For summary-of-the-day observations, the average of the maximum and minimum temperatures recorded that day. In some displays, this is rounded off to the nearest degree.

A portion of a state that is fairly homogeneous in terms of its climate. The maximum number of divisons that any state can have is 10.

Cooling degree days are a value reflecting the amount of energy needed to keep a building cool. It is computed by subtracting a base temperature from the average temperature (usually rounded to the nearest degree) for the day. The base temperature in products is 65 degrees Fahrenheit, unless specified otherwise.

A unique 6-digit cooperative weather station identification number. The first two digits indicate the state. This identifier is the primary means of specifying individual stations.

A site at which weather observations are taken by volunteers or contractors who are not National Weather Service employees and who are not required to pass observation certification examinations. Observations are usually taken only once per day. There are approximately 11,000 cooperative observers in the United States. More info on the cooperative observer program can be found at: http://www.nws.noaa.gov/om/COOP/index.htm

A site at which weather observations are taken by National Weather Service employees or other certified observers. Observations are usually taken on the hour, around the clock. Daily summary statistics are also recorded. A comprehensive array of weather variables are recorded, such as atmospheric pressure, temperature, wind speed and direction, humidity, precipitation type and amount, cloud cover and visibility. Most, but not all, first-order weather stations are located at major airports.

Growing degree days provide a useful means of relating crop growth and insect development to temperature. Numerous methods for calculating GDD exist. In its most basic form, it is computed by subtracting a base temperature from the average temperature (usually rounded to the nearest degree) for the day. The base temperature in products is 50 degrees Fahrenheit, unless specified otherwise.

This is an adaptation of the normal base 50 growing degree days. The difference is that maximum temperatures above 86 degrees F are set to 86 and minimum temperatures below 50 degrees F are set to 50 before the calculations are done. The base temperature is 50 degrees Fahrenheit, unless specified otherwise. This type of GDD is commonly used in applications related to corn growth and development.

Heating degree days are a value reflecting the amount of energy needed to heat a building. It is computed by subtracting the average temperature (usually rounded to the nearest degree) for the day from a base temperature. The base temperature in products is 65 degrees Fahrenheit, unless specified otherwise.

Highest temperature recorded for the 24 hours ending at the time of observation.

Lowest temperature recorded for the 24 hours ending at the time of observation.

Data can be missing for a number of reasons, including: the data were not recorded by the observer, the equipment was not functioning properly, or the data were deemed to be bad by quality control procedures.

Average of all the non-missing daily average temperatures for a month. Full precision of the daily averages are used in this calculation (i.e. the values before rounding).

Average of all the non-missing daily maximum temperatures for a month.

Average of all the non-missing daily minimum temperatures for a month.

Monthly sum of daily cooling degree day values. Base temperature of 65° F is used and average temperatures are rounded away from zero before calculating degree days. For months with between 1 and 5 days of missing data, the monthly total is estimated by assigning the average of the non-missing days to this day. For days with more than five days of missing data, a partial monthly total is displayed.

Greatest of the daily precipitation observations recorded during the month. Values that were accumulated over more than one day are ignored when determining this extreme.

Greatest of the daily snowfall observations recorded during the month. Values that were accumulated over more than one day are ignored when determining this extreme.

Greatest of the daily snow water equivalent observations recorded during the month.

Greatest of the daily snow depth observations recorded during the month.

Greatest of the daily temperature ranges recorded during the month.

Monthly sum of daily growing degree day values. Base temperature of 50° F is used and average temperatures are rounded away from zero before calculating degree days. For months with between 1 and 5 days of missing data, the monthly total is estimated by assigning the average of the non-missing days to this day. For days with more than five days of missing data, a partial monthly total is displayed.

Same as sum of growing degree day (base 50) totals, except any maximum temperatures greater than 86°F are set to 86 and any minimum temperature less than 50°F are set to 50 before calculating the average temperature.

Monthly sum of daily heating degree day values. Base temperature of 65° F is used and average temperatures are rounded away from zero before calculating degree days. For months with between 1 and 5 days of missing data, the monthly total is estimated by assigning the average of the non-missing days to this day. For days with more than five days of missing data, a partial monthly total is displayed.

Greatest of the daily maximum temperatures recorded during the month.

Highest of the daily minimum temperatures recorded during the month.

Lowest of the daily maximum temperatures recorded during the month.

Lowest of the daily minimum temperatures recorded during the month.

Monthly sum of daily pan evaporation values.

Monthly sum of daily precipitation values. Trace values do not contribute to the monthly sum. Daily values that are flagged as being included in a subsequent observation are not counted as missing. The accumulated value that follows is included in the monthly total. The exception is a string of subsequent-flagged values that cross a month boundary. These days will be counted as missing.

Monthly sum of daily snowfall values. Trace values do not contribute to the monthly sum. Daily values that are flagged as being included in a subsequent observation are not counted as missing. The accumulated value that follows is included in the monthly total. The exception is a string of subsequent-flagged values that cross a month boundary. These days will be counted as missing.

Amount of snow that has fallen since the last observation. Values of "T" or "Trace" indicate that a trace of snow fell.

A 30-year average consisting of three consecutive decades. Currently the years 1971 through 2000 are used for calculating normals. Products use both monthly and daily normals. Daily temperature and preciptation normals are computed by doing a spline-fit to the monthly normals, unless indicated otherwise.

Also known as the Gaussian distribution. It is a two-paremeter frequency distribution defined by the mean and standard deviation.

The amount of water (in inches) that has evaporated from a Class A evaporation pan. These pans are unpainted, constructed of monel or galvanized metal, 47.5 inches in diameter, 10 inches deep, and mounted on a platform which raises the pan base a few inches above the ground. In cooler climates, observations are only taken from April or May through October.

A three-paremeter frequency distribution defined by the mean, standard deviation and skewness.

Rain and/or the liquid equivalent of frozen precipitation. Values of "T" or "Trace" indicate that a trace of precipitation occurred.

Data in within a database can have one of several thresholds of quality. Preliminary data are usually of the lowest level of quality, since they have undergone little or no quality control. These are usually data that have been captured via electronic means. These data are made available to users before higher quality data becomes available at a later time.

In products, when rounding is performed, it is done away from zero. That is, a value of 2.5 becomes 3 and -2.5 becomes -3.

Sum of the daily snowfall totals from July 1 through the date of interest.

Depth of snow on the ground at the time of observation. Values of "T" or "Trace" indicate that there was a trace of snow on the ground.

Water equivalent (or content) of the snow on the ground (i.e. snow depth). These data are available primarily for first-order weather stations, and measurements are usually only taken when there are more than 2 inches of snow on the ground. The measurement is usually made by taking a representative sample of the snow on the ground, melting it, and measuring the resulting water content.

Difference between the daily average temperature and the daily normal. Negative values indicate that the average temperature for the day was cooler than normal.

Difference between the daily maximum temperature and the daily minimum temperature.

The time that weather observations are taken. At first-order weather stations, this is usually midnight. For cooperative weather stations, however, this time can vary from station to station. A common observation time for coop stations is 7am or 8am. Cooperative station observations are for the twenty-four hours ending at the observation time on the date indicated.

A trace of precipitation, snowfall or snow on the ground indicates that some occurred or is present, but it was below the detectable limit. Generally, this limit for precipitation is 0.005 inch, for snowfall 0.05 inch and for snow depth 0.5 inch.

Sum of the daily precipitation totals from January 1 through the date of interest.