If no other forces are acting on the wind, it will maintain its speed and wind chills will remain constant. But as the wind flows through the city, it's forced through narrow passageways between buildings, and the wind speed picks up dramatically. This acceleration of the wind produces the lower wind chill temperatures. Expect west-northwesterly winds from 20 to 30 mph on Tuesday, with much stronger gusts. As we get further into December conditions become more favorable for sleet and freezing rain.
All precipitation begins as ice crystals in the upper levels of the atmosphere.
As long as the air is below freezing they will hit the ground as snow. However, if a layer of warm air begins to override the cold air the snow will melt into rain. As it continues to fall the rain passes through another level of below freezing air and refreezes into ice. This is what is known as sleet. If it is raining when temperatures at the surface are below freezing the rain will freeze on contact with the ground.