UNDERSTANDING WINTER WEATHER ALERTS

2/12/2016 (Permalink)

Since we do 24 hour emergency water damage cleanup from frozen pipes we definitely understand bad weather.  When temperatures drop into a deep freeze we can get quite busy.  When Mother Nature decides to add heavy winds to the already low temperatures we know we’ll get even busier, faster!  The combination of freezing temperatures coupled with the driving winds blast frigid air into areas of your home and/or business and cause damage that would otherwise likely be Ok. 

A winter weather event is a winter weather phenomenon (such as snow, sleet, ice and wind chill) that impacts public safety, transportation and/or commerce.  It typically occurs during the climatological winter season between October 15 and April 15.

Winter weather related Warnings, Watches and Advisories are issued by your local National Weather Service office.  Each office knows the local area and will issue Warnings, Watches or Advisories based on local criteria.  For example, the amount of snow that triggers a “Winter Storm Warning” in the Northern Plains is typically much higher than the amount needed to trigger a “Winter Storm Warning” in the Southeast.

So, what does this mean?

Outlook – Winter weather that may cause significant impact in the day 3 to 7 forecast time period and eventually lead to the issuance of a watch or warning is contained in the Hazardous Weather Outlook.  More scientific discussion on the event can also be found in the Area Forecast Discussion.  Forecasts in the day 3 to 7 time period typically have a lot of forecast uncertainty.  Uncertainty is generally in the 30 to 50% range that the event will occur and reach warning criteria.  It is intended to provide information to those who need considerable lead time to prepare for the event.

Advisory – These products are issued when a hazardous winter weather event is occurring, is imminent, or has a very high probability of occurrence (generally greater than 80%).  An advisory is for less serious conditions that cause significant inconvenience and if caution is not exercised, could lead to situations that may threaten life and/or property.  Advisories are issued using the WSW Winter Weather Message product and will appear as a headline in some texts products such as the Zone Forecast.  It will change the color, as shown in the table below, of the counties on the NWS front page map according to what type of advisory has been issued.

Watch – A watch is generally issued in the 24 to 72 hour forecast time frame when the risk of a hazardous winter weather event has increased (50 to 80% certainty that warning thresholds will be met).  It is intended to provide enough lead time so those who need to set their plans in motion can do so.  A watch is issued using the WSW Winter Weather Message product and will appear as a headline in some text products such as the Zone Forecast.  It will change the color, as shown in the table below, of the counties on the NWS front page map according to what type of watch has been issued.

Warning – These products are issued when a hazardous winter weather event is occurring, is imminent, or has a very high probability of occurrence (generally greater than 80%).  A warning is used for conditions posing a threat to life or property.  Warnings are issued using the WSW Winter Weather Message product and will appear as a headline in some text products such as the Zone Forecast.  It will change the color, as shown in the table below, of the counties on the NWS front page map according to what type of warning/advisory has been issued.

Advisories: Be Aware

Winter Weather Advisories are issued when a winter storm event (sleet, ice, snow, freezing rain, snow and blowing snow, or a combination of events) is expected to meet or exceed local winter weather advisory criteria in the next 12 to 36 hours but stay below warning criteria. Criteria for snow is 4 inches or more in 12 hours or less covering at least 50 percent of the zone or encompassing most of the population. Use "mid-point" of snowfall range to trigger advisory (i.e. 2 to 5 inches of snow = advisory). Criteria for ice is any ice accumulation less than 1/2 inch over at least 50 percent of the zone or encompassing most of the population. Winter Weather Advisory can also be issued for black ice. This is optional.  Be prepared for winter driving conditions and possible travel difficulties.  Use caution when driving. 

Freezing Rain Advisories are issued when light ice accumulation (freezing rain and/or freezing drizzle) is expected in the next 12 to 36 hours, (but will remain below 1/2 inch) for at least 50 percent of the zone or encompassing most of the population and not reach warning criteria.  Expect a glaze on roads resulting in hazardous travel.  Slow down and use caution while driving because even trace amounts of ice on the roads can be dangerous. 

Wind Chill Advisories are issued when low wind chill temperatures are expected to meet or exceed local wind chill advisory criteria in the next 12 to 36 hours, but will not reach local warning criteria. Wind chill temperatures may reach or exceed -15°F.  Extremely cold air and strong winds will combine to generate low wind chill readings.  If you must venture outdoors, take precautions against frostbite and hypothermia.  See the NWS Wind Chill Chart.

Lake Effect Snow Advisories are issued for a lake effect snow event that is expected to meet or exceed local lake effect snow advisory criteria in the next 12 to 36 hours. Widespread or localized lake induced snow squalls, blowing snow or heavy snow showers which produce snowfall accumulating to 4 or more inches in 12 hours or less, but remain less than 7 inches and below warning criteria. Expect lake effect snow showers and assume travel will be difficult in some areas.  Lake effect snow usually develops in localized narrow bands which will be intense enough to produce several inches in a few areas with sudden restrictions in visibility and impacts a limited area within a county or forecast zone. Use "mid-point" of snowfall range to trigger advisory (i.e. 2 to 5 inches of snow = advisory).

