December 15-21, 2004
Midwest Weekly Highlights - December 15-21, 2004
Colder Weather, More
Lake-Effect Snow
It was a generally dry week across the Midwest, although cold air
streaming across the relatively warm waters of the Great Lakes brought
more lake-effect snow to northern Indiana and the Michigan Upper
Peninsula. After two weeks of seasonably mild weather, the
first
outbreak of arctic air knifed through the Midwest early in the
period. Temperatures averaged well below normal over the
eastern
two-thirds of the region, and near to above normal in the western third
(Figure 1). Daily average temperatures
ranged from 8F below normal from
eastern Michigan south through eastern Ohio and into eastern Kentucky,
to near normal from eastern Minnesota to southwestern Missouri. From
far western Minnesota to northwestern Iowa, temperatures were 4F to 7F
above normal. Precipitation this week was limited to the
northern
Midwest and to the lake-effect snow belts (Figure 2).
First
Arctic Blast
The first surge of cold air was already plunging south out of Canada on
December 15, and by December 17 the leading edge of the cold airmass
had reached the Ohio River (Figure 3, Unisys).
This was only a prelude,
however, to Arctic air that knifed south into the Midwest on December
18-19. By Sunday morning, December 19 the leading edge of
this
cold air mass had pushed almost to the Gulf coast (Figure 4).
Strong northerly winds generated by high pressure over Minnesota and a
strong low over New York pulled the cold air southward.
Daytime
temperatures on December 19 hovered at 0F and below over the northern
Midwest and in the teens as far south as the Ohio Valley. Low
temperatures were -20F to -30F in northern Minnesota and the Michigan
UP (Figure 5). Sault Ste Marie, MI tied a record low of -20F. The
extreme cold was accompanied by sustained winds 25 30 mph which
produced dangerous wind chill temperatures. Three deaths in
Minnesota were attributed to cold weather over the weekend.
Snow
Machine Cranks Up Over
Indiana
The strong northerly
winds streaming south over the open
and relatively warm waters of the Great Lakes produced heavy snow in
northern Indiana. A narrow but strong band of snow set up
north
to south over lake Michigan, targeting the northern Indiana shore of
the lake. The radar images from Grand Rapids, MI (Figure 6) and
Romeoville (Chicago), IL (Figure 7) show this band on the morning
of
December 19. The result was extremely heavy snow over a
relatively small area. Michigan City, IN piled up 26 inches
of
snow from this event, and Westville, IN received 20 inches, both in
LaPorte County. Outside this heavy core of snow, amounts
dropped
off considerably, but still were significant with South Bend receiving
8 inches of snow (Figure 8, NWS).
Lake-effect snow also occurred in the Michigan UP and in northeastern
Ohio, but amounts were in the 3 to 8 inch range as the fetch of the
northerly wind over Lakes Superior and Erie was considerable smaller
than that over Lake Michigan.
Widespread
Snow Across Upper
Midwest
A low pressure system moving out of the northern plains ahead of the
next Arctic air mass brought snow to a large portion of the upper
Midwest on December 20-21. Snow fell across Iowa,
southeastern
Minnesota, much of Wisconsin, and the northern half of lower Michigan,
much to the delight of winter sports enthusiasts. Snowfall
from
Iowa through southwestern Wisconsin was in the 2 to 4 inch range, while
in central Wisconsin 6 to 10 inches of snow fell from La Crosse across
to Green Bay (Figure 9).
Developing
Storm Threatens to
Snarl Holiday Travel
As the snow was tapering off over the northern Midwest, a low pressure
system organizing over Texas on December 21 was threatening to spread
heavy snow across much of the lower Midwest. By the evening of December
21 winter storm watches and warnings were posted from northern Arkansas
through the Ohio Valley northeastward to eastern New York (Figure 10, SPC).
Snow began
to fall across southern Illinois and Indiana late on December
21.
This storm and its impacts will be covered in the December 22-31
edition of the Midwest Climate Watch.