System on Schedule, Very Little Change to its Progression

It’s far from a powerful system, but tonight’s weather maker is a good reminder of what’s on the way, cold and snow.

Snow has fallen in sections of the mountains throughout the day Sunday, but colder temperatures tonight will prompt the better high country snowfall through Monday. The arrival of the colder air will also allow rain and snow showers to develop for the greater Denver area.

For the Front Range, precipitation chances will climb from 20% at 10pm to 60% by 6am. This will be mostly a rain chance for Denver, a rain/snow chance elsewhere. With the peak in that precipitation chance dropping after the lunch hour, this will be a very quick system.

Now, as far as the precipitation type. It’s easy if you are above 7,500’ll have snow. Between 5,000 to 7,500 feet will likely see rain initially then a mix of rain and snow for most of the morning.

Before we talk snowfall amounts, let’s see how much water we have coming in. NAM, GFS, ECM, and SREF bring an average of about 0.25” liquid to Denver, but closer to 0.50 to 0.75” for the higher terrain. And, all models are pretty consistent with the placement of that moisture. For example, here’s SREF QPF from the 15z model run.

Matt Makens | Weather5280

If all snow, that 0.50 to 0.75” liquid will equate to 5 to 10” of snowfall for the higher elevations. However, since Denver will have more rain than snow, the potential amount of snow accumulation here is far less. A 10:1 ratio (reasonable given the warm temperatures) would yield a trace to 2.5” with our 0.25” liquid. If half, or more, of that liquid falls as rain, we are now faced with a trace to 1” situation. That’s the most probable as shown in the “Snowfall Gambler’s Charts” from around the city. Further, consider how warm the ground is, and well...maybe something will stick to the grass. Plus, the temperature profile of the lower atmosphere may stay too warm for snow to form. NAM leans toward a colder profile than the GFS in the 12z Sunday runs, but the 18z NAM warmed to near the GFS profile which suggests with greater confidence it’ll be too warm for snow over Denver. NAM’s profile for Monday morning isn’t all that snow-favorable.

With all that said, don’t be shocked if you wake to some snow on the grass, but for snow-lovers this is not your dream come true.

Cold start to the week:
The temperature impact with this system is just as dramatic, if not more so, than any moisture we will receive. Denver hit 72 Saturday and 69 Sunday, but will struggle to maintain 40s Monday. With morning upslope and cloud cover throughout the day to further the cold air advection, we will be looking at a midnight high (mid-40s), and 11:59pm low (mid-to-low 30s) for Monday. I wouldn’t expect much of a warm-up feel to the day, so winter gear from start to finish.

Josh Larson has been keeping tabs on our temperature trend within the modeling and adds this... See how the 2-Nov section shows a model trend of dropping temperatures from 12z Monday morning to Monday night? For example, 12z NAM starts the day at 43, then hits 33 midday and 32 by the evening. The ECM shows a similar cooling trend to the day, versus any kind of midday warm-up. Regardless, plan on it being chilly and the coldest afternoon of the season, so far.

As the system clears Monday night, lows will fall into the 20s for the metro area. Clear and warmer days expected Tuesday through Thursday.

Matt Makens

Matt Makens has won 5 Emmys for his weather coverage. He has the seal of approval from the NWA and is a certified Broadcast Meteorologist as designated by the AMS. He works for Colorado's Own Ch 2.

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