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Posted at 07:00 PM ET, 07/18/2011

Heat wave and hot weather guide


Heat is the top weather-related killer in the United States. Older adults, the sick, and the very young are most vulnerable to extreme heat.

During extreme heat, the best way to stay cool and safe is spend time in an air-conditioned environment. Be sure to check on older friends and relatives and never, ever leave a child or pet unattended in a parked car.

This page contains basic information about extreme heat events, heat safety, local cooling center information, and heat weather forecast information and data.

Basic information

What is the difference between a heat watch, heat advisory, and heat warning?

An excessive heat watch (or simply heat watch) is issued by the National Weather Service when the forecast calls for heat indices above 105°F during the day and nighttime low temperatures of 80°F or higher for two consecutive days.

A heat advisory is issued when a significant heat event is expected within the next 36 hours. An excessive heat warning (or simply heat warning) is issued when conditions are dangerous to life or property, whereas the advisory indicates less serious, but still significant conditions that require caution, especially for the young and elderly.

Current heat watches, warnings or advisories in the D.C. area | Map
Map of national watches, warnings or advisories

What is the heat index?

The heat index measures the apparent temperature (the “feels like” factor) when relative humidity is factored into the air temperature. Higher humidity at the same temperature means a higher heat index.

The National Weather Service has a heat index calculator available here.


Heat index chart (National Weather Service)

National Weather Service Heat Index Forecasts
The origins of heat index and why it’s important

What’s the relationship between temperature and dew point?

The dew point is simply the temperature at which the air cannot hold all the moisture in it and dew begins to form. The higher the dew point, the more humid it is. The chart below relates dew point to how humid it feels.

Dew point
How Humid it Feels (and subjective description)
Below 55 Dry (Pleasant)
55-60Hint of humidity (Still comfortable)
60-65Moist (Tolerable)
65-70Sticky (Becoming unpleasant)
70-75Muggy (Gross)
Above 75 Sultry (Oppressive and unbearable)

Related links

Heat and relative humidity
Dew points for dummies
Reader Mail: Use of the dew point should die

Heat safety: During extreme heat…

(adapted from EPA Heat Guidebook)

Do

• Use air conditioners or spend time in air-conditioned locations such as malls and libraries
• Use portable electric fans to exhaust hot air from rooms or draw in cooler air
• Take a cool bath or shower
• Minimize direct exposure to the sun
• Stay hydrated – regularly drink water or other nonalcoholic fluids
• Eat light, cool, easy-to-digest foods such as fruit or salads
• Wear loose fitting, light-colored clothes
• Check on older, sick, or frail people who may need help responding to the heat
• Know the symptoms of excessive heat exposure and the appropriate responses.

Don’t

• Direct the flow of portable electric fans toward yourself when room temperature is hotter than 90°f
• Leave children and pets alone in cars for any amount of time
• Drink alcohol to try to stay cool
• Eat heavy, hot, or hard-to-digest foods
• Wear heavy, dark clothing.

Cooling Centers in the Washington, D.C. area

D.C. Homeland Security and Emergency Management Page (home page)
D.C. Cooling Center Locations (organized by ward)
Maryland cooling centers

Virginia cooling centers: Fairfax County | Loudon County | Arlington County

Cooling Centers for Senior Citizens

Tips for traveling in hot weather (Dr. Gridlock)

Additional heat safety resources

National Weather Service

NOAA heat portal
National Weather Service Heat Resource Page
NWS Heat Wave Educational Brochure (.pdf)
Tips for Staying Healthy and Cool in Summer

Environmental Protection Agency

Extreme Heat Homepage
The do’s and don’ts for dealing with extreme heat
Excessive Heat Events Guidebook: This resource, developed by the Environmental Protection Agency in partnership with NOAA and FEMA, is designed to help community officials, emergency managers, meteorologists, and others plan for and respond to excessive heat events.
Urban Heat Island Reduction Initiative

Federal Emergency Management Agency

Extreme Heat Homepage
Heat-related terms
What to do during a heat-related emergency
First aid for heat-induced illness

Centers for Disease Control and Protection

Extreme heat media toolkit

Keep Your Cool in Hot Weather
Extreme Heat: FAQ
Heat Stress and the Elderly

The Humane Society

Heat safety for your pets

Heat data: What’s normal vs. extreme?

90 degree days in Washington, D.C.: Yearly, seasonal and monthly averages and extremes
What’s D.C. like in June? Breaking down norms and extremes
What’s D.C. like in July? Breaking down norms and extremes
What’s D.C. like in August? Breaking down norms and extremes
What are Washington, D.C.’s records for heat index and dew point?

Average and record temperatures for all three local airports (all months):

Reagan National (DCA)
Dulles (IAD)
Baltimore (BWI)

Records look-up: search daily, monthly and all-time record temperatures for any state in the U.S.

Air Quality Resources

Because DC heat waves are often accompanied by poor air quality, we have included useful links to understanding and monitoring the Air Quality Index (AQI):

Understanding the Air Quality Index
Map of current air quality conditions (NWS)
Map of current air quality conditions - Northeast U.S. (NWS)
AIRNow homepage (airnow.gov)
Washington, D.C. air quality forecast page (Metropolitan Council of Governments)

Sun safety information

Extreme heat is often accompanied by very high to extreme levels of ultraviolet (UV) radiation which causes sunburn, premature aging of the skin and is a risk factor for skin cancer and cataracts. Here are some useful links:

UV Index Forecast
Sun safety tips

Capital Weather Gang heat features

Global warming as a heat wave enhancer
A deadly combo: heat, cars, and kids
Heat safety tips
Making hotter Augusts not quite as hot in D.C.

Page compiled by Justin Grieser and Jason Samenow

By  |  07:00 PM ET, 07/18/2011

Categories:  Extreme Heat

 
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