October 1-10, 2005
Midwest Weekly Highlights - October 1-10, 2005
Summer-Like Start to
October
Unusually warm weather continued into the first week of October across
much of the Midwest. It was warmer than normal across the
entire region, with temperature departures of +8°F to
+9° from
northern Wisconsin eastward across northern lower Michigan (Figure 1).
The coolest weather was found from western Minnesota south
through Missouri, where temperatures were only 1°F to
2°F above normal.
The cooler weather in Minnesota was in part due to more
cloudiness and rain than the rest of the region and a front that
bisected the state the early part ofthe period. Rainfall was
particularly heavy from east-central Minnesota through northwestern
Wisconsin (Figure 2). Rainfall was also above normal across
northern Missouri and in southeastern Ohio. However, much of
the central Midwest saw very little rainfall, and parts of Iowa,
Illinois, and southern Wisconsin remained in Extreme Drought on the
U.S.
Drought Monitor (Figure 3).
Warm and Muggy
As the month started a large area of high pressure was sprawled across
the eastern half of the U.S. The high, in combination with a
developing low over the Northern Plains, produced strong southwesterly
winds over the Midwest (Figure 4).
The result was unseasonably warm and humid weather
across much of the region. On October 2 the minimum
temperature at Minneapolis-St. Paul, MN reached only 65°F, a
record high minimum for the date (old record 62°F in 1897).
On October 3 the minimum temperature at Minneapolis-St. Paul
was only 72°F, a new record high minimum for the date and the
new record monthly high minimum temperature. The old record
was 69°F in 1997. Maximum temperatures in the mid and
upper 80s were common as far north as Minnesota and Wisconsin.
First Autumn Blast
By October 4 another area of low pressure was developing in the central
Rockies along a strong cold front which divided very cool air to the
north from the unseasonable warm and muggy air south. As a
strong upper level trough of low pressure approached the northern U.S.
late on October 4 the surface low pressure system went through rapid
intensification. By the morning of October 5 this low moved to south
central Minnesota, producing torrential rains in a band from
east-central Minnesota to northwestern Wisconsin (Figure 5).
Snow was falling in the cold air over northwestern
Minnesota, and as far west as the Dakotas, where blizzard warnings were
issued. Thunderstorms repeatedly developed along the
slow-moving boundary, and rainfall amounts in eastern Minnesota and
western Wisconsin on October 4-5 exceed nine inches in a number of
locations, and mounts in excess of five inches were common producing
widespread flash flooding. The
low moved to the north of the Great Lakes by the morning of October 6,
and much colder air spilled into the Midwest as the front pushed south
into the Gulf of Mexico. On October 6 maximum temperatures
were in the 40s in Minnesota and struggled to reach 60°F as far
south as Illinois and Missouri, some 25°F to 30°F
colder than the highs the day before. Ahead of the front in Ohio
temperatures again reached the mid 80s. With the center of the cold
high pressure system well north of the
Great Lakes, freezing minimum temperatures were generally limited to
Minnesota, Iowa, northern Missouri, Wisconsin, and Michigan.
Steady northerly breezes kept temperatures above freezing to
the south of these areas, but some scattered patchy frost was
reported in parts of Illinois and southern Missouri.
Although this system was a copious rain producer in the upper Midwest,
the air dried out somewhat ahead of the front in the central Midwest.
This drying, combined with the timing of the frontal passage
overnight resulted in little significant rainfall in the
central Midwest. As the front moved through Ohio on October 6
it ran into moisture associated with Tropical Storm Tammy, and as a
result much of the eastern half of Ohio received from one-half to one
inch of rain.
The ridge of high pressure dominated the weather the
remainder of the period and temperatures gradually moderated, returning
to near to above normal levels on October 10 (Figure 6).
-SDH