: 

National Climatic Data Center 

DATA DOCUMENTATION 

FOR 

DATA SET 9712B (DSI-9712B) 

Last Spring and First Fall Freeze Dates, 1951-1980

December 26, 2002 

National Climatic Data Center 

151 Patton Ave. 

Asheville, NC 28801-5001 USA 
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Table of Contents 

Topic Page Number

1. Abstract................................................... 3 

2. Element Names and Definitions: ............................ 3 

3. Start Date................................................. 6 

4. Stop Date.................................................. 6 

5. Coverage................................................... 6 

6. How to order data.......................................... 6 

7. Archiving Data Center. .................................... 6 

8. Technical Contact.......................................... 6 

9. Known Uncorrected Problems................................. 6 

10. Quality Statement.......................................... 6 

11. Essential Companion Data Sets.............................. 7 

12. References................................................. 7 
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1. Abstract: The major parameters that make up the Freeze Date file are 

dates (year, month, day) of the last occurrence in Spring and the first 

occurrence in Fall where temperatures were less than or equal to 36, 32, 28, 

20, and 16 degrees Fahrenheit. The selection of freeze dates was performed 

for 3,240 stations in the United States (including Alaska and Hawaii) for the 

1951-1980 period. The stations were selected from the 1951-1980 Climate 

Normals station list (DSI-9641). The Spring and Fall distributions in this 

data set were then used to produce freeze dates and growing season lengths 

associated with specified probability levels (10, 20, 30, 40, 50, 60, 70, 80, 

90 percent). These are available in the digital file 1951-80 Probability 

Levels for Freeze Dates and Growing Season Lengths (DSI-9712c). 

Data from the NCDC Summary of the Day (SOD) file (DSI-3200) were used in 

producing the Freeze Data dates. The SOD temperature data were put through 

extensive validation and interpolation procedures based upon the departure 

from the normal in conjunction with those from surrounding stations. As a 

result, the freeze data were produced from high quality, serially-complete 

station records of daily temperatures (Steurer, 1985). This alleviated the 

many possible biases or errors associated with developing freeze data 

statistics from an incomplete and lower quality data set. 

Yearly station values of the last Spring and first Fall occurrence of selected 

low temperatures were chosen for the period 1951 through 1980. The low 

temperature thresholds were the values of 36, 32, 28, 24, 20, and 16 degrees 

Fahrenheit. All freeze dates were based upon the season August 1 through July 

31 for each threshold temperature. Last Spring dates of occurrence were 

chosen for the period August 1 of the previous year through July 31 of the 

selected year (e.g., Spring season for 1961 runs from August 1, 1960 through 

July 31, 1961. However, the year 1951 begins on January 1, 1951). First Fall 

dates of occurrence were chosen for the period August 1 of the selected year 

through July 31 of the next year (e.g., Fall season for 1961 runs from August 

1, 1961 through July 31, 1962. However, the year 1980 ends on December 31, 

1980). 

The season definition is an improvement over that previously used when the 

selection of freeze dates was performed for data from the 1931-1960 period 

(DSI-9712a). During the 1931-1960 period freeze dates were selected using a 

six month season definition ending with June 30 for the last Spring freeze and 

beginning with July 1 for the first Fall freeze. The new season definition 

coincides more closely with the annual march of temperature in which the 

warmest time of year occurs closer to August 1. The change of season 

definition is expected to produce more realistic dates in the extreme northern 

and mountainous regions of the United States where temperatures frequently are 

at the threshold temperatures near the June 30 date. However, it is important 

to note that the change of season definition should have no effect on other 

station where temperatures do not reach or exceed the preselected temperature 

during the summer. 

