1951-80 NORMAL GROWING DEGREE UNITS TO
                          SELECTED BASE TEMPERATURES

                                  TD-9641

This data set contains daily 30-year average growing degree units (GDU)  
for the period 1951-1980.  These units are used as in indicator of crop 
development and for classifying regional agroclimates.     

Data from the NCDC Summary of the Day (SOD) file were used in producing the
growing degree units.  The SOD temperature data were put through extensive 
validation and interpolation procedures based on the departure from normal
in conjunction with those from surrounding stations.  As a result, the   
growing degree units were produced from high quality, serially complete
station records of daily maximum and minimum temperatures.  This alleviated
the many possible problems associated with developing growing degree unit
statistics from an incomplete and poor quality data set.

Station values of average daily GDU were computed for 10 base temperatures
(degrees F): 40, 45, 50, 55, 57, 60, 65, 70, and the truncated bases 
48/86 and 50/86.  The bases correspond to many of the common phenological
cycles in the United States.  The truncated bases represent adjustments
of the daily maximum and minimum temperatures, which better describe 
specific growth patterns.  Here, minimum temperatures below the lower
bases are set to the lower bases (48 or 50) and maximum and/or minimum
temperatures above the upper base are set to the upper base (86).  
Average daily station values of GDU were computed for each base temperature
by using:
       ___   
       GDU = (1/N) SUM (GDUi) = (1/N) SUM [(TMAXi + TMINi)/2 - BASE]

where GDUi = growing degree units for the date from year i
     TMAXi = maximum temperature for the date from year i
     TMINi = minimum temperature for the date from year i
      BASE = base temperature
         N = 30 years

In the above equation, when the average of TMAXi and TMINi was less than
the base temperature, the value for GDUi was set to zero, and the average
was always rounded up to the nearest degree.  The values of the average 
GDU for each base temperature were then summed to produce monthly and 
accumulated monthly totals produced in the publication of "Climatography
of the United States No. 20".

The data are in station number, month, and base temperature sort.

ELEMENT                                        WIDTH     COLUMNS

STATION IDENTIFICATION                           6        001-006
DIVISION                                         2        007-008
MONTH                                            2        009-010
BASE TEMPERATURES                                4        011-014
DAY 1 GDU VALUE (IMPLIED DECIMAL TO TENTHS)      4        015-018
      .
      .             
      .
DAY 31 GDU VALUE (IMPLIED DECIMAL TO TENTHS)     4        135-138


BASE TEMPERATURES ARE CODED WITH 2 LEADING ZEROES
TRUNCATED BASE TEMPERATURES ARE CODED EITHER 4886 OR 5086

GDU VALUES = -999 ARE FOR IMPOSSIBLE DATES (E.G., APRIL 31)
           = -111 REPRESENTS A VALUE GREATER THAN ZERO AND LESS THAN .05