CPC Climatologies in GRIB2 format

Description of Climatological Limits for CPC Outlooks in the NDFD

Overview:

The Climate Prediction Center (CPC) provides the 8-14 day, monthly and seasonal probabilistic forecasts of temperature and precipitation to the NDGD. These forecasts are presented as the probability of the average temperature (or accumulated precipitation) exceeding climatological upper or lower limits. The upper limit is defined as the 66th percentile of the distribution and the lower limit is defined as the 33rd percentile of the distribution over the 30 year normal period (1971-2000). The upper and lower limits are now being provided to give the user the proper context for these forecasts. For temperature, the limits are in degreed Fahrenheit. For precipitation, the units are inches. The climatologies are stored using GRIB template 4.10 (percentile forecasts). The end date in section 4 is the end of the forecast interval. Seasonal limits are for three month time periods, monthly limits are for one month time periods and 8-14 day limits are for seven day time periods. For example, if a seasonal limits file that has a section 4 end time of August 1 at 00:00Z, it's valid period is the May-June-July season.

The upper and lower limits are provided to the user as groups of headerless GRIB2 files. The files are as follows:

File Name Element Limit Type Forecast Interval # of Files Included Region

ds.nprecp33p30d Precipitation lower monthly 12 CONUS

ds.nprecp66p30d Precipitation upper monthly 12 CONUS

ds.nprecp33p90d Precipitation lower seasonal 12 CONUS

ds.nprecp66p90d Precipitation upper seasonal 12 CONUS

ds.ntmp33p30d Temperature lower monthly 12 CONUS

ds.ntmp66p30d Temperature upper monthly 12 CONUS

ds.ntmp33p90d Temperature lower seasonal 12 CONUS

ds.ntmp66p90d Temperature upper seasonal 12 CONUS

The files for the 8-14 day climatologies are as follws:

File Name Element Limit Type Forecast Interval # of Files Included Region

ds.nprecp33pMMM_48 Precipitation lower 8-14 day 12 CONUS

ds.nprecp66pMMM_48 Precipitation upper 8-14 day 12 CONUS

ds.ntmp33pMMM_48 Temperature lower 8-14 day 12 CONUS

ds.ntmp66pMMM_48 Temperature upper 8-14 day 12 CONUS

ds.nprecp33pMMM_AK Precipitation lower 8-14 day 29-31 Alaska

ds.nprecp66pMMM_AK Precipitation upper 8-14 day 29-31 Alaska

ds.ntmp33pMMM_AK Temperature lower 8-14 day 29-31 Alaska

ds.ntmp66pMMM_AK Temperature upper 8-14 day 29-31 Alaska

NOTE: MMM is the 3-letter abreviation for the month

GRIB2 Specifications

GRIB2 - SECTION 1 IDENTIFICATION SECTION

Octet No. Content

1-4 Length of the section in octets (21 or N)

5
Number of the section (1)

6-7
Identification of originating/generating center: 7 for CPC

8-9 Identification of originating/generating subcenter: 7 for CPC

10
GRIB master tables version number: 2

11
Version number of GRIB local tables used to augment Master Tables: 0

12
Significance of reference time: 1 for start of "forecast" period

13-14
Year: Set to 2000 (or 1999 for January 3 or ealier 8-14 day periods

15
Month

16
Day

17
Hour

18
Minute

19
Second

20
Production Status of Processed data in the GRIB message: 0

21
Type of processed data in this GRIB message: 1

22-N
Reserved

GRIB2 - GRID TEMPLATE 3.30 Lambert conformal for CONUS grids

Octet Contents

15
Shape of the Earth: 1

16
Scale factor of radius of spherical Earth: 0

17-20
Scale value of radius of spherical Earth: 6371200

21
Scale factor of major axis of oblate spheroid Earth: 0

22-25
Scaled value of major axis of oblate spheroid Earth: 0

26
Scale factor of minor axis of oblate spheroid Earth: 0

27-30
Scaled value of minor axis of oblate spheroid Earth: 0

31-34
Nx ― number of points along the x-axis: 1073

35-38

Ny — number of points along the y-axis: 689

39-42
La₁― latitude of first grid point:20190001

43-46
Lo₁― longitude of first grid point: 238449997

47

Resolution and component flags (see Flag Table 3.3)

48-51
LaD ― latitude where Dx and Dy are specified: 25000000

52-55
LoV ― longitude of meridian parallel to y-axis along which latitude increases as the y-coordinate increases: 265000000

56-59

Dx ― x-direction grid length: 5078616

60-63

Dy ― y-direction grid length: 5080491

64

Projection centre flag: 0

65 Scanning mode: 64

66-69
Latin 1 ― first latitude from the pole at which the secant cone cuts the sphere: 25000000

70-73
Latin 2 ― second latitude from the pole at which the secant cone cuts the sphere: 25000000

