Definitions of Weather Watch, Warnings and Advisories

Winter Storm Outlook

Issued 3-7 days in advance for anticipated snow/ice

Winter Storm Watch

A winter storm watch is issued when there is the potential for significant and hazardous  winter weather within 48 hours.  It does not mean that significant and hazardous winter weather will occur...it only means it is possible.

Significant and hazardous winter weather is defined as:
1)  Over 5 inches of snow (and/or sleet)
OR
2)  Glaze accumulation (freezing rain) of 1/4 inch or more
OR
3)  Enough ice accumulation to cause damage to trees or powerlines.
OR
4)  a life threatening or damaging combination of snow and/or ice accumulation with wind.

Blizzard Warning

A Blizzard Warning means that the following conditions are occurring or expected within the next 12 to 18 hours.
1) Snow and/or blowing snow reducing visibility to 1/4 mile or less for 3 hours or longer

AND
2)  Sustained winds of 35 mph or greater or frequent gusts to 35 mph or greater.
There is no temperature requirement that must be met to achieve blizzard conditions.

Winter Storm Warning

A winter storm warning is issued when a significant combination of hazardous winter weather is occurring or imminent.

Significant and hazardous winter weather is defined as a combination of:
1)  Over 5 inches of snow/sleet
AND/OR
2)  Glaze accumulation (freezing rain) of 1/4 inch or more
AND/OR
3)  Enough ice accumulation to cause damage to trees or powerlines.
AND/OR
4)  a life threatening or damaging combination of snow and/or ice 
accumulation with wind.

Heavy Snow Warning
 

5 inches or more of snow in 12 hours. 7 inches or more in 24 hours.

Ice Storm Warning

¼ inch or more of ice accumulation

Snow Advisory

2-4 inches of snow in a 12 hour period

Freezing Rain Advisory

Ice accumulations of less than 1/4 inch

Winter Weather Advisory

A winter weather advisory is issued when snow, sleet, freezing rain, or
a combination of precipitation types is expected to cause a significant 
inconvenience but not serious enough to warrant a warning.

Freeze Warning

A freeze warning is issued when significant, widespread freezing temperatures are expected.

A freeze warning is issued in the autumn until October 15th west of a line from 
Frederick, Maryland to Charlottesville, Virginia.  It is issued in the autumn until 
November 1st east of that line.

A freeze warning is issued in the spring when it is late enough to cause damage to 
new plants and crops.

Frost Warning

A frost warning is issued when significant, widespread frost is expected.

A frost warning is issued in the autumn until October 15th west of a line from 
Frederick, Maryland to Charlottesville, Virginia.  It is issued in the autumn 
until November 1st east of that line.

A frost warning is issued in the spring when it is late enough to cause damage
 to new plants and crops.

Wind Chill Advisory

A wind chill advisory is issued when wind chills of -5F to -19F are expected.

Wind Chill Warning

A wind chill warning is issued when wind chills of -20F or lower are expected.

Dense Fog Advisory

A dense fog advisory is issued when widespread fog is expected to reduce 
visibilities to 1/4 mile or less over a large area for an extended period of
 time (more than 3 hours).

High Wind Watch

A high wind watch is issued when the following conditions are possible:

1) sustained winds of 40 mph or higher for one hour or more

OR

2) wind gusts of 58 mph or higher for one hour or more.
 

High Wind Warning

A high wind warning is issued when the following conditions are occuring or imminent:

1) sustained winds of 40 mph or higher for one hour or more

OR

2) wind gusts of 58 mph or higher for one hour or more.

Hurricane Watch

A hurricane watch is issued when the following conditions are possible.

1) storm surge, coastal flooding, river flooding

AND

2) winds of 74 mph or higher

The watch is issued for areas that border the Potomac River from Washington
 DC southward and for areas that border the Chesapeake Bay.

The watch does not mean that hurricane conditions will occur.  It only means 
that these conditions are possible.

Hurricane Warning

A hurricane warning is issued when the following conditions are occurring
 or imminent.

1) storm surge, coastal flooding, river flooding

AND

2) winds of 74 mph or higher

The warning is issued for areas that border the Potomac River from 
Washington DC southward and for areas that border the Chesapeake Bay.
 

Inland Hurricane Wind Watch

This watch is issued when there is a possibility that hurricane force winds 
(74 mph or higher) will move inland from the coast beyond areas that are
 covered by the hurricane watch.

The watch does not mean that the hurricane force winds will occur.  It just 
means that they are possible.

Inland Hurricane Wind Warning

This watch is issued when hurricane force winds (74 mph or higher) are expected
 to  move inland from the coast beyond areas that are covered by the hurricane warning.

Coastal Flood Watch

A coastal flood watch is issued when moderate to severe coastal flooding is possible.

Coastal flood watches are issued for areas along the Tidal Potomac River and
 areas along the Chesapeake Bay.

Coastal Flood Warning

A coastal flood warning is issued when moderate to severe coastal flooding is 
occurring or imminent.

Coastal flood warnings are issued for areas along the Tidal Potomac River
  and areas along the Chesapeake Bay.

Excessive Heat Outlook