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) of 0.25" (1/4 inch) or greater
 
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) of 0.25" (1/4 inch) or greater 
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.
Ice Storm Warning (WSW)  
An "Ice Storm Warning" is issued when greater than 0.25" (1/4 inch) of ice is expected to accumulate during freezing rain situations.  Heavy accumulations of ice can 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) up to 0.25" (1/4 inch) 
Freezing Rain Advisory (WSW)  
A "Freezing Rain Advisory" is issued when rain or drizzle freezes (air temperature at or below 32 degrees), or is expected to freeze, on surfaces and objects, making walking and travel dangerous. Ice accumulations are expected to be less than 0.25" (1/4 inch).  More significant accumulations of ice would require an Ice Storm Warning (see above).
Wind Chill Advisory (WSW)  
A "Wind Chill Advisory" is issued when very cold temperatures and gusty winds combine to create a wind chill (how it feels on exposed skin) below zero (0F) for an hour or more.  If wind chills drop below -10F, a "Wind Chill Warning" will be issued (see below).
Wind Chill Warning (WSW)  
A "Wind Chill Advisory" is issued when very cold temperatures and gusty winds combine to create a wind chill value at or below -10F (10 degrees below zero) an hour or more.  This is an extremely dangerous situation, as temperatures/wind chill values that are this cold can cause frostbite and hypothermia to set in within 30 minutes or less. 
 
 
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