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<br />United States AiNk
<br />i Climate Normals
<br />1971-2000
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<br />j P M A SA J J A S O N D
<br />CLIMATOGRAPHY OF THE UNITED STATES NO. 81
<br />Monthly Normals of Temperature, Precipitation, and Heating and Cooling Degree Days
<br />1971-2000
<br />COLORADO Page 3
<br />NOTES
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<br />Product Description:
<br />This Climatography includes 1971-2000 normals of monthly and annual maximum, minimum, and mean temperature (degrees F), monthly and annual
<br />total precipitation (inches), and heating and cooling degree days (base 65 degrees F). Normals stations include both National Weather Service
<br />Cooperative Network and Principal Observation (First-Order) locations in the 50 states, Puerto Rico, the Virgin Islands, and Pacific Islands.
<br />Abbreviations:
<br />No. = Station Number in State Map
<br />COOP ID = Cooperative Network ID (1:2=State ID, 3:6=Station Index)
<br />WBAN ID = Weather Bureau Army Navy ID, if assigned
<br />Elements = Input Elements (X=Maximum Temperature,
<br />N=Minimum Temperature, P= Precipitation)
<br />Call = 3-Letter Station Call Sign, if assigned
<br />MAX = Normal Maximum Temperature (degrees Fahrenheit)
<br />MEAN = Average of MAX and MIN (degrees Fahrenheit)
<br />MIN = Normal Minimum Temperature (degrees Fahrenheit)
<br />HDD = Total Heating Degree Days (base 65 degrees Fahrenheit)
<br />CDD = Total Cooling Degree Days (base 65 degrees Fahrenheit)
<br />Latitude = Latitude in degrees, minutes, and hemisphere (N=North, S=South)
<br />Longitude = Longitude in degrees, minutes, and hemisphere (W=West, E=East)
<br />Elev = Elevation in feet above mean sea level
<br />Flag 1 = * if a published Local Climatological Data station
<br />Flag 2 = + if WMO Fully Qualified (see Note below)
<br />HIGHEST MEAN/YEAR = Maximum Mean Monthly Value/Year, 1971-2000
<br />MEDIAN = Median Mean Monthly Value/Year, 1971-2000
<br />LOWEST MEAN/YEAR = Minimum Mean Monthly Value/Year, 1971-2000
<br />MAX OBS TIME ADJUSTMENT = Add to MAX to Get Midnight Obs. Schedule
<br />MIN OBS TIME ADJUSTMENT = Add to MIN to Get Midnight Obs. Schedule
<br />Note: In 1989, the World Meteorological Organization (WMO) prescribed standards of data completeness for the 1961-1990 WMO Standard Normals.
<br />For full qualification, no more than three consecutive year-month values can be missing for a given month or no more than five overall values can be
<br />missing for a given month (out of 30 values). Stations meeting these standards are indicated with a '+' sign in Flag 2. Otherwise, stations are included in
<br />the normals if they have at least 10 year-month values for each month and have been active since January 1999 or were a previous normals station.
<br />Map Legend: Numbers correspond to'No.' in Station Inventory; Shaded Circles indicate Temperature and Precipitation Stations, Triangles (Point Up)
<br />indicate Precipitation-Only Stations, Triangles (Point Down) indicate Temperature-Only Stations, and Hexagons indicate stations with Flag 1 = *.
<br />Computational Procedures:
<br />A climate normal is defined, by convention, as the arithmetic mean of a climatological element computed over three consecutive decades
<br />(WMO,1989). Ideally, the data record for such a 30-year period should be free of any inconsistencies in observational practices (e.g., changes in station
<br />location, instrumentation, time of observation, etc.) and be serially complete (i.e., no missing values). When present, inconsistencies can lead to a non-
<br />climatic bias in one period of a station's record relative to another, yielding an "inhomogeneous" data record. Adjustments and estimations can make a
<br />climate record "homogeneous" and serially complete, and allow a climate normal to be calculated simply as the average of the 30 monthly values.