Watches: Be Prepared

Blizzard Watches are issued when conditions are favorable for a blizzard event in the next 24 to 72 hours. There is a potential for falling and/or blowing snow with strong winds or frequent gusts greater than or equal to 35 mph and extremely poor visibilities to less than a ¼ mile for three or more hours.  This can lead to whiteout conditions and make travel very dangerous. 

Winter Storm Watches are issued when conditions are favorable for a significant winter storm event (heavy sleet, heavy snow, ice storm, heavy snow and blowing snow or a combination of events.)  There is a potential to meet or exceed local winter storm warning criteria in the next 24 to 72 hours. Criteria for snow is 7 inches or more in 12 hours or less; or 9 inches or more in 24 hours covering at least 50 percent of the zone or encompassing most of the population. Use "mid-point" of snowfall range to trigger a watch (i.e. 5 to 8 inches of snow = watch). Criteria for ice is 1/2 inch or more over at least 50 percent of the zone or encompassing most of the population.

Wind Chill Watches are issued when Conditions are favorable for wind chill temperatures to meet or exceed local wind chill warning criteria in the next 24 to 72 hours. There is the potential for a combination of extremely cold air and strong winds to create dangerously low wind chill values.  See the NWS Wind Chill Chart.  Wind chill temperatures may reach or exceed -25°F.

Lake Effect Snow Watches are issued when conditions are favorable for a lake effect snow event to meet or exceed local lake effect snow warning criteria in the next 24 to 72 hours.  Travel and commerce may be significantly affected. Widespread or localized lake induced snow squalls or heavy snow showers which produce snowfall accumulation to 7 or more inches in 12 hours or less. Lake effect snow usually develops in narrow bands and impacts a limited area within a county or forecast zone. Use "mid-point" of snowfall range to trigger a watch (i.e 5 to 8 inches of snow = watch).

Warnings: Take Action!

Blizzard Warnings are issued when a blizzard event is imminent or expected in the next 12 to 36 hours and means severe winter weather conditions are expected or occurring.  There is potential for frequent gusts greater than or equal to 35 mph accompanied by falling and/or blowing snow with strong winds, frequently reducing visibility to less than ¼ mile for three hours or more.  May lead to whiteout conditions making travel extremely difficult.  Do not travel.  If you must travel, have a winter survival kit with you.  If you get stranded, stay with your vehicle and wait for help to arrive. 

Winter Storm Warnings are issued for a winter storm event (heavy sleet, heavy snow, ice storm, heavy snow and blowing snow or a combination of events) and is expected to meet or exceed local winter storm warning criteria in the next 12 to 36 hours. Criteria for snow is 7 inches or more in 12 hours or less; or 9 inches or more in 24 hours covering at least 50 percent of the zone or encompassing most of the population. Use "mid-point" of snowfall range to trigger warning (i.e. 5 to 8 inches of snow = warning). Criteria for ice is 1/2 inch or more over at least 50 percent of the zone or encompassing most of the population. Travel will become difficult or impossible in some situations.  Delay your travel plans until conditions improve.

Ice Storm Warnings are usually issued when there is an ice storm event is expected to meet or exceed local ice storm warning criteria in the next 12 to 36 hours. Criteria for ice is 1/2 inch or more over at least 50 percent of the zone or encompassing most of the population.

This amount of ice accumulation will make travel dangerous or impossible and likely lead to snapped power lines and falling tree branches.  Travel is strongly discouraged. 

Wind Chill Warnings are issued when wind chill temperatures are expected to meet or exceed local wind chill warning criteria in the next 12 to 36 hours and for a combination of very cold air and strong winds that will create dangerously low wind chill values. Wind chill temperatures may reach or exceed -25°F.  This level of wind chill will result in frostbite and lead to hypothermia if precautions are not taken.  Avoid going outdoors and wear warm, protective clothing if you must venture outside.  See the NWS Wind Chill Chart.

Lake Effect Snow Warnings are issued when a lake effect snow event is expected to meet or exceed local lake effect snow warning criteria in the next 12 to 36 hours and widespread or localized lake induced snow squalls or heavy showers are expected to produce significant snowfall accumulation of 7 or more inches in 12 hours or less.  Lake effect snow usually develops in narrow bands and impacts a limited area within a county or forecast zone. Use "mid-point" of snowfall range to trigger warning (i.e. 5 to 8 inches of snow = warning).

These bands can produce very heavy snow with sudden restrictions in visibility.  Driving conditions may become hazardous at times.

SERVPRO of Upper Darby, PA & SERVPRO of Bear/New Castle, DE, proudly serves those in need!  We will be on site quickly and our staff will give you the personalized attention you deserve.  We specialize in the cleanup of water damage, fire damage, smoke damage, mold removal, trauma cleanup, vandalism cleanup, carpet cleaning and duct cleaning.  Let us help you make it, “Like it never even happened!”  Visit either of our websites for assistance.  Pennsylvania customers visit –www.SERVPROupperdarby.com or www.SERVPRObearnewcastle.com if you’re located in Delaware.  To speak to a qualified team member, call 1-877-352-0700.