During the month of June 2013, Denver, CO’s (link updated monthly) temperatures were 3.7°F above normal (71.1°F vs. 67.4°F). The National Weather Service recorded the maximum temperature of 100°F on the 11th and they recorded the minimum temperature of 39°F on the 2nd. Here is the time series of Denver temperatures in June 2013:
Figure 1. Time series of temperature at Denver, CO during June 2013. Daily high temperatures are in red, daily low temperatures are in blue, daily average temperatures are in green, climatological normal (1981-2010) high temperatures are in light gray, and normal low temperatures are in dark gray. [Source: NWS]
In comparison to April 2013, June 2013 brought less extreme weather to the Denver area. After a moderate start to the month’s temperature, high pressure began to dominate the area by the 11th through the end of the month. This high pressure brought warmer than average temperatures, which offset the early month cool snap. This same pattern brought warmer than average temperatures to much of the southwestern United States, culminating in extremely dangerous heat at the end of the month from Idaho to Arizona.
Denver’s temperature was above normal for the past two months in a row. May 2013 ended a short streak of four months with below normal temperatures. Seven of the past twelve months were warmer than normal. October broke last year’s extreme summer heat including the warmest month in Denver history: July 2012 (a mean of 78.9°F which was 4.7°F warmer than normal!).
Precipitation was lighter than normal during June 2013: only 0.75″ precipitation fell at Denver during the month instead of the normal 1.98″. Precipitation is a highly variable quantity though. The west side of the Denver Metro area received rainfall on days that the official Denver recording site did not, which is the usual case for convective-type precipitation.
Precipitation a couple of months ago alleviated some of the worst drought conditions in northern Colorado. The link goes to a late April 2013 post; further relief occurred in May with regular rain events. With below average precipitation in June for most areas, drought conditions unfortunately worsened during the month. All of Colorado continues under at least some measure of drought in early July 2013. The worst drought conditions (D4: Exceptional) continue to impact southeast Colorado however and the area with D4 conditions slowly expanded during the past few months. Absent a significant shift in the upper-level jet stream’s position, the NWS expects dry conditions to persist over CO during the next one to three months, which will likely worsen drought conditions. I will write an updated drought post within the week.
I have written hundreds of posts on the effects of global warming and the evidence within the temperature signal of climate change effects. This series of posts takes a very different look at conditions. Instead of multi-decadal trends, this series looks at highly variable weather effects on a very local scale. The interannual variability I’ve shown above is a part of natural change. Climate change influences this natural change – on long time frames. The climate signal is not apparent in these figures because they are of too short of duration. The climate signal is instead apparent in the “normals” calculation, which NOAA updates every ten years. The most recent “normal” values cover 1981-2010. The temperature values of 1981-2000 are warmer than the 1971-2000 values, which are warmer than the 1961-1990 values. The interannual variability shown in the figures above will become a part of the 1991-2020 through 2011-2040 normals. If temperatures continue to track warmer than normal in most months, the next set of normals will clearly demonstrate a continued warming trend.