Denver’s July Weather and June Summary

June Summary

June finished up with a total of 1.62 inches of rain, which is .36 inches below normal. The average temperature was 70.8 degrees F, which is 3.4 degrees above normal. I find the precipitation number to be a bit misleading since the official Denver station is at DIA. The airport only recorded a trace of rain while downtown got pounded by a strong thunderstorm on the 28th. Finishing up the month 3.4 degrees above average is pretty significant, but not enough to get in the top 5 warmest June’s. 12 days were above 90 degrees with 98 as the hottest temperature recorded.

July Climatology

July is Denver’s hottest month on average with normal highs in the upper 80’s and low 90’s, and average low’s around 60. July tallies 2.16 inches of rain on average, almost a full inch less than June! (With .61 inches of rain already recorded on the 1st of this month, we’re already 1/4th the way there!) The typical day consists of a warm sunny morning, and hot early afternoons followed by afternoon clouds and showers, more so towards the end of the month when the North American Monsoon kicks in. The North American Monsoon is a seasonal change in the upper level patterns. The subtropical ridge, which has clockwise flow around it, is usually centered just to our east or south brining moist air all the way from the Gulf of Mexico. This is moisture in the upper levels, which usually translates to high-based thunderstorms that don’t provide a whole lot of rain, and can be wildfire starters. Cool fronts from the north can slip in cooling things off about 10 degrees and helping to spark some storms.

July 2016 Outlook

Looking at patterns that could affect our monthly weather, one major player is the ENSO oscillation (El Nino and La Nina) over the tropical Pacific Ocean. Summer effects are less so than other seasons, but there is still some correlation. In years transitioning from an El Nino to a La Nina as we likely are this year, July was slightly warmer and wetter than average (Figures 1, 2). The average upper level pattern during those years had a ridge centered just to our south, bringing the usual monsoonal moisture our way (Figure 3). There are other oscillations that can alter long-term weather patterns such as the Pacific North American Oscillation, but those patterns don’t have a whole lot of correlation to our weather in July. Current CFS model runs show a general trough to our west and in our area during the second week of the month indicating normal to slightly cooler temperatures. The subtropical high is shown to build back in during the second half of the month leading to warm temperatures and some monsoonal flow. The Climate Prediction Center is calling for a slightly warm and dry first half of the month, and a warm second half with near average precip.

Enjoy the weather!

JulyTempAnomLaNina

(Figure 1) Temperature Anomalies in Celsius, warm colors are above average temperatures, cool colors below normal.

JulyPrecipAnomLaNina

(Figure 2) Precipitation anomalies in mm per day. Blue colors indicate above average precip.

July500HeightMeanLaNina

(Figure 3) Average 500mb Heights with clockwise flow around the High pressure center

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