The July 2005 Denver heat wave: how unusual was it?

Abstract

In mid July 2005, very hot temperatures developed over the Rocky Mountains and western Great Plains. This paper summarizes the heat wave and places it in historical perspective. The core of the heat wave was centered near Denver where several weather stations approached or exceeded their all-time record high temperatures on 20-21 July. Denver International Airport rose to 105[degrees]F on 20 July and two National Weather Service (NWS) Cooperative stations in the Denver metro area reached 108[degrees]F exceeding any previous records for the city. Based on 5-day running mean temperatures, this heat wave ranks first for Denver, Edgewater/Lakewood, and Fort Collins. For July as a whole, the month was not the warmest on record, however, due to sharply cooler weather shortly after the heat wave. An alternative method for evaluating heat waves--moist enthalpy which combines temperature and humidity--provides a markedly different perspective and shows the Denver heat wave to be less extreme due to very low humidity accompanying the event.

1. Introduction

Extremely hot weather developed over the Western U.S. during July 2005. Numerous high temperature records were broken from California and Arizona eastward into Colorado and New Mexico as cited in the Weekly Weather and Crop Bulletin [United States Department of Agriculture (USDA) 2005]. An unusually late onset of the summer monsoon played a large role in the hot weather. For example, the NOAA/National Weather Service (NWS) Weather Forecast Office (WFO) in Tucson, AZ recorded 2005 as the second latest arriving monsoon (1987 is the latest) since 1949 (NOAA 2005b). This nearly record breaking late arrival of the monsoon was associated with Tucson tying its record for the longest string of 100[degrees]F+ readings (39 days; op. cit.).

Meanwhile brief episodes of extreme heat, beginning on 13 July, were observed over the northern Rockies (Wyoming and Montana). Then from 19-23 July, temperatures soared daily to 100[degrees]F and above from the Front Range of Colorado across the northern and central Great Plains as reported in the Weekly Weather and Crop Bulletin (USDA 2005). The Denver-Boulder WFO (NOAA 2005a) summarized July 2005 as the second hottest (the hottest average month remains July 1934) and the third driest since 1872. This assessment was based on data collected at Denver International Airport (DIA) where six record high temperatures were set, each at or above 100[degrees]F (Fig. 1). The high of 105[degrees]F observed on 20 July 2005 tied 8 August 1878 for the all-time highest temperature ever recorded at Denver's primary weather station. There were 25 days with maximum temperatures at 90[degrees]F or higher, which tied with the third most since 1963 (1964 had 27 days). Were it not for a strong cold front and sharply cooler temperatures later in the month, July could have been the hottest on record. The 500 hPa analysis for the five-day average from 20 July through 24 July is shown (Fig. 2) to illustrate the average synoptic pattern with this event. The upper-level ridge over Colorado was anomalous by more than 70 gpm, which reflects the warmth of the air column underneath this level rather than surface pressure anomalies.

This heat wave resulted in considerable news coverage and some public debate regarding just how extreme this event was and the integrity of the data used to assess it (Denver Channel 7 2005; Rocky Mountain News 2005). One question regarding the hot temperatures at DIA is whether the instrument is properly sited. This is not always the case (Davey and Pielke 2005). The DIA site's exposure (Fig. 3) was examined for this study and shown to have a good exposure, such that its record high temperatures cannot be attributed to local conditions. The DIA site (lat 39[degrees]49'58"N and long 104[degrees]39'27"W) began taking observations in March 1995. The temperature sensor was moved one-quarter mile north in June 2003 from the original location and another 1 mile north in 2004 to make room for a new runway (personal communication, Byron Louis, National Weather Service, 2006).

[FIGURE 1 OMITTED]

The purpose of this paper is to examine the heat wave in greater detail to better assess its place in Colorado climate history. Several different approaches to assessing heat are presented below, including the monthly average temperature surrounding the heat wave, the number of days above commonly used temperature thresholds, the highest daily temperature, the five-day running average of mean daily temperatures, and the highest value of moist enthalpy.

The evaluation of moist enthalpy (also known as the "effective temperature") is a new approach to assess heat waves, and permits the incorporation of the contribution of water vapor content to the heat of the air in units of Joules. Although historic records of surface water vapor content are comparatively short, they allow for a revealing perspective on recent Colorado heat waves. It should be noted that the occurrence of a single extreme heat wave in a limited geographic region cannot be used to prove or disprove the existence of a recent "global warming" fingerprint, even though moist enthalpy is a better metric for measuring heat content change than surface temperature alone.

2. Climatological Analysis

a. Monthly mean, maximum, and minimum temperature

Table 1 displays the July 2005 monthly maximum, minimum, mean temperatures, and period of record across Colorado for selected long-term stations. The locations of these long-term weather stations are shown in Fig. 4. The rank for the period of record is also given.

