It hit with the ferocity of a spring squall line. Winds gusted, precipitation came down in torrents, and visibility was reduced. Travel was difficult. But this was no spring thunderstorm event. It was the "burst of snow" that blasted parts of southeast Wisconsin late Tuesday afternoon, Feb. 11.

A band of heavy snowfall was created in a short amount of time from Madison east through central Jefferson and Waukesha counties and into southern Milwaukee County. Five and six-inch snowfall amounts in two hours were not uncommon. People living north or south of this band of heavy snow didn't receive much more than an inch or two of snow, and some even less. And it wasn't just the amount of snow; it was the timing of the snow. The snow squall roared through between 4 and 6:30 p.m., disrupting the evening rush hour and closing Mitchell International Airport.

As you can imagine, the e-mails, phone calls and letters that came pouring into the weather office after this surprise storm were not pleasant! There is no doubt that nature always gets the last word, and it produced a freak weather event. After a weather surprise like this, I always look back on the data to see if there was anything that may have given me a clue that this snow burst would occur. Perhaps I missed something that would tip me off the next time one of these things approaches. Nope, no hints were given in the weather charts.

This snow burst was a cold-weather version of a summertime squall line of thunderstorms, the kind that produces strong straight-line winds as well as torrential rainfall. A sharp cold front approached southeast Wisconsin on the morning of Feb. 11, producing lift in the atmosphere as the heavier air (cold air) plowed underneath the warmer air ahead of it. The limiting factor on snow amounts was the lack of moisture.

Cold winter air is usually quite dry. Dew points are low and our skin gets dry and cracked this time of year. Moisturizer on our skin is a big help. The lower part of the atmosphere, however, didn't have any moisturizer. The flow of the wind aloft was out of the northwest and the surface wind was out of the southwest. There was no Gulf of Mexico moisture moving north into the Great Lakes region. My forecast called for up to 1" of snowfall with the passage of the cold front. So what happened?

There was no surge of moisture into our region that would boost the snowfall amounts. Instead, the lift in the atmosphere became great enough along our portion of the cold front to overcome lack of moisture. The previously weak weather system intensified quickly on the afternoon of February 11, and the timing couldn't have been worse for travelers. Surface reports out of the Madison area indicated a strong band of snow moving east along the I-94 corridor into Jefferson County. Weather advisories for southeast Wisconsin were quickly posted at mid-afternoon, but those who had to be out on the roads were caught in the thick of it.

So what is the moral of the story? Despite a forecaster's best efforts, and despite good weather data and accurate computer projections, nature can still cook up a surprise. Many people are cynical of weather forecasters and believe that most of the outlooks are inaccurate. That's not true, of course, but surprise snowstorms won't help change those opinions. The reality is that weather events on small scales, i.e. less than 50 miles in diameter can develop and change rapidly, often without warning. We see that in the spring and summer with small but severe thunderstorms, and now we have seen it in the winter season. Just one more reason to add gray hair to my head!