" is the
value of pressure change. (use the absolute value of ppp since the code
0-8 gives the sign as increasing or decreasing).

For example, you have a table 200 value of "7" (eg pressure decreasing),
and the amount of the decrease is .3 mb, then you would create a
P03D value of 7003. A packing table entry for P03D would be
P03D         0.         8999.    1.

With P03D defined, you can determine P03C which would be -0.3 mb.
PTSY is the graphics symbol only (which would be 7999).

When plotting a map with sfparm in SFMAP:

P03D    shows the combined "appp" number
P03C    shows the pressure change in millibars (use p03c*10 for tenths)
PTND    draws the change value (tenths of mb) and symbol
PTSY    draws the graphics symbol (withot the change value)

Steve Chiswell
Unidata User Support




On Wed, 5 Sep 2001, Dorothy Durnford-Sutton wrote:

> Hi Steve,
>
> I am trying to plot the surface pressure tendency with gempak's sfmap.
> The data comes from the NCEP observation data set - UCAR's ds464.0.  The
> data set's documentation states that "Characteristic of pressure
> tendency during the 3 hours preceding the time of observation" is
> provided, using WMO code table 0200, and also "Amount (magnitude) of the
> pressure tendency " in tenths of millibar.  I label these parameters for
> gempak PTSY and P03C, and give their packing information as "0.  8.  1."
> and "-20.  20.  0.1", respectively.  When I plot them, the symbol is
> identical for all stations at all times, and the magnitude is always
> positive.  If I try to plot PTND, I'm told it's not computable.  Do you
> have any suggestions?
>
> Thanks, Dorothy.
>
>