Two More Rounds of Snow In the Forecast

Saturdays Snow Could Be Significant Based on Current Data

After two rounds of snow moved through the forecast area earlier this week, some of us may be… tired of snow, to say the least. Unfortunately, there’s more snow on the way for the Sioux Empire; the first round of snow is going to move through portions of the forecast area on Thursday while the second round of snow is expected on Saturday. Saturdays snow could be significant, based on current data.

GFS Futurecast, Saturday February 24th

The first round of snow is expected to move into southern parts of the forecast area going into Wednesday evening and last through the morning hours on Friday. A high pressure system currently overhead is expected to exit and push eastward throughout the day. Since winds turn clockwise around a high pressure system’s center, or anti-cyclonically, those southerly winds throughout the day will be moving moisture northwards, along with cloud cover. Clouds are expected to move into southern parts of the Sioux Empire starting in the overnight hours and by the morning, central and eastern parts could be seeing snow falling. Some of that snow may be on the heavier side. By the time Friday rolls around, parts of the KDLT forecast area could have picked up an additional 2-4″ of snow.

Wednesday Morning Futurecast through Friday Morning

Possible Snow Fall Accumulations Thursday into Friday (Subject to Change)

But what myself, Alex and Joe are watching is where a weak surface low will be moving throughout the day on Thursday. Where this low ultimately develops will determine where the more intense snow could fall. Latest data suggests that if this weak low takes its current path, central parts of South Dakota will have a better chance at seeing the stronger snow. But, as you may know by now, weather is more than just what is at the surface.

To ensure that an area is going to see snow or rain, the column of air, from about 300mbs (~5.5 miles above the surface) to the surface, is moist. One thing that we are watching, since a high pressure system is exiting and southerly winds are taking over, is whether or not there are going to be any dry layers in the atmosphere. If there is a dry layer in the atmosphere, say at the ice layer or closer to the surface, not only could it be hard for ice crystals to form in a dry environment but any moisture that enters into the dry layer would evaporate. Evaporation would continue until that layer of the atmosphere becomes moist, then any remaining moisture entering that layer would continue towards the surface.

Area in circle showing dry layer in the atmosphere

The North American Model (NAM) has more dry air over the Sioux Empire than the Global Forecasting System (GFS); the NAM is bringing moisture back into the forecast area slower than the GFS. This difference will not only impact the entire forecast area but parts of the southeast especially. A more moist column of air would support the likelihood of snowing falling whereas a more dry column of air would result in more of a freezing drizzle.

850mb Dew Point Advection Between GFS (Left) and NAM (Right) Thursday Afternoon

However, both models, as well as the European Model (EURO), agree that this first round of snow will be an all day event. Starting in the morning and lasting through the evening hours, we’ll see the chance for precipitation across central and eastern portions of the forecast area. Into the afternoon a quick little bit of vorticity, or lift, will move through the mid-layers of the atmosphere and help the expected snow fall through the late afternoon into the evening hours.

Thursday Futurecast

The forecast looks to quiet down but another low pressure system is expected to develop and move into the forecast area starting Friday night into Saturday. This low pressure system looks to be one that could bring a significant amount of snow to the forecast area going into the last half of the weekend. Unlike the low that is forecasted to move through the Sioux Empire Thursday, this weekend low will be a Colorado Low (which tend to bring the Sioux Empire heavy snow).

As of now, only our long range models like the EURO and the GFS are picking up on this system since it’s too far out for the NAM’s data time. As of Wednesday morning, the GFS has consistently shown the center of this low pressure system in northeastern portions of Kansas Saturday morning. Between the 00z and the 06z runs of the GFS has showed more of a southwesterly trend with that center… taking with it the heavy snow potential. If you are someone who wants snow, you’ll want warm air to be advected, or transported, farther north at 850mb. If you recall, surface lows follows warm air advection at 850mb. If you look at the temperature advection between the two runs on Saturday morning, you can see a big difference.

GFS 850mb Temp. Advection, Area in Circle Showing Importance Difference from 00z (Left) to 06z (Right)

One trend that we have noticed with some of our more… organized systems is a southerly trend as we closer to the day of the event. That’s not to say that it’ll happen with this next system, but it is a possibility. We’ll also have to see how our short range models, like the NAM, RPM and HRRR interpret this system. Since Monday late afternoon, the GFS has consistently had this low pressure system developing and moving through the forecast area Saturday and has heavy precipitation rates. We’ll keep you updated throughout the rest of the week leading up to this potential system.

Blaise Keller
KDLT News Morning Meteorologist
Twitter – @blaisekellerr

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