2. Element Names and Definitions: 

The data are archived in a fixed length ASCII format. The total data volume 

is 10 megabytes. The data are sorted by the state number (ISTATE) as the 

primary key followed by station number (ISTATN), and year (IYEAR) as secondary 

keys. 
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 Start End 

Element Type Width Column Column

ISTATE Integer 2 1 2 

ISTATN Integer 4 3 6 

IDIV Integer 2 7 8 

IYEAR Integer 4 9 12 

ISPRNG(1) Integer 8 13 20 

ISPRNG(2) Integer 8 21 28 

ISPRNG(3) Integer 8 29 36 

ISPRNG(4) Integer 8 37 44 

ISPRNG(5) Integer 8 45 52 

ISPRNG(6) Integer 8 53 60 

IFALL(1) Integer 8 61 68 

IFALL(2) Integer 8 69 76 

IFALL(3) Integer 8 77 84 

IFALL(4) Integer 8 85 92 

IFALL(5) Integer 8 93 100 

IFALL(6) Integer 8 101 108 

Element Name Element Definition______________________ 

 ISTATE Characters 1-2 

 Cooperative State code number. 

 Range 01-48, 50, 51 

ISTATN Characters 3-6 

 Cooperative Station code number. 

 Range 0001-9999. 

IDIV Characters 7-8 

 Cooperative Division code number. 

 Range 01-10. 

IYEAR Characters 9-12 

This is the year of the occurrence of the last Spring 

 or first Fall freeze season within the specified 

 threshold. (E.g., Spring season for 1961 runs from 

 August 1, 1960 through July 31, 1961; except for 1951 

 which began on January 1, 1951). (E.g., Fall season 

 for 1961 runs from August 1, 1961 through July 31, 

 1962; except 1980 which ends on December 31, 1980). 

 Range 1951-1980. 

LAST-SPRING-FREEZE-36 Characters 13-20 

ISPRNG(1) This is the date (year/month/day) of the 

occurrence of the last Spring freeze where the 

 temperature was less than or equal to 36 degrees 

 Fahrenheit. The last Spring dates are chosen from the 

 period August 1 of the previous year to July 31 of the 

 selected year. (E.g., Spring freeze period for 1961 

 runs from August 1, 1960 through July 31, 1961.) A 

 value of “0" indicates no minimum temperature reached 

 or exceeded a freeze threshold for the specified year. 

 Year - 4 characters, Range 1951-1980 

 Month - 2 characters, Range 01-12 
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 Day - 2 characters, Range 01-31 

LAST-SPRING-FREEZE-32 Characters 21-28 

ISPRNG(2) This is the date (year/month/day) of the 

 occurrence of the last Spring freeze 

 where the temperature was less than 

 or equal to 32 degrees Fahrenheit. 

LAST-SPRING-FREEZE-28 Characters 29-36 

ISPRNG(3) This is the date (year/month/day) of the 

 occurrence of the last Spring freeze 

 where the temperature was less than 

 or equal to 28 degrees Fahrenheit. 

LAST-SPRING-FREEZE-24 Characters 37-44 

ISPRNG(4) This is the date (year/month/day) of the 

 occurrence of the last Spring freeze 

 where the temperature was less than or 

 equal to 24 degrees Fahrenheit. 

LAST-SPRING-FREEZE-20 Characters 45-52 

ISPRNG(5) This is the date (year/month/day) of the 

 occurrence of the last Spring freeze 

 where the temperature was less than or 

 equal to 20 degrees Fahrenheit. 

LAST-SPRING-FREEZE-16 Characters 53-60 

ISPRNG(6) This is the date (year/month/day) of the 

 occurrence of the last Spring freeze where 

 the temperature was less than or equal to 

 16 degrees Fahrenheit. 

FIRST-FALL-FREEZE-36 Characters 61-68 

IFALL(1) This is the date (year/month/day) of the 

 occurrence of the first Fall freeze where 

 the temperature was less than or equal to 

 36 degrees Fahrenheit. The first Fall 

 freeze dates are chosen from the period 

 August 1 of the selected year to July 31 

 of the next year. (E.g., the Fall freeze 

 period for 1961 runs from August 1, 1961 

 through July 31, 1962; except for 1980 

 which ends on December 31, 1980). 

