Non-Precipitation Weather

Sun and CloudsNon-precipitation phenomena such as high wind, frost, heat, wind chill, and dense fog also affect Kentucky and Southern Indiana, and can be just as hazardous as rain or snow, or thunderstorms or lightning.

Like winter weather events, non-precipitation events often cover large geographic areas, and thus advisories and warnings are issued for relatively large portions of states, rather than individual counties or small groups of counties. Non-precipitation watches are generally not issued. 

Non-precipitation advisories and warnings are typically issued for the first period of the seven day forecast, and can be extended to 24 hours if the event is expected to continue. Advisories are reissued whenever there is a change to the timing, areal extent, or expected weather conditions. The advisory provides important details about the location affected, potential impacts, scientific basis for the advisory, and precautionary statements. 

A non-precipitation product (NPW) is used to...

  • Issue the initial warning or advisory,
  • Change the type of warning or advisory,
  • Add or delete affected areas,
  • Extend the cancellation time of the event,
  • Update information pertaining to the warning or advisory, or
  • Terminate the warning or advisory.
  Types of Products   

The advisories are the most common, and ALERT the public of situations that do not contain precipitation.  These conditions may cause inconvenience or difficulty to travelers, or for people who must be outdoors. 

Dense Fog Advisory Issued when dense fog covers a widespread area reducing visibility to 1/4 mile or less.
Frost Advisory Issued during the growing season if overnight lows are expected to reach the lower or middle 30s, with light winds, resulting in frost accumulation.
Wind Advisory Used when sustained winds of 30 mph or greater are expected to last for one hour or longer.
Heat Advisory  Issued when daytime heat indices are above 105°F, along with nighttime heat indices are above 80°F.

The following warnings are the most common, and WARN the public of non-precipitation events that could pose a threat to life or property.

Freeze Warning  Issued during the growing season when air temperatures are expected to be below 32°F over a widespread area for a significant period of time. Adjectives such as "killing" or "hard" will be used as appropriate.
High Wind Warning   Used when sustained winds of 40 mph or greater are expected to last for one hour or longer, or for non-thunderstorm winds of 58 mph for any duration.
Excessive Heat Warning  Issued when the heat index equals or exceeds 115°F for three hours or longer. In this instance, the heat becomes dangerous for a large portion of the population.
Wind Chill Warning Issued when wind chill temperatures are expected to reach -25°F or colder, with a minimum wind speed of about 10 mph. 

  Heat Index   

Sun and ThermometerHeat kills by taxing the human body beyond its abilities. In a normal year, about 175 Americans succumb to the demands of summer heat. Human bodies dissipate heat by varying the rate and depth of blood circulation, by losing water through the skin and sweat glands, and as a last resort, by panting, when blood is heated above 98.6°F. Sweating, by itself, does nothing to cool the body, unless the water is removed by evaporation. High relative humidity retards evaporation.

Heat disorders generally have to do with a reduction or collapse of the body's ability to shed heat by circulatory changes and sweating. When heat gain exceeds the level the body can remove, the temperature of the body's inner core begins to rise and heat related illnesses may develop.

As a result, the "Heat Index" (HI) has been developed. The HI is the temperature the body feels when heat and humidity are combined. The table below correlates the actual temperature and relative humidity, producing a HI. (This chart is based upon shady, light wind conditions. Exposure to full sunshine can increase the HI by up to 15°F.)

Heat Index Chart

Any value less than 80 is considered comfortable.
Any value greater than 90 is considered extreme.
Any value greater than 100 is considered hazardous.
Any value greater than 110 is considered dangerous.

 Heat Index  Possible Heat Disorder
 80°F to 90°F Fatigue possible with prolonged exposure and physical activity.
 90°F to 105°F Sunstroke, heat cramps and heat exhaustion possible.
 105°F to 130°F Sunstroke, heat cramps, and heat exhaustion likely, and heatstroke possible.
 130°F or greater Heat stroke highly likely with continued exposure.

                              All About Heat Waves  Non-Precipitation Terminology is the U.S. government's official web portal to all federal, state and local government web resources and services.