December 2005
Midwest Overview - December, 2005
A Cold, Snowy Start, A
Mild End
The first three weeks of December were cold and snowy throughout most
of the nine-state Midwest region, with only Kentucky missing out on
much of the snow. Temperatures the first three weeks of the
month
ranged from 6°F to 12°F below normal from central
Minnesota and
Wisconsin on south through the region (Figure 1).
Only the far northwestern corner of Minnesota experienced
near
normal temperatures. A number of locations in the central
Midwest
set record low maximum and low minimum temperatures the first week of
the month. The upper level wind pattern shifted to a more
west-to-east (zonal) flow the last 10 days of the month, shutting off
the flow of cold air and replacing it with milder air of Pacific
origin. As a result, temperatures the last ten days of the
month
ranged from 2°F above normal in southern Kentucky to as much as
20°F above normal in northwestern Minnesota (Figure 2).
The warm period was not enough to totally erase the effects
of
the first three weeks of the month, and December temperatures
ranged from 2°F to 4°F below normal across the southern
two-thirds of the region to 7°F above normal in northwestern
Minnesota (Figure 3).
Snowfall was abundant during December (Figure 4),
with significant snowfalls occurring as the month began. By
December 9 a series of storms had laid a blanket of snow across the
Midwest, and snow cover of at least an inch extended as far south as
the Ohio River (Figure 5).
Only a small portion of southwest Missouri and western
Kentucky
received below normal snowfall. However, by Christmas the
snow
cover had retreated to a line from central Iowa to northern Illinois
and northern Indiana. Despite the abundance of snow across the region,
precipitation was generally well below normal except across the
northern Midwest (Figure 6).
Much of the snow that fell in the early part of the month
came
during very cold conditions which favored snow to water ratios
on
the order of 15 to 1 or higher. At a ratio of 15 to 1, 6
inches
of snow only results in .0.40 inches of water. In the
northwestern Midwest, frequent snows did produce above normal
precipitation. Duluth, MN received 34.5 inches of snow during
December, the sixth highest total on record (the record is 44.3 inches
set in 1950). Minnesota is the only state in the nine-state Midwest
region that is not affected by the on-going drought. The
driest
area during December was the southern quarter of Missouri, which
received less than 25 percent of the normal monthly precipitation.
Rainfall in southwestern Missouri was below normal for much
of
the year, and the drought is affecting streamflows in that part of the
state. The U.S. Geological Survey reports that many streams were
flowing at a rate below the 10 percentile (flows have been lower only
10 percent of the time). Similar streamflow conditions also
exist
in northwestern Illinois, which has been experiencing Extreme Drought
(as depicted on the U.S. Drought Monitor) since late summer.