Docs are here

https://www1.ncdc.noaa.gov/pub/data/normals/1981-2010/readme.txt

Data Units

tenths of degrees Fahrenheit for maximum, minimum, average, dew point, heat 
index, wind chill, and air temperature normals and standard deviations. 
e.g., "703" is 70.3F

tenths of days for the number of days per month above or below certain threshold, 
such as days above 90F. e.g., "256" is 25.6 days.

whole degrees Fahrenheit for heating and cooling degree days (except high
precision files while are in hundredths of degrees Fahrenheit).

hundredths of inches for average monthly/seasonal/annual precipitation, 
month-to-date/year-to-date precipitation, and percentiles of precipitation. 
e.g., "1" is 0.01" and "1486" is 14.86"

tenths of inches for average monthly/seasonal/annual snowfall, 
month-to-date/year-to-date snowfall, and percentiles of snowfall. 
e.g. "39" is 3.9"

whole inches for percentiles of snow depth.

tenths of percent for probabilities of precipitation, snowfall, or snow 
depth exceeding a specific threshold, as well as cloud and wind percentages. 
e.g., "207" is 20.7%

tenths of degree hours for heating and cooling degree hours. e.g., "152" is 15.2

tenths of millibars for mean sea level pressure normals. 
e.g., "10147" is 1014.7 mb

tenths of percent for prevailing and secondary wind direction percentages. 
e.g., "299" is 29.9%

prevailing and secondary wind directions can take on 8 values: 
1=N, 2=NE, 3=E, 4=SE, 5=S, 6=SW, 7=W, 8=NW

tenths of mph for wind speeds and vector magnitudes. e.g. "73" is 7.3 mph

whole degrees for mean vector wind directions