74-77
Latitude of the southern pole of projection: -90000000

78-81
Longitude of the southern pole of projection: 0

GRIB2 - GRID TEMPLATE 3.20 Polar stereographic projection for Alaska

Octet Contents

15 Shape of the Earth: 1

16 Scale factor of radius of spherical Earth: 0

17-20 Scaled value of radius of spherical Earth: 6371200

21
Scale factor of major axis of oblate spheroid Earth: 0

22-25 Scaled value of major axis of oblate spheroid Earth: 0

26
Scale factor of minor axis of oblate spheroid Earth: 0

27-30
Scaled value of minor axis of oblate spheroid Earth: 0

31-34
Nx ― number of points along the x-axis: 825

35-38
Ny ― number of points along the y-axis: 553

39-42
La₁― latitude of first grid point: 40530102

43-46
Lo₁― longitude of first grid point: 181429001

47 resolution and component flags: 56

48-51
LaD ― latitude where Dx and Dy are specified: 60000000

52-55
LoV ― orientation of the grid: 210000000

56-59
Dx ― x-direction grid length: 5953125

60-63
Dy ― y-direction grid length: 5953125

64
Projection centre flag: 0

65
Scanning mode: 64

GRIB2 - TEMPLATE 4.10: percentile forecasts at a horizontal level or in a horizontal layer in a continuous or non-continuous time interval

Octet Contents

10
Parameter category: 0 for temperature; 1 for precipitation

11
Parameter number: 0 for temperature; 8 for precipitation

12
Type of generating process: 2

13
Background generating process identifier: 0

14
Forecast generating process identifier: 0

15-16
Hours after reference time data cutoff: 65535

17
Minutes after reference time data cutoff: 255

18
Indicator of unit of time range: 2

19-22
Forecast time in units defined by previous octet: varies

23
Type of first fixed surface: 1

24
Scale factor of first fixed surface: 0

25-28
Scaled value of first fixed surface: 0

29
Type of second fixed surfaced: 255

30
Scale factor of second fixed surface: -1

31-34
Scaled value of second fixed surfaces: -1

35
Percentile value (from 100% to 0%): 33 for lower limit; 66 for upper limit

36-37
Year of end of overall time interval: 2000

38
Month of end of overall time interval

39
Day of end of overall time overall time interval

40
Hour of end of overall time interval

41
Minute of end overall time interval

42
Second of end of overall time interval

43
n ― number of time range specifications describing the time intervals used to calculate the statistically-processed field: 1

44-47
Total number of data values missing in the statistical process: 0

48
Statistical process used to calculate the processed field from the field at each time increment during the time range: 1

49
Type of time increment between successive fields used in the statistical processing: 255

50
Indicator of unit of time range over which statistical processing is done: 6

51-54
Length of the time range over which statistical processing is done, in units defined by the previous octet: 1

55
Indicator of unit of time for the increment between the successive fields used: 0

56-59
Time increment between successive fields, in units defined by the previous octet (see Note 3)
60-nn These octets are included only if n>1, where nn = 47 +12 x n: 0

GRIB2 - GRID TEMPLATE 5.2 Grid point data ― complex packing

Octet Contents

12-15
reference value (R) (IEEE 32-bit floating-point value): -1002536960

16-17
Binary scale factor (E): 0

18-19
Decimal scale factor (D): 2

20
Number of bits used for each packed value for simple packing, or for each group reference value for complex packing or spatial differencing: 14

21
Type of original field values (see Code Table 5.1): 0

22
Group splitting method used (see Code Table 5.4): 1

23
Missing value management used (see Code Table 5.5): 1

24-27
Primary missing value substitute:
1176255488 (9999.0 in floating point)

28-31 Secondary missing value substitute: 0

32-35
NG ― number of groups of data values into which field is split: 55123

36
Reference for group widths (see Note 12): 0

37
Number of bits used for the group widths (after the reference value in octet 36 has been removed): 4

38-41
Reference for group lengths (see Note 13): 1

42
Length increment for the group lengths (see Note 14): 1

43-46
True length of last group: 32

47
Number of bits used for the scaled group lengths (after subtraction of the reference value given in octets 38-41 and division by the length increment given in octet 42): 5

File Name	Element	Limit Type	Forecast Interval	# of Files Included	Region
ds.nprecp33p30d	Precipitation	lower	monthly	12	CONUS
ds.nprecp66p30d	Precipitation	upper	monthly	12	CONUS
ds.nprecp33p90d	Precipitation	lower	seasonal	12	CONUS
ds.nprecp66p90d	Precipitation	upper	seasonal	12	CONUS
ds.ntmp33p30d	Temperature	lower	monthly	12	CONUS
ds.ntmp66p30d	Temperature	upper	monthly	12	CONUS
ds.ntmp33p90d	Temperature	lower	seasonal	12	CONUS
ds.ntmp66p90d	Temperature	upper	seasonal	12	CONUS

File Name	Element	Limit Type	Forecast Interval	# of Files Included	Region
ds.nprecp33pMMM_48	Precipitation	lower	8-14 day	12	CONUS
ds.nprecp66pMMM_48	Precipitation	upper	8-14 day	12	CONUS
ds.ntmp33pMMM_48	Temperature	lower	8-14 day	12	CONUS
ds.ntmp66pMMM_48	Temperature	upper	8-14 day	12	CONUS
ds.nprecp33pMMM_AK	Precipitation	lower	8-14 day	29-31	Alaska
ds.nprecp66pMMM_AK	Precipitation	upper	8-14 day	29-31	Alaska
ds.ntmp33pMMM_AK	Temperature	lower	8-14 day	29-31	Alaska
ds.ntmp66pMMM_AK	Temperature	upper	8-14 day	29-31	Alaska

