Convective Addiction

Winter is officially upon us

Posted on 02. Dec, 2010 by Ryan in Uncategorized

While it is not officially the true start of the winter season according to astronomy, one look outside confirms it: Meteorological winter is upon us.

After a October and November that were marked with temperatures well above normal – and near record breaking in certain cases – December has taken us back to reality.

October Temperature Departure From Average

A series of fast moving ‘clipper‘ systems is keeping the northern half of the country in more Canadian air. Several bouts of flurries and the first light snow accumulations were noted this week in Illinois, Indiana, Kentucky and Ohio.

The colder air aloft is also creating the first headaches of the season in the lake effect snow belts. So far Buffalo has stolen the headlines with over 3 feet reported in locations south of town.

Lake effect snow develops when very cold air is driven over the relatively warm waters of the Great Lakes.

Satellite image of Lake Erie following large lake effect snow event

The warm air immediately above the water creates instability in the low levels of the atmosphere, generating lift. If the air is cold enough, this lift can be rather significant. Snow bands develop parallel with the prevailing winds, allowing heavy snow to sit over one location on shore for long periods of time. When you add in that these snow squalls can generate snow rates of 2″+ per hour, its not wonder you can end up with totals above 100″ in extreme cases.

Courtesy of 'http://www.weatherquestions.com'

Lake Effect Snow in New York -2007

(Want to become a better forecaster with lake effect snow?  There are countless great papers. Here is a helpful one that I quickly found.)

Aside from the snow belts in the Great Lakes another, faster moving, clipper system is setting its eyes on the heart of the Midwest. Setting the stage for the first significant snowfall. Models had their first shot to sample the storm tonight (12-2) as the systems moved on the pacific coast.

02z 12-3-10

A general consensus thus far has been to generate a swath of moderately heavy snow in the Dakotas, dropping through Minnesota, Wisconsin, Iowa, Illinois, Indiana, and Ohio. Widespread 1-3″ reports are likely, as are common with clippers. But a band of 5-7″ totals are likely in the heart of the snow swath. Right now that band looks to set-up near southern Minnesota, NE Iowa, SW Wisconsin and into Northern Illinois.

Likelyhood of 4"

Likelyhood of 8"

Mother Nature sure had her calender right this year. Meteorological winter starts on time. Is your watch set?