Winter Weather/Storms – Warning Alert Notifications

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A winter storm is an event in which varieties of precipitation are formed that only occur at low temperatures, such as snow or sleet, or a rainstorm where ground temperatures are low enough to allow ice to form (i.e. freezing rain).

Winter storms have the capability to completely immobilize large areas of a state, and possibly several states simultaneously. Thus, winter weather warnings, watches, and advisories are issued by the National Weather Service (NWS) for relatively large geographic areas, rather than for one specific county or a small group of counties.[1]

The National Weather Service’s (NWS) Marine and Coastal Weather Services Branch is responsible for oversight of the Marine and Coastal Weather Services Program. This program provides current, accurate information relating to the U.S. coastal and offshore waters, the Great Lakes, and the open oceans.[2]

Winter Storms

The following Winter Storm Alert Messages are issued by the National Weather Service (NWS):[3]

Winter Storm[4]

A Winter Storm Outlook is issued when there is a chance of a major winter storms from 3 to 5 days in the future. This is meant to assist people with their long range plans. However, since the outlook is issued so far in advance, the accuracy of the prediction may be limited.

 

 

 

 

A Winter Storm Watch is issued when hazardous winter weather conditions including significant accumulations of snow and/or freezing rain and/or sleet are possible generally within 48 hours. These watches are issued by the local Weather Service Forecast Office.

A Winter Storm Warning is issued when hazardous winter weather conditions that pose a threat to life and/or property are occurring, imminent, or highly likely. The generic term, winter storm warning, is used for a combination of two or more of the following winter weather events; heavy snow, freezing rain, sleet, and strong winds.

A Winter Storm Advisory is issued when hazardous winter weather conditions are occurring, imminent, or likely. Conditions will cause a significant inconvenience and if caution is not exercised, may result in a potential threat to life and/or property.

The generic term, winter weather advisory, is used for a combination of two or more of the following events: snow, freezing rain or freezing drizzle, sleet, and blowing snow.

 

Snow/Blizzards

The following Snow / Blowing Snow / Blizzard Messages are issued by the National Weather Service (NWS):[5]

Heavy Snow[6]

A Snow Advisory is issued when moderate snowfall amounts are imminent and the criteria for amounts vary significantly over different county warning areas.

 

 

 

 

A Heavy Snow Warning is issued when heavy snowfall amounts are imminent and the criteria for amounts vary significantly over different county warning areas.

A Blowing Snow Advisory is issued when sustained winds or frequent gusts of 25 to 35 mph (40 to 56 km/h) accompanied by falling and blowing snow, occasionally reducing visibility to 1/4 mile (0.4 km) or less.

A Blizzard Watch is issued when sustained winds or frequent gusts of 35 mph (56 km/h) or greater, considerable falling, and/or blowing snow reducing visibility frequently to 1/4 mile (0.4 km) or less for a period of three hours or more are possible generally within the next 48 hours.

A Blizzard Warning is issued when sustained winds or frequent gusts of 35 mph (56 km/h) or greater, considerable falling, and/or blowing snow reducing visibility frequently to 1/4 mile (0.4 km) or less for a period of three hours or more.

There are no temperature criteria in the definition of a blizzard but freezing temperatures and 35 mph (56 km/h) winds will create sub-zero (below -18°C) wind chills.

 

Lake Effect Snow

The following Lake Effect Alert Messages are issued by the National Weather Service (NWS):[7]

Lake-Effect Snow Potentials[8]

A Lake-Effect Watch is issued when very heavy lake-effect snowfall amounts of generally 6 inches (15 cm) in 12 hours or less or 8 inches (20 cm) in 24 hours or less are possible generally within 48 hours.

Lake-effect snow squalls can significantly reduce visibilities with little notice.

 

 

 

A Lake-Effect Snow Warning is issued when very heavy lake-effect snowfall amounts of generally 6 inches (15 cm) in 12 hours or less or 8 inches (20 cm) in 24 hours or less are imminent or highly likely.

A Lake-Effect Snow Advisory is issued when heavy lake-effect snowfall amounts of generally 4 inches (10 cm) in 12 hours or less or 6 inches (15 cm) in 24 hours or less are imminent or highly likely.

 

Freezing Rain/Ice

The following Freezing Ran / Ice Alert Messages are issued by the National Weather Service (NWS):[9]

Freezing Rain[10]

A Freezing Rain Advisory is issued when freezing rain or freezing drizzle of a trace to 1/4 inch (1–6 mm) of expected freezing rain is imminent or highly likely - but does not meet warning criteria (typically greater than 1⁄4 inch or 6.4 mm of ice accumulation).

 

 

 

 

An Ice Storm Warning is issued when freezing rain produces a significant and possibly damaging accumulation of ice.

