Hailstorm Climatology for Central and Southwestern Kansas

by
Jonathan Finch
Meteorologist
National Weather Service
Dodge City, KS

There are 27 counties served by the Dodge City National Weather Service office. This area encompasses Scott City, Syracuse, Elkhart and Liberal in the west, Hays, Stafford, Pratt and Medicine Lodge in the east, and Dodge City, Ness City and Ashland in between. The number of days with at least 1 report of golfball or larger sized hail were counted for each 1/3 month period through each year from 1955 to 2008. For example, for June 1957, the number of days with at least 1 report of golfball or larger sized hail were counted for June 1-10, June 11-20 and June 21-30. These results are graphed below.

There were no reports of golfball or larger sized hail in any November to January period from 1955 to 2008. There was only one report in February and this occurred on February 24, 2000. There has been only 1 report in late October. So large hail is extremely rare from late October through February. During this time of year, severe weather tends to occur in states such as Mississippi and Alabama where moisture from the Gulf of Mexico is occasionally abundant and the jet stream is strong. Southwest Kansas has a fairly dry and cool climate during this period although significant snowstorms and even an occasional rainy day can occur.

The frequency of hailstorms increases only slightly in March, but more so by mid April when 14 days with at least 1 report of golfball or larger sized hail have occurred. This number shoots up to 38 by early May, 57 by late May and 53 in early June. The most favorable time of the year for large hail for the Dodge City area of forecast/warning responsibility is mid June as there have been 73 days with at least 1 report of golfball or larger hail since 1955. In years with active mid June periods, there tends to be multiple days in a row of active weather. The same is not true of April and early May when severe weather tends to progress across the region followed by a cold front that sweeps the moisture away. So why are May and June the most active months for large hail? During these months, the sun is becoming much higher in the sky so that the air near the ground becomes much warmer. However, the air in the upper troposphere (where airplanes fly) is still fairly cold since this part of the troposphere warms up last (there is a lag time). As a result, there is a sharp difference in temperature from the surface of the earth up to the jet stream level. This difference in temperature is called the “lapse rate”. When lapse rates are large, the chances for severe weather increase provided there is sufficient moisture from the Gulf of Mexico at low levels (surface to 4000 feet above ground level). Deep, rich moisture return from the Gulf of Mexico tends to occur at about the same time that the lapse rates are becoming steep. Finally, although the jet stream weakens some by late spring, it is still strong enough to promote severe storm development. This means that high lapse rates, rich low level moisture and the jet stream overlap to the greatest extent in May and June. In the winter, the jet stream is strong but the other ingredients are lacking. Deep into summer, the warmth and moisture are often present at low levels, but the jet stream has typically retreated into the northern United States and Canada by this time. Also, lapse rates tend to decrease in summer due to the delayed warming of the upper troposphere.

Late June is still fairly active, with 43 days of at least 1 report of golfball or larger sized hail. Interestingly, there are more days with golfball or larger hailstorms in late June (43) than early May (38) or mid May (38). This is probably because there are more days with isolated storms in late June in general. While some ferocious severe weather outbreaks can occur in early and mid May, strong cold fronts can often lead to stable conditions in May for extended periods of time. So outbreaks of severe weather are often intense but less frequent in early to mid May. However, hail events in mid to late June are generally more isolated than in April or early to mid May and can occur on several days within a period of a week.

Even in the dog days of summer, severe storms are no stranger to southwest and central Kansas. In July and August, there have been 75 and 51 days respectively with at least one report of golfball or larger sized hail. It may come as a surprise to some that large hail is more common in August (54 days) than in March (13 days) or April (33 days). But compared to June, severe weather is definitely on the decline in July since the high level jet stream becomes very weak.

Next, the number of days (shown in the graph below) in which there was at least 1 report of golfball or larger sized hail in Dodge City’s 27 county warning area for each year from 1955 to 2009 were counted.

This graph shows clearly that there are many more days after 1991 in which golfball size or larger hail was reported. This is likely due to National Weather Service modernization which resulted in greater staffing and an increased push to warn for severe storms and then seek ground truth severe weather occurrences. In fact, 47% of the large hail days in southwest Kansas have occurred in the 14 years from 1995 to 2008. The other 53% occurred from 1955 to 1994. Also, 72% of the large hail days occurred in the 27 year period from 1981 to 2008, but only 28% in the 26 year period from 1955 to 1980. Some improvement in hail documentation occurred in the mid 1970s but it is unclear as to the exact reason. Possible reasons for the apparent further increase in large hail reports since the late 1990s include a large increase in the number of storm enthusiasts, the increased use of rural phone directories by the National Weather Service during warning verification, and heightened severe weather awareness by the local communities.

Despite the differences in reporting practices, some years clearly stand out from the others, with some being more active and some less active. For example, 1958 and 1959 were active compared to the years before and after. 1967 and 1968 were active years as well. It would be very interesting to see how these years would compare to recent years using modern methods and technology. 1960, 1972, 1976 and 1978 were fairly inactive years in terms of very large hail, while 1977 and 1986 were very active. 1988 and 1990 were extremely inactive, especially given the increased reporting during these years. Further research would probably show that the storm track was north of our area during the spring and summer of 1990 since this was an active severe weather year from northeast Colorado into Nebraska. 2000 and 2005 were less active than adjacent years. Interestingly, the most active year so far was 2008 as there were 25 days with at least 1 report of golfball or larger sized hail!


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