June is typically warm and pleasant in the Denver area, with average highs ranging from the upper 70’s at the start of the month to the mid 80’s at the end of the month. Rainfall usually comes in the form of thunderstorms, some of which can be severe as June is part of Denver’s severe weather season. Cold fronts coming from the north bring cooler temperatures, but can also enhance the severe weather threat a day or two later, as moisture sometimes is pushed into the area from easterly winds. June can also feature very hot temperatures, as was the case in 2012 when Denver tied its all-time record high of 105º F, two days in a row on the 25th and 26th in a 5 day heat wave featuring highs above 100 every day.
The intense El Nino event that occurred over the last year has weakened rapidly and will likely transition to a La Nina in the fall and winter. The ENSO cycle as it’s called, can lead to changes in the upper level weather patterns across the globe, including the US. Comparing four previous years with a transition from El Nino to La Nina conditions in the summer (1988, 1998, 2007, 2010). Warmer than normal temperatures occurred in the center of the country, with Denver averaging about 1.4º F warmer than average on those years (Figures 1 and 2). Rainfall was also less than normal during these transition years, averaging about 0.7 inches less (Figure 3). Denver’s average June rainfall is just under 2 inches, which translates to about a third less rainfall than normal during the transition years.
Figure 1 Average Air Temperature for June in Celsius. (16C = 61F)
Figure 2 Difference from Average Temperature During Transition Years (Warm colors are hotter, cool colors are colder)
Figure 3 Difference from Average Rainfall During Transition Years (Warm colors show less rain, cool colors are more)
(A brief explanation of what upper level ridges and troughs mean: Ridges are usually associated with dry and warm weather, while troughs are associated with cooler and more unsettled weather.)
Looking ahead to this June, weather models show a ridge in the jetstream to the west and near our area for about the first 10 days, indicating generally dry and warm conditions (Figure 4). That could change around the 8th, when we could see a weather system bring us a few thunderstorms and cooler temperatures. A stronger system is predicted to move into our area around the 10th, bringing cooler temperatures and the chance for more precipitation. Beyond this, the GFS (a mid range weather model) has a general ridge centered over us or just to our west mid-month, while the CFS (a long range climate model) has a ridge centered to our east. Both models have warm temperatures either way.
Figure 4 Jetstream on June 5th
Looking farther out gets tricky, as models rarely make the correct forecast. However, the CFS does a pretty good job at predicting general trends, and it has been showing an upper level ridge centered to our east and a trough to our west for most of the remainder of June. If this verifies, we could see generally warmer conditions to finish the month. (Sounds a lot like the pattern in the previous transition years doesn’t it?)
The Climate Prediction Center is calling for a warmer first half of June, with about average precip. The rest of the month is shown to have equal chances of above or below temperatures and precipitation. Only time will tell!
Enjoy the weather! I will likely be posting monthly outlooks and other interesting events in the future.
For more info about these topics check out:
(Climate Re-analyzer) http://www.esrl.noaa.gov/psd/