Snow on the Way!
November 19, 2011 12:00 AM
WINTER STORM WARNINGS and ADVISORIES remain in effect through Saturday evening, with the bulk of the activity coming to an end by later this afternoon. As of 1pm a moderate to heavy band of snow continues to fall from Huron eastward into Watertown and Marshall, Minnesota. So far Pierre tops the list with around 7 inches reported. In the southeast freezing drizzle continues to create treacherous conditions along the interstates and highways…with multiple wrecks already reported…check out the video to your left from earlier Saturday morning. The video includes footage from a semi truck getting jack knifed along I-29 south, just around the 229 exit…stay tuned to KDLT and KDLT.com for further updates.
***Make sure to read the Blog below for more details
We have been really luck so far this fall. Temperatures the last couple of months have stayed above average across much of the area, and boy has it been dry. Some areas are more then 6” of rain below average since August. But it looks like our luck is about to run out. A storm will be developing in the northern Rockies Friday, which will make an easterly trek across our area Saturday and bring much of the area the season’s first accumulating snowfall. At the moment, we are not expecting a huge storm with tons and tons of snow and blizzard conditions. However, with soil temperatures now near freezing and air temperatures in most cases down into the 20’s during the storm, snow will likely accumulate on not only grassy surfaces, but roads, bridges, and houses as well. This is South Dakota after all, so we have to add a bunch of wind on top of that snow, so I can say right now that if you have travel plans Saturday, especially north of I-90, you will want to find an alternative. So the question remains, how much snow will we get?? Well, that is always a much harder question then it sounds. Let me show you…
Snow is a finicky animal. As you may know, one snowflake is never the same as another. They all have different shapes, sizes, and compositions, which means that every snowflake will fall a little different, settle on the ground a little different, and accumulate a little different. Now, the majority of these differences depend on temperature. Let me give you an example… lets say we are going to have a storm move through the area much like the one expected Saturday and forecasting models are showing a quarter of an inch of liquid precipitation for both Sioux Falls and Aberdeen. So you are thinking, “oh that’s easy… typically an inch of snow equals a tenth of an inch of liquid water so that means that both Sioux Falls and Aberdeen received 2.5 inches of snow right??” Wrong. Let’s say for argument sake that Aberdeen received 5 inches of snow and Sioux Falls totaled 2 inches. So how is that possible?? Well in many cases it stems around the temperature. The temperature while the snow was falling in Aberdeen was 15 degrees, but it was 30 in Sioux Falls. So the warmer the temperature, typically the less accumulation you will get. Why?? Well it stems back to what I first talked about, that every snowflake is different.
So look at the temperatures expected across our area Saturday afternoon:
Much colder to the north and west then it is in the southeast. So with this particular storm, there might be just as much liquid water falling in Sioux Falls as there is in Aberdeen, but Aberdeen will likely have more to show for it because temperatures are far cooler. So when forecasting snowfall, we have to account for many variables like temperature, wind speed, and dewpoint to make our predictions.
Some forecasting models will generate their own snowfall accumulation maps based on the components I was just talking about. Below are two different models and their interpretation of the upcoming snowfall event:
You can see that both have similar characteristics, but are still quite different. This first image keeps this storm a little more compact with almost all of the snow in the north and tallies up to 6” locally. Meanwhile the second image has the snowfall a little bit more spread out, but has higher amounts with a widespread 6”, and locally 8”.
So accounting for all of the models and all of the components we have discussed we can now come to a conclusion of our own. So here ya go…..as of right now it looks like the north will end up with more snow then the south. Here is our current forecast.
Now, considering we are still a good day away from the start of the event, things may change. There is also one little hiccup. Check out our futurecast below. The futurecast we use is in itself a forecasting model. So here is what it spits out in terms of snow totals.
You can see that it does place the heaviest snow in the north, but it has a thin band of some heavier snow from around Pierre to Milbank. So, it looks like there could be a band of heavier snow inside the swath of snow that develops. This is pretty common and is what we call a deformation zone. I know… big word. But it just means that heavier bands of snow develop inside a snowstorm much like thunder and lightning develop inside of a rainstorm. So the potential is there for somebody to end up with 7 or 8 inches, but it would likely stay very localized. Now remember, this can still shift course and move a little bit further south or a little bit further north, so check back often to get the very latest.