<br />The methodology employed to generate the 1971-2000 normals is not the same as in previous normals, as it addresses inhomogeneity and missing
<br />data value problems using several steps. The technique developed by Karl et al. (1986) is used to adjust monthly maximum and minimum temperature
<br />observations of conterminous U.S. stations to a consistent midnight-to-midnight schedule. All monthly temperature averages and precipitation totals are
<br />cross-checked against archived daily observations to ensure internal consistency. Each monthly observation is evaluated using a modified quality
<br />control procedure (Peterson et a/.,1998), where station observation departures are computed, compared with neighboring stations, and then flagged and
<br />estimated where large differences with neighboring values exist. Missing or discarded temperature and precipitation observations are replaced using a
<br />weighting function derived from the observed relationship between a candidate's monthly observations and those of up to 20 neighboring stations whose
<br />observations are most strongly correlated with the candidate site. For temperature estimates, neighboring stations were selected from the U.S.
<br />Historical Climatology Network (USHCN; Karl et a/. 1990). For precipitation estimates, all available stations were potential neighbors, maximizing
<br />station density for estimating the more spatially variable precipitation values.
<br />Peterson and Easterling (1994) and Easterling and Peterson (1995) outline the method for adjusting temperature inhomogeneities. This technique
<br />involves comparing the record of the candidate station with a reference series generated from neighboring data. The reference series is reconstructed
<br />using a weighted average of first difference observations (the difference from one year to the next) for neighboring stations with the highest correlation
<br />with the candidate. The underlying assumption behind this methodology is that temperatures over a region have similar tendencies in variation. If this
<br />assumption is violated, the potential discontinuity is evaluated for statistical significance. Where significant discontinuities are detected, the difference in
<br />average annual temperatures before and after the inhomogeneity is applied to adjust the mean of the earlier block with the mean of the latter block of
<br />data. Such an evaluation requires a minimum of five years between discontinuities. Consequently, if multiple changes occur within five years or if a
<br />change occurs very near the end of the normals period (e.g., after 1995), the discontinuity may not be detectable using this methodology.
<br />The monthly normals for maximum and minimum temperature and precipitation are computed simply by averaging the appropriate 30 values from
<br />the 1971-2000 record. The monthly average temperature normals are computed by averaging the corresponding monthly maximum and minimum
<br />normals. The annual temperature normals are calculated by taking the average of the 12 monthly normals. The annual precipitation and degree day
<br />normals are the sum of the 12 monthly normals. Trace precipitation totals are shown as zero. Precipitation totals include rain and the liquid equivalent
<br />of frozen and freezing precipitation (e.g., snow, sleet, freezing rain, and hail). For many NWS locations, indicated with an '*' next to 'HDD' and 'CDD' in
<br />the degree day table, degree day normals are computed directly from daily values for the 1971-2000 period. For all other stations, estimated degree day
<br />totals are based on a modification of the rational conversion formula developed by Thom (1966), using daily spline-fit means and standard deviations of
<br />average temperature as inputs.
<br />References:
<br />Easterling, D.R, and T.C. Peterson, 1995: A new method for detecting and adiusting for undocumented discontinuities in climatological time series. Intl. J. Clim.,15, 369-377.
<br />Karl, T.R., C.N. Williams, Jr., P.J. Young, and W.M. Wendland,1986: A model to estimate the time of observation bias associated with monthly mean maximum, minimum, and mean
<br />temperatures for the United States, J. Clim. Appl. Met., 25, 145-160.
<br />Peterson, T.C., and D.R. Easterling, 1994: Creation of homogeneous composite climatological reference series. Intl J. Clim., 14,671-679.
<br />Peterson,T.C., R. Vose, R. Schmoyer, and V. Razuvaev, 1998: Global Historical Climatology Network (GHCN) quality control of monthly temperature data. Intl. J. Clim.,18,1169-1179.
<br />Thom, H.C.S., 1966: Normal degree days above any base by the universal truncation coefficient Month. Wea. Rev., 94, 461-465.
<br />World Meteorological Organization, 1989: Calculation of Monthly and Annual 30-Year Standard Normals, WCDP-No. 10, WMO-TD/No. 341, Geneva: World Meteorological Organization.
<br />Release Date: Revised 02/2002* National Climatic Data Center/NESDIS/NOAA, Asheville, North Carolina
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