September is typically a warm month for much of the lower 48. But September is also a month where we start to see some changes in our summer weather patterns with cold fronts and lower humidity values beginning to show up.

This September was dominated by heat and high pressure for much of the continental US. It was also dominated by the talk of tropical cyclones and hurricanes, some of which actually played a roll in the heat that was felt. The talk of heat or tropical cyclones during September isn’t groundbreaking but what is groundbreaking, is the overall extent and duration of heat that was felt.

Temperature difference as compared to normal

The image above is a look at the national departure from normal temperatures over the last 30 days. What you can take away from this image is the overwhelming amount of positive color (yellow, orange, red) we see. If your area of the country is shaded in yellow, orange or red, you experienced above-normal temperatures for the entire time period. Few areas, like New England and areas in the West, saw below normal temperatures for this time period. Notice how the heartland of the country and points eastward to the Carolinas and Virginias saw the bulk of the heat.

This is largely because of an anomalously strong ridge of high pressure that sat and parked itself over the eastern 2/3rds of the country most of the month. While that increased our heat, it decreased the amount of rain we saw.

Amount of precipitation measured through the month of September

Some Southeast states saw either their driest September on record or their driest month on record. Drought has become an issue for an increasingly large area of the US because of this. For those hoping for changes, inevitably, the temperature will fall as we lose daylight and head into winter but for some, that will take longer than wanted.

Let’s talk Colorado. Colorado, through the 29th of September, is holding on to the number one rank of Warmest September’s ever recorded. Here’s a look at the current rankings for the month.

Top 20 Warmest Septembers on record.

Note how the warmest September currently in the number 1 spot, happened back in 2015 with an average temperature of 69.4º F. This September is rivaling that. Below is the current temperature data for Denver.

Temperature Data for Denver during Septmeber 2019 

The current monthly average temperature of 69.6ºF is beating the current record that was set back in 2015. The only thing that would inhibit us from breaking that record would be a high-temperature reading on September 30 2019 of less than 80ºF. As of 4PM on the 30th, the high temperature was only 72º. There is a possibility that we don’t break the record because of that but the fact that we are even within the realm of a record is worth noting.

Above-average temperatures were felt through the entire month of September

Colorado is in the midst of its hottest September on record or at least in the top 5. There is no area in the state that saw below-average temperatures but what stands out is the amount of heat that was so expansive. Much of the Eastern half of Colorado saw temperatures ranging between 4-10º above the normal average temperature. To say that it was a warm month would be an understatement.  And like what was aforementioned, the heat in Colorado was accompanied by a shocking lack of rain.

Lack of rain/Drought encompasses much of Colorado 

There was a point this summer when Colorado had no drought in any location (which was the first time since drought records began in Colorado that that has happened) but now, close to 75% of the state is running drier-than-normal. The hopes of rain, or snow, are on the minds of many as we enter into our more wintry time of year. Hopefully, we have some moisture-rich systems that roll through and according to the Climate Prediction Center (CPC) much of Colorado will see above-normal precipitation through November. That is not guaranteed but as the models are suggesting and based on global weather patterns, the chance at above normal moisture is there.

Let’s talk temps. Everyone wants to feel the crisp fall air. Thankfully, it’s coming!

Temperature anomaly, or difference, as compared to normal values

Some models are hinting at some very cold air moving into the Centennial State by the first full week of October. Highs will be below average and overnight lows will dip below average as well. That means highs in the 40s/50s for Denver and overnight lows in the upper 20s/30s for much of the metro will be felt. That will be a welcome but shocking change for many.

~Rain or Shine
  I’m Andy Stein

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