Winter Weather Advisory kicks in jeopardizing safe commutes

(FOX 9) - A Winter Weather Advisory was issued for parts of central and southern Minnesota as well as western Wisconsin and the Twin Cities metro.

The melt continued Sunday with temperatures in the metro holding in the low to middle 30s with plenty of fog around. A Dense Fog Advisory goes through at least noon for much of the area, but will slowly be chipped away from northwest to southeast through this evening.  

Then, a low accumulation but potentially high impact event will begin to unfold. Snow starts to fly in northern Minnesota late this evening and tonight. For the metro and much of the southern half of the area, it will be fog and drizzle through the early overnight, but temperatures will start to fall below freezing, leading to some freezing rain and freezing drizzle overnight.  

The big question though is, just how quickly can temperatures get back below freezing? The earlier this occurs, the higher the impact will be in the metro.

That said, the potential bust for this event is rather high and here’s why: With northwest winds and significantly colder air not likely moving into the metro until mid to late morning on Monday, when most if not all of the precipitation is done, temperatures may hold right at or just above freezing. The reason for this is the act of refreezing the snowpack when the temp dips back to 32° actually has a warming effect on the atmosphere. This can then actually off set cooling and keep temps a degree or so above freezing, leading to just plain old rain instead of freezing rain.

The way to offset this effect is to have northwest winds ushering in much colder air, which would overtake this process and force the area to cool below freezing. If the northwest winds hold off, it would give the area a long period of drizzle, then a very quick period of freezing drizzle/sleet/snow combo before ending. This would be the lowest impact solution for the metro. It would still create some slippery roads, but likely for a much shorter period of time and potentially after most of the morning commute is over with.

Still, there is still a pretty high probability of a high impact icing event in and around the metro, so we should plan for that. Overall accumulations would be minor - only a few hundredths of an inch - but it takes just a trace to cause major issues on untreated surfaces. So, temperatures will likely fall to or just below freezing by the start of the Monday morning commute, with freezing drizzle and freezing rain around the area.  Then the gusty northwest winds hit and temperatures plummet through the rest of the day on Monday falling to the low 20s by lunch and the low teens or even single digits by dinner.

This “flash freeze” could have an equally high impact on area roads for the evening commute, especially those that are untreated.

Twin Cities metro takeaways:

• Overnight freezing drizzle or freezing rain, possibly ending as a touch of sleet/snow during the morning rush.
• Total ice accumulation of a tenth of an inch or less.
• Total snow/sleet accumulation of an inch or less.

Commute impacts:

• Monday AM: High impact. Quite likely a slow commute with plenty of spinouts and crashes early before people realize how icy it is and slow down.
• Monday PM: Moderate-high Impact. This will heavily depend on how much ice we get and how long the precipitation lingers, but with drastically falling temps, there is the potential for some icy roads leading to a slow commute.