Despite selecting the best of Colorado's long-term climate monitoring stations in Table 1, nearly all of them have experienced station moves, changes in thermometers, and changes in the landscape and environments around the station all of which can impact rankings. Nevertheless, it is apparent that 2005 July monthly temperatures were hot statewide but were most anomalous in the Denver area and the Front Range urban corridor from Fort Collins to Pueblo.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

b. Number of days above a temperature threshold

Table 2 presents the number of days during July 2005 with daily maximum temperatures greater than or equal to 90[degrees]F and 100[degrees]F, respectively, and where these rank in the period of record for each available station. The information we have is more limited than for the monthly averages, but it does show that in terms of days greater than or equal to 100[degrees]F, Denver Stapleton tied and Lakewood exceeded the record number. Both sites, however, had fewer days at this level than DIA.

While it was clearly hot statewide, the number of days with temperatures of 90[degrees]F or higher were not exceptional. The number of days of 100[degrees]F or greater were more impressive with most locations ranking in the top 5 years. The only stations showing the most days ever recorded with temperatures of 100[degrees]F or higher were in the immediate Denver area (DIA, Stapleton and Lakewood).

[FIGURE 4 OMITTED]

c. Highest daily temperature

Table 3 presents the highest maximum temperature reached in July 2005, the date of occurrence and its ranking with respect to previous highest July temperatures. Also shown is the highest recorded temperature for any day in July and the year it occurred. For stations where July 2005 was the highest, the previous highest temperature and date of occurrence are shown. The absolute (or the all-time record) highest recorded temperature and the date it occurred is also shown, and for some stations this occurs in late June or early August. In addition to DIA, several sites reported their highest temperature ever (Denver Stapleton, Fort Collins, Grand Junction, Leroy, Waterdale, and Lakewood). Fort Collins, Waterdale, Leroy, and Grand Junction have temperature records that extend back through the 20th century.

The highest temperatures in Colorado during major heat waves are usually found at lower elevation stations east of the Rockies and in the Colorado River valley of western Colorado near the Utah border. This was generally the case in July 2005, but of note were the very high temperatures at the base of the Rockies from Fort Collins to Pueblo (Fig. 4). At the same time that DIA reported the record-tying 105[degrees]F, two stations within urbanized areas hit 108[degrees]F: Denver Water Department and Northglenn (Fig. 5). These are the highest temperatures ever measured in the Denver metropolitan area, but these two stations have only been in existence since 1997 and 1984, respectively.

d. Running five-day averages of mean daily temperatures

There are arguably better ways to define heat waves than with mean monthly temperatures or with individual daily extreme values. The impacts from heat waves are often cumulative--the result of consecutive days of extreme heat. A centered 5-day running average computed from daily maximum and minimum temperatures captures these cumulative effects (Fig. 6).

For a few selected stations near Denver, CO, July mean daily temperatures were computed for the available record. For each day with a mean daily temperature greater than or equal to an extreme threshold value, a centered 5-day average was computed (Figs. 7-9). This value was chosen based on local experience to represent only days of extreme heat. Since 1950, for example, Fort Collins has only had one mean daily temperature of 83[degrees]F or above while the combined Denver and Lakewood stations have had 33 and 21 such days, respectively. Therefore, we picked 80[degrees]F for the Fort Collins threshold to show periods of extreme heat, while an 83[degrees]F threshold was used for Denver and Lakewood.

This analysis shows the July 2005 heat wave as the most extreme on record for these stations when applying this particular criterion. The number of days above the local threshold was comparable to other heat waves at each station, but the highest 5-day running mean exceeded any previous values for all three stations. For the combined Denver station, the highest 5-day running mean of 84.8[degrees] was nearly 1.5[degrees]F higher than any previous record.

3. An Alternative Metric for Evaluating the July 2005 Heat Wave

The surface air temperature is often used to quantify how hot it is. However, temperature is not actually a measure of heat, since heat is energy, and energy is measured in Joules, not degrees. To obtain the heat content of the surface air, one should compute the moist enthalpy, which requires three standard observed quantities: the air temperature, dew point temperature (or relative humidity), and the surface pressure (Pielke et al. 2004; Davey et al. 2005). Moist enthalpy is expressed as:

H = [c.sub.p]T + [L.sub.v]q (1)

where [c.sub.p] is the specific heat of air at constant pressure and was approximated as 1005 J [kg.sup.-1] [K.sup.-1], T is the observed air temperature (in K), [L.sub.v] is the latent heat of vaporization and is equal to 2.430x[10.sup.6] J [kg.sup.-1] (at 30[degrees]C), and q is the specific humidity (in kg [kg.sup.-1]), which can be found from the dew point temperature and surface pressure via the following relation:

q = 0.622e/[p - 0.378e], where e = 6.112 exp([17.67[T.sub.d]]/[[T.sub.d] + 243.5]) (2)

In the previous equations, e is the saturated vapor pressure (in hPa), p is the surface pressure (in hPa), and [T.sub.d] is the dew point temperature (in [degrees]C). To scale the enthalpy into degrees for easy comparison to air temperature, divide by [c.sub.p]:

H/[c.sub.p] = [T.sub.E] = T + [[[L.sub.v]q]/[C.sub.p]] (3)

Here, [T.sub.E] is called the effective temperature and has units of Kelvin. It is clear that the effective temperature will always be greater than or equal to the air temperature. The two are only equal when there is no moisture in the air, and the difference between the two becomes greater as the humidity increases. In other words, [T.sub.E] has contributions from both sensible and latent heat, and the latter should not be ignored when evaluating the intensity of heat waves.

