...PUBLIC INFORMATION STATEMENT... GOVERNOR TERRY MCAULIFFE HAS DECLARED THE WEEK OF NOVEMBER 30 TO DECEMBER 6, 2014 AS WINTER PREPAREDNESS WEEK IN VIRGINIA. THE NATIONAL WEATHER SERVICE /NWS/ OFFICES SERVING VIRGINIA...IN COOPERATION WITH THE VIRGINIA DEPARTMENT OF EMERGENCY MANAGEMENT...WILL SEND PUBLIC INFORMATION STATEMENTS OVER THE NOAA WEATHER WIRE SERVICE EACH DAY THROUGH SATURDAY. THESE STATEMENTS WILL FOCUS ON DIFFERENT ASPECTS OF WINTER WEATHER IN THE MID ATLANTIC REGION...AND PREPAREDNESS ACTIONS THE PUBLIC SHOULD TAKE FOR THE UPCOMING WINTER SEASON. TODAYS TOPIC - SNOW...SLEET AND FREEZING RAIN...HOW DO THEY FORM? SEVERAL WINTER WEATHER SITUATIONS AFFECTED VIRGINIA EACH WINTER FOR THE LAST SEVERAL YEARS...BRINGING SNOW AND/OR MIXED PRECIPITATION TO THE COMMONWEALTH. PAST ICE EVENTS IN VIRGINIA HAVE RESULTED IN TREES...LADEN WITH ONE-HALF INCH TO AN INCH AND A HALF OF ICE SNAPPED LIKE TOOTHPICKS...KNOCKING DOWN POWER LINES...AND SHUTTING OFF POWER OUT POWER FOR SEVERAL DAYS. MANY PRIMARY AND SECONDARY ROADS WERE LITTERED WITH DOWNED TREES AND TREE LIMBS. FORECASTING WHETHER A PARTICULAR WINTER STORM WILL PRODUCE SNOW...ICE... RAIN...OR A MIXTURE OF PRECIPITATION IS ONE OF THE MOST DIFFICULT FORECAST PROBLEMS METEOROLOGISTS FACE. VIRGINIAS CLOSE PROXIMITY TO BOTH THE ATLANTIC OCEAN AND A COLD AIR SOURCE OVER EASTERN CANADA AND NEW ENGLAND MAKE FORECASTING THE EXACT POSITION OF THE RAIN/SNOW LINE A MAJOR FORECAST CHALLENGE. IN FACT...A DEVIATION IN FORECAST STORM TRACK OF ONLY 50 MILES CAN MEAN THE DIFFERENCE BETWEEN A FOOT OF SNOW... AN INCH OF ICE...OR TWO INCHES OF RAIN. THE KEY FACTOR IN DETERMINING PRECIPITATION TYPE WITH A PARTICULAR WINTER STORM IS THE DEPTH OF COLD AIR ABOVE THE GROUND. IF THE AIR FROM GROUND LEVEL UP SEVERAL THOUSAND FEET IS ABOVE FREEZING...RAIN WILL FALL. IF THE AIR FROM THE GROUND UP THROUGH THE DEPTH OF THE ATMOSPHERE IS BELOW FREEZING...SNOW WILL FALL. HOWEVER, IF COLD AIR IS ENTRENCHED AT THE GROUND WITH A LAYER OF WARM AIR ABOVE IT... SLEET AND/OR FREEZING RAIN ARE LIKELY. FOR SLEET TO FALL...THE COLD AIR NEAR THE GROUND MUST BE DEEP ENOUGH AND/OR COLD ENOUGH TO ALLOW THE RAINDROPS FALLING THROUGH TO RE-FREEZE BEFORE REACHING THE GROUND. FOR FREEZING RAIN TO FALL...COLD AIR NEAR THE GROUND IS SHALLOW. RAINDROPS REMAIN IN LIQUID FORM UNTIL THEY CONTACT OBJECTS AT GROUND LEVEL. ALL THREE OF THESE PRECIPITATION TYPES CAN CAUSE SIGNIFICANT DISRUPTION TO OUR NORMAL DAILY ACTIVITIES. SLICK OR ICY ROADS PROVIDE A HAVEN FOR MOTOR VEHICLE ACCIDENTS...AND POTENTIALLY MASSIVE TRAFFIC JAMS. AT THE VERY LEAST DRIVING SPEEDS WILL BE SLOWED SIGNIFICANTLY BY SNOWY OR ICY CONDITIONS. WALKING ON AN ICE COVERED STREET OR SIDEWALK CAN BE ADVENTUROUS OR EVEN PROHIBITIVE. ADDITIONAL INFORMATION ON WINTER WEATHER PREPAREDNESS CAN BE OBTAINED ON-LINE THROUGH THE VIRGINIA DEPARTMENT OF EMERGENCY MANAGEMENT HOME PAGE AT: WWW.VAEMERGENCY.GOV/READYVIRGINIA/STAYINFORMED/WINTER
Posted on: Mon, 01 Dec 2014 12:13:13 +0000
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