PHOTOS: Weekend Hoar Frost Glistens Midwest, Northeast

An unusually hard frost known as hoar frost created stunning views, but also travel problems across parts of the Northeast and Midwest this weekend.

All the key ingredients were in place for hoar frost to glisten the Midwest and Northeast during the overnight and morning hours of this weekend. The result was a winterlike scene amid what has been a mild start to December.

Hoar frost is essentially when "frost formation is taken to the next level," stated AccuWeather Meteorologist Jim Andrews. "The air is so saturated and cold that ice crystals continue to grow and any surface is fair game."

That is why drivers were faced with isolated slick spots this weekend with the danger greatest on bridges and overpasses. Normally, frost will not form on road surfaces.

Clear skies, calm winds, long nights and abundant moisture allowed the hoar frost and dense fog to form.

The cousin to hoar frost, rime ice, forms when wind blows supercooled water droplets (liquid water at temperatures colder than freezing) onto a freezing cold surface, according to Andrews.

The unusual nature of the hoar frost this weekend was how much moisture was available. Often, colder and drier air is covering the Midwest and Northeast in early December.

One clear indication that moisture was abundant and the stage was set for hoar frost to develop and create the following spectacular views was the formation of dense fog that led to another hazard for motorists.

There will once again be areas of fog and frost in the Northeast Sunday night, while a storm system leads to numerous clouds in the Midwest.