Potent winter storms moves through Monday night, but will it be a direct hit or near miss?

As we covered yesterday on Weather5280 Insider, our targeted active period for winter weather is upon us, and with it another chance of snow for Northern Colorado following quickly on the heels of yesterday's snow.

Today there is better consensus on the modeling for this next system, but the devil is in the details. While the trend overall has been toward the GFS solution (a deeper, more impactful snow event for the northern urban corridor), the consistency is not there yet between the other models. The European and NAM models continue to wobble with the eventual track, and while at times not by much –– their slight differences mean the difference of significant snowfall for the Denver metro area, and well... perhaps not much snow. Last night's Euro looked more in line with GFS (snowier for Denver), this morning it has moved back north. With its ensemble (shown below) also showing a northern track for this event, I wouldn't bet against the Euro just yet –– as fun as the GFS looks for you snow lovers out there.

As of this morning's runs, the GFS and Euro are about 150 miles apart on the placement of the low as it closes off early Tuesday. While in some ways that may not seem like much, it's the difference of the sweet spot for snow in Denver (GFS), and it ending up just north of the sweet spot (Euro).

How that looks from a precipitation forecast standpoint is as follows. The GFS (top) shows what's almost certainly the high-end (probably too high end) potential for this storm, with upwards of 1" (over a foot of snow) of liquid for the greater Denver area and points north, while the Euro (bottom) has less than half the amount for the city, with the greatest totals north of the state line across Southeast Wyoming:

Ensembles and probabilities
Probabilistically, there's undoubtedly more support for snowfall today than we saw yesterday... however, not all ensembles are onboard with high-end snowfall totals for the Denver metro area at this point. Much like their operational runs, the GFS ensemble is more bullish on snow than the Euro, and this is reflected in the Euro probabilities as well.

One graphic we often show is the GEFS forecast for Denver. The top chart shows the temperature forecast (red line is the mean forecast of all 20 members), while the bottom graph shows precipitation forecasts by member (y-axis). Each green square is a 6-hour precipitation forecast. As you can see, all ensemble members are now showing precipitation in the Monday PM - Tuesday. Some more, some less, but all snow and pretty consistent in timing and intensity.

Meanwhile, the European probabilities are lower, with it taking the storm just a hair too far north.

Probabilities for 3" or more of snow:

Probability of 3 inches or more

Probabilities for 6" or more of snow:

Probability of 6 inches or more

Our gamblers, on the other hand, show increased probabilities since this time yesterday. With Fort Collins, Boulder, and Denver all showing 50% or higher odds at seeing 6" of snow (I've highlighted the 50% line in pink), and lesser probabilities along and south of the Palmer Divide. Again, in many respects, similar to the European above, but about 50 miles further south with the higher-end probabilities.

Weather5280 snowfall gambler charts

Timing and impacts
Exact timing and impacts will depend on just how strong this system is, and how far south it digs. Generally speaking; however, we expect the best chance of snow across Northeast Colorado to come Monday night into Tuesday morning. Some models are a bit faster, some a bit slower, but that's the timing of most significant probability at this time.

With that, we see precipitation chances start to climb Monday afternoon For Denver (below), and peaking between midnight and 6 am Tuesday morning. Temperatures will climb to near 60°F on Sunday in Denver, but only into the 40s Monday before the cold front moves through:

Given the travel week ahead, a lot of eyes will be on this forecast. Still, plenty of detail to be worked out, but here are the brief takeaways:

  • A winter storm will impact Northern Colorado Monday afternoon through Tuesday afternoon. Snow will begin first in the northern and central mountains midday Monday, before gradually moving into northeast Colorado Monday afternoon and evening. The highest chance of snow in Denver at this time looks to be between 8 pm Monday night and 11 am on Tuesday. Depending on the final track, heaviest snow may end up along the Northern Colorado/Wyoming border, or directly over the greater Denver area Monday night.

  • Winter travel conditions ahead, with the stronger scenarios indicating travel will be very difficult if not impossible across northeast Colorado Monday night.

  • Snow is likely across all of Northern Colorado with this system, just how much remains to be seen. A slightly more southern track and the cities could see a significant snowfall (upwards of 6"), a more northern track and it'll just be a glancing blow to the metro areas. Either way, expect cold temperatures and at least some snow across the urban corridor and Northeast Plains.

  • Travel improves across the plains Tuesday night and Wednesday, with more rain and snow returning to the forecast for Western Colorado Wednesday through the end of the week. Great news for mountain resorts, but likely to cause some travel headaches at times in the high country.

If you're hoping for a big holiday week snow in Denver, you better hope the GFS sees something the Euro does not. If you're flying Monday night or Tuesday morning, feel good (for now) knowing the European usually has the better idea. Let's see how things look after another round or two of data.

Stay tuned!

Brendan Heberton

Brendan is founder of Weather5280. He is co-founder of FreshyMap, and develops software for geospatial data analysis and visualization.

Denver, Colorado
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