February 1-7, 2008
Midwest Weekly Highlights - February 1-7, 2008
Midwest Clobbered by Severe Weather of All Kinds
The winter-weary Midwest experienced another week of major weather events ranging from severe thunderstorms and tornadoes to heavy rain, dense fog, flooding, and heavy snow.
The average temperatures across the Midwest more or less defined the corridor of the active storm track this week from southwest to northeast. Temperatures were above normal across the region, but there was a large difference in the departures from west to east. Temperature departures ranged from 0°F to 3°F above normal from western Minnesota south through western Kansas (Figure 1). In contrast, temperatures were 10°F to 12°F above normal in the Ohio Valley.
Precipitation was exceptional this week throughout all but northwestern Minnesota through northwestern Wisconsin, where conditions were generally dry. Elsewhere, precipitation this week was from three to seven times normal, with the heaviest amounts from western Illinois through northern Ohio (Figure 2). Most locations in the central Midwest received twice the normal precipitation for the month of February in the course of two days. The precipitation was mostly snow from northwestern Missouri eastward across southeastern Iowa, northern Illinois, southern Wisconsin, and lower Michigan (Figure 3), while areas to the south received heavy rain. The recent precipitation is rapidly diminishing the last vestiges of drought in the Midwest with the exception of northwestern Minnesota, northern Wisconsin, and the Michigan Upper Peninsula where the frequency of precipitation has been less (Figure 4). The greatest improvement was in southeastern Kentucky, where drought status improved one category.
February Begins with Snow
A major winter storm spun up over northern Texas on January 31 and took aim on the Midwest. On the morning February 1 residents from Missouri to Michigan woke to a blanket of snow. The low pressure center's path from Texas through Arkansas and into the Ohio Valley placed much of the central Midwest in the band of heaviest snow (Figure 5). Snowfall in excess of 12 inches occurred from southwestern Illinois northeastward into the Chicago area (Figure 6).
There was only a brief respite from the winter weather before the next weather system affected the area. On February 3 another low pressure system was organizing over the Central Plains. As this system intensified warmer air began to push northward through the Midwest. The warmer air, combined with an upper level disturbance, set off convection from Missouri through Illinois. In southern portions of the region there were thunderstorms with rain, and a few reports of dime to quarter size hail in central Missouri and southeastern Illinois. In central Missouri through central Illinois the thunderstorms were reported with sleet, freezing rain and some snow. "Thunder snow", a generally rare occurrence, was reported in a band from southeastern Iowa through northeastern Illinois including the Chicago metropolitan area. Snow fell at rates up to 3 inches per hour, reducing visibility to near zero and snarling travel. More than 250 flights were cancelled at Chicago's O'Hare International Airport and flight delays grew to more than two hours. More than a foot of snow was reported in south-central Iowa with Bussey, IA (Marion County) reporting 13 inches. Three to five inches of snow fell in northern Illinois. On the morning of February 4 more than four inches of snow blanketed the ground from north-central Iowa through the northern two-thirds of Illinois and Indiana (Figure 7).
Prelude to a Storm - Dense Fog Shrouds Midwest
A very dense fog with horizontal visibilities of less than 1/4 mile occurred over a wide area of the central Midwest, extending from eastern Iowa through central and northern Illinois to northern Indiana and southern Michigan (Figure 8). Warm, moist air streaming north over the snow cover caused significant melting. The combination of the cold snow surface, warm surface temperatures, and plentiful moisture available from the snow melt led to this unusual fog event. The temperature contrast from north to south over the Midwest was remarkable, with high temperatures on February 4 in the 30s and 40s from southern Iowa across central Illinois and northern Indiana. South of the snow covered area, high temperatures reached the mid 60s to mid 70s from central Missouri through the Ohio Valley (Figure 9). The dense fog developed overnight February 3-4, with visibilities generally less than 1/4 mile, and conditions deteriorated during the day. This event was unusual in that the very dense fog occurred during the afternoon and early evening hours and persisted in many locations for more than 6 hours (Figure 10). The fog brought air travel to a standstill and driving conditions were extremely hazardous. There were numerous traffic accidents throughout the Midwest as a result of the fog, a few with fatalities.
