Climate is the accumulative record of weather and, like weather, is changing all the time. The causes of these changes are highly complex; some are caused naturally and some are caused by human development. Currently, the earth is in an interglacial period where some glaciers persist at high altitudes and at high latitudes. Over 10,000 years ago, the end of the last ice age saw the retreat of two-mile high glaciers. However, if one went back a billion years, one would see that today's average annual global temperature is nearly as cold as it has ever been.

Climate is affected naturally in the short term by volcanic eruptions, in a human life span by subtle solar variations, and in the extremely long term by the earth's orbital variations and continental drift. Weather is influenced by the changing amount of snow and cloud cover, topography, and landscape (grass vs. asphalt), and this in turn changes the ocean currents and the mean position of the jet stream. Eventually, the ocean and upper atmosphere affects the snow and cloud cover and the cycle attempts to find some sort of equilibrium. The manmade introduction of gases and aerosols further complicates the balance of forces, where some elements provide positive feedback and some negative feedback. Feedback is what happens when a part of the output of a process or a system returns to affect the input. Negative feedback, which occurs when what comes out lessens the strength of what subsequently goes in, tends to suppress the original process (this is what happens with the valve regulating a steam engine). Positive feedback, on the other hand, which occurs when the output goes back to add force to the input, can magnify the whole process until it takes on a "runaway" character. For example, positive feedback with snow results in snow cover lasting longer into spring, then into summer, and eventually accumulating year after year as average temperatures are forced to decrease because of the increased albedo (reflecting away any incoming solar radiation). If, on the other hand, the earth continues to warm, more surface water evaporation will result and more clouds will form. Whether or not the earth will continue warming will depend somewhat on which type of cloud dominates over time. High clouds tend to trap incoming solar radiation while low clouds tend to reflect this energy back out to space.

One of the greatest obstacles in explaining the cause of climate change is the climate record itself. Instrumentation from weather stations has been limited geographically (spatially) and temporally. In the state of Wyoming, there are currently only four first order weather stations (located at airports) that have been reporting, more or less continuously, for at least the past 50 years. Other secondary stations and cooperative observer sites number over 1,000 but have been recording data intermittently for generally less than 30 years. Besides broken periods of observations, weather equipment technology and reporting standards have varied over time. Additionally, there is always the possibility for human error when transcribing the data into digital format and sometimes the equipment malfunctions without being noticed. Stations' surroundings also change. Changing vegetation or urbanization (the so-called "heat island" effect caused by the increased use of concrete and asphalt) near a station will introduce bias. Occasionally, a station may have been relocated only a few 100 feet or changed in elevation by a few feet. This could cause a significant change to the natural longer period trends. Thus a homogeneous weather record over time is quite rare, and the methodology to fill in these gaps and inconsistencies to create an accurate picture of climate change is difficult at best.

With advances in technology, we now have satellites that can continuously monitor the entire state. They can measure most of the atmosphere for temperature and winds in addition to clouds. Surface atmospheric profilers can scan the skies with great detail to determine turbulence aloft. Doppler radar can measure precipitation amounts as a storm moves through an area while lightning detectors can pinpoint a strike that may start a forest fire. With the aid of computer models, climate data can be accurately derived to less than one square mile resolution.

Many of the charts contained in this atlas are the result of modeling existing climate data with fine topographic features within the state. As with all computer-generated products, such as Geographical Information Systems (GIS), the data shown are considered reasonably accurate.Depictions of a given weather element should therefore not be considered an exact value. This means that the data shown can be used for planning purposes. If exact data are required, actual climate data of existing stations are available in this atlas' Appendix and on the CD that can be purchased through this website. If a location does not have a station and exact data are needed, it is strongly recommended that instrumentation be placed in this area and monitored over time. However, remember that there is considerable inter-annual variability in weather and that one year's worth of data will probably not accurately reflect the long term averages.

This atlas is intended to serve as a data and reference source for the general public and for educators. Most readers will probably consult the Appendix and CD for actual climate averages and totals. Some might find specific chapters of interest since they contain unique climate data sets that can be applied to unusual applications. English units are used whenever possible and most graphs, charts, and tables are self-explanatory and non-technical. Efforts were made to maintain the same scaling factors for similar graphs and charts. Each chapter represents a specific element of climate and can be read in isolation from the others, although some overlapping cannot be avoided. Websites noted in footnotes are provided for those interested in further research or expanded discussion of a topic. Since the climate record is constantly evolving, updates can be acquired through many of the websites identified in the chapter folders under each climate element on the accompanying CD. This atlas is available on-line at: and updated regularly. Much of the data in this atlas and CD are public domain. Every effort was made to acquire permission for its use if copyrighted. Therefore, the data from this atlas and CD can be used without these authors approval if used for educational purposes (non profit). However, appropriate citations are required. If any data are used for public consumption, especially for profit, then please contact the originator of the data for permission for its use.

Jan Curtis
Kate Grimes

Laramie, Wyoming
January 2004