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Deciphering the F-6 Climate Form
(Preliminary Local Climatological Data)
The climate observation tables on our homepage (hereinafter referred to as
the F-6 tables) consist of two pages:
Page 1 contains daily information, and some summation
data for the month. It is broken up into 18 columns, containing data for the
calendar day (i.e. midnight to midnight). If any of these values are not available,
a "M" (missing) is listed in the column.
Column 1: Day of the month Columns 2 through 5: Daily high temperature, low
temperature, mean temperature, and departures from normal. All of these are in
degrees Fahrenheit. Columns 6a and 6b are used for degree days. 6a lists
heating degree days, and 6b lists cooling degree days. Degree days use a base of 65
degrees, and are computed by comparing this to the mean temperature. For each degree
the mean temperature is above 65 degrees, a cooling degree day results. For each
degree the mean is below 65, a heating degree day results. It is possible for both
of these to read zero in a single day (i.e. mean temperature is exactly 65), but otherwise
one of the two must contain a zero value.
Column 7 contains 24-hour precipitation values, measured to the
nearest 0.01 inch. For values less than 0.01 inch but more than zero, a T (trace) is
listed on the form.
Column 8 contains 24-hour snowfall values, to the nearest 0.1
inch. For values less than 0.1 inch but more than zero, a T (trace) is used.
Column 9 contains the snow depth, measured at 6 AM CST (7 AM
CDT) on that particular day. This is measured to the nearest inch. For
unmeasurable snow on the ground, a T (trace) is used.
Columns 10 through 12 contain wind information, in miles per
hour. Column 10 is the daily average wind speed, taken by averaging the hourly
average wind speeds reported over the course of a day. An average wind speed is
reported each hour, based on a 2-minute period. Columns 11 and 12 indicate the
"fastest 2-minute wind" (sometimes referred to as the "fastest mile");
basically, this is the highest value reported for the average wind speed on an observation
over the course of a day. The direction (Column 12) is reported to the nearest 10
degrees (360=north, 90=east, 180=south, 270=west).
Columns 13 and 14 refer to the minutes of sunshine recorded in
a day, and the percentage possible. In central Illinois, only the station at Lincoln
reports sunshine totals.
Column 15 is an average of the sky cover from sunrise through
sunset. Values of 0 to 3 indicate mainly clear skies, 4 to 7 indicates partly cloudy
skies, and 8 to 10 indicates mainly cloudy skies. These values are computed using
hourly observations; since automated stations do not report clouds above 12,000 feet in
elevation, the values thus indicate sky cover at or below 12,000 feet.
Column 16 indicates weather types reported at the station that
day. These are listed on page 2 of the form, but are summarized below:
| Value |
Definition |
| 1 |
Fog |
| 2 |
Fog reducing visibility to 1/4 mile or less |
| 3 |
Thunder |
| 4 |
Ice pellets (sleet) |
| 5 |
Hail |
| 6 |
Glaze (resulting from freezing rain) |
| 7 |
Blowing dust or sand, reducing visibility to 1/4 mile or less |
| 8 |
Smoke or Haze |
| 9 |
Blowing snow |
| X |
Tornado |
Columns 17 and 18 summarize the highest wind gust reported
(also known as the "peak wind"), in miles per hour. Column 17 contains the
speed, and Column 18 contains the direction, reported to the nearest 10 degrees.
Also on Page 1, the sum of the high temperatures and low temperatures is
given. Below that, the sum is divided by the number of days in the month, to give an
average high and low. Summarized values for degree days, precipitation, snowfall,
average wind speed, minutes of sunshine, and average sky cover are listed in the row
labeled "SM". Averages for these values are listed in the row labeled
"AV".
Page 2 contains monthly averages, departures from normal,
and extreme precipitation values, as well as some additional summation data:
The average temperature (to the nearest 0.1 degree F) is given, with its
departure from normal (1971 through 2000 period). The highest and lowest values, and
dates of occurrence, are listed.
Total precipitation (to the nearest 0.01 inch) is given, along with
departure from normal. The highest 24-hour value (sometimes spread over two calendar
days) is listed, along with date(s) of occurrence.
Snowfall (to the nearest 0.1 inch) is given, along with the highest
24-hour value. The highest snow depth during the month is also listed.
Summation values are given for: Number of days with highs 90 or
higher, highs 32 or lower, lows 32 or lower, and lows zero or lower; number of days with
at least 0.01 inch, 0.10 inch, 0.50 inch, and 1.00 inch of precipitation; and number of
days clear, partly cloudy, or cloudy.
Degree days for the month are listed, and compared to normal; values for
the current season (beginning July 1 for heating degree days, and January 1 for cooling
degree days) are also listed.
At the end of the month, values for highest and lowest barometric
pressure (reduced to sea level, listed in inches) will be included for Peoria and
Springfield.
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