precipitation probability

[Stefan Gofferje]

Hei,

PEEP schrieb:

> Is there a way to find out precipitation probability from GRIB data? I can
> find all kinds of precipitation types and amounts but what about
> probability?

I suppose you refer to NOAA NCEP data?
AFAIK, there is no precipitation probability. In fact, there are parameters:

CPRAT Convective Precipitation Rate [kg/m^2/s]:surface:0-3 hour ave fcst:
PRATE Precipitation Rate [kg/m^2/s]:surface:0-3 hour ave fcst:
APCP Total Precipitation [kg/m^2]:surface:0-3 hour acc fcst:
ACPCP Convective Precipitation [kg/m^2]:surface:0-3 hour acc fcst:
CSNOW Categorical Snow (yes=1; no=0) [non-dim]:surface:0-3 hour ave fcst:
CICEP Categorical Ice Pellets (yes=1; no=0) [non-dim]:surface:0-3 hour
ave fcst:
CFRZR Categorical Freezing Rain (yes=1; no=0) [non-dim]:surface:0-3 hour
ave fcst:
CRAIN Categorical Rain (yes=1; no=0) [non-dim]:surface:0-3 hour ave fcst:

The Categorical parameters (precip type) indicate what type the precip
will be while the rate or total params indicate how much precipitation
is to be expected. So, GFS does not give a probability but just how much
precip will fall.

If you e.g. want to draw a meteogram for one location, you first set
gxout bar, then 'd CRAIN*PRATE*3600' 'd CSNOW*PRATE*3600' 'd
CICEP*PRATE*3600' 'd CFRZR*PRATE*3600' which will give you a meteogram
which shows the expected rates (mm/h) and the type of rain.
See http://www.saakeskus.fi/index.php?function=showmeteo&chart=helsinki

Greetings from Finland,
Stefan Gofferje

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