Weather Terms Explained

This page offers a description of the different types of warnings, watches, advisories and statements that may be issued.  One of the most important distinctions to make is the one between
a Watch and a Warning. 
Indicates that conditions are favorable for a particular type of event, but that the event is not occurring or imminent. Listen to your local media, or keep an eye on this website, for statements and possible warnings. Watches are intended to heighten public awareness and should not be confused with warnings.  

A warning means that a particular event is occurring or imminent. Measures should be taken to safeguard life and property.  
Non-Precipitation Weather Events 
High Wind Watches and Warnings 
For a High Wind event, one or both of the following must occur:      
1) sustained wind speeds of 40 MPH or greater lasting for 1- hour or longer      
2) winds of 58 MPH or greater for any duration  
Wind Advisories
A Wind Advisory may be issued for one or both of the following conditions:           
1) sustained winds of 31-39 MPH for a period of 1 hour or longer       
2) gusts in the 46 to 57 MPH range for any duration of time          
Dense Fog Advisory
Dense Fog Advisories may be issued for visibilities 1/4 mile or below. These     Advisories will usually be posted for widespread events, not small local events     such as valley fog in the summer.  
Excessive Heat Advisory
The National Weather Service will issue Excessive Heat Advisories for events that put the Heat Index above 105 degrees for a period of 3 hours or longer. Remember the Heat Index is the combination of temperature and humidity, which gives a value that is perceived by the human body.   
Frost and Freeze Warnings
These warnings are most commonly issued during the fall months from late September to early November. During this period, advisories will be issued until the first killing frost or freeze occurs. Warnings will not be needed again until the following fall unless during the spring months a late season arctic outbreak threatens vegetation. Frost Warning- used when temperatures at ground level are expected to drop low enough to form frost on exposed surfaces. This would not necessarily be a killing frost. Frost Warnings will normally be issued when temperatures are forecast to fall into the lower or mid 30s. Freeze Warning- used to describe conditions when temperatures at ground level are forecast to drop low enough to cause a hard freeze. Usually, this would be enough to cause significant damage to tender vegetation. Freeze warnings will be posted if temperatures plunge to around 30 degrees F or lower. Remember in these types of situations the forecaster is issuing for temperatures at ground level. Since temperature instruments are 5 feet above the ground, frost will often occur when temperature sensors read 36F. A forecaster may choose to use the wording "patchy frost" or "chance of frost in low lying areas" when temperatures are expected in the mid 30's to around 40 degrees F.
Air Stagnation Advisory
If during the summer months winds are very light at the surface and aloft, with no precipitation for a long duration of time, pollution may build up enough to issue this type of advisory.
Severe Weather Watches and Warnings
Severe Thunderstorm and Tornado Watches These watches will be issued for the potential of severe thunderstorms or tornadoes. Typically, they are issued for a particular region for a 6 hour time frame. Severe thunderstorms and/or tornadoes are possible in and close to the watch area during that time period. It is important to remember that watches do not indicate immediate danger...but the sky should be watched very closely. Watch or listen to the local media for future statements and possible warnings.  
Flash Flood or Flood Watch
These are issued to indicate the potential of flooding or flash flooding over a particular area. Again, there is no immediate danger, but keep an eye on the water, and be sure to listen for possible warnings. A flood watch will be issued for situations related to widespread general flooding. These are generally less changeable but longer term flooding situations. Flash Flood Watch- will be issued for situations relating to short term, intense flooding of small streams and creeks. These situations can be particularly dangerous and safeguards to life and property should be completed without delay.  
Note: The following events are short term life threatening events. Immediate action should be taken upon issuance.

Tornado Warning

Any of the following may require the issuance of a Tornado Warning.   1. Tornado on the ground   2. Funnel Cloud   3. Rotating Wall Cloud   4. Doppler Indicated Tornado - In this case the Doppler Radar shows rotation in a storm, in which the radar operator may issue a warning  
Severe Thunderstorm Warning
Any of the following fall into the criteria of severe:
1) Damaging Winds- sustained or gusty surface winds of 58 mph or greater.
2) Hail- at the surface with 3/4 inch or larger diameter
*Remember that severe thunderstorms can produce tornados with little or no advanced warning.  
Flash Flood or Flood Warning
Flash flooding or flooding has been reported or is imminent-take necessary precautions at once.  
Urban and Small Stream Flood Warning/Advisory
Flooding of small streams, streets and low-lying areas, such as railroad underpasses and urban storm drains, is occurring.  
River Flood Warning
River Flood Warnings are initiated when a river at a gauge site is expected to, or has, exceeded flood stage.