12:15 PM MDT, Thursday, September 3, 2020
Labor Day weekend is looking hot and dry, at least through Sunday, but maybe Monday too. The record highs for Saturday-Sunday-Monday are 98, 97, 95 in Denver, and 97, 97, 93 in Boulder. We should at least get close to those, perhaps with a dry wind at times, so be aware of the fire danger.
We may get an initial weak cold front on Monday, but right now it is looking more likely that much of that day will be quite warm too. Late Monday or Monday night is when a strong cold front is forecast to move down the Front Range bringing unseasonably cold temperatures for a couple days.
There are increasing indications that the cold air mass may combine with a developing storm system over western Colorado, drawing moisture in from the plains, for the first “upslope” storm of the season. The result could be the first real snow for the Front Range Mountains and places like Estes Park and Nederland. Depending on the intensity and duration of the precipitation, and the time of day, a rain-to-snow progression can’t be completely ruled out for lower elevation areas like Denver, Boulder, and Fort Collins on Tuesday. I will certainly plan to update that possibility. At the very least, it’s looking likely that Tuesday will have some cold rain.
For those who moved to this area in the last 20 years, September snow in Boulder and Denver may seem like science fiction. But in Boulder, for example, the season’s first measurable snow occurred in September about 25% of the time between 1898 and 2000. September produced the first snow of the season 5 times in the 1990s. Occasionally a big wet snow (8 inches or so) caused considerable damage to trees since they are still in their vulnerable leafed-out condition. That occurred in 1995 with 8.6″ in Boulder on September 20-21 (6-10 inches throughout much of the Denver area). But since 2000, measurable snow at the Boulder station only occurred once when a mere 0.5″ fell in the predawn hours of September 12, 2014, and melted almost as quickly as it fell.
If it does snow next Tuesday, the earliness of the date would be highly unusual, but not unheard of. Measurable snow occurred around the Denver-Boulder area on September 3, 1961. In Boulder the snowfall on that date is officially listed as a “trace,” but local accounts at the time report the ground and cars were whitened. Denver (Stapleton) reported 4.2″ with that one.