Cold Blast Set for the Weekend
by Cody Matz
November 08, 2012 7:01 PM
As cool as it has been over the last few weeks, nothing will compare to what’s going to arrive by Saturday night. A large trough is digging into the Pacific Northwest, which allows Arctic air to sink southward into the U.S. This trough will slowly edge eastward as we head into the weekend eventually leading to a pretty significant storm system for much of the northern U.S. along with frigid temperatures for this time of year as highs tumble some 20-30 degrees below normal. Not only will we have to contend with chilly temperatures, but winds of 20-35 mph across the region. These winds combined with the falling temperatures, will make it feel near zero in many areas Saturday night through Sunday night. This storm though is not a typical one with a very complex and elongated structure. This will likely lead to spotty precipitation versus more widespread which we are typically used to with winter like storms. However, the potential is there for some of us to get rain, sleet, freezing rain, and snow all in a 12-hour period. But we seem to have the same question we always do, how much??
The most noticeable and arguably the most impactful part of this storm will be the cold and the winds, so lets start with that. First of all, the temperature contrast across the area Saturday as the center of low pressure lifts northeastward will be pretty amazing. Southerly flow out ahead of the low will help temperatures increase to well above seasonal normals and then northerly flow behind the low will help temperatures fall. With the low traveling straight through the middle of our area will allow a wide range of temperatures to develop. Take a look at the picture below. This is a forecast from a very specific and short-range computer model. This shows just how drastic the temperature differences could be Saturday.
In northwest Iowa, highs could actually top 70 degrees, but as you travel northwest, temperatures fall fast. By the time you get to Mobridge, temperatures will be in the low to mid 30’s. Yikes!!!
Dangerously cold temperatures are likely to follow on Sunday as our first true arctic air surge moves in from Canada. What makes this worse is that we haven’t seen temperatures like this in a while, not to mention with last winter so mild, our bodies may take even longer to get acclimated to the change in climate then a normal year. Below is the wind chill chart showing what it feels like outside at a certain temperature combined with a certain wind speed. Below the wind chill chart, is a look at temperatures across the area Sunday afternoon.
You can see that temperatures will be in the 20’s to about 30 degrees. With 25mph sustained winds, which will be pretty likely to experience, it feels more like the single digits and teens, and unfortunately temperatures will only get colder from there Saturday night.
Now of course, we all want to know what’s going to happen with that terrible s-word….. snow! Right now, it’s a really big question mark. For the moment, chances don’t look great for a lot of accumulating snow, however, there are a couple of computer forecasting models that continue to go back and forth from run to run. A run of a model is basically pressing the start button allowing the computer to process information and come out with a forecast. That happens 4 times daily. So by run to run, I mean one forecast after the other forecast. So in this instance, the first image below is the snowfall forecast for a computer-forecasting model from 6am this morning. The second image is from the very next model run (pressing that start button) at Noon.
Notice how different they look. The first image shows a couple of bands of snowfall developing and dropping a few inches of snow on some of us. The second image shows just a few spots getting an inch or so of snow, and that’s about it. This is the dilemma we have been having so far. But this is typical with storms of this nature, because the window for precipitation to fall is quite small, and temperatures are close to freezing which makes precipitation type an even bigger challenge.
Here is another forecast for snowfall from the Hydrometeorological Prediction Center (HPC). Remember that they show their forecasts based on probability. In this case, the picture below shows the probability of receiving at least one inch of snow from Saturday evening through Sunday evening.
According to the HPC, areas generally west of I-29 have a 50-70 percent chance of getting at least one inch of snow. So at this point, I would just expect lots of cold along with some areas of rain, freezing rain, sleet, and snow. Dust off your winter driving skills because they may be needed by Saturday night.