Wintry Weather Returns Friday Night
by Cody Matz
December 13, 2012 8:22 PM
Here comes the next one….. and we need it! Another storm is headed our way, which is great news for the drought considering it continues to worsen. But this storm will be far warmer then what is typical for the winter months. It is currently over the desert southwest and will be transporting plenty of moisture and warm air along with it, which will make precipitation type very problematic. Temperatures will likely be within a few degrees of freezing through much of this storm, which can create a wide variety of what’s falling from the sky. Rain, freezing rain, sleet, and snow are all possible with this storm, however it looks like plain old rain may be the main culprit with temperatures likely above freezing through much of Friday night in many areas that are expecting this storm. The problem is that the difference in just a couple degrees can mean the difference between a lot of rain or a mix of rain and snow so this forecast may change as we learn new information. For now though, this is where we stand.
Northwest Iowa and parts of southwest Minnesota and southeast South Dakota are likely to stay mostly plain old rain with this storm with some light snow on the tale end of the storm early Saturday. To the north and west though it becomes a little more complicated… the pink shading shows an area of transition with precipitation starting as a quick period of freezing rain and then switching to rain through about dawn Saturday. After that, rain will switch to snow at some point, but when and where that occurs is just impossible to nail down. Further north and west it could be a mix of pretty much everything. With temperatures hovering very very close to freezing, much of the blue areas will start as light freezing rain or drizzle, then transition to a rain or sleet mixture and then eventually some snow. The good news with areas east of the James River is that precipitation amounts will be quite light. However for parts of the northeast, heavier precipitation is expected with higher potential for accumulating ice thanks to freezing rain. The areas with the greatest chance for icing are in purple generally from Huron and Brookings northeast through Watertown, Milbank, and Ortonville Minnesota. This pretty much sums up the type of precipitation each location should and could see. But what about amounts?
Well, here you go… the following three images are what our futurecast is showing for overall amounts of rain, freezing rain, and snow. Remember that if the track or intensity of this system changes, precipitation amounts will change as well.
Now, some of our computer forecasting models have a little bit different idea on how much snow we will get. Check out the image below of snowfall accumulation through the weekend.
You can see the band of snow setting up right along I-29 with upwards of 5 inches in some spots. But as of right now, I believe this forecasting computer model is just a little too cold with temperatures which would make some of this precipitation snow and knock the totals back by a couple inches or so.
As for freezing rain accumulation, it can be an even larger crapshoot than snowfall. Remember that freezing rain is just rain that falls when temperatures are at or below 32° at the surface. For this to occur over a long period of time, temperatures above the surface have to be warm enough to melt the snow that’s falling into rain before it reaches the ground AND you need a persistent breeze ushering in colder air. Now thankfully it doesn’t look like we will have that breeze so once rain starts falling, temperatures will actually rise. But the question is just how fast will the temperature go up and how big of an impact on local terrain will it have. Well below is an image from the Hydrometeorological Prediction Center (HPC) showing the probability of receiving at least one hundredth of an inch of freezing rain.
Notice that the majority of this will fall in the north and west with some areas showing an 80% chance.
Now to the rainfall… This will be very beneficial to the areas that need it, however the ground is frozen. So the amount of water that will go into the soil is regrettably much smaller than it would be if it weren’t, but we could use anything we can get. Below are two images with the first showing the probability of at least a quarter inch of rain through the storm and the second showing the probability of at least a half inch of rain through the storm.
You can see that the southeast will likely get the most with at 95% chance or higher of receiving a quarter inch of rain and a 50% chance or higher of receiving a half inch of rain.