Information about the file naming conventions used in the PWPF subdirectories

At this top-level directory,  you'll notice that there are 4 subdirectories.  These correspond to the length of the forecast.  
So the "12hr" directory houses any forecasts that are valid for 12-hour periods, and so on.

Directory Contents
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Inside these directories (and I'll use the 24hr one as an example), there are files representing 3 probabilistic fields:
1.  Files containing probabilities of snow or ice exceeding set thresholds 
2.  Files containing percentile accumulations.  
3.  "Sigma" files containing the standard deviation of snow and freezing rain accumulations from WPC's multi-model ensemble.

Graphical examples of the first 2 data sets are available at http://www.wpc.ncep.noaa.gov/pwpf/wwd_accum_probs.php for probability of exceeding set thresholds 
and http://www.wpc.ncep.noaa.gov/pwpf/wwd_percentiles.php?ftype=percentiles&fpd=24&ptype=snow for percentile accumulations.  

http:://www.wpc.ncep.noaa.gov/pwpf/about_pwpf_products.shtml


File naming convention for probability of exceedence files:
------------------------------------------------------------
p[snow,icez]24_ge[some threshold in inches]_yyyymmddccfhhh.grb where yyyymmdd is the year/month/day of the initial forecast time, 
cc is the hour of the initial forecast (00 or 12) and hhh is the forecast projection.  This hour always represents the ending valid time of the forecast.  
A couple of examples:

psnow24_ge2_2018011500f036.grb.  This is the probability of snow exceeding 2 inches from the forecast issued on Jan 15, 2018 
at 00Z for the 24-hour period valid from 12Z Jan 15th - 12Z Jan 16th, since 36 hours from 00Z Jan 15th (the initial date/time of the forecast) 
would equate to 12Z Jan 16th.  Please note that snow in the GRIB files is expressed in meters.

picez24_ge.10_2018011500f048.grb.  This is the probability of freezing rain accumulating more than .10" from the forecast issued on Jan 15, 2018 
at 00Z for the 24-hour period valid from 00Z Jan 16th - 00Z Jan 17th, since 48 hours from 00Z Jan 15th (the initial date/time of the forecast) 
would equate to 00Z Jan 17th.  Please note that freezing rain in the GRIB files is expressed in millimeters.


File naming convention for the percentile accumulation files is:
----------------------------------------------------------------------------------------------------------
2.5kmprcntil_24h[snow,icez]_[05,10,25,50,75,90,95]pt_yyyymmddccfhhh.grb where yyyymmdd is the year/month/day of the 
initial forecast time, cc is the hour of the initial forecast (00 or 12) and hhh is the forecast projection.  
This hour always represents the ending valid time of the forecast.  A couple of examples:

2.5kmprcntil_24hsnow_25pt_2018011500f036.grb.  This represents the 25th percentile accumulation (in inches) of snowfall 
from the forecast issued on Jan 15, 2018 at 00Z for the 24-hour period valid from 12Z Jan 15th - 12Z Jan 16th, 
since 36 hours from 00Z Jan 15th (the initial date/time of the forecast) would equate to 12Z Jan 16th.
Please note that snow in the GRIB files is expressed in meters.

2.5kmprcntil_24hicez_90pt_2018011500f048.grb.  This is the 90th percentile accumulation (in inches) of freezing rain 
from the forecast issued on Jan 15, 2018 at 00Z for the 24-hour period valid from 00Z Jan 16th - 00Z Jan 17th, 
since 48 hours from 00Z Jan 15th (the initial date/time of the forecast) would equate to 00Z Jan 17th.
Please note that freezing rain in the GRIB files is expressed in millimeters.

File naming convention for the sigma files is:
--------------------------------------------------
2.5kmsigma_24h_[snow,icez]_yyyymmddccfhhh.grb where yyyymmdd is the year/month/day of the 
initial forecast time, cc is the hour of the initial forecast (00 or 12) and hhh is the forecast projection.