The coldest air of the 2008-2009 winter spread across much of the United States this week as a large area of surface high pressure dropped southward out of Canada. While this wasn't the first arctic blast of the winter, the impacts of this cold air were felt across a much broader area of the country. Low temperatures have bottomed out well below zero with several locations across North and South Dakota as well as Minnesota and Wisconsin experiencing mininum temperatures -40F at times. Life-threatening wind chills also accompanied this cold air, with wind chill readings as low as -60 below in portions of the country. Several records were broken across the Midwest. For more information on how the cold weather impacted other areas of the Midwest, please visit the following stories by fellow NWS offices:
NWS-Omaha/Valley -"Brr! Cold temperatures on January 15!"
NWS-Sioux Falls, SD - "Coldest Temperatures Since 1996 this Morning"
NWS- Duluth, MN - "How Cold Was It?"
NWS- Milwaukee, WI - "Coldest Weather in 9-13 Years?"
NWS - Chanhassen/Minneapolis, MN - "How Cold Were the Wind Chills..."
Locally, much of Missouri and northeastern Kansas fell below zero on the morning of the 15th. The coldest readings were located along the Iowa border where local snow cover in southern Iowa allowed temperatures to radiate cooler than in other areas further south. Some locations which experienced double digit below zero temperatures included: Albany (-10F), Conception (-11F), Gallatin (-10F), Maryville (-10F), Tarkio (-10F), Downing (-12F), Kirksville (-11F), Linneus (-10F), Princton (-10F), Spickard (-10F). The coldest readings recorded by NWS cooperative observers were located at Green City and Unionville where readings dipped as low as -13F.
Colder air wasn't just isolated to northern Missouri, Kansas City International reached a low temperature of -6F, Kansas City Downtown Airport bottomed out at -2F, Chillicothe reached -7F, and even the city of Sedalia reached -3F.
What truly made this spell of cold weather unusual was the fact that nearly all of the state of Missouri and Kansas were without snow cover, a usual precursor to below zero temperatures for this portion of the country. Below is an national snow depth map generated by the National Operational Hydrologic Remote Sensing Center as of 12am January 15th. The map concurs with the coldest readings during the event, which were located across the deeper snow pack of the Dakotas, Minnesota, and further east into the Great Lakes region.
|National Snow Depth (click to enlarge image)|
Taking a more in-depth into this forecast oddity, focuses our attention to Kansas City given its extensive observation history. Compiling a listing of days in which the minimum temperatures dropped below zero and comparing that data to observations of snow depth/cover revealed that from the period of time from 1990-2008 Kansas City reached below zero 52 times. Of those 52 days, there were only 6 days where there was no snow on the ground indicating Kansas City has an 11.5 percent chance of reaching below zero with no snow on the ground. When you increase the amount of snow depth to 1 inch or less of snow (15 days out of 52), the percentage begins to increase with a 25% chance of below zero temperatures.
Expanding the dataset to 1973 revealed a total of 118 days with readings below zero. However of note, the probabilities of reaching below zero decreases in the expanded dataset with only a 6.9 % chance of reaching below zero with no snow cover. If we increase the amount of snow up to an inch, the probabilities double, proving just how valuable having snow and how deep the snow is to forecasting temperatures in the wintertime.
|Kansas City Below Zero Climatology|
|Period of Time||Number of Days Below Zero||Number of Days With No Snow (probability of occurance)||Number of Days with 1 inch or less (probability of occurance)|
|1990-2008||52||6 (11.5%)||15 (25%)|
|1973-2008||118||13 (6.9%)||31 (16.5%)|
We can also take a glance at the data from 1973-2008 in regards to how ENSO factors into our probabilities of having a below zero temperatures with little or no snow. Looking back through the ENSO phases in the 31 days of below zero temperatures with an inch or less of snow, there is some indication that below zero temperatures are more likely to occur when La Nina/Neutral conditions prevail. In fact, only 5 of the 31 days occurred when El Nino conditions prevailed, likely indicative of below normal snowpack favored across the Northern Plains.
|La Nina||Neutral||El Nino|
Kansas City minimum temperature of -6F on January 15th marked the coldest readings observed in the local area since January 2003 when the temperature dropped to -9F. Below is a listing of the 15 coldest days since 1990 in Kansas City.
Date MinT Snow on Ground
1/28/1997 -14F 5"
2/3/1996 -12F 0"
2/2/1996 -11F 0"
1/7/1996 -10F 5"
1/23/2003 -9F 2"
12/22/2000 -9F 5"
3/12/1998 -7F 4"
2/4/1996 -7F 0"
1/19/1996 -7F 4"
1/15/2009 -6F 0"
1/2/2001 -6F 4"
1/11/1997 -6F 1"
2/18/1993 -6F 4"
1/30/1991 -6F 4"
1/26/1991 -6F 6"
12/22/1990 -6F 1"
**Statistics and Story compiled by General Forecasters Matthew Dux and Mark O'Malley of the Kansas City/Pleasant Hill WFO