National Weather Service Weather Forecast Office

The persistent heat wave over much of the central and northern U.S. came to an end on Wednesday (7/20) as a weak cold front moved across the area.  This cold front dropped temperatures back to near mid-July averages, and more importantly brought a much drier airmass into the region.  For an interesting visual animation of this heat wave over the U.S., click HERE.

Below are a several other interesting facts about this recent heat wave:

• This was the worst heat wave to affect central and northeastern South Dakota and west-central Minnesota since July 2006.  Beginning on Friday July 15th and persisting through Wednesday July 20th, many locations saw high temperatures rise into the 90s to low 100s, with low temperatures only falling into the 70s each night.
• In addition to the hot temperatures, humidity levels during this heat wave rose to extreme levels at times.  Surface dewpoint values were commonly in the mid-70s Fahrenheit, which most people percieve as uncomfortable.  However, at times dewpoint values soared into the 80-83F range, which when combined with temperatures in the 90s to near 100 F, lead to very oppressive heat indicies.  For a more detailed look at the maximum daily heat indicies, click HERE.
• Although not considered official weather records, the extremely high dewpoint temperatures recorded during this heat event were likely some of the highest values ever recorded in South Dakota.  Research is ongoing to verify this fact.  Below is summary of the highest dewpoint values recorded during this event:

   * Multiple cccurrences of this value.  The date/time of the last occurrence is noted.

•  Several locations experienced their first 100F readings of 2011 (see chart below).  In Aberdeen, this was the first time temperatures exceeded 100F since July 2007.