Below zero characteristics for Central, South Central and Southeat Kansas

Assessment of Snow Depth Characteristics During Extreme Cold Events in Central, South-central, and Southeast Kansas

Kenneth R. Cook and Austin Colbert
National Weather Service, Wichita Kansas

April 09, 2008

1.0 Introduction

Extreme cold is a significant threat to persons living in this region of the country. Given its low frequency; humans, animals, etc., are not acclimated to weather extremes such as these. This study was completed in an attempt to give operational forecasters additional insight into the role that snow depth plays in forecasting extreme cold events to improve customer service.

2.0 Methodology

Observation sites used were identified by location and/or length of station record. These were, Russell (KRSL), Salina (KSLN), Hutchinson (KHUT), Wichita, (KICT), and Chanute (KCNU). Data were gathered for these sites using the xmACIS climate database, which is a quality controlled database that utilizes official observational data. Table 1 shows the date range used for each station. This enabled us to maximize the number of cases for this study.

Station	Year
KRSL	1950 - present
KSLN	1949 - present
KHUT	1948-1959
KICT	1954 - present
KCNU	1942 - present

Table 1: Date periods available and used for each station studied.

For the purpose of this study, extreme cold was defined as a minimum temperature of zero degrees Fahrenheit or below. From the 5 stations used, 817 cases were identified using this definition. Data were then sorted by snow depth, a measurement of how deep the snow is which covers the ground at 12 UTC (or 6 am local time). Comparisons were drawn from these data. A second assessment of extreme cold was studied, examining days where the maximum failed to exceed zero degrees Fahrenheit.

3.0 Results and Discussion

Snow cover was analyzed to ascertain its role in forecasting extreme cold events. Snow was chosen for study due some of its properties. More specifically insulation, radiation, and albedo, which contribute significantly to the lowering of daytime maximum temperatures and nighttime minimum temperatures.

Assessing the 817 cases in the area of study yielded a result that largely favored snow cover being present to observe a minimum temperature less than or equal to zero degrees Fahrenheit as depicted in table 2. In fact, only 10.5 percent of the cases contained a 0 snow depth, meaning that 89.5 percent of the cases contained a snow depth of a trace or greater. Furthermore, 77.3 percent of the cases occurred when a snow depth was at least one inch.

Snow Depth	Percent of Observations Zero Degrees F or Below
0"	10.5
Trace	12.2
Trace or Greater	89.5
1" or Greater	77.3

Table 2: Percent of observations for a given snow depth.

The second assessment of maximum temperatures at or below zero degrees Fahrenheit produced a similar result. A total of only 20 cases were identified. All of the these cases occurred during a period of snow depth of at least one inch, with the mean snow depth being 5.4 inches. Of the 20 cases, 13 occurred during one event, the arctic outbreak of 1983, which is one of the coldest, deepest penetrating arctic outbreaks to have occurred east of the Rocky Mountains in U.S. History. Table 3 shows the distribution of these cases.

Year	Occurrences
1983	13
1989	6
1990	1

Table 3: Year and number of occurrences of maximum temperatures at or below zero in the area of study.

Extreme cold is a significant threat to persons living in this region of the country given our limited exposure to it. The mission of the National Weather Service (NWS) is to provide a service to the public where warnings and advisories cause decision makers and the general population take actions that will be life saving. This material is a continued effort by the science community within the NWS to further that mission.