Index has to remain at or above 100°F for a minimum of 2 hours. Heat advisories are issued by zone when any location
within that zone is expected to reach criteria. For example: If you expected the heat index to reach
100°F in the city of Elmira, a heat advisory would be issued for that county.
A heat advisory means that people can be affected by heat if precautions are not taken. A quick
study in the Corning area from the 2005 summer showed that early in the summer, emergency room
visits increased when the heat index surpassed 95°F. The issuance of a heat advisory is
important to raise public awareness that these precautions need to be taken. Heat advisories are
also used to trigger other actions and regulations such as no evictions, no turning off of power,
changing outdoor work requirements, etc.
Criteria for an Excessive Heat Warning is a heat index of 105° F or greater that will last
for 2 hours or more. Heat Warnings are issued by zone when any location within that zone is expected
to reach criteria. For example: If you expected the heat index to reach 105°F in the city of
Elmira, an Excessive Heat Warning would be issued for that zone.
A heat warning means that some people can be seriously affected by heat if precautions are not
taken. Studies in Canada, Europe, and the U.S. have indicated that mortality begins to increase
exponentially as the heat increases or stays above a heat index of 104°F. Note: This threshold
will be a rare event in our CWA. Even the warm summer of 2005, would not have produced a heat
In addition to raising public awareness, the issuance of a heat warning will alert hospitals
and officials to take certain actions to prepare and respond to an increase in emergency calls, and
activate programs to check on elderly and the home-bound. In some cases cooling centers can be open
or designated and donation programs activated for fans and air conditioners. As in the case of an
advisory, certain regulations may change such as turning off people's electricity, evictions,
and outside work requirements.
Issued when Heat Warning criteria is possible (50-79%) 1 to 2 days in advance.
and Geographic Factors that increase the Impact of Heat
Direct sun on
buildings or people
minimum heat index - houses and buildings that do not have air conditioning will not cool down if
the overnight minimum heat index remains above 75 - 80° and the area goes into a second hot day.
of heat with high nighttime temperatures is really bad - fatalities will occur. Impacts will begin
to increase exponentially. Urbanization - more concrete, less green - impacts temperatures
particularly at night.
heat - a heat index of 95° - 100° will impact people in May and June or with the first few
occurrences, where as later in the summer (August) it may take a heat index of 100° - 105°
for the same effect. People modify their behavior after being affected by it and are less likely to
be impacted again.
Factors that increase the Impact of Heat
exertion Exposure to sun
alert procedures are based mainly on Heat Index Values. The Heat Index, sometimes
referred to as the apparent temperature is given in degrees Fahrenheit. The Heat Index is a
measure of how hot it really feels when relative humidity is factored in with the actual air
To find the Heat Index temperature, look at the Heat Index Chart below. As an example, if the
air temperature is 96°F and the relative humidity is 65%, the heat index--how hot it feels--is
121°F. The National Weather Service will initiate alert procedures when the Heat Index is
expected to exceed 105°-110°F (depending on local climate) for at least 2 consecutive