It's Monday morning, the skies over Colorado are clear, and the leaves on some trees are starting to show their colors. But don't let Monday's calm condition fool you into thinking this will be a week of mundane weather.

Rainy Tuesday, Wednesday, and Thursday

From Tuesday to Thursday (September 20-22), a LOT of moisture will be pulled northward into Colorado. The amount of moisture over Colorado during this time will be 200-300% of the average for this time of year. Those are high numbers.

Big moisture can lead to big precipitation, and there are signals that the rain we could see from Tuesday to Thursday may be significant, in the 1-2 inch range. 

Below is the forecast precipitation for Aspen (I zero in on Aspen because it's centrally located in Colorado). Each horizontal line shows the amount of rain from one of the 31 versions of the American GEFS model. The colors of each box show the amount of rain. And the green line at the bottom shows the average of all 31 versions. This is a strong signal for a lot of rain with an average of about 1 inch (some versions show up to 2 inches).

Looking at the map view of the storm, the average of the 31 versions of the American GEFS model paints the western half of Colorado with 1-2 inches of precipitation, and there will be a higher chance for the most rain over the southwestern part of Colorado.

The American GEFS model above is not an outlier.

Below, the average of the 51 versions of the European ECMWF model also shows about 1-2 inches of rain with the highest amounts over the southwestern part of Colorado.,

So enjoy the calm weather on Monday because Tuesday, Wednesday, and Thursday will be showery with a lot of rain. Within this Tuesday-to-Thursday time period, Wednesday's 24 hours have the highest odds of being the rainiest time period. Again, total rainfall could be 1-2 inches (maybe more in a few spots) and this amount of rain could cause some flooding, especially over wildfire burn scars.

In terms of potential snowfall, it will be limited to the highest peaks. The incoming storm will be warm (winds from the southwest) and snow levels will likely fluctuate between 13,000 to 15,000 feet. The highest peaks will likely see some snowflakes, but by the time the atmosphere cools and snow levels drop later on Thursday into Friday, most of the moisture will be gone.

Gusty winds on Friday

As the storm exits on Friday, the typically windier areas of the northern mountains will see gusty winds of up to about 50mph. Normally during the dry fall season, a forecast for gusty winds would concern since it could help to quickly spread a wildfire. However, since we'll see a LOT of rain on Tuesday, Wednesday, and Thursday, there should be little to no risk of a new fire starting on Friday.

Back to warm and dry weather…

Following this week's storm, the upcoming weekend (Sep 24-25) and the final week of September should be mostly dry and warmer than average. If the changing leaves survive this week's rain, then there could be some beautiful viewing during the final ~7 days of September as the weather turns back to more typical calm autumn conditions.

Thanks for reading and enjoy the upcoming rain (seriously...it's always a treat to get a lot of precipitation here in typically arid Colorado, though hopefully, any flooding is minimal).

I'll be back with another update on Monday, September 26 and we'll see if there are any signs of cooler weather as we head into early October.

JOEL GRATZ