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Unseasonably Cool Temperatures in May - Summary
With normal high temperatures in the low to mid 70s, the middle of May is supposed to be the heyday of spring in the Ohio Valley. From May 16th-18th 2011, however, the weather resembled more of early April. The culprit was an unseasonably deep and stagnant area of low pressure which became detached from larger scale wind patterns across the Northern Hemisphere. These "cut-off" lows (appropriately named due to the low pressure becoming cut off from the larger scale flow and becoming nearly stationary) are not uncommon in the Ohio Valley and western Great Lakes during the middle and late spring, but their presence is seldom welcome.

This particular low pressure brought a period of wet, cloudy weather to the region, and record low temperatures. Several days of occasional light rain and drizzle, thick clouds, and cold air aloft associated with the low pressure were the primary contributors to the spate of cool weather.

While precipitation was not overly heavy, the thick clouds prevented solar insolation from reaching the surface, keeping daytime temperatures in particular on the cool side. On the flip side, the thick clouds held in heat at night, thus the records that were broken were not record lows, but instead were record low maximum temperatures, meaning the daytime highs were the lowest high temperatures ever recorded for certain dates.

Low Pressure - Graphically

In the following image is a water vapor satellite image, overlaid with atmospheric heights of the 500mb surface, which is a field meteorologists use to look for areas of high and low pressure aloft. The cut-off low pressure is clearly seen sitting over Ohio, with the trademark swirl of thicker clouds and higher moisture rotating well north of the low. Directly underneath the low, there are often widespread low clouds, and cool temperatures.

satellite image

Record Low Maximum Temperatures

As discussed above, these systems very rarely produce record low minimum temperatures, but often times produce record low maximum (afternoon high) temperatures due to the thick clouds, drizzle, and cool temperatures aloft associated with these systems. Below is a summary of the 3 days of cool temperatures that affected the Ohio Valley from May 16th through May 19th 2011.

May 16 2011 (Image courtesy National Climatic Data Center)


May 16th Record Low Maximum Temperatures

In the image above, are locations in Indiana, Kentucky, and Ohio that broke their record low maximum temperatures for the date. An "X" through the blue dot is a record that has been broken, otherwise it is a tied record. The observations are a combination of automated weather observations at local airports, and cooperative observers across the area. A complete map and table of this data is available by following this link.

May 17 2011 (Image courtesy National Climatic Data Center)


Record low maximum temperatures for May 17th

In the image above, are locations in Indiana, Kentucky, and Ohio that broke their record low maximum temperatures for the date. An "X" through the blue dot is a record that has been broken, otherwise it is a tied record. The observations are a combination of automated weather observations at local airports, and cooperative observers across the area. A complete map and table of this data is available by following this link.

May 18 2011 (Image courtesy National Climatic Data Center)

Record Low Maximum Temperatures May 18

In the image above, are locations in Indiana, Kentucky, and Ohio that broke their record low maximum temperatures for the date. An "X" through the blue dot is a record that has been broken, otherwise it is a tied record. The observations are a combination of automated weather observations at local airports, and cooperative observers across the area. A complete map and table of this data is available by following this link.

Records at Local Climate Sites

The cool temperatures affected the 3 main climate sites in the NWS Wilmington, OH, forecast area. Below is a summary of the records tied or broken

Dayton

 Maximum Temperatures
DayHigh TemperatureStanding
May 16th 201151
2nd Coolest (49 in 1940)
May 17th 201149
RECORD (previous 51 in 1915)
May 18th 201157
7th Coolest (49 in 1981)

Cincinnati


 Maximum Temperatures
DayHigh TemperatureStanding
May 16th 201154
2nd Coolest (52 in 1893)
May 17th 201151
RECORD (previous 54 in 1915)
May 18th 201158
4th Coolest  (54 in 1904)

Columbus


 Maximum Temperatures
DayHigh TemperatureStanding
May 16th 201149
RECORD (previous 50 in 1927)
May 17th 201151
RECORD (previous 52 in 1915)
May 18th 201161
10th Coolest (49 in 2002/1945)


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Wilmington Ohio Weather Forecast Office
1901 South State Route 134
Wilmington, OH 45177
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Page last modified: May 19, 2011.
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