Octet No.	Content
1-4	Length of the section in octets (21 or N)
5	Number of the section (1)
6-7	Identification of originating/generating center: 7 for CPC
8-9	Identification of originating/generating subcenter: 7 for CPC
10	GRIB master tables version number: 2
11	Version number of GRIB local tables used to augment Master Tables: 0
12	Significance of reference time: 1 for start of "forecast" period
13-14	Year: Set to 2000 (or 1999 for January 3 or ealier 8-14 day periods
15	Month
16	Day
17	Hour
18	Minute
19	Second
20	Production Status of Processed data in the GRIB message: 0
21	Type of processed data in this GRIB message: 1
22-N	Reserved

Octet	Contents
15	Shape of the Earth: 1
16	Scale factor of radius of spherical Earth: 0
17-20	Scale value of radius of spherical Earth: 6371200
21	Scale factor of major axis of oblate spheroid Earth: 0
22-25	Scaled value of major axis of oblate spheroid Earth: 0
26	Scale factor of minor axis of oblate spheroid Earth: 0
27-30	Scaled value of minor axis of oblate spheroid Earth: 0
31-34	Nx ― number of points along the x-axis: 1073
35-38	Ny — number of points along the y-axis: 689
39-42	La₁― latitude of first grid point:20190001
43-46	Lo₁― longitude of first grid point: 238449997
47	Resolution and component flags (see Flag Table 3.3)
48-51	LaD ― latitude where Dx and Dy are specified: 25000000
52-55	LoV ― longitude of meridian parallel to y-axis along which latitude increases as the y-coordinate increases: 265000000
56-59	Dx ― x-direction grid length: 5078616
60-63	Dy ― y-direction grid length: 5080491
64	Projection centre flag: 0
65	Scanning mode: 64
66-69	Latin 1 ― first latitude from the pole at which the secant cone cuts the sphere: 25000000
70-73	Latin 2 ― second latitude from the pole at which the secant cone cuts the sphere: 25000000
74-77	Latitude of the southern pole of projection: -90000000
78-81	Longitude of the southern pole of projection: 0

Octet	Contents
10	Parameter category: 0 for temperature; 1 for precipitation
11	Parameter number: 0 for temperature; 8 for precipitation
12	Type of generating process: 2
13	Background generating process identifier: 0
14	Forecast generating process identifier: 0
15-16	Hours after reference time data cutoff: 65535
17	Minutes after reference time data cutoff: 255
18	Indicator of unit of time range: 2
19-22	Forecast time in units defined by previous octet: varies
23	Type of first fixed surface: 1
24	Scale factor of first fixed surface: 0
25-28	Scaled value of first fixed surface: 0
29	Type of second fixed surfaced: 255
30	Scale factor of second fixed surface: -1
31-34	Scaled value of second fixed surfaces: -1
35	Percentile value (from 100% to 0%): 33 for lower limit; 66 for upper limit
36-37	Year of end of overall time interval: 2000
38	Month of end of overall time interval
39	Day of end of overall time overall time interval
40	Hour of end of overall time interval
41	Minute of end overall time interval
42	Second of end of overall time interval
43	n ― number of time range specifications describing the time intervals used to calculate the statistically-processed field: 1
44-47	Total number of data values missing in the statistical process: 0
48	Statistical process used to calculate the processed field from the field at each time increment during the time range: 1
49	Type of time increment between successive fields used in the statistical processing: 255
50	Indicator of unit of time range over which statistical processing is done: 6
51-54	Length of the time range over which statistical processing is done, in units defined by the previous octet: 1
55	Indicator of unit of time for the increment between the successive fields used: 0
56-59	Time increment between successive fields, in units defined by the previous octet (see Note 3) 60-nn These octets are included only if n>1, where nn = 47 +12 x n: 0

Octet	Contents
12-15	reference value (R) (IEEE 32-bit floating-point value): -1002536960
16-17	Binary scale factor (E): 0
18-19	Decimal scale factor (D): 2
20	Number of bits used for each packed value for simple packing, or for each group reference value for complex packing or spatial differencing: 14
21	Type of original field values (see Code Table 5.1): 0
22	Group splitting method used (see Code Table 5.4): 1
23	Missing value management used (see Code Table 5.5): 1
24-27	Primary missing value substitute: 1176255488 (9999.0 in floating point)
28-31	Secondary missing value substitute: 0
32-35	NG ― number of groups of data values into which field is split: 55123
36	Reference for group widths (see Note 12): 0
37	Number of bits used for the group widths (after the reference value in octet 36 has been removed): 4
38-41	Reference for group lengths (see Note 13): 1
42	Length increment for the group lengths (see Note 14): 1
43-46	True length of last group: 32
47	Number of bits used for the scaled group lengths (after subtraction of the reference value given in octets 38-41 and division by the length increment given in octet 42): 5