FIRST-FALL-FREEZE-32 Characters 69-76 

IFALL(2) This is the date (year/month/day) of the 

 occurrence of the first Fall freeze 

 where the temperature was less than 

 or equal to 32 degrees Fahrenheit. 

FIRST-FALL-FREEZE-28 Characters 77-84 

IFALL(3) This is the date (year/month/day) of the 

 occurrence of the first Fall freeze where 

 the temperature was less than or equal to 

 28 degrees Fahrenheit. 

FIRST-FALL-FREEZE-24 Characters 85-92 
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IFALL(4) This is the date (year/month/day) of the 

 occurrence of the first Fall freeze where 

 the temperature was less than or equal to 

 24 degrees Fahrenheit. 

FIRST-FALL-FREEZE-20 Characters 93-100 

IFALL(5) This is the date (year/month/day) of the 

 occurrence of the first Fall freeze where 

 the temperature was less than or equal 

 to 20 degrees Fahrenheit. 

FIRST-FALL-FREEZE-16 Characters 101-108 

IFALL(6) This is the date (year/month/day) of the 

 occurrence of the first Fall freeze 

 where the temperature was less than or 

 equal to 16 degrees Fahrenheit. 

3. Start Date: 19510101 

4. Stop Date: 19801231 

5. Coverage: contiguous United States 

a. Southernmost Latitude: 18N 

b. Northernmost Latitude: 65N 

c. Westernmost Longitude: 160W 

d. Easternmost Longitude: 65W 

6. How to Order Data: 

 Ask NCDC’s Climate Services about the cost of obtaining this data set. 

 Phone: 828-271-4800 

 FAX: 828-271-4876 

 E-mail: NCDC.Orders@noaa.gov

7. Archiving Data Center: 

 National Climatic Data Center 

 Federal Building 

 151 Patton Avenue 

 Asheville, NC 28801-5001 

 Phone: (828) 271-4800. 

8. Technical Contact: 

 National Climatic Data Center 

 Federal Building 

 151 Patton Avenue 

 Asheville, NC 28801-5001 

 Phone: (828) 271-4800. 

9. Known Uncorrected Problems: None. 

10. Quality Statement: Data from the NCDC Summary of the Day (SOD) file (DSI3200) were put through a vigorous quality control prior to producing the 

Freeze Data. These temperature data were put through extensive validation and 
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interpolation procedures based upon the departure from the normal in 

conjunction with those from surrounding stations. As a result, the freeze 

data were produced from high quality, serially-complete station records of 

daily temperatures. This alleviated the many possible biases or errors 

associated with developing freeze data statistics from an incomplete and lower 

quality data set. The serially complete data for the 1951-1980 period are 

archived in DSI-9641B. 

11. Essential Companion Datasets: The use of NCDC’s Station History file 

(DSI-9767) is required in order to determine metadata on each station (name, 

location, elevation, etc.). This can be accomplished by comparing the station 

number in bytes 1 through 6 of this data set with the corresponding station 

number in the Station History data set. 

12. References:

Environmental Information Summaries C-26 - Climatography of the United States 

No. 20 

Koss, W.J., Owenby, J.R., Steurer, P.M., and Ezell, D.S., 1988: Freeze/Frost 

data, Climatography of the U.S. No. 20, Supplement No. 1. National Oceanic and 

Atmospheric Administration, NCDC, Asheville, NC. 186 pp. 

Steurer, P.M., 1985: Creation of a serially complete data base of high quality 

maximum and minimum temperatures. Unpublished document, NOAA, National 

Climatic Data Center, Asheville, NC, 21 pp. 

Thom, H.C.S. and Shaw, R. H. 1958: Climatological analysis of freeze data for 

Iowa. Monthly Weather Review, 86, 251-257. 

Thom, H.C.S., 1959: The distribution of freeze-date and freeze-free period of 

climatological series with freezless years. Monthly Weather Review. 87, 136-

144. 

Vestal, C.K., 171: First and last occurrence of low temperatures during the 

cold season. Monthly Weather Review, 99,650-652.