Colorado Weather Forecast | Sep. 1–6, 2021
Hurricane remnants, then a dryer, cooler (but warming) pattern into Labor Day weekend. Heavy smoke concerns by the start of next week, some monsoonal moisture in southern CO.
Hello everyone. Summer heat is continuing to hold on as we start this week, but changes are coming quick — and meteorological fall begins tomorrow!
Summary
- Widespread light to moderate rain tomorrow with some heavier cells, focused on western Colorado earlier in the day but spreading east of the Divide by the afternoon. Severe weather possible on the plains, the urban corridor will miss much of the precipitation but could see some afternoon storms and light/moderate precipitation around sunset.
- Scattered thunderstorms on Thursday due to lingering moisture. Cooling off.
- Cooler on Friday / Saturday, weak cold front for the Front Range late Friday / early Saturday. Some smokiness continues, could be fairly heavy in spots.
- Friday: Isolated to scattered thunderstorm activity, highest chances near the Divide.
- Saturday: Only isolated activity near the Divide and further south down in the Sangres.
- Sunday and Labor Day: Warming. Isolated thunderstorm activity for the Sangres, lower chances in the San Juans, minimal elsewhere. Smoke likely becoming a big problem in northern Colorado, potentially getting very bad on Monday.
- Next week: Heavy to very heavy smoke is likely across most of Colorado.
Forecast Discussion
Our previous forecast is quite stale right now, but everything we discussed is in play.
The remnants of Hurricane Nora (which made landfall on the western coast of Mexico, not the Baja California Peninsula) are currently over Arizona.
This large influx of moisture puts a lot of rain in our forecast from Wednesday to Thursday. Nora’s (and likely Ida’s) track and intensity has also helped minimize the potential impact from a potent low pressure to our northwest.
When we wrote our previous forecast, that interaction was unclear and model guidance had suggested that system tracking further southeast, bringing a spell of cooler weather and snow at high elevations. Models trended back towards Nora being the main weather driver this week with some lingering moisture into Labor Day weekend, though that system to the north will still provide a bit of a cooldown. More on the weekend in a second.
The next couple days certainly look interesting. Nora (or at least remnants of Nora) is already knocking at the door, with widespread storms and showers across Arizona, southern Utah, and far southwestern Colorado.
These storms will continue into Wednesday morning, with decent precipitation chances across western and southern Colorado before noon. These areas are under a Flash Flood Watch.
This moisture is progged to surge across the state tomorrow and linger into Thursday.
On the Blend we see decent coverage of significant precipitation totals across western Colorado.
This is likely underdone in certain areas, but distribution looks correct. Mesoscale models are selling some big totals in areas that pick up stronger cells.
This certainly supports the NWS’s concerns for flash flooding — and something to be wary of if you’re travelling through Glenwood Canyon over the next 48 hours, which has closed repeatedly this season due to flash flooding concerns, realized or not.
Despite some cores of heavy precipitation, the nature of this moisture doesn’t look to support strong storms. There wont be too much lightning west of the Divide, but if you’re recreating you may struggle to identify embedded cells in the large scale stratiform precipitation that will be commonplace. East of the Divide, it’s likely we’ll see some severe storms across much of the plains of eastern Colorado, but the urban corridor looks like it should come out with the least amount of precipitation thanks to the timing of everything and a poor convective environment.
For the urban corridor, look for some isolated, weaker thunderstorms on Wednesday afternoon and then more widespread light to moderate precipitation around sunset, lasting for a few hours. On Thursday, lingering moisture should result in decent thunderstorm coverage across the high country and the Front Range.
We start drying out on Friday, but temperatures remain cooler thanks to the aforementioned system to our northwest, which could spit out a weak cold front late Friday or early Saturday. Models are in agreement with temperatures remaining lodged in the 80s or high 70s for much of the Front Range from Thursday to Saturday.
Labor Day weekend goes as follows: for northern/central Colorado and into Wyoming, smoke is the main concern. Just look at this:
As a subtropical high builds over the Great Basin by the end of the weekend, smoke will start getting directed southeast down into Colorado.
That’s not accounting for any new fires (such as the Black Mountain fire in Colorado) or the continued development of extensive historic fires in the rest of the west. However —most of Colorado should hopefully avoid serious smoke through the weekend.
This starts to break down as we get into next week, even as early as Sunday or Monday. In fact, since the above run was rendered, the Euro has moved the center of high pressure further west, which would redirect the worst of the smoke directly into Colorado earlier — next week could get really bad unless this forecast changes.
For southern Colorado, monsoonal moisture will be the focus at least earlier on in the weekend, with decent storm potential down the Sangres and into New Mexico.
As a whole, temperatures will be a bit cooler earlier in the weekend (Friday / Saturday) before returning to more summer-like conditions on Sunday and Monday, including highs in the 90s for Denver. At this point, it looks like thunderstorms will be fairly minimal outside of southern Colorado for much of the holiday weekend.
We’ll provide some final updates for the holiday weekend in a few days, in addition to an updated smoke outlook.
Questions and comments are welcome, feel free to interact with us on social media.
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