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WEATHER

Heat Index Information

To help you prepare and be safe in this inevitable heat, the National Weather Service uses the ?heat index? as a tool to measure how stressful the heat will be. We have some charts and calculators below to help you decide what to do and what to wear in the heat.

The heat index (HI) is an apparent temperature felt by the human body due to the combined effects of temperature and humidity. Most people understand that as the air temperature goes up, so does the heat index. But why does humidity play a role? It?s because the body?s perspiration cannot evaporate as well when the humidity increases. Therefore, the cooling effects of your sweat are reduced as the humidity rises, and your body is unable to cool itself naturally. Combine high heat and high humidity and you?ve got trouble!

Although it is convenient to use a single number (the heat index) to describe the apparent temperature your body feels, keep in mind that heat and humidity affect every body (and everybody) differently. Several assumptions are used to calculate the heat index. The heat index assumes that the body is:

5' 7" tall.
147 pounds.
Caucasian.
At 98.6°.
Clothed in long trousers and a short-sleeved shirt.
In shade.
Walking at a speed of 3.1 mph.
In a breeze of 6 mph.
Not dripping with sweat.

If any of these factors change, e.g., more exertion, more clothing, and/or more weight, the heat index will change for that individual. For example, if you weigh 250 pounds, are wearing long-sleeved work clothes, and are working outside in the sun, the heat index value you hear reported on the radio is lower than what you are personally feeling.

Heat Index Charts

To use the heat index charts, find the appropriate temperature at the top of the chart. There are two charts on this page. Read down until you are opposite the humidity/dewpoint. The number which appears at the intersection of the temperature and humidity/dewpoint is the heat index.

**Heat Index Chart (Temperature & Dewpoint)**
Dewpoint (° F)	Temperature (° F)
Dewpoint (° F)	90	91	92	93	94	95	96	97	98	99	100	101	102	103	104	105
65	94	95	96	97	98	100	101	102	103	104	106	107	108	109	110	112
66	94	95	97	98	99	100	101	103	104	105	106	108	109	110	111	112
67	95	96	97	98	100	101	102	103	105	106	107	108	110	111	112	113
68	95	97	98	99	100	102	103	104	105	107	108	109	110	112	113	114
69	96	97	99	100	101	103	104	105	106	108	109	110	111	113	114	115
70	97	98	99	101	102	103	105	106	107	109	110	111	112	114	115	116
71	98	99	100	102	103	104	106	107	108	109	111	112	113	115	116	117
72	98	100	101	103	104	105	107	108	109	111	112	113	114	116	117	118
73	99	101	102	103	105	106	108	109	110	112	113	114	116	117	118	119
74	100	102	103	104	106	107	109	110	111	113	114	115	117	118	119	121
75	101	103	104	106	107	108	110	111	113	114	115	117	118	119	121	122
76	102	104	105	107	108	110	111	112	114	115	117	118	119	121	122	123
77	103	105	106	108	109	111	112	114	115	117	118	119	121	122	124	125
78	105	106	108	109	111	112	114	115	117	118	119	121	122	124	125	126
79	106	107	109	111	112	114	115	117	118	120	121	122	124	125	127	128
80	107	109	110	112	114	115	117	118	120	121	123	124	126	127	128	130
81	109	110	112	114	115	117	118	120	121	123	124	126	127	129	130	132
82	110	112	114	115	117	118	120	122	123	125	126	128	129	131	132	133
Note: Exposure to full sunshine can increase Heat Index values by up to 15° F

Heat Illness Possible

Heat Illness Likely

Heat Illness Highly Likely

**Heat Index Chart (Temperature & Relative Humidity)**
Relative Humidity (%)	Temperature (° F)
Relative Humidity (%)	90	91	92	93	94	95	96	97	98	99	100	101	102	103	104	105
30	89	90	92	93	95	96	98	99	101	102	104	106	108	110	112	114
35	91	92	94	95	97	98	100	102	104	106	107	109	112	114	116	118
40	92	94	96	97	99	101	103	105	107	109	111	113	116	118	121	123
45	94	96	98	100	102	104	106	108	110	113	115	118	120	123	126	129
50	96	98	100	102	104	107	109	112	114	117	119	122	125	128	131	135
55	98	100	103	105	107	110	113	115	118	121	124	127	131	134	137	141
60	100	103	105	108	111	114	116	120	123	126	129	133	136	140	144	148
65	103	106	108	111	114	117	121	124	127	131	135	139	143	147	151	155
70	106	109	112	115	118	122	125	129	133	137	141	145	149	154	158	163
75	109	112	115	119	122	126	130	134	138	143	147	152	156	161	166	171
80	112	115	119	123	127	131	135	140	144	149	154	159	164	169	175	180
85	115	119	123	127	132	136	141	145	150	155	161	166	172	178	184	190
90	119	123	128	132	137	141	146	152	157	163	168	174	180	186	193	199
Note: Exposure to full sunshine can increase Heat Index values by up to 15° F

Heat Index Calculation

Calculate Heat Index in Fahrenheit using Relative Humidity Enter in the air temperature the dew point temperature in degrees Fahrenheit, then click on the Calculate Heat Index to compute the heat index.
Air Temperature in °F		Relative Humidity
Heat Index		Dew Point

Calculate Heat Index in Fahrenheit using Dew Point Enter in the air temperature, the dew point temperature in degrees Fahrenheit, then click on the Calculate Heat Index to compute the heat index.
Air Temperature in °F		Dew Point in °F
Heat Index		Relative Humidity

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