Record Heat, Then Snow? |

Record Heat, Then Snow?

Allison Finch
Updated: September 04, 2020 02:40 PM
Created: September 04, 2020 02:36 PM

While Labor Day plans in the northeast include low humidity, average temperatures and sunny conditions, this is not the case for other areas in the United States. Parts of Colorado are gearing up for some record-breaking heat this weekend, followed by snow. Yes, you read that right, snow.

So far, Colorado has had 69 days of temperatures above 90 degrees and one day of temperatures hitting 100 degrees this year. Needless to say, it’s been a hot summer. As we head towards the “unofficial end of summer” also known as Labor Day, Denver, CO is forecasted to hit 90 degrees (or near 90) four more times before the weather takes on a big change. Denver, CO will need to hit 90 degrees or higher four more times to tie the record for the “most 90 degree days.” Right now, the record is 73 days set back in 2012. 2020 is on track to tie the record or take on second place. The National Weather Service (NWS) in Denver-Boulder, CO is forecasting a high of 98 degrees on Sunday, September 6th. If this temperature verifies, this will break the old high temperature record for that date set back in 2013 at 97 degrees. So, what is causing this record warmth and what’s to come?

Currently there is high pressure in place over Colorado due to “an elongated area of relatively high atmospheric pressure” also known as a ridge. (NWS Glossary) This upper level ridge places high pressure over Colorado, which creates prefect atmospheric conditions for hot weather. As we head into the holiday, this high pressure will start to move westwards towards California and Nevada and a weak trough or “an elongated area of relatively low atmospheric pressure” will build into the region. (NWS Glossary) This will bring cooler temperatures on Labor Day as well as breezy conditions. Throughout the day on Monday, a stronger trough will dive south from the north and will strengthen into a closed low over the Four Corners on Tuesday. The difference between a trough and a closed low is that within a trough there is no distinct center of cyclonic (counterclockwise) circulation. When it strengthens to a “closed low”, it will have a distinct center of cyclonic circulation and will distinguish low pressure aloft. A cold front associated with this closed low moving in from the north will bring cold temperatures and the chance for precipitation along with it. The dramatic change for record-breaking heat to cold will all happen within a two-day period. The NWS is forecasting a high of 90 degrees on Labor Day, a low of 35 degrees Monday night, and then a high of 42 degrees on Tuesday. Between the high temperatures on September 7th to the low temperature on September 8th, they are forecasting a temperature difference of 55 degrees. This temperature change doesn’t even coming close to breaking the largest 2-day temperature change since 1872. This occurred on December 14, 2008, where the temperature went from 58 degrees to -18 degrees – a change of 76 degrees – in just 48 hours.


Extended Forecast for Denver, CO. | National Weather Service Extended Forecast for Denver, CO. | National Weather Service

Along with these cold temperatures comes the chance for some precipitation as well. Snow is forecasted for late Monday night into Tuesday. Even though the forecast is still far out, confidence is high. Any slight change to the track or a slightly weaker low most could result in just rain for the area. The NWS says their “main message is cold and heavy snow is possible Monday night through Tuesday night.” (NWS) The ECMWF forecast model has upwards of 8 inches of snow falling in some places by midnight September 9th. While it is important to not follow this forecast exactly, because a lot can change between now and Tuesday night, it gives us a good estimate of what to expect.


ECMWF Snowfall Forecast (Forecast Period: 9/7 5PM - 9/9 12AM) | WNYT ECMWF Snowfall Forecast (Forecast Period: 9/7 5PM - 9/9 12AM) | WNYT

While snow in September seems a bit early, or unprecedented, this actually isn’t all that uncommon for Colorado. Denver’s first snowfall of the year on average is October 8th, but has seen snowfall as early as September 3rd, which happened in 1961. The last measurable snowfall in September in Denver was back in the 2000, where 0.2’’ of snow fell. The most amount of snow to fall in the Denver during the month of September was back in 1971 when 17.2’’ of snow fell throughout the entire month.  

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