The NWS adopted a "heat index" (Steadman 1979) to assess the severity of predicted heat waves, but this measure is different from the effective temperature that is used in our study. In particular, the NWS heat index is designed to model the human response to heat, and requires additional observations of radiation and wind speed to be properly computed. It is therefore much more complicated than the effective temperature, which is based solely on heat content in Joules.

[FIGURE 5 OMITTED]

Using automated hourly observations at two stations encompassing three recent heat waves, one will see that there is a difference in the heat waves when effective temperature is used as the metric instead of air temperature. The two stations used in this section are Fort Collins, CO, and Denver International Airport, CO (FCL and DIA), and the three heat waves occurred during July of 2002, 2003, and 2005. It should be noted that the data presented here are the automated hourly observations, not the official observations. The FCL station is located amidst irrigated grass, some trees, and further away are parking lots and buildings. The DIA station is in an open field near the airport's runways. In Fig. 10a-c, only the peak values of T and [T.sub.E] are plotted on each day during July 2002, 2003, and 2005 (hourly data not shown). The average of each curve is given in the legend.

Although not as obvious in 2002 and 2003, one feature that stands out in 2005 is that T is typically higher at DIA, but [T.sub.E] is typically higher at FCL. This is actually true in all three years if one considers the average values provided in the legends, and is likely due to the different environments in which the two sensors record (irrigated grass versus open prairie), as mentioned earlier.

There is a notable difference in the heat waves depending on which metric one uses, air temperature or effective temperature. Table 4 reveals that the days with highest T are typically not the days with highest [T.sub.E], and vice versa. All times are Mountain Daylight Time, and T and [T.sub.E] are in [degrees]F. In each month, the top five days with highest air temperature are shown, along with the date and time at which the peak occurred, as well as the effective temperature at that time. The second set of numbers for each month is the top five days with highest effective temperature, along with the date and time at which the peak occurred, as well as the air temperature at that time. To put the effective temperatures in context, the highest value observed at FCL during a ten-year period (1996-2005) was 150.4[degrees]F, which occurred on 6 July 1999.

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

The time at which the air temperature reaches a maximum and the time at which the effective temperature reaches a maximum often do not coincide due to boundary layer mixing in the late afternoon. In fact, the maximum [T.sub.E] typically occurs a few hours before the maximum T. Figure 11 shows this temporal difference very clearly. It is a composite of the top five hottest days in each of the three years considered here, for FCL (see the left side of Table 4 for the fifteen days that go into making this composite). Both quantities have a minimum just before sunrise, but the effective temperature peaks at approximately 1100 Local Time, while the air temperature peaks at approximately 1500 Local Time.

[FIGURE 8 OMITTED]

4. Conclusions

Several different metrics are shown here for comparing heat wave severity and ranking the recent July 2005 Colorado heat wave: monthly temperatures, frequency of temperatures above specified threshold values, daily temperature extremes, 5-day running means, and moist enthalpy. Based on daily temperature extremes, July 2005 was a record heat wave for several locations. New all-time records included 108[degrees]F at Northglenn and Denver Water Department, 105[degrees]F on 20 July 2005 at DIA (tying an old record previously set in 1878), and 103[degrees]F at Fort Collins on 21 July. The heat wave was persistent, and record or near-record 5-day running means were observed near Denver. Also, several stations reported the greatest number of days of 100[degrees]F or higher.

However, in terms of frequency of monthly temperatures and daily temperatures of 90[degrees]F or above, July 2005 was not exceptional. Cooler weather earlier in the month, and a notable cold front in late July cut the duration of this heat wave short. Finally, a new metric for assessing heat, moist enthalpy, showed significantly different results. Very low humidities reduced the peak moist enthalpy values of the July 2005 heat wave compared to earlier heat waves in 2002 and 2003, despite higher temperatures. Cooler but more humid locations (like Fort Collins) actually have greater heat (effective temperature) when compared to the relatively hot but dry conditions observed at DIA. Based on the moist enthalpy diagnostic, the 2005 heat wave was not exceptional.

