Parties interested to establish a dedicated ftp line to receive NWP forecast data should contact Julie Hayes <Julie.Hayes@noaa.gov> at OOS/NWS headquarters and ask for information on "SAS" lines.
In addition, a file containing probabilistic quantitative precipitation forecasts (PQPF), derived from the ensemble, is also available.
Take a look at the README file. Read that and then cd to the subdirectories
to download the software.
You can use subroutine getgbex from the nw3lib for handling data with the ensemble extension in the header.
Currently, there are no WMO standards for including this extra information on ensemble data; below the PDS GRIB extension adopted at NCEP (which is somewhat similar to that used at ECMWF) is described.
EXTENSION OF PDS SECTION FOR THE IDENTIFICATION OF ENSEMBLE PRODUCTS |
||
---|---|---|
Byte (or Octet) |
Content |
|
41 |
Identifies application1 = Ensemble |
|
42 |
Type
1 = Unperturbed control forecast
|
|
43 |
Identification number
If Byte 42 = 1, byte 43 will = 1 or 2:
If Byte 42 = 2 or 3, byte 43 will = 1,2,3,4 or 5:
|
|
44 |
Product Identifier
1 = Full field (individual forecast) / Unweighted mean (cluster/ens)
|
|
45 |
Spatial smoothing of product (number of highest total wavenumber included)255 = Original resolution retained |
|
Octet 46 and above are used only if needed |
||
Probability Section |
||
46 |
Probability product definition:If octet 9=191 or 192, defines variable in terms of octet 9 table (see below for more details) |
|
47 |
Probability type
1 = Probability of event below lower limit
|
|
48-51 | Probability lower limit (unit as in octet 9; floating point number) | |
52-55 | Probability upper limit (unit as in octet 9; floating point number) | |
56-60 | Reserved | |
Octet 61 and above are used only if octet 42=4 or 5 |
||
Clustering Section |
||
61 |
Ensemble size (number of members, including controls) | |
62 | Cluster size (number of members) | |
63 | Number of clusters | |
64 | Clustering Method
1 = AC
|
|
65-67 | Northern latitude of clustering domain (in thousandths of degree) | |
68-70 | Southern latitude of clustering domain (in thousandths of degree) | |
71-73 | Eastern longitude of clustering domain (in thousandths of degree) | |
74-76 | Western longitude of clustering domain (in thousandths of degree) | |
77-86 | Cluster membership:
If octet 42=4, shows, in binary (on/off) format, which members of the ensemble belong to the current cluster. Membership table defined by product generators. |
|
87-100 | Reserved |
ADDITIONAL ENSEMBLE-RELATED CHANGES IN MAIN PDS DEFINITIONPlease refer to the "GRIB Manual" (Office Note 388) for further details |
---|
Octet 9 (Indicator of parameter and units) |
|||
---|---|---|---|
VALUE |
PARAMETER | UNITS | ABBREV. |
191 |
Probability from ensemble (Octet 41=1) | non-dim | PROB |
192 | Probability from ensemble, normalized with respect to climate expectancy (Octet 41=1) | non-dim | PROBN |
193 |
Difference between two height levels | gpm | HGTD |
Octet 21 (Time Range Indicator) |
|
---|---|
VALUE |
MEANING |
119 |
Standard deviation of N forecasts, all with the same reference time, with respect to the time average of forecasts; the first forecast has a forecast period of P1, the remaining forecasts follow at intervals of P2 |
Octet 26 (Identification of sub-center) |
|
---|---|
VALUE |
MEANING |
2 |
NMC Ensemble Products (Perturbed forecasts and other products) (See octet 41). i.e., if octet 26 = 2, then this GRIB record contains ensemble data AND an extension to the PDS. |
Octet 29 |
||
---|---|---|
BIT NUMBER |
VALUE | DEFINITION |
1 |
0 | Full forecast field |
1 | Forecast error field (forecast minus analysis) | |
2 | 0 | Original forecast field |
1 | Bias corrected forecast field | |
3 | 0 | Original resolution retained |
1 | Smoothed field | |
(Mean model error fields can be identified by setting the first bit of octet 29 to 1 and specifying a time-averaging process in octets 19-24.) |