Hot, Humid Weather: How US Cities Compare

The information here reveals 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 to 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 to 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