[FIGURE 9 OMITTED]

The diversity of observations of the heat wave suggests that we need to address the question, should we record temperatures that register the full impact of heat waves that affect people both in terms of human health impacts (mortality) and electrical power consumption (air conditioning) inside the "urban heat island," or should we keep the observing sites out at airports where we get a more objective record of regional temperatures that are often substantially lower than those affecting the majority of the population? Over the past 50 years, data have been collected at airports, but the value of also retaining urban observation sites is clear.

Acknowledgments

This paper was prepared by the Colorado Climate Center. The Colorado Climate Center is supported by the Colorado Agricultural Experiment Station at Colorado State University. Klaus Wolter is supported through the Western Water Assessment (WWA) project which is funded through the NOAA-Office of Global Programs. Brian McNoldy is partially supported by NSF Contract ATM-0332197.

Authors

Roger A. Pielke, Sr. is Senior Research Scientist at the Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, CO and State Climatologist Emeritus for the State of Colorado. Dr. Pielke's research focuses on mesoscale meteorology and climatology, and on developing improved techniques for weather forecasting. He received a B.S. from Towson State in 1968 and M.S. and Ph.D. degrees from The Pennsylvania State University in 1969 and 1973 respectively.

[FIGURE 10 OMITTED]

Klaus Wolter is a Research Associate at CIRES. His primary research interests lie in empirical climate research, particularly the application of statistical methods to societal relevant problems, such as the impact of ENSO on world-wide climate and improved seasonal climate predictions. He received a Diplom (equivalent to M.S.) in Meteorology from the University of Hannover, Germany in 1981, and his Ph.D. in Meteorology from the University of Wisconsin, Madison in 1987.

[FIGURE 11 OMITTED]

Odilia Bliss is Research Coordinator for the Colorado Climate Center (CCC) at Colorado State University. She has been employed at CCC since 1978. Her principal research interests are climatology, outreach education, climate change, and GIS applications.

Nolan Doesken is Colorado State Climatologist and Senior Research Associate in the Department of Atmospheric Science, Colorado State University, Fort Collins, CO. His research interests include the climate of Colorado, climate data collection, data quality, information dissemination, precipitation patterns, extreme rainfall, drought monitoring, climate and water, hail and severe weather, snow climate and energy, mountain climates, climate history, and long-term climate variations. He received his B.S. in Atmospheric and Oceanic Science from University of Michigan in 1974 and M.S. in Atmospheric Science from the University of Illinois in 1976.

Brian McNoldy is a Research Associate at Colorado State University in the Department of Atmospheric Science. His responsibilities include assisting with writing grant proposals, publishing technical papers, presenting results at conferences, assisting graduate students with research, and community outreach. Mr. McNoldy's research interests include mid-latitude severe weather, mesovortices, concentric eyewalls, and intensity changes associated with tropical cyclones as well as climatology, ranging from the multidecadal to monthly scale and from the global to local scale. He received a B.A. from Lycoming College (Williamsport, PA) in 1998 where he majored in Physics and Astronomy with a minor in Mathematics. In 2001, he earned his M.S. in Atmospheric Science from Colorado State University.

References

Davey, C.A., and R.A. Pielke Sr., 2005: Microclimate exposures of surface-based weather stations--implications for the assessment of long-term temperature trends. Bull. Amer. Meteor. Soc., 86, 497-504.

______, ______, and K.P. Gallo, 2006: Differences between near-surface equivalent temperature and temperatures trends for the eastern United States--Equivalent temperature as an alternative measure of heat content. Global and Planetary Change. 54, 19-32.

Denver Channel 7, cited 2005: Denver ties all-time record of 105 degrees, July 20, 2005. [Available online at http://www.thedenverchannel.com/weather/4746329/detail.html]

NOAA/NWS WFO Denver/Boulder, 2005a: Denver Monthly Summary (July, 2005). [Available online at http://www.crh.noaa.gov/bou/?n=climo]

______, Tucson, 2005b: Year-by-Year Monsoon Statistics for Tucson (1949-2005). [Available online at http:www.wrh.noaa.gov/twc/monsoon/monsoon.php]

Pielke Sr., R.A., C.A. Davey, and J. Morgan, 2004: Assessing "global warming" with surface heat content. Eos, Trans. Amer. Geophys. Union, 85, No. 21, 210-211.

Rocky Mountain News, cited July 26,2005: Hot streak has experts divided. [Available online at http://www.highbeam.com/browse/NewsLocal+Interest+Rocky+Mountain+News+(Denver,+CO)/July-2005-p14]

Steadman, R.G., 1979: The assessment of sultriness. Part I: A temperature-humidity index based on human physiology and clothing science. J. Appl. Meteor., 18, 861-873.

