Good afternoon everyone! Not much in the way of any changes to the weather bulletins issued by the National Weather Service for this upcoming winter storm. We are still noting Winter Storm Warnings extending from northern SD/southern ND through most of eastern SD into a large sliver of central MN. Watch for the core of the snow to work into the Dakotas tonight into the day Saturday, then MN through the daytime hours into the overnight. Beware of strong wind gusts accompanying this heavy snow, leading to blizzard conditions at times particularly in southeastern SD into southern MN. More on this later!
The heaviest snows will likely be situated in the eastern Dakotas into a large portion of MN, excluding the far southern reaches where rain and freezing rain can mix in. This is a result of building areas of frontogenesis (or the development of a boundary that aids in lift), first in the eastern Dakotas Saturday morning that slowly propagates eastward through the day into the overnight across MN. These areas also remain positioned in the right front entrance region of an upper-level jet (areas circled in the right image). This promotes upper-level divergence (shown by the diverging arrows) and low-level convergence, aiding in developing bands of heavier snow in the area.
Simulated radar through 7pm CDT Sunday: The storm really begins to ramp up during the overnight hours tonight and will intensify through the day Saturday as it tracks northeastward across the region. Timing the precipitation out…watch for snows to get going in western SD mainly after 6pm this evening, though the snow will be combating dry air initially. However, the lower-levels of the atmosphere will quickly become saturated and lead to snow falling in the western half of SD and southwestern ND by midnight tonight, then encompassing all of SD and the southern half of ND by 4am EST Saturday morning. Watch for some warm air intrusion in the southeastern tip of SD that will likely result in more of a transition to freezing rain and even plain rain late tonight through the morning hours Saturday while heavy snow continues to spread eastward across the western half of MN through the morning as well. Eventually, all of MN will be encompassed within a precipitation shield by Saturday evening with that warm air intrusion helping to transition some of the snow to freezing rain early in the day Saturday in far southern MN before colder air quickly works back in (changes back over to snow) during the afternoon and evening. Given the location of the low pressure system and where the system deepens (Central Plains), the eastern half of the region, generally in the aforementioned areas, stand the best chance for the heaviest snow.
With that frontogenesis doing work across the eastern Dakotas into MN coupled with the region draped within the right front entrance region of an upper-level jet, watch for snowfall rates during the peak of the storm to range between 1-2″/hour at times. This will promote steeply reduced visibilities at times especially since the winds will be picking up as well, helping to blow and drift the snow.
Here’s a look at temperatures through Sunday night: Temperatures in the far eastern Dakotas into MN will likely be on the modest side and hovering through most of the event at or slightly below freezing. Given these circumstances, expect the snow that will fall to be on the wetter side compared to previous systems this winter, but will definitely put a strain on trees and power lines as the snow collects. Behind the system, colder air will work back in and by Monday morning, the vast majority of the region will be in the single digits with even a few readings falling back below 0ºF in the Dakotas.
As stated on multiple occasions, the winds will be on the increase with this system as it progresses across the region this weekend. Watch for wind speeds to be gusting as the snow comes to an end up to 40mph+ in eastern SD and southern MN. While the criteria for Blizzard Warnings will likely not be met, this does not mean that the threat is not there, so definitely be on guard as blizzard conditions at times will be likely (leading to reduced visibilities and blowing/drifting snow). Winds will gradually die down as the system exits late in the day Sunday.
Total snowfall Sunday reveals the greatest amount of snow will fall within close proximity to the location of low-level frontogenesis and where the upper-level jet is. The low-level jet will also help to enhance snowfall totals (convergence) in west-central MN as well (where 8-12″ is expected). We can’t rule out locally more than 1 foot of snow falling, but will depend on where the greatest lift sets up. Otherwise, a large corridor of 5-8″ extends through most of MN into southeastern ND and most of eastern SD. Lower confidence still remains in the western Dakotas where discrepancies in model data can still be found. Odds are that the snow will be lighter in those locations compared to their eastern counterparts, but definitely beware locally higher amounts will be possible given some of the data. Regardless, travel conditions will be very hazardous for the vast majority of the region as Saturday wears into the overnight.
Ice accumulations with this complex storm system will remain generally confined to the southeastern tip of SD and the far southern rows of counties in MN. Watch for a glaze of ice accretion in these areas (mainly a 0.1″ or less) before the transition to snow occurs and leads to snow accumulations on top of the glaze of ice.
If you have any questions do not hesitate to reach out! Have a great evening!