Winter Weather Preparedness Week Message 2
By Gannon Medwick
Monday, December 01, 2008
North Carolina Winter Weather Preparedness Week continues this Monday. Today’s focus is:
THE ANATOMY OF WINTER STORMS
WINTER WEATHER IS THE MOST COMPLEX WEATHER PHENOMENA FORECASTERS FACE IN NORTH CAROLINA. WINTER STORMS OFTEN SEEM TO TAKE ON A CHAOTIC NATURE AS RAIN TURNS INTO SLEET…THEN TO SNOW…AND BACK TO SLEET BEFORE ENDING AS FREEZING RAIN. IT IS THIS HODGE PODGE MIXTURE THAT FORECASTERS CONTEND WITH MANY TIMES DURING THE WINTER SEASON…AS THEY WORK TO KEEP THE FORECAST ON TRACK AND YOU PREPARED.
WINTER STORMS NEARLY ALWAYS BRING SIGNIFICANT AND SOMETIMES RAPID CHANGES IN THE WEATHER WHICH CAN GREATLY AFFECT OUR LIVES AND SAFETY. WINTER STORMS CAN DEVELOP AND LAST FOR JUST A FEW HOURS OR LINGER FOR DAYS. SOME OF THE WORST WINTER STORMS IN NORTH CAROLINA PRODCING HEAVY SNOW AND ICE HAVE TRAPPED PEOPLE IN THEIR CARS…OR ISOLATED THEM IN THEIR HOMES WITHOUT UTILITIES OR OTHER SERVICES FOR DAYS AND SOMETIMES OVER A WEEK. EVEN SMALL AMOUNTS OF SNOW AND ICE CAN CREATE HAVOC AS RESIDENTS OF RALEIGH LEARNED ON THE AFTERNOON OF JANUARY 19, 2005 WHEN JUST A HALF INCH OF SNOW FROZE ONTO MAJOR HIGHWAYS. THE FREEZING OF THE SNOW ONTO THE ROAD SURFACES RESULTED IN HOURS OF GRIDLOCK STRANDING MANY MOTORISTS AND SCHOOL BUSES LOADED WITH CHILDREN FOR HOURS. JUST A LITTLE BIT OF SNOW IN COMBINATION VERY COLD TEMPERATURES AND THE TIME OF DAY CAN CREATE DANGEROUS CONDITIONS CRIPPLING MAJOR CITIES.
WINTER STORMS RESULT FROM A VARIETY OF WEATHER PATTERNS. NORTH CAROLINA SITS IN THE BATTLEGROUND BETWEEN COLD AIR FROM THE NORTH AND WARM MOIST AIR FROM THE SOUTH. THE TIMING OF THE COLD AIR COLLIDING WITH MOISTURE STREAMING IN FROM THE GULF OF MEXICO AND ATLANTIC OCEAN TYPICALLY DICTATES THE TYPE OF PRECIPITATION YOU SEE FALLING IN YOUR BACKYARD. GEOGRAPHY ALSO PLAYS A LARGE ROLE IN OUR WEATHER. THE APPALACHIAN MOUNTAINS OUR WEST AND THE WARM WATERS OF THE GULF STREAM JUST OFF THE COAST BOTH PLAY VITAL ROLES IN WITNER STORM DEVELOPMENT. THE MOUNTAINS ACT TO PILE UP COLD AIR OVER THE STATE WHILE THE WARM WATERS OF THE GULF STREAM PROVIDE MOISTURE AND LOTS OF ENERGY TO WINTER STORMS.
TWO MOST COMMON AND DANGEROUS WEATHER FEATURES WHICH SUPPORT WINTER STORMS ARE COASTAL LOWS…KNOWN AS NOREASTERS…AND COLD AIR DAMMING.
NOREASTERS ARE LOW PRESSURE SYSTEMS WHICH DEVELOP OVER THE OCEAN AND TRACK NORTHEAST ALONG THE COAST. THE REASON NORTH CAROLINA WATERS ARE SO FAVORABLE FOR NOREASTER DEVELOPMENT IS DUE TO THE PROXIMITY OF THE GULF STREAM. WHEN COLD AIR RUSHES OUT OVER THE OCEAN AND THE GULF STREAM A VERY UNSTABLE AND VOLATILE SITUATION IS CREATED. WHEN THIS INSTABILITY COMBINES WITH THE JET STREAM IN THE UPPER LEVELS OF THE ATMOSPHERE…A MASSIVE LOW PRESSURE SYSTEM KNOWN AS A NOREASTER CAN DEVELOP. THIS WAS THE CASE IN JANUARY OF 2000 WHEN RALEIGH RECEIVED 18 TO 24 INCHES OF SNOW IN LESS THAN 24 HOURS.
COLD AIR DAMMING TYPICALLY IMPACTS THE CENTRAL AND WESTERN PORTIONS OF THE STATE. THIS OCCURS WHEN COLD HIGH PRESSURE PASSES TO THE NORTH AND COLD NORTH TO NORTHEAST WINDS DEVELOP. THIS COLD AIR IS HEAVY AND PILES UP AGAINST THE MOUNTAINS AS IT RUSHES SOUTH. THE MOUNTAINS ACT AS A DAM CAUSING THE COLD AIR TO DEEPEN ACROSS THE PIEDMONT AND SOMETIMES AS FAR EAST AS THE COASTAL PLAIN. WHEN LIGHTER…WARM MOIST AIR COMING UP FROM THE SOUTH OVERRUNS THE COLD AIR AT THE SURFACE FREEZING RAIN…SLEET AND SNOW CAN BE THE RESULT. THIS WAS THE SCENARIO WHICH CRIPPLED CENTRAL NORTH CAROLINA WITH AN INCH OF FREEZING RAIN IN DECEMBER 2002.
WINTER STORMS SUCH AS THESE CAN MAKE DRIVING AND WALKING EXTREMELY DANGEROUS. THE AFTERMATH OF A MAJOR WINTER STORM CAN HAVE A DEVASTATING IMPACT ON A COMMUNITY OR AN ENTIRE REGION FOR DAYS…WEEKS…OR EVEN MONTHS. WINTER STORMS ARE CONSIDERED TO BE DECEPTIVE KILLERS BECAUSE MOST DEATHS ARE INDIRECTLY RELATED TO THE STORM. PEOPLE DIE IN TRAFFIC ACCIDENTS ON ICY ROADS…HAVE HEART ATTACKS WHILE SHOVELING SNOW OR SUCCUMB TO FIRES OR CARBON MONOXIDE WHILE TRYING THE HEAT THEIR HOME IMPROPERLY.
For more winter weather information, please continue to check my blog through this week!
Gannon Medwick
Storm Team 9 Meteorologist
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