U.S. Department of Agriculture, 2005: Weekly Weather and Crop Bulletin, Vol. 92, No. 30,39 pp. [Available online at http://www.usda.gov/oce/weather/pubs/Weekly/Wwcb/index.htm]

Roger A. Pielke Sr. and Klaus Wolter

Cooperative Institute in Environmental Sciences and Department of Atmospheric and Oceanic Sciences

University of Colorado at Boulder

Boulder, Colorado 

Odilia Bliss, Nolan Doesken, and Brian McNoldy

Atmospheric Science Department

Colorado State University

Fort Collins, Colorado 

Table 1. Monthly average maximum, minimum and mean temperatures for
selected stations for July 2005 for period of record. Most stations are
NWS Cooperative Stations (Coop), but for the larger cities data come
from the NWS Automated Surface Observing Sites (ASOS).

                                                       Period of
                                Elevation  Type        Record
Climatic Stations               (feet)     of Station  (POR)

Akron 4E                        4550       Coop        1905-2005
Alamosa                         7533       ASOS        1948-2005
Aspen / 1SW (combined*)         7936/8163  Coop        1914-2005
Boulder                         5484       Coop        1893-2005
Buena Vista                     7946       Coop        1905-2005
Center 4 SSW                    7673       Coop        1942-2005
Cheesman                        6880       Coop        1902-2005
Cheyenne Wells                  4250       Coop        1897-2005
Cochetopa Creek                 8000       Coop        1947-2005
Collbran / 2SW (combined*)      5980/6100  Coop        1901-2005
Colorado Springs WSO            6181       ASOS        1948-2005
Del Norte 2E                    7864       Coop        1920-2005
Denver Intl Airport             5414       ASOS        1995-2005
Denver Stapleton                5286       Coop        1948-2005
Denver (combined*)              5325/5286  C/A         1872-2005
Dillon                          9065       Coop        1910-2005
Fort Collins                    5001       Coop        1895-2005
Fraser (combined*)              8560/8563  Coop        1910-2005
Grand Junction WSO              4858       ASOS        1900-2005
Grand Lake 1NW                  8720       Coop        1940-2005
Kassler                         5587       Coop        1918-2005
Lakewood                        5640       Coop        1962-2005
Lakewood/Edgewater (combined*)  5640/5453  Coop        1902-2005
Las Animas                      3890       Coop        1893-2005
Leadville 2SW                   9938       Coop        1976-2005
Leadville 2SW (combined*)       9941/9938  Coop        1949-2005
Leroy 7WSW                      4470       Coop        1893-2005
Meeker                          6180       Coop        1894-2005
Mesa Verde NP                   7115       Coop        1923-2005
Montrose No. 2                  5785       Coop        1896-2005
Pueblo WSO                      4720       ASOS        1954-2005
Rocky Ford 2SE                  4170       Coop        1892-2005
Sedgwick5S (combined)           3990       Coop        1909-2005
Taylor Park                     9206       Coop        1941-2005
Waterdale (Loveland)            5230       Coop        1902-2005

                                July 2005 Temperature
                                Max        Min        Mean
Climatic Stations               (Rank)     (Rank)     (Rank)

Akron 4E                        93.3(5+)   61.0(2)    77.2(2)
Alamosa                         86.9(1)    45.7(47)   66.3(8)
Aspen / 1SW (combined*)         81.1(16)   48.7(5)    64.9(6)
Boulder                         91.6(4)    58.5(53)   75.1(21)
Buena Vista                     87.2(5)    50.8(2)    69.0(3+)
Center 4 SSW                    84.1(7)    46.5(28)   65.3(5)
Cheesman                        87.7(9)    52.5(11)   70.1(4)
Cheyenne Wells                  93.1(26+)  59.4(54+)  76.2(34+)
Cochetopa Creek                 86.1(3)    41.4(33+)  63.8(6+)
Collbran / 2SW (combined*)      92.0(8)    52.3(40)   72.1(14+)
Colorado Springs WSO            89.3(5)    57.2(26)   73.3(9)
Del Norte 2E                    79.6(32)   45.8(77)   62.7(52)
Denver Intl Airport             94.5(1)    60.8(4)    77.7(1)
Denver Stapleton                92.6(3)    60.1(13)   76.4(6+)
Denver (combined*)              94.5(1)    60.8(33)   77.7(2)
Dillon                          78.2(6)    37.4(42+)  57.8(11)
Fort Collins                    91.7(2+)   58.8(10+)  75.4(3)
Fraser (combined*)              78.7(3)    35.8(27+)  57.3(8)
Grand Junction WSO              97.7(3+)   62.2(93+)  80.0(21)
Grand Lake 1NW                  80.9 (5)   39.8(16)   60.2(6)
Kassler                         91.9(2)    61.3(12+)  76.6(5)
Lakewood                        93.5(1)    60.0(7)    76.8(2)
Lakewood/Edgewater (combined*)  93.5(5)    60.0(11)   76.8(5+)
Las Animas                      97.5(24+)  62.8(23)   80.1(22)
Leadville 2SW                   74.6(6)    39.4(4+)   57.0(15+)
Leadville 2SW (combined*)       74.6(6)    39.4(24+)  57.0(14+)
Leroy 7WSW                      93.5(7)    60.3(14+)  77.0(8)
Meeker                          89.3(10)   48.1(22)   68.7(12+)
Mesa Verde NP                   88.5(23+)  59.0(15)   73.8(17)
Montrose No. 2                  92.7(5+)   54.1(80+)  73.4(32+)
Pueblo WSO                      97.7(2)    58.9(37+)  78.3(12)
Rocky Ford 2SE                  98.7(1)    54.2(111)  76.5(44)
Sedgwick5S (combined)           94.7(14)   60.9(21+)  77.8(16+)
Taylor Park                     74.7(4+)   41.7(17+)  58.2(7+)
Waterdale (Loveland)            91.6(6)    57.0(9)    74.3(6)

