A string of record breaking maximum temperatures and numerous fires and almost no precipitation in Colorado during the month of June 2012 had people wondering - What's up with the weather? For example Boulder, Colorado had the hottest average maximum temperature (91.2° F) for the month of June. The period from March to June was the driest in the city's weather records dating back to 1894. Is this natural variation? Is it climate change? Has this happened before? The pages below give some background information to help answer these questions.
- Regional Trends
- Colorado Story
- Historical Analog
- Colorado Fires
- Is This Climate Change?
- Additional Information
Over the past year, Colorado has seen drier and warmer than normal conditions. Click on a station in the map (or the arrow next to the station name) to see the time series for July 2011 to July 2012 for that station.
Images generated by the High Plains Regional Climate Center
The plots below show the record maximum, minimum and average temperatures (left) and the chance of precipitation (right) for Boulder, Colorado from 1950 to 2010. Some things to note about the graphs below in relation to 2012. Historically, the maximum high temperatures of the year (> 100 °F) occur in late June and early July. Also, note that there is a climatologically normal period of relatively dry weather at the end of June and into the beginning of July during the period between the usual wet spring season and the onset of the July-August monsoon season.
Since 1901, both the maximum and minimum June temperatures have risen. Maximum temperatures have generally increased by 1-1.5 degree Celsius (2-3 degrees Fahrenheit). Minimum temperatures have risen more in western Colorado than the east.
Trends in precipitation are most important on shorter timescales. In the image on the left below, one can see that over the past 2 years, the southern states have had generally dry conditions while the northwest and northeast have been wetter than average. This is consistent with the precipitation pattern associated with La Niña - a cooling of the Eastern Pacific Ocean. As described in the Southwest Climate Assessment: "It is likely that most of recent dryness over the Southwest is associated with a natural, decadal coolness in tropical Pacific sea surface temperatures." (Hoerling et al, 2012)
In 1956, Colorado experienced a dry spring and a hot June. This was also a La Niña year as was the case in 2012 until late spring. The maps below compare the patterns of 1956 to those in 2012. These maps show a similar story in terms of circulation patterns and their effects.
On June 26, 2012, lightning sparked the Flagstaff Fire above the NOAA building in Boulder, CO. The timelapse video below was taken by Dustin Henderlon shows the view from Boulder from 3 pm, June 26 to 10 am June 28th.
The fires in Colorado and elsewhere in the US have people asking what is causing this and is this more extreme than usual?
A good discussion on some of the factors leading to the large loss of property and 3 lives is here:
According to the National Interagency Fire Center, through July 3, the acreage burned and number of fires are
- Acreage - 2,199,484
- Number - 28,420
This compares to the average over the period available 2003-2012
- Acreage - 2,461,795
- Number - 39,502
So far this year, the U.S is slightly below average for acreage and considerably below average for number of fires. To compare with a relatively bad year over this short period, 2006 had
- Acreage - 3,779,450
- Number - 57,609
In this 10-year record, on a most-to-least scale, so far 2012 ranks fourth out of ten for acres burned and ninth out of ten for number of fires. So while CO has experience severe fire loss, the US fire season as a whole has not been exceptional to date.
A recent web chat was held between weather and climate experts and communicators (including Marty Hoerling from NOAA/ESRL/PSD) on the fires and other extreme events of June. The video below provides more information on the possible causes of these events:
- How have changing conditions over the Southwest been symptomatic of human-induced climate change?
- Is recent Southwest dryness a symptom of human-induced climate change?
The charts below compare the observed trends of March-April-May (MAM) temperature and precipitation to two different model systems. These box and whisker plots show the observed values (green dot) compared to the range of values from the model ensembles. The range is denoted by the line (whisker) between the maximum (red asterisk) and the minimum (blue asterisk). The bottom and top of the box are the 25th and 75th percentile (the lower and upper quartiles, respectively), and the band near the middle of the box is the 50th percentile (the median). In each of the plots, the top half shows the temperature comparison and the bottom half shows the precipitation comparison.
The CMIP5 (Coupled Model Intercomparison Project Phase 5) dataset is a set of coordinated model experiments from 20 climate modelling groups around the world. This ensemble of different solutions can be used to examine the observed change in temperature with model simulations that include forcings due to increasing CO2. In the plot below, the observed temperature trend aligns with the rise in temperature due to human-induced forcings. However, the observed change in precipitation (drying) is not well simulated by the CMIP5 model runs.
The AMIP (Atmospheric Model Intercomparison Project) is a standard experimental protocol for global atmospheric general circulation models (AGCMs). The AGCMs are constrained by realistic sea surface temperature and sea ice so the output is forced by ocean surface processes instead of greenhouse gasses. In the plot below, the precipitation much more closely matches the AMIP solutions, indicating that the primary driving force of the reduced precipitation is a natural variation of the ocean related to El Niño/La Niña cycles.
- Hoerling, M.P., M. Dettinger, K. Wolter, J. Lukas, J. Eischeid, R. Nemani, B. Liebmann, and K. E. Kunkel, 2012. Evolving Weather and Climate Conditions of the Southwest United States. Chapter 5 in Garfin, G., Jardine, A., Merideth, R., Black, M. and Overpeck, J., (eds.) Assessment of Climate Change in the Southwest United States: a Technical Report Prepared for the U.S. National Climate Assessment. Tucson, AZ: Southwest Climate Alliance. (in press)
- McQueen, H. R. and H. J. Shellum, 1956: The Heat Wave From the Intermountain Area to the Northern Great Lakes, June 9-13, 1956. Mon. Wea. Rev., 84, 242–251.
- Christian Science Monitor, Death Valley heat in Kansas? How the end of June got so hot