Heat Index

Heat Index
Temperature vs. Humidity

How to read the chart: find the temperature on the left hand side, then move to the right until you find the column for the approximate relative humidity. That number will be the temperature that it will "feel" like. Example: A temperature of 95 and relative humidity of 50% will "feel" like 107 degrees.

	0%	5%	10%	15%	20%	25%	30%	35%	40%	45%	50%	55%	60%	65%	70%	75%	80%
115	103	107	111	115	120	127	135	143	151
110	99	102	105	108	112	117	123	130	137	143	151
105	95	97	100	102	105	109	113	118	123	129	135	142	149
100	91	93	95	97	99	101	104	107	110	115	120	126	132	136	144
95	87	88	90	91	93	94	96	98	101	104	107	110	114	119	124	130	136
90	83	84	85	86	87	88	90	91	93	95	96	98	100	102	106	109	113
85	78	79	80	81	82	83	84	85	86	87	88	89	90	91	93	95	97
80	73	74	75	76	77	77	78	79	79	80	81	81	82	83	85	86	86
75	69	69	70	71	72	72	73	73	74	74	75	75	76	76	77	77	78
70	64	64	65	65	66	66	67	67	68	68	69	69	70	70	70	70	71

IMPORTANT: Heat index values were devised for shady, light wind conditions. Exposure to full sunshine can increase values by up to 15 degrees! Also, strong winds, particularly with very hot, dry air, can be extremely hazardous.

Or, if you know the temperature and the dewpoint, figure out the heat index and relative humidity (RH) using this calculator.

HEAT INDEX using Temp and Dew Point

HEAT INDEX using Temp and RH

Dew Point vs. Humidity

The dew point is the temperature the air needs to be cooled to (at constant pressure) in order to achieve a relative humidity (RH) of 100%. At this point the air cannot hold anymore water in the gas form. If the air were to be cooled even more, water vapor would have to come out of the atmosphere in the liquid form, usually as fog or precipitation.

The higher the dew point rises, the greater the amount of moisture in the air. This directly effects how "comfortable" it will feel outside. Many times, relative humidity can be misleading. For example, a temperature of 30 and a dew point of 30 will give you a relative humidity of 100%, but a temperature of 80 and a dew point of 60 produces a relative humidity of 50%. It would feel much more "humid" on the 80 degree day with 50% relative humidity than on the 30 degree day with a 100% relative humidity. This is because of the higher dew point.

So if you want a real judge of just how "dry" or "humid" it will feel outside, look at the dew point instead of the RH. The higher the dew point, the muggier it will feel.

General comfort levels that can be expected during the summer months:

less than or equal to 55: dry and comfortable
between 55 and 65: becoming "sticky" with muggy evenings
greater than or equal to 65: lots of moisture in the air, becoming oppressive

Heat Index/Heat Disorders

Heat Index	Possible heat disorders for people in higher risk groups
80-90	Fatigue possible with prolonged exposure and/or physical activity.
90-105	Sunstroke, heat cramps and heat exhaustion possible with prolonged exposure and/or physical activity.
105-130	Sunstroke, heat cramps or heat exhaustion likely, and heat stroke possible with prolonged exposure and/or physical activity.
130 or higher	Heatstroke/sunstroke highly likely with continued exposure.

Heat Disorder	Symptoms	First Aid
Sunburn	Redness and pain. In severe cases swelling of skin, blisters, fever, and headaches.	Ointments for mild cases if blisters appear and do not break. If breaking occurs, apply dry sterile dressings. Serious, extensive cases should be seen by a physician.
Heat Cramps	Painful spasms usually in muscles of the legs and abdomen possible. Heavy sweating.	Firm presure on the cramping muscles, or gentle massaging to relieve the spasm. Give sips of water. If nausea occurs, discontinue use.
Heat Exhaustion	Heavy sweating, weakness, skin cold, pale and clammy. Pulse thready. Normal temperature possible. Fainting and vomiting.	Get victim out of sun. Lay down and loosen clothing. Apply cool, wet cloths. Fan or move victim to air conditioned room. Sips of water. If nausea occurs, discontinue use. If vomiting continues, seek immediate medical attention.
Heat Stroke (sunstroke)	High body temperature (106 F or higher). Hot dry skin. Rapid and strong pulse. Possible unconsciousness.	Heat stroke is a severe medical emergency. Summon emergency medical assistance or get the victim to a hosiptal immediately. Delay can be fatal. Move the victim to a cooler environment. Reduce body temperature with cold bath or sponging. Use extreme caution. Remove clothing, use fans and air conditioners. If temperature rise again, repeat process. Do not give fluids.

Safety Tips

Slow down. Strenuous activities should be reduced, eliminated, or rescheduled to the coolest time of the day. Individuals at risk should stay in the coolest available place, not necessarily indoors.
Dress for summer. Lightweight, light-colored clothing reflects heat and sunlight, and helps your body maintain normal temperatures.
Foods (like proteins) that increase metabolic heat production also increase water loss.
Drink plenty of water or non-alcoholic fluids. Your body needs water to keep cool. Drink plenty of fluids even if you don't feel thirsty.
Do not drink alcoholic beverages.
Spend more time in air-conditioned places. Air conditioning in homes and other buildings markedly reduces danger from the heat. If you cannot afford an air conditioner, spending some time each day (during hot weather) in an air conditioned environment affords some protection.
Don't get too much sun. Sunburn makes the job of heat dissipation that much more difficult.

Air Temperature
F	C
Dew Point Temperature
F	C

Heat Index:
Relative Humidity:

Storm Impacting the Northwest U.S.; Fire Weather Conditions in Southern California; Severe Weather in the South

Heat Index