+ means that temperature tied previous years
* Data combined for Aspen 1914-1979; Aspen 1SW 1980-2005
* Data combined for Collbran 1901-1999; Collbran 2SW 2000-2005
* Data combined for Denver City 1872-1950; Denver Stapleton 1950-1994;
DIA 1995-2005
* Data combined for Fraser 1910-1973; 1989-2005
* Data combined for Edgewater 1908-1961; Lakewood 1962-2005
* Data combined for Leadville 1949-1975; Leadville 2SW1976-2005

Table 2. The number of days during July 2005 where daily maximum
temperatures equaled or exceeded 90[degrees]F and 100[degrees]F for
selected weather stations in Colorado. The rankings, with respect to the
period of record, are shown in parentheses.

                                                    Number of Days
                           Elevation  Period of     .GE. 90  .GE. 100F
Climatic Stations          (feet)     Record (POR)  (Rank)   (Rank)

Akron 4E                   4550       1905-2005     21(12+)   6(4+)
Alamosa                    7533       1948-2005      9(2+)    0
Aspen / 1SW (combined*)    7936/8163  1914-2005      0        0
Boulder                    5484       1893-2005     22(6+)    1(7)
Buena Vista                7946       1905-2005     11(5)     0
Center 4 SSW               7673       1942-2005      3(4)     0
Cheesman                   6880       1902-2005     12(10)    0
Cheyenne Wells             4250       1897-2005     22(17+)   5(20+)
Cochetopa Creek            8000       1947-2005      6(3+)    0
Collbran/2SW (combined*)   5980/6100  1901-2005     23(8+)    0
Colorado Springs WSO       6181       1948-2005     20(2+)    0
Del Norte 2E               7864       1920-2005      0        0
Denver Intl Airport        5414       1995-2005     25(2)     7(1)
Denver Stapleton           5286       1948-2005     22(6+)    5(1+)
Denver (combined*)         5325/5286  1872-2005     25(3+)    7(1)
Dillon                     9065       1910-2005      0        0
Fort Collins               5001       1895-2005     22(2+)    3(2)
Fraser (combined*)         8560/8563  1910-2005      0        0
Grand Junction WSO         4858       1900-2005     28(12+)  10(5+)
Grand Lake 1NW             8720       1940-2005      0        0
Kassler                    5587       1918-2005     20(5+)    3(3+)
Lakewood                   5640       1962-2005     22(2)     6(1)
Lakewood/Edgewater         5640/5453  1902-2005     22(7+)    6(3+)
  (combined*)
Las Animas                 3890       1893-2005     27(33+)  12(26+)
Leadville 2SW              9938       1976-2005      0        0
Leadville 2SW(combined*)   9941/9938  1949-2005      0        0
Leroy 7WSW                 4470       1893-2005     22(11+)   6(6+)
Meeker                     6180       1894-2005     13(17+)   0
Mesa Verde NP              7115       1923-2005     12(32+)   0
Montrose No. 2             5785       1896-2005     23(12+)   2(4+)
Pueblo WSO                 4720       1954-2005     28(7+)   12(2+)
Rocky Ford 2SE             4170       1892-2005     29(8+)   16(3)
Sedgwick 5S (combined)     3990       1909-2005     25(13+)   8(13+)
Taylor Park                9206       1941-2005      0        0
Waterdale (near Loveland)  5230       1902-2005     22(7+)    3(4+)

+ means that temperature tied previous years
* Data combined for Aspen 1914-1979; Aspen 1SW 1980-2005
* Data combined for Collbran 1901-1999; Collbran 2SW 2000-2005
* Data combined for Denver City 1872-1950; Denver Stapleton 1950-1994;
DIA 1995-2005
* Data combined for Fraser 1910-1973; 1989-2005
* Data combined for Edgewater 1908-1961; Lakewood 1962-2005
* Data combined for Leadville 1949-1975; Leadville 2SW 1976-2005

Table 3. The highest maximum temperature, the rank for its period of
record, the date it occurred and time of observation for July 2005
compared to the highest recorded temperature for all July's and the year
it occurred or for stations where July 2005 was the highest, then the
previous highest temperature and date of occurrence are shown. The last
two columns show the absolute highest temperature for the station and
date(s) of occurrence.

