ROANOKE, Va. – The mountains on a can of Coors Light will go from sweating to blue within two days, as the Rocky Mountains are in for a wild and unprecedented swing in seasons. Blistering summer heat Sunday is followed up by winter chill and snow nearly 48 hours later.
Brian Brettschneider, a PhD climatologist in Alaska, says that this has only happened two other times since 1900.
Some forecast models are calling for a high temp in Denver in the mid to upper 90°Fs on Sunday and measurable snow 2 days later. Since 1900, only Valentine, NE (twice), and Guymon, OK, have achieved this feat. Note: only 1st order midnight-to-midnight stations were evaluated.— Brian Brettschneider (@Climatologist49) September 4, 2020
The National Weather Service in Boulder is forecasting a high temperature of 99° in Denver Sunday, which would break the Sunday’s record of 95°. By Wednesday morning, the city will have dropped to 29° according to the same forecast. That would break that day’s record low of 31° set in 1962.
Similarly, the National Weather Service in Riverton, Wyoming is forecasting that Casper is forecast to hit a near-record 93° Sunday. By Monday night and Tuesday, snow is forecast to develop with low temperatures falling to a record low of 25° by Wednesday morning.
How does a swing like this happen?
The area of high pressure that is producing record heat along the West Coast will force the jet stream to go way north. This also allows the heat to build into the western U.S., but it also keeps the cold air bottled up in Canada for the holiday weekend.
As the jet stream drops, the cold air that’s been bottled up unleashes itself onto the Rockies. Cold, wintry air will rise up the mountains and dump several inches of snow on parts of Montana, Wyoming, Colorado and maybe even northern New Mexico.
It’s not at all uncommon to see snow in the Rockies in September, but even this is a lot (especially after record heat).
Casper, previously mentioned in this article, averages 1.8″ of snow in the month of September. Its earliest measurable snow on record, however, came on September 8th of 1962. Denver’s earliest measurable snow came on September 3rd of 1961.
Why do we care?
We don’t expect a wild temperature swing or record snow out of this, but this does have an indirect impact on our weather. While this storm system is digging south into the Rockies, warm and more humid air will be drawn toward our region.
By the middle of next week, we’ll be looking at more rain and storms. (Exactly what time this starts and how much rain we get are still to-be-determined.)
The bulk of cold air likely stays north and west of here, as high pressure off the East Coast guides it in that direction. That same high pressure system will need to be watched, as it could guide a few more tropical systems toward the U.S.
The National Hurricane Center is tracking three different disturbances that at least have the chance of being named within the next few days.
Any potential impact to the U.S. wouldn’t be until well after a week from now. The next three names are Paulette, Rene and Sally.