DEFINITIONS: WATCH, WARNING, ADVISORY - NWS

NATIONAL WEATHER SERVICE


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  • 1401 Constitution Avenue NW, Room 5128
    Washington, District Of Columbia
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NOAA/National Oceanic and Atmospheric Administration (NOAA) - Weather watch/warning/advisory definitions This information can help with emergency preparedness. In addition to web links below, the National Weather Service Sacramento office can be reached 24/7 at 916-979-3051.

SOME KEY ONES IN NEVADA COUNTY (fire, heat, flooding):

FIRE
The National Weather Service issues Red Flag Warnings & Fire Weather Watches to alert fire departments of the onset, or possible onset, of critical weather and dry conditions that could lead to rapid or dramatic increases in wildfire activity.
  • A Red Flag Warning is issued for weather events which may result in extreme fire behavior that will occur within 24 hours.
  • A Fire Weather Watch is issued when weather conditions could exist in the next 12-72 hours.

A Red Flag Warning is the highest alert. During these times extreme caution is urged by all residents, because a simple spark can cause a major wildfire. A Fire Weather Watch is one level below a Red Flag Warning, but fire danger is still high.

Conditions that can cause a Red Flag Warning or a Fire Weather Watch include:
  • Strong winds
  • Hgh temperatures
  • Low humidity levels (20% and below)
  • Dry fuels
  • The possibility of dry lightning strikes
  • Any combination of the above
In addition to the above conditions, the following may cause PG&E to do a Public Safety Power Shutdown:
  • Fire threat to electric infrastructure
  • Real-time observations by on-the-ground field experts

Ready Nevada County Handbook
English Handbook - 2022 READY, SET, GO! Handbook
Includes info about evacuation planning and checklists.

Spanish Handbook - 2021 ¡PREPARADOS, LISTOS, A EVACUAR! Manual

Download a weather app to receive Red Flag Warning notices on your phone or tablet. For a full list of email and text weather alert services visit: https://www.weather.gov/enterprise/ (formerly: Weather.gov/subscribe)

Always take the following precautions on a Red Flag Warning day:
• Be prepared for the possibility of a public utility power shut off. Have food, lighting, water, and charged batteries that will last for several days.
• Park your vehicle towards the roadway and load your Go Bag. Prepare for quick evacuation.
• Know how to open your garage if power is unavailable.
• Be sure you have a full tank of gas.
• Keep pets nearby.
• Have a plan to transport large animals and livestock.
• Always check towing equipment and eliminate dragging hazards.
• Do not mow or trim dry grass.
• Do not use equipment outdoors that may create a spark.
• Never park on dry grass.
• Never burn on a Red Flag Warning day.

HEAT
Excessive Heat Watch
An Excessive Heat Watch is issued when there is a potential for the heat index value to reach or exceed 110 degrees (east of the Blue Ridge) or 105 degrees (west of the Blue Ridge) within the next 24 to 48 hours.
Excessive Heat Warning
An Excessive Heat Warning is issued when the heat index value is expected to reach or exceed 110 degrees (east of the Blue Ridge) or 105 degrees (west of the Blue Ridge) within the next 12 to 24 hours. An Excessive Heat Warning may be issued for lower criteria if it is early in the season or during a multi-day heat wave.
Heat Advisory
A Heat Advisory is issued when the heat index value is expected to reach 105 to 109 degrees (east of the Blue Ridge) or 100 to 104 degrees (west of the Blue Ridge) within the next 12 to 24 hours. A Heat Advisory may be issued for lower criteria if it is early in the season or during a multi-day heat wave.
Heat Index
The Heat Index is a measure of how hot it really feels when relative humidity is factored in with the actual air temperature. 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. NWS also offers a Heat Index chart for areas with high heat but low relative humidity. Since heat index values were devised for shady, light wind conditions, exposure to full sunshine can increase heat index values by up to 15°F. Also, strong winds, particularly with very hot, dry air, can be extremely hazardous.

FLOODING
Flash Flood Watch
A Flash Flood Watch is issued when conditions are favorable for flash flooding. It does not mean that flash flooding will occur, but it is possible.
Flash Flood Warning
A Flash Flood Warning is issued when flash flooding is imminent or occurring.
Flood Watch
A Flood Watch is issued when conditions are favorable for flooding. It does not mean flooding will occur, but it is possible.
Flood Warning
A Flood Warning is issued when flooding is imminent or occurring.
River Flood Watch
A River Flood Watch is issued when river flooding is possible at one or more forecast points along a river.
River Flood Warning
A River Flood Warning is issued when river flooding is occurring or imminent at one or more forecast points along a river.

Lake Wind Advisory (from Wikipedia)
A Lake Wind Advisory is a product issued by United States National Weather Service local forecast offices when windy conditions on area lakes are expected to be hazardous for boaters and other recreational events on or around lakes. Boats and other objects on lakes will have a large increase of risk during a Lake Wind Advisory.

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