Heavy Rain, Heavy Snow, Severe Thunderstorms
The fog lifted late on February 4 as cooler air pushed south through the Midwest. A low pressure developing in Texas on the leading edge of the cold air began moving northeastward. Late on February 4 a variety of watches and warnings covered all or parts of the nine-state Midwest region. Winter storm watches were in effect for areas north of a Kansas City, MO to Detroit, MI line. South of this line, flood watches and a severe thunderstorm watch were in effect (Figure 11). On February 5 (Figure 12) the Storm Prediction Center outlook targeted the Ohio River Valley and areas south for a Moderate to High Risk of severe weather and was expecting a major severe weather outbreak (Figure 13).
Heavy rain developed along and just behind the front from central Missouri to northwestern Ohio and south to the Ohio River. The rain continued throughout February 5, and by the morning of February 6 more than two inches of rain had fallen across a large area south of a line from St. Louis, MO to Cleveland, OH (Figure 14). For many locations the two-day rainfall total was more than the normal February monthly precipitation. As expected, a major severe weather outbreak occurred during the day from southern Missouri through southern Illinois, Indiana, and Ohio, and south through Kentucky and much of the south-central U.S. There were more than 130 reports of tornadoes in this outbreak, with most occurring from Arkansas east through Tennessee. More than 24 tornadoes were reported in Kentucky alone. Two of the tornadoes in Kentucky, one in Muhlenberg County and one in Allen County, caused a total of nine fatalities and numerous injuries. Tornadoes were also reported in Indiana and southern Missouri. Most of the severe weather reports in the southern Midwest (outside of Kentucky) were for damaging winds, some gusting in excess of 80 mph and causing widespread tree damage and downed power lines. Semis were blown over on Interstate 57 near Salem, IL (Marion County). A gust to 82 mph was reported near Terre Haute, IN (Vigo County).
While severe thunderstorms hammered the southern Midwest and rain soaked the central portions, heavy snow was falling from northwestern Missouri through southern Iowa and then across northern Illinois, southern Wisconsin, and lower Michigan. Many locations in this band received 6 to 10 inches of snow, but the snow was heaviest along the Illinois-Wisconsin border, where more than 12 inches of snow piled up across southeastern Wisconsin and northern Illinois on February 5-6. The highest amount reported was 21 inches of snow near Orfordville, WI (Rock County) (Figure 15, Figure 16). Thousands of motorists were stranded in the snow for up to 12 hours on February 6 along a stretch of Interstate 39-90 between Madison and Janesville, WI, which was in the band of heaviest snow. The backup was 19 miles long, and occurred when semis lost traction on a small hill in the westbound lane. The Wisconsin State Patrol said it did not learn of the backup until hours after the first vehicle became stuck. More than 2,000 vehicles were stranded or stopped on both sides of the four-lane Interstate Wednesday night February 6 and early morning on February 7. Officials reported that over 1,000 flights were cancelled at Chicago's O'Hare International Airport on February 6.
Aftermath - Widespread Flooding
The period of briefly milder weather and the heavy rain caused rapid melting of the snow on the ground on February 4-5 in central portions of the Midwest. The southern extent of the snow retreated to central Iowa, northern Illinois, extreme northern Indiana and northwestern Ohio by the morning of February 5 (Figure 17). The melting snow, heavy rain from this storm, and mostly frozen ground led to rapid runoff to rivers and streams, resulting in flooding on many rivers and streams from Illinois to Ohio. Roads were closed due to flooding in Illinois, Indiana, Kentucky, Missouri, and northwest Ohio. On February 7 major river flooding was occurring in Indiana, and moderate river flooding was occurring in Illinois, Missouri, and northwest Ohio (Figure 18). For some portions of eastern Illinois and western Indiana this was the second major flood event this winter. Residents of Findlay, OH along the Blanchard River were coping with the second major flood in the last six months. For most smaller rivers and streams, water levels began to decline late on February 7. However, moderate to major flooding continued on the Illinois River (Illinois) , the Wabash River (Illinois/Indiana), and the Kankakee and Tippecanoe Rivers (Indiana).
SDH
Data and maps on dense fog compiled by Nancy Westcott, MRCC