Vince_Condella's Blog

The snowbursts that blew through here Monday afternoon and early evening were not out of the ordinary.  In fact, these convective snow showers are quite common in November and December.  But it was all about the wrong timing.  As luck would have it, the strongest and largest snow shower came through the Milwaukee-Waukesha metro area during the evening rush hour.  With temperatures below freezing, any moisture from the snow iced up on the pavement.

Convective snow showers form in a similar way to their counterparts in the summer months.  We have a roaring jet stream overhead providing lift and spin in the atmosphere.  The cold air aloft also added to the instability.  Air parcels rose quickly and condensed into cumulus clouds.  The best lift occured in a layer of the atmosphere that was best for dendritic ice crystal growth, and this resulted in rapid snowflake development.

Just like being caught under a summer snow shower, a convective snowburst will reduce visibility quickly.  But it was the ice that really did the damage.  Moisture froze on contact with the cold pavement of the roadways, and the ice rink formed in a hurry.

Remember that bridges and overpasses are the most slippery.  They are not in contact with the warmer ground.  Wind can whip beneath the roadway of a bridge and freeze it from top and bottom.  Even exit and entrance ramps are slippery.

This snowburst made for a traffic mess and a lot of fender benders, but it served as a solid reminder of the season that lies ahead of us.