                                                      Record Temperature
                                                      July
                                             July     2005
                                             2005     Highest
                         Period of  Time of  Highest  Max      Date of
                         Record     Obs      Max      Temp     July
Climatic Stations        (POR)      LST      Temp     Rank     Tmax

Akron 4E                 1905-2005  08       106       2+      21st
Alamosa                  1948-2005  24        92       4+      17,19,
                                                               20,21
Aspen / 1SW (combined*)  1914-2005  08        89      12+      22nd
Boulder                  1893-2005  17       101       3+      21st
Buena Vista              1905-2005  08        95       5+      22nd
Center 4 SSW             1942-2005  24        92       4+      20th
Cheesman                 1902-2005  07        97       6+      22nd
Cheyenne Wells           1897-2005  19       107       3       20th
Cochetopa Creek          1947-2005  08        93       3+      23rd
Collbran / 2SW           1901-2005  08        99       2+      21st
  (combined*)
Colorado Springs WSO     1948-2005  24        98       5       20th
Del Norte 2E             1920-2005  07        86      32+      15/20th
Denver Intl Airport      1995-2005  24       105       1       20th
Denver Stapleton         1948-2005  06       104       1       21st
Denver (combined*)       1872-2005  24       105       1       20th
Dillon                   1910-2005  07        87       2       21st
Fort Collins             1895-2005  19       103       1       21st
Fraser (combined*)       1910-2005  16        86       5+      21st
Grand Junction WSO       1900-2005  24       106       1       21st
Grand Lake 1NW           1940-2005  16        88       7+      12th
Kassler                  1918-2005  07       102       3+      21/22nd
Lakewood                 1962-2005  07       103       1       21st
Lakewood/Edgewater       1902-2005           103       4+      21st
  (combined*)
Las Animas               1893-2005  24       108      12+      20th
Leadville 2SW            1976-2005  17        83       6+      22nd
Leadville 2SW            1949-2005  17        83       6+      22nd
  (combined*)
Leroy 7WSW               1893-2005  07       108       1+      21st
Meeker                   1894-2005  08        98       5+      22nd
Mesa Verde NP            1923-2005  08        97      12+      21st
Montrose No. 2           1896-2005  08       100       5+      21/22nd
Pueblo WSO               1954-2005  24       108       2       20th
Rocky Ford 2SE           1892-2005  17       108       1       20th
Sedgwick 5S (combined)   1909-2005  07       109       4+      20th
Taylor Park              1941-2005  17        83       2+      21st
Waterdale (near          1902-2005  08       103       2       22nd
  Loveland)

                         Highest
                         Recorded            Absolute Temperature
                         Temp or                          Month
                         Previous            Absolute     and
Climatic Stations        Record    Year      Temperature  Year

Akron 4E                 107       1989      107          1989/07/09
Alamosa                   96       1989       96          1989/07/05
Aspen / 1SW (combined*)   94       1917       94          1917/07/27
Boulder                  104       1954      104          1954/06/23
Buena Vista              102       1927      102          1927/07/13
Center 4 SSW              94       1954       95          1954/06/21
Cheesman                  99       1936,      99          1954/06/23;
                                   1939                   1936/07/23;
                                                          1939/07/12
Cheyenne Wells           109       1936      109          1936/07/24
Cochetopa Creek           94       2002,      94          2002/07/14;
                                   2003                   2003/07/19
Collbran / 2SW           100       2003      100          1902/08/02;
  (combined*)                                             2003/07/14
Colorado Springs WSO     100       1954,     100          1954/06/23;
                                   2003                   2003/07/24
Del Norte 2E              91       1940,      91          1940/07/24;
                                   1951                   1951/07/07
Denver Intl Airport      101       2000,     105          2005/07/20
                                   01, 03
Denver Stapleton         103       1973,     104          1994/06/26;
                                   1989                   2005/07/21
Denver (combined*)       103       1973,     105          1878/08/08;
                                   1989                   2005/07/20
Dillon                    89       1939       89          1939/07/12
Fort Collins             102       1925      103          2005/07/21
Fraser (combined*)        94       1939       98          1969/08/01
Grand Junction WSO       105       1925,     106          2005/07/21
                                   1971,
                                   1976,
                                   2002,
                                   2003
Grand Lake 1NW            92       1978       92          1978/07/15
Kassler                  103       1990      105          1994/06/27;
                                                          2005/07/21
Lakewood                 101       1989      104          1994/06/27
Lakewood/Edgewater       106       1939,     106          1954/06/23;
  (combined*)                      1954                   1938/08/01;
                                                          1939/07/20
Las Animas               114       1933      114          1933/07/01
Leadville 2SW             85       1963,      86          1954/06/23
                                     2003
Leadville 2SW             85       1963,      85          2003/07/18;
  (combined*)                      2003                   1963/07/19
Leroy 7WSW               108       1990,     108          1990/07/02;
                                   2005                   2005/07/21
Meeker                   103       1900      103          1900/07/11
Mesa Verde NP            102       1936      102          1936/07/24
Montrose No. 2           103       1931      106          1947/08/01
Pueblo WSO               109       2003      109          2003/07/13
Rocky Ford 2SE           107       1960,     108          2005/07/20
                                   2003
Sedgwick 5S (combined)   114       1954      114          1954/07/11
Taylor Park               86       1942       86          1942/07/15
Waterdale (near          104       1934      104          1934/07/13
  Loveland)

