April 24-30, 2006
Midwest Weekly Highlights - April 24-30, 2006
Wet End to April
A slow-moving upper level low brought substantial
rainfall to much of the Midwest the last several days of the month,
resulting in marked west to east rainfall pattern this week (Figure 1).
Precipitation for the period ranged from three to four times normal in
southwestern Missouri to less than 25 percent of normal in parts of
Michigan. The heaviest rain fell in south central Minnesota and in
Missouri, as well as adjacent portions of the Central and Southern
Plains that have been affected by prolonged drought (Figure 2).
Much of southwestern Missouri received three to
five inches of rain this week (Figure 3).
Temperatures this week ranged from 3°F to 4°F above
normal in extreme northern Minnesota and northern Wisconsin to
4°F below normal in western Iowa and Missouri (Figure 4).
A large portion of the central Midwest was also cool, with
temperatures running 1°F to 3°F below normal.
April Showers
The last week of April began with damp, dreary weather across the
central Midwest as low pressure developed over central Kansas and moved
through Missouri. Severe thunderstorms developed across far southern
Missouri, producing five reports
of tornadoes and many reports of severe hail (equal to
or greater than 0.75 inch). The inclement weather brought a
halt to spring planting across the central Midwest. The delay was only
temporary, however, as rainfall amounts from the early week system were
generally light. Fields quickly dried as a strong
high pressure system brought sunny skies, dry air, and breezy
conditions to the Midwest. The, cold dry air mass resulted in
low temperatures below freezing across the western and central portions
of the region (Figure 5). A few records lows were set the morning of
April 26: 29°F at Moline, IL (old record
30°F in 1980); 27°F at Chicago, IL (old
record 30°F in 1980); and 29°F at Fort Wayne, IN (old
record 30°F in 1976).
A Slow Low
The ridge of high pressure was moving east by April 28, allowing
cloudiness associated with the next weather system to overspread the
western Midwest. Two upper level low pressure centers, one
over North Dakota and the second over Arizona/New Mexico were headed
east (Figure 6). By April 29 the two lows had merged into one
broad area of low pressure (Figure 7).
Moisture streaming northward ahead of the low resulted in an
extensive area of rain from southern Texas to Minnesota (Figure 8).
Heavy rain across southwestern Missouri resulted in some
flash flooding as thunderstorms repeatedly crossed the same areas. The
low lifted slowly northward on April 30 and by midday was located
over Iowa. (Figure 9).
The atmosphere destabilized as skies cleared south of the low
and sunshine warmed the air. A severe thunderstorm watch was
issued in the early afternoon for eastern Missouri and the southern
half of Illinois, and later in the afternoon a tornado watch was issued
for southern Illinois and southeastern Missouri. There was
one report of a tornado during the evening hours near Parma, MO (New Madrid County) but most occurrences
of severe weather were large hail. A hail stone
2.75 inches in diameter was reported near Zalma, MO (New Madrid County). Heavy rainfall also resulted in some flash
flooding in Illinois.
SDH