As many of us woke up Tuesday morning, we felt the wind, but in some parts of the area, you may have been wondering why there wasn’t more snow. Let's take a look at what happened.
First, let’s talk totals. We expected there to be a sharp gradient in snow totals within the Pikes Peak region, with very little snow south of Downtown, and much higher totals over the Palmer Divide and in Teller County.
Reports from Tuesday morning show five to six inches fell in Woodland Park, four to five in Black Forest with some higher snow drifts, one to three north of about Woodmen Road in Colorado Springs, and the highest totals in the southern mountains.
So, the distribution of snow in terms of relative amounts was about right. But, the snow accumulations were either at the low end of the forecast ranges, or below them.
When we look at radar estimates, we see a similar distribution, but the snow accumulation lines extends a bit further south toward Colorado Springs.
A few things led to the low totals. By far the most important is that this was a classic spring storm.
Heavy snow did fall last night in Colorado Springs. If you were up at 10:00 p.m., you likely saw it out your window. But, air temperatures were above freezing and so were the roads.
So, this snow didn’t accumulate. Also, because of the classic spring storm characteristics of this low, it had very high moisture throughout the atmosphere, from the ground to several miles up.
Normally, precipitation falling in southern Colorado falls through some dry air near the ground early in a storm's progression, and evaporates as it does so, which cools the air. In this type of set up, that cooling would often pull temperatures right to freezing.
Because of the high moisture content in the storm, we had no dry air for the precipitation to evaporate into. This kept the freezing level higher, between 6,500 and 7,000 feet when the heaviest snow was falling.
Even over the Palmer Divide, which sits above 7,000 feet, warm road temperatures prevented snow from sticking for a significant part of the heaviest snowfall. As a result, much of the snow that fell didn't accumulate.
The final contributing factor, some of the dry air that was over us on Monday got sucked into the system as it was developing. Here’s all the dry air on Monday afternoon in the southern plains:
In the evening as the low develops, it pulls in some of that air:
So, after a period where we had very wet air that stopped temperatures from dropping, we then had dry air mix in with the strong downslope winds.
When temperatures did fall a bit overnight, the combination of powerful downslope wind, and what is known as dry air entrainment, combined to fragment the snow bands that were over the I-25 region.
Downslope north winds are often referred to as "snow eaters" for this exact reason, they lead to a sharp and dramatic cutoff in snow as we saw here.
The downslope related cutoff in snow was part of our forecast as we expected much of the Downtown and southern region to be snow free with this set up. But, the dry air entrainment is why the Palmer Divide, northern Colorado Springs, and Woodland Park totals came in low.
By the time temperatures were cold enough for snow to stick, the heaviest precipitation was over.
Springtime is well known for being tricky to forecast for in southern Colorado. In this case, we did get the moisture, we were just too warm.
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