+ means that temperature tied previous years
* Data combined for Aspen 1914-1979; Aspen 1SW 1980-2005
* Data combined for Collbran 1901-1999; Collbran 2SW 2000-2005
* Data combined for Denver City 1872-1950; Denver Stapleton 1950-1994;
DIA 1995-2005
* Data combined for Fraser 1910-1973; 1989-2005
* Data combined for Edgewater 1908-1961; Lakewood 1962-2005
* Data combined for Leadville 1949-1975; Leadville 2SW1976-2005

Table 4. In each of the three recent heat waves--July 2002, July 2003,
July 2005--the top five days with highest air temperature are given. The
date and time at which those temperatures occurred are given, followed
by the effective air temperature at that time. Similarly, the top five
days with highest effective temperature are given. The date and time at
which those temperatures occurred are given, followed by the air
temperature at that time. Times are in MDT, and temperatures are in
[degrees]F. Rarely do the two sets of records coincide.

           FCL JULY 2002                     DIA JULY 2002

Highest T  Date  Time  [T.sub.E]  Highest T  Date  Time  [T.sub.E]

 99.4      7/1   1500  117.7       98.0      7/31  1553  123.3
 96.8      7/31  1700  117.5       98.0      7/1   1353  125.3
 95.8      7/24  1600  121.7       95.0      7/19  1653  124.6
 94.9      7/30  1600  116.0       94.0      7/30  1353  118.2
 94.3      7/16  1700  119.3       94.0      7/29  1553  117.3

Highest                           Highest
[T.sub.E]  Date  Time  T          [T.sub.E]  Date  Time  T

144.5      7/10  1600   82.9      145.3      7/10  1253   86.0
142.8      7/7   1300   84.5      133.9      7/7   1653   86.0
142.3      7/3   1300   84.2      133.5      7/6   1353   76.0
141.0      7/4   1300   81.1      131.6      7/21  1653   78.0
138.2      7/6   1400   79.2      130.8      7/8   1953   80.0

           FCL JULY 2003                     DIA JULY 2003

Highest T  Date  Time  [T.sub.E]  Highest T  Date  Time  [T.sub.E]

 99.0      7/24  1400  123.5      100.0      7/24  1353  131.9
 98.8      7/8   1700  119.8       99.0      7/16  1153  124.1
 97.5      7/16  1600  129.0       98.0      7/13  1253  125.3
 97.3      7/13  1400  116.9       98.0      7/17  1253  131.0
 97.2      7/21  1500  123.8       97.0      7/8   1453  121.4

Highest                           Highest
[T.sub.E]  Date  Time  T          [T.sub.E]  Date  Time  T

149.5      7/18  1300   90.0      145.7      7/19  1653   84.0
145.7      7/28  1600   78.5      145.1      7/27  1053   79.0
142.0      7/19  1300   83.1      143.3      7/18  0953   86.0
140.8      7/27  1400   85.0      141.6      7/26  1653   90.0
140.7      7/25  1500   92.1      138.5      7/28  1253   77.0

           FCL JULY 2005                     DIA JULY 2005

Highest T  Date  Time  [T.sub.E]  Highest T  Date  Time  [T.sub.E]

101.3      7/21  1700  128.3      103.0      7/21  1353  123.6
 98.5      7/19  1700  116.7      102.0      7/20  1053  118.9
 98.2      7/22  1700  130.5      101.0      7/23  1353  127.3
 98.1      7/23  1500  136.7      101.0      7/22  1253  122.5
 95.8      7/14  1500  132.4      101.0      7/16  1353  120.1

Highest                           Highest
[T.sub.E]  Date  Time  T          [T.sub.E]  Date  Time  T

145.5      7/22  1400   92.3      135.7      7/12  1153   88.0
145.4      7/25  1200   77.6      134.0      7/14  1453   97.0
140.9      7/13  1300   86.5      133.9      7/15  1253   94.0
140.9      7/15  1500   88.6      130.2      7/24  1053   84.0
140.6      7/12  1400   86.8      129.9      7/22  1053   93.0