National Weather Service Weather Forecast Office

Information Courtesy of Dr. Mark Seeley
Professor and Extension Climatologist/Meteorologist 
University of Minnesota Extension - Dept of Soil, Water, and Climate
http://www.climate.umn.edu/Seeley/

High Dewpoint Records for May

Tuesday, May 10th was quite a day in Minnesota. During the afternoon strong southeast winds brought in very warm, moist air across southern counties. Many observers reported near-record setting or record setting temperatures in the 90s F, spiking between 4:00 and 6:00 pm.

Some of the record-setters included:

Waseca 92 F (tied record for May 10th in 1987)
Wells, St James, and Fairmont 93 F
Amboy and Winnebago 96 F

The readings at Amboy and Winnebago were just shy of the all-time state record for May 10th of 97 degrees F at Beardsley in 1928.

Even more impressive than these high temperatures was the rise in dewpoints. Many observers reported record high dewpoints by late afternoon, including Minneapolis St. Paul International Airport which reached a July-like 70 degrees F. Windom, Fairmont, St James, and Faribault also reported dewpoints of 70 degrees F. Even higher dewpoints occurred at Hutchinson (73 F), Albert Lea (74 F) and Waseca (78 F).

These numbers are incredible amounts of water vapor for the first half of May. In some cases they pushed the Heat Index Value (combination effect of temperature and dewpoint) to 100 degrees F or higher.

It is believed that the Waseca dewpoint of 78 degrees F is the highest ever measured in the month of May. In the MSP historical records dewpoints of 70 degrees F or higher during the first half of May have only been reached in 1912, 1916, and 1962.