The latest data continue to show a heavy snowfall event to come for Northern Colorado Monday night through Tuesday.
We published our extensive thoughts on the storm this morning but wanted to reiterate some things this evening and bring you the latest in trends in the model data.
The storm's speed is the same as projected. The track of the storm shifted subtly to the north by enough distance that midday model updates dropped snowfall amounts to a minor degree from Denver to the south. We mentioned in our Sunday morning update that the track is our remaining concern for this storm and additional data today has not changed that concern.
What's important is we haven't seen a significant change to that track. A subtle change should not be jumped on. The consensus is a significant amount of snowfall from Denver to the north. Due to this, the National Weather Service has issued a Winter Storm Warning for Northeast Colorado that will begin Monday evening to continue through Tuesday afternoon.
That warning is for all areas in Pink. The other alert for this storm is a winter weather advisory for most of the mountains west of the Divide.
We see rain and snow chances increase across Northern Colorado midday Monday, with about a 50% chance of rain and snow in Fort Collins by early afternoon. Those chances climb to greater than 90% Monday evening, with a good chance of snow continuing well into Tuesday morning:
For Denver, the best chance of precipitation comes a bit later, likely around the evening commute Monday or shortly after that. As we noted earlier today, the best chance of heavy snow in Denver looks to come between 7 pm Monday, and noon Tuesday as timing continues to show:
We stress impacts here on 5280, and with this system it'll be no different. Whether Denver ends up with 5" or 15", this will be an impactful storm. With lots of folks traveling this week for Thanksgiving, there are a few things you need to do.
1. If you are flying, you have to check your flight status with your airline. With a Winter Storm Watch in place and a likely upgrade to a Warning, airlines will likely be canceling flights. Don't be caught by surprise if your flight changes due to the storm.
2. If you are driving, you need to stay current with road conditions and possible closures. Also, if you are driving late Monday night or Tuesday, you need to have a plan B. That means altering the time that you are driving to avoid the worst weather, or taking an alternate route. Areas south of I-70 will likely not see as much snow with the storm. Thus, a likely better place to drive, versus along and north of I-70. If that is an option for you, then it is something to consider. Also, if you travel I-25 between Denver and Colorado Springs, it is possible that "The Gap" could be proactively closed before the storm gets too bad. CDOT has talked about doing this during prior storms, and while it is not a certainty that they will, you need to be prepared in case they do.
The snowfall forecast hasn't changed from this morning despite the subtle model changes noted today. We will reassess those changes if there is consistency to that effect in the Monday morning data.
This is the forecast reasoning as discussed Sunday morning.
This will be a high impact event for much of Northern Colorado. For Denver, the boom and bust potential remains high, despite quite a bit of support for high-end snowfall totals in the city. The European model continues to hint at a track that could end up just about 50 miles or so too far north for Denver to see the heavier snowfall forecast by other models such as the GFS, but GFS and NAM began to hedge ever so slightly in this direction as well in their respective data throughout Sunday.
For Denver, we'll start with 6 - 12" today and adjust tomorrow if needed. Depending on the eventual track of the low as it moves through Monday night, we could see forecast totals upwards of 1 foot in the city OR, have a hard time even hitting our 6" low end. There's not a lot of wiggle room here, only about 50 miles difference in the track. A shift farther south means more snow, a bit farther north less snow.
North of Denver, confidence is high. The Front Range foothills and mountains west of Boulder/Loveland/Fort Collins could easily pick up a couple of feet of snow by Tuesday afternoon. The cities, including those just mentioned, along the urban corridor and points east should manage 8 - 14" in most locations.
Finally, south of the Palmer, this storm looks less likely to have significant impacts. WIND will be a factor, and likely some snow, but the heaviest snow is expected to stay north.
Here is our forecast:
We watched the midday data shift to a minor amount, and that trend is what we saw continue in Sunday evening data.
The NAM is for all intents and purposes the same from the midday update with significant snowfall around Denver and a bullseye in Boulder and Larimer Counties. As we mentioned in our Insider update earlier today, we expect to see some impressive snowfall totals out of the canyons of Boulder and northern Jefferson counties from this storm should things stay on track.
SREF plumes remain rather consistent as well, showing 8 - 12" for most locations along the northern urban corridor, with very little change run to run. Latest SREF guidance has heaviest totals for the urban corridor near Loveland.
The GFS remained pretty steady this evening too, tracking the low right through the sweet spot for heavy snow along the northern Front Range. Overall numbers didn't change much at all from previous runs, with placement of heaviest snow still just north of Denver to Fort Collins and west. Here's its 500mb forecast for Tuesday morning:
And, although we'd wait for the Euro to come in to do a straight 0z comparison, it'll be too late to publish this once that data has arrived. So, we will see what Euro does overnight and bring that to you Monday, and make any adjustments to the forecast at that time if needed.
As always, keep us posted as to conditions are your place as things get going tomorrow! We love to read your comments and answer any questions we can as they come up.