"Extreme" impacts now expected by winter storm for MB/ND


The forecast remains extremely variable and uncertain for southern Manitoba, even only a few days out. The main issues I see is relatively warm ground as well as wet/saturated ground. While a long-duration snowfall event looks likely for southern Manitoba, these factors will likely limit snowfall accumulation. As a general rule, we are thinking of subtracting at least 10-15 cm on model depictions. Above is a loop through Friday where you can see the low occluding and generating multiple rounds of snow (some possibly heavy as dry slot occludes north across Minnesota).

Another issue to heavy accumulation is column filling. As shown above, you can see snow "under the low" as it is occluding. This means the air column is filling with cold air, which usually undercuts the low until it "detaches". This is not particularly favorable for heavy snow bands, but favors long-duration snowfall events.

Below is an experimental "Winter Storm Severity Index", which is being developed by the Weather Prediction Center (WPC). Obviously, the "extreme impacts" extend into Manitoba. Since it is hard to read, here is what extreme impacts mean:


  • Extensive and widespread severe property damage

  • Life saving actions will be needed

  • Results in extreme disruptions to daily life.

Winter storm severity index (experimental) by the US Weather Prediction Center

We think models are out to lunch on snowfall accumulation and this is common during these fall storms since the transition zone may be narrow and the temperatures look to be near the freezing mark. This is why most forecasters rely on QPF rather than snowfall accumulation depictions. Just for fun, here is what models are depicting today (see below), showing 60-70 cm of snow accumulation over a 24-hrs period. While this makes for nice headlines and generates a lot of clicks, it is not an accurate depiction of what will happen.

While we agree the snowfall accumulations may be significant (especially in North Dakota), there won't be 70 cm+ like some models are showing. We generally agree with the NWS Grand Forks, ND, showing 20-30 cm is possible across a vast area extending into Manitoba. Model trends over the last 24 hrs have shown a western shift in transition zone, but we still think the transition line should be along the I-29 corridor, which would bring the axis of heavy snow west of I-29 and west of Hwy 75 in Manitoba.

...WINTER STORM WARNING REMAINS IN EFFECT FROM 1 AM CDT /MIDNIGHT
MDT/ THURSDAY TO 7 AM CDT /6 AM MDT/ FRIDAY...
...WINTER STORM WATCH REMAINS IN EFFECT FROM FRIDAY MORNING
THROUGH SATURDAY MORNING...

* WHAT...For the Winter Storm Warning, heavy snow expected.
  Total snow accumulations of 8 to 12 inches. Locally higher
  amounts are possible. Winds gusting as high as 40 mph. For the
  Winter Storm Watch, heavy snow possible. Total snow
  accumulations could exceed 8 inches with wind gusts as high as
  55 mph, which may create blizzard conditions.

* WHERE...Portions of north central, south central and southeast
  North Dakota.

* WHEN...For the Winter Storm Warning, from 1 AM CDT /midnight
  MDT/ Thursday to 7 AM CDT /6 AM MDT/ Friday. For the Winter
  Storm Watch, from Friday morning through Saturday morning.

* IMPACTS...Travel could be very difficult to impossible.
  Widespread blowing snow could significantly reduce visibility.
  The hazardous conditions could impact the morning or evening
  commute. Strong winds could cause tree damage.