Hot, Humid Weather: How US Cities Compare

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The information here tells how often heat combines with humidity at America's largest cities to create uncomfortably muggy weather.

When humidity climbs above 40 percent, the damp air makes any temperature over 80 degrees Fahrenheit (26.7 degrees Celsius) feel hotter than what the thermometer actually reads.

The apparent temperature, also known as the Heat Index, measures how hot the weather really feels, considering both temperature and humidity. For instance, a temperature of 90 °F (32.2 °C) along with 60 % humidity pushes the apparent temperature to a sweltering 100 °F (37.8 °C).

Days of High Apparent Temperature

The table here lists the number of days when the apparent temperature or Heat Index equalled or rose above 95, 105 or 115 °F (35, 40.6 or 46.1 °C) for at least an hour.

The totals cover the 30 years from 1978 to 2007 for the largest cities in the United States. Major cities missing from the list due to lack of data are Austin TX, Boston MA, Detroit MI, Las Vegas NV, Milwaukee WI, Portland OR, Riverside CA and San Jose CA.

Number of days with apparent temperature, 1978 2007
City 95+ °F 105+ °F 115+ °F
Atlanta, Georgia   804     55   5
Baltimore, Maryland   603     75   2
Birmingham, Alabama 1367   106   2
Buffalo, New York     39       3   0
Charlotte, North Carolina   758     24   0
Chicago, Illinois   375     60   3
Cincinnati, Ohio   407     27   0
Cleveland, Ohio   182     14   1
Columbus, Ohio   285     15   2
Dallas, Texas 2467   352   4
Denver, Colorado       7       0   0
Hartford, Connecticut   251     20   2
Houston, Texas 2917   460 11
Indianapolis, Indiana   462     53   2
Jacksonville, Florida 2484   300 11
Kansas City, Missouri 1030   211   7
Los Angeles, California     12       0   0
Louisville, Kentucky   831   108   4
Memphis, Tennessee 1832   363 11
Miami, Florida 3098     72   0
Minneapolis, Minnesota   262     35   0
Nashville, Tennessee   991     74   1
New Orleans, Louisiana 2560   463 18
New York, New York   332     31   1
Oklahoma City, Oklahoma 1606   185   1
Orlando, Florida     –   120   2
Philadelphia, Pennsylvania   550     72   4
Phoenix, Arizona 3370 1060 12
Pittsburgh, Pennsylvania   134     10   0
Providence, Rhode Island   194     21   0
Raleigh, North Carolina 1002     88   0
Richmond, Virginia 1005   146   3
Rochester, New York   150     11   0
Sacramento, California   683     68   2
Salt Lake City, Utah       7       0   0
San Antonio, Texas 2659     89   1
San Diego, California     13       2   1
San Francisco, California       5       0   0
Seattle, Washington       6       0   0
St. Louis, Missouri 1068   212   7
Tampa, Florida 3129   204   3
Virginia Beach, Virginia   927   107   1
Washington, DC   609     56   3

Hot Days Due to Humidity

Humidity takes hot weather to the extremes more often in some cities than others.

The table below gives the difference in number of days between apparent temperature and actual temperature. This shows how often high humidity pushed the Heat Index above a certain level from 1978 to 2007.

For example, on 54 days in Atlanta, although the thermometer hadn't reached 105 °F, the humidity was so high that the temperature felt at least like 105 for an hour or more.

Negative numbers mean that more commonly dry air brought the apparent temperature below the actual thermometer reading. In San Diego, for instance, although the thermometer climbed to 95 °F on 16 days, the humidity was low enough on three of those days to make the heat feel cooler than 95.

When compared with the table above, you'll see that all the days when the apparent temperature reached 115 °F or more are due to humidity at every city except Phoenix. That means the thermometer never actually reached 115 at those cities, but the muggy air sure felt at least that hot.

Similarly, humidity has the biggest influence on making the weather feel 95 °F or hotter in Miami and Tampa, Florida. The sultry air there takes the Heat Index to at least 95 degrees on an average 100 days a year. In comparison, most of the days above 95 in San Antonio get there from temperature alone.

Hot days due to humidity: Days of apparent temperature minus days of actual temperature, 1978 2007
City 95+ °F 105+ °F 115+ °F
Atlanta, Georgia   555    54   5
Baltimore, Maryland   416    75   2
Birmingham, Alabama   983  104   2
Buffalo, New York     32      3   0
Charlotte, North Carolina   528    24   0
Chicago, Illinois   282    60   3
Cincinnati, Ohio   254    26   0
Cleveland, Ohio   157    14   1
Columbus, Ohio   227    15   2
Dallas, Texas   857  300   4
Denver, Colorado  -211     -1   0
Hartford, Connecticut   164    20   2
Houston, Texas 2416  453 11
Indianapolis, Indiana   406    53   2
Jacksonville, Florida 2080  300 11
Kansas City, Missouri   665  203   7
Los Angeles, California    -15      0   0
Louisville, Kentucky   631  107   4
Memphis, Tennessee 1281  356 11
Miami, Florida 3037    72   0
Minneapolis, Minnesota   187    35   0
Nashville, Tennessee   680    73   1
New Orleans, Louisiana 2296  463 18
New York, New York   216    31   1
Oklahoma City, Oklahoma   667  140   1
Orlando, Florida     –  120   2
Philadelphia, Pennsylvania   454    72   4
Phoenix, Arizona  -929 -775  -2
Pittsburgh, Pennsylvania   106    10   0
Providence, Rhode Island   136    21   0
Raleigh, North Carolina   742    88   0
Richmond, Virginia   670  146   3
Rochester, New York   132    11   0
Sacramento, California  -446      3   2
Salt Lake City, Utah  -244     -3   0
San Antonio, Texas 1205    84   1
San Diego, California      -3      1   1
San Francisco, California     14      0   0
Seattle, Washington    -14      0   0
St. Louis, Missouri   684  207   7
Tampa, Florida 3058  204   3
Virginia Beach, Virginia   717  107   1
Washington, DC   422    56   3
References

Peter Browning and Brian Walawender. 2009. A Climatology of Apparent Temperature. 21st Conference on Climate Variability and Change.

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