Posted at: 04/30/2013 8:41 PM
Updated at: 05/23/2013 8:54 PM
Rare May Snowfall Looming, But How Much?
It's probably the most talked about subject around town. May Snow. And yes, the potential for accumulating snow, while rare, is a real possibility, especially Wednesday night into Thursday.
We have an atmospheric traffic jam in place for the next week ahead. This means a storm system that is currently here, will stay in place all the way through the weekend! We're in for a soaking, up to 3" of liquid will have fallen through Friday!
Right now there is a lot of uncertainty as to how much snow will fall. Here's what we're looking at with the picture at right. This images shows various computer models (and National Weather Service) cumulative forecasts for snowfall over the next week. Note the spike up from 5-13" early Thursday morning? That's how much snow we're expecting right? Not necessarily.
If this were January and the ground were frozen, I'd buy it. Slam dunk really. But not in early May. There are several factors we will likely see a good chunk of this snow melt on contact with the ground and we'll end up with much less than the upper end of that range depicted in the image above. Here's why.
- Warm Ground - 6" soil temperatures as of Tuesday afternoon were around 60°, even warmer closer to the surface.
- Green Vegetation - Plants give off latent heat, which ultimately ends up warms the surrounding air nearest the plant life.
- 'Warm' Air Temperatures - Air temps during the rest of the week will mostly be at or above freezing.
- Low Snow to Liquid Ratio - We're expecting a high water content with this snow. The more water, the more densely the snow will accumulate (less air in the snow pack due to settling)
- High Sun Angle - Lets face it... it's May. The sun is up longer and is higher up in the sky. Even on cloudy days, the sun's radiation can be enough to influence snow and whether it accumulates.
These are factors that the computers won't take into account which will keep the highest of the totals away. Can these factors be overcome. Of course. If we get an intense enough band of snow, it will pile up faster than it will melt. That I do see happening.
At this point, taking everything into consideration we're going to call for up to 5" of snow in parts of SE Minnesota and northern Iowa, not the up to 13" the models are suggesting.
Even calling for up to 5" is going out on a limb. Take a look at the record highest monthly snowfalls for the all May's going back to 1886. In nearly 130 years of data, we've only seen eight years with measurable snowfall. The most we've seen in a particular May was 2.0" in 1944, and that was split across two separate days!
So, not only is this a difficult forecast anyway, what we're forecasting would obliterate any snowfall record in May, making the situation even more difficult.
There's lots of variables out there to take into account, so watch the forecast closely as we go through the next 24 hours waiting for the snow to hit.