May 1-7, 2006
Midwest Weekly Highlights - May 1-7, 2006
The first week of May rolled in with precipitation fairly close to the long-term climatic averages, with a slight edge towards below normal temperatures. The average daily temperature departures across the Midwest illustrate that much of the region was generally close to normal for this time of year (Figure 1), although there was a fairly large west-east gradient across the region. Average daily mean temperature departures for the first week of May ranged from near normal to 3-4°F above normal in Ohio, Michigan, and northern Kentucky to 1 to 3°F below normal across much of Illinois, Wisconsin, Missouri, Iowa, and Minnesota.
Precipitation for the
week was sporadic at times across the central Midwest, with the heavier
precipitation falling across southern Missouri, Illinois, and northern
Minnesota. This week, northern Minnesota, Missouri, and southern
Illinois
experienced precipitation
surpluses ranging from 125 to 200% above normal, while much of Iowa,
northern Wisconsin, and the northeast corner of lower Michigan saw
generally less than 75% of the normal
precipitation (Figure 2).
The lack of precipitation in northern lower Michigan along with
low relative humidities did result in the issuance a few "Red Flag
Warnings", indicating that fire danger was on the rise in this area.
Meanwhile, other areas of the Midwest, including Ohio, Indiana,
and western Kentucky saw precipitation totals near normal for the first
week of May. On account of the welcome precipitation across
portions of the
Midwest
this week, long-term drought conditions eased across much of Illinois
and portions of Missouri (Figure 3).
The entire D2 area of drought was removed across north-central
Illinois, and the area of D0 was removed from northern Indiana.
Welcome rains across Missouri helped farmers get their corn
planted, and the number of acres planted through May 7 is actually
slightly above average for this date. In northern Wisconsin,
however, dry conditions are prevailing, resulting in the addition of a
"D0" category, or "Abnormally dry" across this portion of the Midwest.
A quick review of the streamflows across this area also indicate
that many creeks, rivers, and streams are running at rates below
average for this time of year, supporting the addition of categorical
drought (Figure 4, USGS).
Severe Weather Continues
On Monday, May 1, an upper-level disturbance tracked eastward across
central Kansas, and eventually into Missouri and Illinois. Ahead
of this disturbance, numerous showers and thunderstorms broke out
across central and southern Missouri and Illinois. As the evening
progressed, a mature bow echo (Figure 5)
traversed across southern Illinois and into portions of northern and
central Kentucky. There were several reports of severe weather
associated with these thunderstorms and the large-scale mesoscale
convective system (MCS), primarily in the form of wind damage and large
hail (Figure 6).
On May 2-3, a strong cold front (Figure 7)
dissected the Midwest, bringing at least two rounds of severe weather.
Fortunately, no injuries or major damage occurred with the severe
weather. There were, however, numerous reports of pea-sized hail,
and even one-inch hail covering the ground in western Iowa and southern
Minnesota on May 2 (Figure 8). During the early morning hours on May 3, an MCS rolled through eastern Missouri and into western Illinois (Figure 9)
before dissipating near the Illinois/Indiana border. This MCS
left an outflow boundary to its south across the I-64 corridor of
southern Illinois and southern Missouri where new thunderstorms
developed. These thunderstorms rapidly became severe, and were
also slow moving, causing several roads in the Ozarks to be flooded.
In Greenfield, MO, 2.25" of rain fell in just 70 minutes!
Unfortunately, the heavy rains resulted in one fatality in the
Ozarks of Missouri. According to local news reports, a 22 year
old man, driver of a van carrying eight persons home from work, tried
to cross a water-covered bridge when the water rushed into the van
forcing evacuation of its passengers. Seven of the eight
passengers were later found down the creek from where the van was
washed off the road. In Springfield, MO, the heavy thunderstorms
caused numerous power outages and downed several trees as the official
automated sensor observing system recorded a 52mph gust. There
were also several reports of large hail in southern Missouri (Figure 10) ranging from 1.00" to 1.75".
Quiet But Cool to End the Week
The end of the first week of May featured below normal temperatures, including some frost advisories in Iowa, northern Illinois, northern Indiana, and parts of lower Michigan, but little in the way of precipitation. Temperatures did dip into the upper 20's across northern Wisconsin on May 6th, but no record low temperatures were reported. A change in the jet stream configuration aloft, from southwest to northwest, resulted in cooler and drier weather filtering into the Midwest from Canada. A large area of high pressure dominated the weather across much of the Midwest near the end of the week, while a stalled cold front with attendant showers and thunderstorms, raked across Arkansas and Tennessee. The high "blow off" clouds from these storms spread northward into Missouri and Illinois, tempering the strong May sunshine. A secondary cold front dropped through the Midwest on May 5-6, bringing a period of stratocumulus and ushering in cooler air, helping to keep temperatures below seasonal averages (Figure 11).
The long-range forecast for the second week of May is for wetter and generally cool conditions across the Midwest. Will there be more severe weather this week, and will the planted corn get its needed precipitation? Find out in next week's edition of the Midwest Climate Watch.
Kruk