Outlook for the first 2 weeks of fall in CO

09/01/25 10am: Happy first day of meteorological fall! Happy Labor Day 2025. I go by the seasons that really do fit our weather in CO: Fall: Sep, Oct, Nov. Winter: Dec, Jan, Feb. Spring: Mar, Apr, May. Summer: Jun, Jul, Aug. In fitting fall fashion we will have a mix of summer-like and fall-like weather over the next 2 weeks.

Generally speaking it will be more fall-like for eastern CO, including the front-range (Den/Bou) and more summer-like for western CO / mountains. This is due to several intrusions of abnormally chilly fall-like air that will enter the upper-Midwest this week Tue/Wed and then another front on Fri/Sat

In terms of moisture: relatively dry through Friday, then an increase in tropical / monsoon moisture as current Invest 94E (near southwest MX) is likely to become a tropical storm that will move into the southwest U.S. next weekend and bring much better rain chances to CO starting next Sat-Mon (Sep 6th-9th).

So you can see with the new 6-10 outlooks, cooler than average for eastern CO but wetter than average for the entire state, especially for western CO (related to the tropical moisture).

The other story will be a chance to see the northern lights tonight and tomorrow night (if we can get some clear skies, looks pretty good for cloud-cover). Best viewing will be near the CO/WY border and north

For today, seasonable hot / warm across the state, almost no storms.

For tomorrow a short-wave and some cooler air starts to move in from the northwest and this will bring a slight chance for isolated storms along the front-range (including Den/Bou and foothills) from 2pm-8pm, most areas stay dry.

A strong surface cold-front moves into northeast CO and the front-range by Wed morning (should cool highs down into the 70s for Den/Bou)

Then a slight chance for isolated storms over the state on Wed and Thu with seasonable temps

Then another strong cool-front will move into northern CO / front-range and eastern CO on Thu evening into Fri morning (may kick off some better storm chances late Thu, after 6pm)

By Friday deeper moisture moves in from the southwest, so a better chance for afternoon storms, especially in mountains / southwest CO

By Sat, deep moisture associated with the tropical storm will start to move up across CO...so likely numerous rounds of storms and turning wetter each afternoon, Sat, Sun and Mon (6th-9th)

Anyway, that is all for now. Stoked its finally fall. We are heading back from Crestone this afternoon (its been so nice here).

First image is the 6-10 day outlook valid Sep 6-10th from NCEP. Second image loop shows forecast air temperature over the next 12 days from latest GFS, you can see the intrusions of cooler air to our east (and coming into eastern CO at times). Third image shows the much deeper moisture associated with the tropical storm moving into CO by next Sat morning. Fourth image shows the Northern Lights viewing potential from meteorologist Matthew Cappucci post from yesterday.