This November rain could have been crippling snow

- When we talk weather and the month of November, it’s one of those months where truly anything can happen.  It is one of our big transition months from one season to the next so anything from severe weather and tornadoes, to heavy rain, to crippling snows can fall.  The rains we experienced late Wednesday and early Thursday wasn’t what we would call crippling by any stretch of the imagination, but A LOT for the month.  Over 2 inches of rain fell in many parts of the metro with over 3 inches of rain in isolated locations in western Wisconsin.

Consider though what would have happened if enough cold air was in place to have all of that rain actually fall as snow.  While this sounds like a straight forward proposition, it isn’t quite so easy.  However, I will attempt to simplify.

In the world of snows, we have what’s called a snow to liquid ratio.  That is the ratio determined from the amount of liquid water in the atmosphere to total number of inches of snow.  For example, the industry standard for extreme simplification is 10 to 1.  This means that 10 inches of snow equals about 1 inch of liquid water.  So, in the easiest of terms, the 1.5 to 2.5 + inches of rain that fell in the metro could have been 15 to 25 + inches of snow.  A lot right??  But like I said, it’s not always that easy.  Many factors play a role in the snow ratio and EVERY storm is different.  From air temperature, to ground temperature, wind speeds, time of year, time of day… as well as a host of others ALL play a role in the snow ratio.  So for this specific storm… because the ground isn’t frozen, there would have been some melting and compacting… also, temperatures would have likely been closer to freezing (Cause we are talking typical November snows), which would have melted the snow even further.  So if we were looking at a typical “November style” storm, snow ratios would have been closer to 8 to 1.  Doesn’t sound like much of a difference, but when you are getting 2 or 3 inches of rain, that simple change in snow ratio can have a HUGE impact on snow totals.  Take the difference between type of snow for example in the image below…

With temperatures near the freeze mark, the average snow ratio is somewhere around 10 to 1… meaning 10 inches of snow equals 1 inch of liquid.  But when temperatures dip into the teens, like our January powdery snows, ratios can be closer to 30 to 1… meaning that 30 inches of snow equals 1 inch of liquid.  So with this storm, the metro would have seen 45 to 75 + inches.  Now, that’s next to IMPOSSIBLE in actually occurring because we simply can’t get this much moisture into the atmosphere in January, but gives you a little perspective.  So here is the general rule of thumb when the National Weather Service if forecasting snowfall and their ratios…

The closer you get to the Gulf of Mexico where there is more moisture and warmer temperatures the lower your snowfall ratio.  It is the opposite as you head to the dryer, colder, higher elevations with ratios typically double of those near the Gulf.  For much of Minnesota, the “typical” snow storm has ratios of about 13 to 1.