We talked Monday about the incredible amount of humidity in the air to go along with this massive heat wave and its impact on our “feels like” condition, or heat index. Today’s heat indices will be similar to those we experienced on Monday with 110 to 120 likely through the day into the evening thanks to dew points in the lower and even middle 80s and high temperatures in the 90s. I can’t underscore how unusual this humidity is for our area as 82° and 83° dew points are way above anything we normally deal with. Upper 70s are more typical and maybe for just a handful of days through the entire season, not a long stretch like this. We actually even set a record for the highest heat index in Rochester history with a reading of 118 just after 5:00pm Monday! Incidentally, our current Excessive Heat Warning will remain in effect until 9:00 Thursday evening so we can expect more of this intense, oppressive heat for another couple of days.
Here’s a summary from the National Weather Service in La Crosse of our area’s historical humidity and heat index records. This is from NWS climatologist Jeff Boyne:
Looking back at the hourly temperatures and dew points back to 1948, I could only find 3 days in which the heat index topped out above 110F.
Yesterday (July 18) was the highest one with a heat index of 118F
Temp Dew Point Heat Index
July 18 2011 4:54 PM 94°F 82.9 °F 118F
July 11 1980 4:00 PM 97.0 °F 77.0 °F 113F
July 13 1995 5:00 PM 98.1 °F 75.0 °F 111F