Product Guide: Winter Weather Products

When winter weather threatens, your National Weather Service in Huntsville issues watch, warning, and advisory products to warn you of the impending hazard.  Winter weather is often the most difficult weather for the Tennessee Valley, both because it causes travel problems, and because it is difficult to forecast.

Winter Storm Outlook (SPS)  
A "Winter Storm Outlook" may be issued when there is a good chance of a major winter storm, but the occurrence is expected to be beyond 48 hours into the future.  It is intended to provide information to those who need considerable lead time to prepare for the event.  This product sometimes is issued as a "Special Weather Statement" as well.
Winter Storm Watch (WSW)   
A "Winter Storm Watch" will be issued when conditions are favorable for hazardous winter weather conditions to develop.  Unlike a Tornado Watch or a Severe Thunderstorm Watch, Winter Storm Watches are issued by the local office.  Generally, this type of watch is issued for weather conditions that could occur 24 to 48 hours in the future.  Information in the watch will include the affected area, the weather threat involved, potential precipitation amounts, explanation of what a watch is, the uncertainty involved, precautions recommended, and the storm's potential impact. NWS Huntsville issues a Winter Storm Watch when one or more of the following is possible (50% or greater confidence) during the next 12 to 36 hours:

· Sleet and/or snowfall of 2+ inches in 12 hours, or 4+ inches in 24 hours
· Accumulation of freezing rain (ice) greater than 0.25".
· Greater than 0.25" of ice expected.
Winter Storm Warning (WSW)  
A "Winter Storm Warning" is issued when a combination of hazardous winter weather is occurring, is imminent, or is expected.  Winter Storm Warnings are issued when one or more of the following is expected:

· Sleet and/or snowfall of 2+ inches in 12 hours, or 4+ inches in 24 hours
· Accumulation of freezing rain (ice) greater than 0.25".
· Greater than 0.25" of ice expected.
Blizzard Warning (WSW)  
A "Blizzard Warning" will be issued when winds of 35 mph (sustained or frequent gusts) or stronger combine with considerable falling, blowing, and/or drifting snow, for 3 hours or more with visibilities of 1/4 mile or less.  This condition will be extremely infrequent in the Tennessee Valley.
Heavy Snow Warning (WSW)  
A "Heavy Snow Warning" is issued when snowfall of 2+ inches in 12 hours, or 4+ inches in 24 hours is expected.  If strong winds and low wind chills are expected in addition to the heavy snow, then a Winter Storm Warning or Blizzard Warning will be issued instead. 
Ice Storm Warning (WSW)  
An "Ice Storm Warning" is issued when greater than 0.25" of ice is expected during freezing rain or sleet situations.  Heavy accumulations of ice produce extremely dangerous and damaging situations, primarily by pulling down trees and utility lines.
Winter Weather Advisory (WSW)  
A "Winter Weather Advisory" is issued for a winter weather situation that causes significant inconveniences, but does not meet warning (see above) criteria.  The winter weather can still be life threatening if caution is not exercised, and frequently a winter weather advisory will be issued if travel impacts can be expected.   A Winter Weather Advisory is issued if more than one type of hazardous winter weather is expected, is occurring, or is imminent:

· Sleet and/or snowfall of 1-2 inches in 12 hours.
· Accumulation of freezing rain (ice) less than 0.25".

Blowing Snow Advisory (WSW)  
A "Blowing Snow Advisory" is issued if blowing snow is expected to reduce visibilities to around 1/2 mile or less, causing hazardous travel.  This can also be issued for drifting snow, in which case it is called a "Drifting Snow Advisory."  The two can also be combined.  This is also very infrequent in the Tennessee Valley.
Snow Advisory (WSW)  
A "Snow Advisory" is issued when snow is expected to accumulate 1 to 2 inches in a 12-hour period, or if the snowfall will cause travel impacts.
Freezing Rain Advisory (WSW)  
A "Freezing Rain Advisory" is issued when rain or drizzle freezes, or is expected to freeze, on surfaces and objects, making walking and travel dangerous. Accumulations would be less than 0.25".  Heavy accumulations of ice would require an Ice Storm Warning (see above).
Wind Chill Advisory (WSW)  
A "Wind Chill Advisory" is issued when cold temperatures and breezy winds combine to create a wind chill below zero for an hour or more.  If wind chills drop below -10, a "Wind Chill Warning" will be issued.
Wind Chill Warning (WSW)  
A "Wind Chill Advisory" is issued when cold temperatures and breezy winds combine to create a wind chill below zero for an hour or more.  If wind chills drop below -10, a "Wind Chill Warning" will be issued.
 
 
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