Graphical HWO Web Help

The Hazardous Weather Outlook (HWO) text product is issued daily around 530 AM, and is updated as needed. The Graphical Hazardous Weather Outlook product is issued shortly after the issuance of the text product. The color key on the right side of each map describes the color coding used in conveying a particular hazardous weather threat. Text describing the hazardous weather threats over the entire 7-Day period is displayed at the bottom of each map.

Day One Outlook
The Day One Outlook is valid until 6 AM the next day (Day 2), and consists of five individual threat maps. The following information provides explanations of the various categories on each map:

Thunderstorms
The definition of a severe thunderstorm is a storm that produces winds of 58 mph or greater, and/or hail 3/4ths inch in diameter or greater, and/or tornadoes. An explanation of shadings for the various counties follows:

  • Purple - High Risk of Severe Tstms (widespread coverage) Used for the most dangerous events.

  • Red - Moderate Risk of Severe Tstms (scattered coverage)

  • Orange - Slight Risk of Severe Tstms (isolated coverage)

  • Yellow - Strong Tstms (isolated to widespread coverage) (small hail and/or winds 40-57 mph)

  • Light Blue - NON-Severe Tstms (isolated to widespread) (small hail and/or winds less than 40 mph.

Flooding
Flooding on this map refers to rises in water levels along smaller rivers and streams (not the larger rivers) and in low lying or other flood prone areas. Flash Flooding refers to rises in water levels in the same areas, but occurs in a much shorter time frame, and therefore can be more life-threatening. Flash Flooding may also occur due to a dam failure.

  • Green - Flooding Possible - A Flood or Flash Flood Watch will typically be in effect, unless the flooding will only affect isolated areas. The flooding can be short-lived (lasting 6 hours or less) or long-lived (lasting a day or more).

  • Light Blue - Heavy Rain/Ponding on Roads - Heavy rain may cause ponding of water on roads and highways, and in low-lying and other flood-prone areas. The flooding will affect isolated to widespread areas. These events are usually short-lived (lasting 12 hours or less).

Wind & Fog
The Wind categories on this map refer to Non-thunderstorm winds.

  • Red - Wind > 40 mph - A High Wind Warning will typically be in effect.

  • Orange - Wind > 25 mph - A Wind Advisory will typically be in effect.

  • Dark Blue - Dense Fog - A Dense Fog Advisory will typically be in effect when visibilities are expected to be less than 1/4th mile, unless fog coverage will only affect isolated areas.

  • Light Blue - Freezing Fog - A Freezing Fog Advisory will typically be in effect when temperatures will be less than 32 F and visibilities will be a few miles or less, unless fog coverage will only affect isolated areas.

Temperature Extremes, Frost / Freeze
The Heat Index categories on this map represent the combination of high temperatures and humidities that can result in hazardous or even life-threatening conditions if protective measures are not taken. The Wind Chill categories represent the combination of cold temperatures and winds that can result in hazardous or even life-threatening conditions if protective measures are not taken.

  • Red - Heat Index > 110 F - An Excessive Heat Warning may or may not be in effect,
    depending on nighttime minimum temperatures expected and how long these conditions will last.
  • Orange - Heat Index > 105 F - A Heat Advisory may or may not be in effect, depending on
    nighttime minimum temperatures expected and how long these conditions will last.
  • Dark Blue - Freeze < 33 F - A Freeze Warning or Hard Freeze Warning will typically be in
    effect. Freezing temperatures may occur only in low-lying and sheltered areas, or may be expected over the entire area. Frost may also occur.
  • Light Blue - Frost 33 to 36 F - A Frost Advisory will typically be in effect. Frost may occur only in low-lying and sheltered areas, or may be expected over the entire area.
  • Purple - Wind Chill < -25 F - A Wind Chill Warning will typically be in effect.
  • Light Purple - Wind Chill -10 F to -24 F - A Wind Chill Advisory will typically be in effect.

Snow / Sleet / Ice

  • Dark Blue - Snow > 3 inches - A Winter Storm Warning for Heavy Snow will typically be in effect.
  • Light Blue - Snow 1 to 3 inches - A Winter Weather Advisory for Snow will typically be in
    effect.
  • Gray - Snow < 1 inch - A Winter Weather Advisory for Snow will usually not be in
    effect for this amount of snowfall.
  • Purple - Sleet - A Winter Storm Warning for Heavy Sleet will typically be in
    effect if 1/2 inch or more of sleet is expected. If a lesser amount is expected, a Winter Weather Advisory for Sleet may or may not be in effect.
  • Pink - Mix of Snow/Sleet/Ice - A Winter Storm Warning or Winter Weather Advisory will
    typically be in effect.
  • Red - Ice Storm ( > .25”) - An Ice Storm Warning will typically be in effect.
  • Orange - Light to Moderate Icing (.01” - .24”) - A Freezing Rain Advisory will typically be in effect.

Days 2-3 Outlook
The Days 2-3 Outlook is more general than the Day One Outlook, and will be valid from 6 am the next day (Day 2) until 6 am on Day 4. Seven potential weather hazard categories are listed in order of importance, from top to bottom. If more than one hazard is expected in a county, the most important hazard is plotted. A hazard is only plotted if there is a potential for the issuance of an Outlook, Watch, Warning or Advisory.

Days 4-7 Outlook
The Days 4-7 Outlook is even more general than the Days 2-3 Outlook, and will be valid from 6 am on Day 4 until 6AM on Day 8. Five potential weather hazard categories are listed in order of importance, from top to bottom. If more than one hazard is possible in a county, the most important hazard is plotted. A hazard is only plotted if there is a potential for the issuance of an Outlook, Watch, Warning or Advisory.


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