The criteria for this warning vary from state to state, but typically an ice storm warning will be issued any time more than 1⁄4 inch (6.4 mm) of ice is expected to accumulate in an area; in some areas, the criterion is 1⁄2 inch (13 mm).

 

Freezing Fog/Sleet

The following Feezing Fog / Sleet Alert Messages are issued by the National Weather Service (NWS):[11]

Freezing Fog[12]

A Freezing Fog Advisory is issued when widespread dense fog reducing visibility to less than 1/4 mile (400 m) that occurs in a sub-zero environment, leaving a thin glazing of ice.

Freezing Fog refers to fog where water vapor is super-cooled, filling the air with small ice crystals similar to a very light snow.

 

 

 

 

Sleet[13]

A Sleet Warning is issued when heavy sleet accumulations of 2 inches (5 cm) or more in 12 hours or less are imminent. Usually issued as a winter storm warning for heavy sleet.

Sleet is defined as pellets of ice composed of frozen or mostly frozen raindrops or refrozen partially melted snowflakes.

 

 

 

 

 

Freezing Spray

The following Freezing Spray Alert Messages are issued by the National Weather Service (NWS):[14]

Freezing Spray[15]

A Heavy Freezing Spray Watch is issued when there is an increased risk of a heavy spray event that meets the necessary criteria, but the occurrence, timing, and/or location are still uncertain.

A watch will be issued when forecasters expect freezing water droplets to be able to accumulate on sea vessels at rates of 2 cm per hour or greater. This accumulation must be caused by an "appropriate combination of cold water, wind, cold air temperature, and vessel movement".

 

 

A Heavy Freezing Spray Warning is issued to warn vessels that accumulation of freezing water droplets due to a combination of cold water, wind, cold air, and vessel movement is likely. Accumulation rates of 2 cm per hour or greater must be possible for a warning to be issued.

A Freezing Spray Advisory is issued to warn vessels that accumulation of freezing water droplets due to a combination of cold water, wind, cold air, and vessel movement is possible, however, accumulations are not expected to reach rates of 2 cm per hour.

 

References:

  1. NOAA – National Weather Service Weather Forecast Office – Louisville, KY: http://www.crh.noaa.gov/lmk/winter_wx/
  2. NOAA – Marine and Coastal Weather Services: http://www.nws.noaa.gov/om/marine/marine.shtml
  3. NOAA – National Weather Service Weather Forecast Office – New Orleans/Baton Rouge, LA: http://www.srh.noaa.gov/lix/?n=wwa_criteria#Winter%20Storm%20Outlook
  4. Image Source: http://sema.dps.mo.gov/images/plan/snow_plows.jpg [Accessed September 5, 2013]
  5. NOAA – National Weather Service Weather Forecast Office – New Orleans/Baton Rouge, LA: http://www.srh.noaa.gov/lix/?n=wwa_criteria#Winter%20Storm%20Outlook
  6. Image Source: http://readywisconsin.wi.gov/winter/images/Winter%20Chicago%20Groundhog%20Storm.jpg [Accessed September 5, 2013]
  7. NOAA – National Weather Service Weather Forecast Office – New Orleans/Baton Rouge, LA: http://www.srh.noaa.gov/lix/?n=wwa_criteria#Winter%20Storm%20Outlook
  8. Image Source: http://www.erh.noaa.gov/buf/lakeffect/lake0607/a/aphid.gif [Accessed September 5, 2013]
  9. NOAA – National Weather Service Weather Forecast Office – New Orleans/Baton Rouge, LA: http://www.srh.noaa.gov/lix/?n=wwa_criteria#Winter%20Storm%20Outlook
  10. Image Source: http://www.srh.noaa.gov/images/ama/education/Freezing_rain_on_tree.jpg [Accessed September 7, 2013]
  11. NOAA – National Weather Service Weather Forecast Office – New Orleans/Baton Rouge, LA: http://www.srh.noaa.gov/lix/?n=wwa_criteria#Winter%20Storm%20Outlook
  12. Image Source: http://www.crh.noaa.gov/unr/?n=2009-12-23-freezing-fog [Accessed September 7, 2013]
  13. Image Source: http://www.erh.noaa.gov/rnk/Newsletter/Fall%202006/sleet2.jpg [Accessed September 7, 2013]
  14. NOAA – National Weather Service Weather Forecast Office – New Orleans/Baton Rouge, LA: http://www.srh.noaa.gov/lix/?n=wwa_criteria#Winter%20Storm%20Outlook
  15. Image Source: http://scijinks.jpl.nasa.gov/_media/en/highlight/photos-medium/1096.jpg [Accessed September 7, 2013]

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