Author Topic: The Crazy Dew Point Day!  (Read 2347 times)

0 Members and 1 Guest are viewing this topic.

Offline Jim's Weather

  • Forecaster
  • *****
  • Posts: 330
The Crazy Dew Point Day!
« on: August 22, 2014, 05:27:10 PM »
I was working at the FCWOS (FAA Contract Weather Observing Station) at the Cedar Rapids Municipal Airport on July 13, 1995. I had never seen the dew point go over 80 degrees before. I went to take the 4 pm weather readings and looked at the hygrothermometer. It was indicating the dew point was 84 degrees. I was in disbelief and figured the HO83 sensor was malfunctioning. So I decided to take a manual reading with a sling psychrometer. When I walked outside I found it was slightly difficult to breathe it was so humid. I spun the psychrometer for 2 minutes. I read the dry bulb and it said 100 degrees. That matched what the hygrothermometer said for air temperature. Then I read the wet bulb and it said 87.5 degrees. The wet bulb is not the dew point. The dew point is calculated from the wet and dry bulb and station pressure readings. Next I had to calculate the station pressure. The station pressure is the barometric pressure not reduced to sea level. That came out to 29.027 inches. I went back inside and entered the wet and dry bulb and station pressure readings into the computer. It spit out 84.04 degrees for the dew point. So it was correct!

That was not the highest dew point of the day. At the 8 pm observation the dew point had climbed to 87 degrees. Once again I checked the hygrothermometer readings with the manual instruments. It was correct! Both observations are below. The first observation recorded the highest heat index of the day. The second observation recorded the highest dew point of the day. The high temperature for the day was 100F. The low temperature the following morning was 80F.


Weather observed at Cedar Rapids Municipal Airport, Cedar Rapids, IA July 13, 1995 15:52 CDT

CID SA 2052 CLR 10 133/100/84/1609/995

Sky/Wx: Clear
Visibility: 10 miles
Temperature: 100F
Dew Point: 84F
Relative Humidity: 61%
Wind 160 at 9 knots
Altimeter Setting: 29.95"
Heat Index: 131F

Remarks: None


Weather observed at Cedar Rapids Municipal Airport, Cedar Rapids, IA July 13, 1995 19:52 CDT

CID SA 0052 CLR 10 123/94/87/1606/992

Sky/Wx: Clear
Visibility: 10 miles
Temperature: 94F
Dew Point: 87F
Relative Humidity: 80%
Wind 160 at 6 knots
Altimeter Setting: 29.92"
Heat Index: 129F

Remarks: None


Iowa Climate Review July 1995 by Iowa State Climatologist Harry Hillaker

Temperatures: Easily the greatest weather event of the month was the mid-month heat wave. Temperatures edged into the low 90's over far western Iowa on the 8th marking the end of a prolonged period of unseasonably cool weather. The heat quickly intensified with Glenwood reaching 100 on the 10th. This marked the end of an amazing streak of nearly 4 years without any 100 weather in Iowa. Specifically, 1,438 days passed since temperatures lasted reached 100 on August 2, 1991, far surpassing the previous Iowa record of 715 consecutive days without 100 heat set between June 25, 1950 and June 11, 1952. A few more 100 readings followed in far southwest Iowa on the 11th as 90's spread through nearly all of the rest of the state. The next two days brought incredible combinations of heat and humidity never seen before across all of Iowa. Actual temperatures reached 108 in Sioux City on the 12th, the highest reading in Iowa since August 15, 1988, while heat indices exceeded 114 at all major Iowa reporting points on either the 12th or 13th. Dewpoint temperatures were in the 80's over eastern Iowa. Cedar Rapids recorded a 100 air temperature with an 84 dewpoint temperature to combine for a heat index of 131 at 4 pm on the 13th. Temperatures finally fell to near seasonal levels by the 16th. After a brief respite from the heat above normal temperatures returned to most areas from the 22nd through the end of the month. On the other extreme, record lows were recorded in many areas at the beginning of the month with a state low of 41 at Elkader on the second.

More information:

« Last Edit: April 27, 2015, 11:28:44 AM by kcidwx »
Meteorological Technician
NWS Certified Aviation Weather Observer
B.S. Meteorology

Offline SlowModem

  • Weather at the speed of dialup!
  • Forecaster
  • *****
  • Posts: 6641
  • WX @ 26.4 kbs
    • Watts Bar Weather
Re: The Crazy Dew Point Day!
« Reply #1 on: August 22, 2014, 09:04:45 PM »
Looking back, the best I can do is 84F DP, August 2010.
Greg Whitehead
Ten Mile, TN USA

Offline chief-david

  • Educational Weather
  • Forecaster
  • *****
  • Posts: 2764
  • Space Academy for Educators
    • Benilde-St. Margaret's Weather
Re: The Crazy Dew Point Day!
« Reply #2 on: August 22, 2014, 10:24:48 PM »
terrible summer.

I think Dallas has 3 weeks over 100.   I was in KC and there were at least 2 weeks over 90.

Terrible humidity. We moved to back to Iowa later that year. We all were soaked after the move.

Right now-I have an acurite that is reading -35 dew point.   I think it needs some work.
« Last Edit: August 22, 2014, 10:50:56 PM by chief-david »

You can't phase me-I teach Middle School.
It's not you-It's WU.