Just how rare is this heat in the Twin Cities?

The high temperature barely missed hitting the century mark in the Twin Cities on Monday as the mercury peaked at 99 degrees.  However, this did break the previous record of 96 degrees set over a century ago in 1911.

Just how often do we see these hot temperatures in the Twin Cities?  In the past 30 years, the temperature reached 100 degrees or more only 10 times.  That is once every three years on average.  The most recent 100 degree or higher reading was last year on June 7, when the temperature hit 103 degrees.  In most cases to top triple digits, a lower dew point, below the mid-60s, is needed for air to mix down to the surface efficiency.  Not often do you see temperatures greater than 100 when the dew point is at 70 degrees or more.  Here is a look at a few case studies:

On June 7, 2011, temperatures climbed as the dew point decreased.  Temperatures reached the 100 degree mark when the dew point dropped into the high 50s.  A humidity level in the “comfortable” range for most people.

The opposite was found to be true on July 31, 2006.  On this day, the maximum temperature of 101 was obtained as the dew point was rising steadily.  At 4 pm, the dew point was 68 degrees as the temperature peaked.  Would the temperature have hit 100 if the dew point was at 70?  Close call, but probably not.  98 or 99 degrees would have been more likely in that instance.

Jumping back over 10 years from 2006 to 1995 was the next occurrence of temperatures 100 degrees or greater.  July 13 was the date as temperatures soared to 101 degrees yet again.  This was one of the few times where the temperature hit 100 degrees as the dew point was over 70 degrees.  When this happened at the 4 pm hour, the dew point observation was 71.  The heat index was 109.

Monday’s 99 degrees was reached as the dew point was 67 degrees at the 6 pm hour.

RS