GRIB Edition 1: WMO Code Table 5

WMO Code table 5 - Time range indicator

Code figure	Meaning
0	Forecast product valid for reference time + P1 (P1 > 0), or Uninitialized analysis product for reference time (P1 = 0), or Image product for reference time (P1 = 0)
1	Initialized analysis product for reference time (P1 = 0)
2	Product with a valid time ranging between reference time + P1 and reference time + P2
3	Average (reference time + P1 to reference time + P2)
4	Accumulation (reference time + P1 to reference time + P2) product considered valid at reference time + P2
5	Difference (reference time + P2 minus reference time + P1) product considered valid at reference time + P2
6-9	Reserved
10	P1 occupies octets 19 and 20; product valid at reference time + P1
11-50	Reserved
51	Climatological Mean Value: multiple year averages of quantities which are themselves means over some period of time (P2) less than a year. The reference time (R) indicates the date and time of the start of a period of time, given by R to R + P2, over which a mean is formed; N indicates the number of such period-means that are averaged together to form the climatological value, assuming that the N period-mean fields are separated by one year. The reference time indicates the start of the N-year climatology. N is given in octets 22 and 23 of the PDS. If P1 = 0, then the data averaged in the basic interval P2 are assumed to be continuous (i.e., all available data are simply averaged together). If P1 = 1 (the units of time - octet 18,Code table 4 - are not relevant here), then the data averaged together in the basic interval P2 are valid only at the time (hour, minute) given in the reference time, for all the days included in the P2 period. The units of P2 are given by the contents of octet 18 and Code table 4.
52-112	Reserved
113	Average of N forecasts (or initialized analyses); each product has forecast period of P1 (P1 = 0 for initialized analyses); products have reference times at intervals of P2, beginning at the given reference time
114	Accumulation of N forecasts (or initialized analyses); each product has forecast period of P1 (P1 = 0 for initialized analyses); products have reference times at intervals of P2, beginning at the given reference time
115	Average of N forecasts, all with the same reference time; the first has a forecast period of P1, the remaining forecasts follow at intervals of P2
116	Accumulation of N forecasts, all with the same reference time; the first has a forecast period of P1, the remaining forecasts follow at intervals of P2
117	Average of N forecasts; the first has a forecast period of P1, the subsequent ones have forecast periods reduced from the previous one by an interval of P2; the reference time for the first is given in octets 13 to 17, the subsequent ones have reference times increased from the previous one by an interval of P2. Thus all the forecasts have the same valid time, given by the reference time + P1
118	Temporal variance, or covariance, of N initialized analyses; each product has forecast period of P1 = 0; products have reference times at intervals of P2, beginning at the given reference time
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
120-122	Reserved
123	Average of N uninitialized analyses, starting at the reference time, at intervals of P2
124	Accumulation of N uninitialized analyses, starting at the reference time, at intervals of P2
125-254	Reserved

For analysis products, or the first of a series of analysis products, the reference time (octets 13 to 17) indicates the valid time.
For forecast products, or the first of a series of forecast products, the reference time indicates the valid time of the analysis upon which the (first) forecast is based.
Initialized analysis products are allocated code figures distinct from those allocated to unitialized analysis products.
Code figure 10 allows the period of a forecast to be extended over two octets; this is to assist with extended range forecasts.
Where products or a series of products are averaged or accumulated, the number involved is to be represented in octets 22 and 23 of Section 1, while any number missing is to be represented in octet 24.
Forecasts of the accumulation or difference of some quantity (e.g. quantitative precipitation forecasts), indicated by values of 4 or 5 in octet 21, have a product valid time given by the reference time + P2; the period of accumulation, or difference, can be calculated as P2 - P1.
A few examples may help to clarify the use of Code table 5:
For analysis products, P1 will be zero and the time range indicator (octet 21) will also be zero; for initialized products (sometimes called "zero hour forecasts"), P1 will be zero, but octet 21 will be set to 1.
For forecasts, typically, P1 will contain the number of hours of the forecast (the unit indicator given in octet 18 would be 1) and octet 21 would contain a zero.
Code value 115 would be used, typically, for multiple day mean forecasts, all derived from the same initial conditions.
Code value 117 would be used, typically, for Monte Carlo type calculations; many forecasts valid at the same time from different initial (reference) times.
Averages, accumulations, and differences get a somewhat specialized treatment. If octet 21 has a value between 2 and 5 (inclusive), then the reference time + P1 is the initial date/time and the reference time + P2 is the final date/time of the period over which averaging or accumulation takes place. If, however, octet 21 has a value of 113, 114, 115, 116, 117, 123, or 124, the P2 specifies the time interval between each of the fields (or the forecast initial times) that have been averaged or accumulated. These latter values of octet 21 require the quantites averaged to be equally separated in time; the former values, 3 and 4 in particular, allow for irregular or unspecified intervals of time between the fields that are averaged or accumulated.