May 1-7, 2005
Midwest Weekly Highlights - May 1-7, 2005
Freeze Dried Midwest Turns to More Seasonable Weather
The first week of May began with a continuation of the cool and dry conditions of April. Only a small region along the Minnesota/Iowa border received more than 1 inch of rain from May 1 to May 7 (Figure 1). Most of the Midwest received little if any precipitation away from the Great Lakes, and even those areas were still below normal for the week (Figure 2). Record low temperatures were recorded over much of the Midwest on the mornings of May 3 and May 4, leading to well below normal temperatures for the week, especially in the southern and eastern Midwest (Figure 3). While somewhat dry conditions have been favorable to rapid planting of corn, proper moisture and temperature levels are need for germination and growth. Due to continued dryness, the abnormally dry region around the Great Lakes was expanded all the way to Iowa in this week's U.S. Drought Monitor (Figure 4), National Drought Mitigation Center). Fortunately, toward the end of the week, southerly flow resumed, and atmospheric temperature and moisture levels increased ahead of a slow moving weather system approaching late on the 7th.
Record Cold May 2-4
As the month began, a very strong upper level trough was situated over the Great Lakes (Figure 5, College of DuPage - COD). A number of locations in northern Wisconsin and Michigan reported snowfall on the 1st, including a record snowfall for the day of 1.2 inches at Marquette, MI. Snow was detected as far south at La Crosse, WI. The strong flow around the trough brought a very cold high pressure center into the central U.S. by the 2nd, when minimum temperature records started to fall. About 8 first order locations recorded either a record low or tied a record low for maximum or minimum temperature on the 2nd, but this does not even compare to the 27 first order stations on the 3rd or 20 first order stations on the 4th that set or tied new record minimum temperatures. The freezing line plunged south all the way to Arkansas and Tennessee on the 3rd, encompassing most of the western Midwest (Figure 6, Unisys). Only the locations downwind of the relatively warmer Great Lakes did not have sub-freezing conditions. But the lakes did not protect the Ohio Valley region on the morning of the 4th, when sub-freezing conditions moved eastward (Figure 7, Unisys).
A few noteworthy events deserve specific mention. In the state of Minnesota, the cold spot of Embarrass in the far northern part of the state recorded a temperature of 8°F on the morning of the 3rd. In northwestern Illinois on the same morning, the cooperative observer in Mt. Carroll recorded a minimum of 20°F, which, if confirmed, will go in the record books as the all-time coldest temperature ever recorded in Illinois during the month of May. This temperature was not a fluke, as two nearby stations recorded 21°F on the same morning. Both Moline, IL, and DuBuque, IA, set or tied record minimum temperatures on all three days of cold wave, May 2-4.
Because of favorable warm and dry conditions in early to mid-April, many farmers in the Midwest had an early start to the planting season for corn, only to see the early gains in crop progress wiped out by the cold conditions in late April and early May. Many of the corn plants that had emerged suffered from an inability to extract nitrogen from the soil and turned yellow. These plants may recover with a return to warmer conditions. However, some corn plants actually lost leaf surfaces that turned brown and died, and even entire plants succumbed to the cold. Corn seeds planted just prior to the cold snap have not even emerged from the ground. It will take a week or two of favorable warmth before some farmers know if they need to replant fields damaged by the cold.
Warmer With a Hint of Moisture
By May 5, the high pressure center dominating the central U.S. finally moved to the southeast, allowing a return to southerly flow. This shift brought seasonable warmth to the Midwest, and allowed some atmospheric moisture into what had become an abnormally dry area in the central and northern Midwest. Numerous wild fires were reported throughout the region, with the largest in Wisconsin. A small fire in the central part of the state near Big Flats was whipped by high winds and burned nearly 4,000 acres before being brought under control. About 30 permanent and seasonal homes, and another 30 camper trailers that could not be moved in time, were destroyed by the fire. More than 100 families had to flee for their lives, and 250 firefighters had to be called in to stop the fire. Dryness is beginning to affect pasture conditions in some places, compounding problems with winter kill and with recent frosts. Some tilled fields were developing a dry soil crust.
A clipper system dragged a front through the upper Midwest on
May 5 and 6, supplying enough energy to generate storms (Figure 8, NWS),
but not enough to supply widespread rain to the area. A cluster of
storms on May 6 hit southern and eastern Wisconsin with severe hail (Figure 9, Storm
Prediction Center), and another significant set of storms brought some
hail and an inch or more of rain to the Minnesota/Iowa border region.
By the 7th, an upper level ridge had moved over the Midwest (Figure 10, COD),
and maximum temperatures reached 70°F in far northern Minnesota
where only 4 days earlier, it was 8°F (Figure 11,
Unisys). A potent surface low pressure center waited to slowly enter
the region from the west (Figure 12, COD)
at the end of the period.