4:50 PM MDT, Sunday, September 29, 2019
A cold front late Monday will bring the coolest weather so far this season Monday night through Wednesday morning. We are not expecting any early-season snow in the urban corridor, but it might get a bit damp by Tuesday morning.
Most of the daytime hours on Monday will be ahead of the front, so another warm day is likely. It may start to cool by late in the day, especially in southeastern Wyoming. Cool upslope (northeasterly) flow Monday night will bring in the cooler air. For the lower foothills and plains (including the urban corridor) there is a good chance for a period of low clouds and areas of fog and drizzle late Monday night into Tuesday. Depending on how quickly those clouds thin out, Tuesday could have a high in the 50s for Denver, Boulder, and Fort Collins.
With clearing skies likely Tuesday night we are likely to see some local frosts in the normally colder spots such as the river valleys in northeastern Colorado. Milder weather is likely to make a comeback Wednesday afternoon.
6:30 AM MDT, Thursday, September 26, 2019
After a long stretch of dry days, Friday will bring a chance for showers and thunderstorms along with cooler weather. Mainly dry and warmer weather should return for Saturday and Sunday.
The rain on Friday will be scattered and mainly in the afternoon and evening. It appears that most areas should get at least a sprinkle, with a few spots getting a brief heavier shower or thunderstorm.
After a mainly dry weekend, another cold front late Monday or Tuesday will bring cooler weather, but that air mass may be limited in moisture. However, by midweek some of the cooler river valleys of northeastern Colorado may have to prepare for frost.
1:30 PM MDT, Wednesday, September 18, 2019
I haven’t written much because we have been in a rather uneventful pattern for a while. With a few local exceptions, the Front Range region has generally been warmer and drier than average since mid July. Average afternoon temperatures in the lower elevations have now fallen to the mid 70s, and we are likely to be around that (or a little warmer) through the Monday (and the autumnal equinox is Monday at 1:30 AM MDT). There is a small chance for afternoon showers or thunderstorms (and maybe a light coating of wet snow in the highest elevations), mainly Thursday or Friday, but many areas are likely to come through with no significant precipitation. The weekend is looking dry.
The next chance for significant widespread precipitation is late Monday or Tuesday, but even that is iffy. The path and development of that particular storm is too uncertain at this time for me to be confident of some good precipitation, but it’s worth watching.
The average time for the first measurable snow in places like Denver, Boulder, and Fort Collins is mid October. In the last 70 years the odds are about 1-in-4 for the first snow to occur in September. In the last 18 years measurable snow only occurred once in September (in 2014) along the urban corridor. So you can say we are due, but there are no obvious signs yet that this will be a year for September snow.
5:50 AM MDT, Friday, September 6, 2019
The 90-degree days are gone for at least the weekend, and you should expect more late-day cloud cover along with a scattering of afternoon showers and thunderstorms for the next three days. Today may be the first time in a while when measurable rain occurs at more than just a few isolated locations, and there may even be some locally intense thunderstorms. Although thunderstorms may be around both afternoons of the weekend, it appears that the chance for thunderstorms is greater on Sunday than it is on Saturday.
Drier and warmer weather will likely return early next week, but we don’t expect the same levels of record heat to return.