GOVERNOR BOB MCDONNELL HAS DECLARED THE WEEK DECEMBER 5 TO 11, 2010
AS WINTER PREPAREDNESS WEEK IN VIRGINIA. THE NATIONAL WEATHER SERVICE
OFFICES SERVING VIRGINIA...IN COOPERATION WITH THE VIRGINIA
DEPARTMENT OF EMERGENCY MANAGEMENT...WILL SEND PUBLIC INFORMATION
STATEMENTS EACH DAY THROUGH SATURDAY AT APPROXIMATELY 11 AM.
THESE STATEMENTS WILL FOCUS ON DIFFERENT ASPECTS OF WINTER WEATHER 
...AND PREPAREDNESS ACTIONS THE PUBLIC SHOULD TAKE FOR THE UPCOMING WINTER
SEASON.

TODAY'S TOPIC: SNOW...SLEET AND FREEZING RAIN...HOW DO THEY FORM?

SEVERAL WINTER WEATHER SITUATIONS AFFECTED VIRGINIA LAST WINTER...
BRINGING SNOW AND/OR MIXED PRECIPITATION TO THE COMMONWEALTH. 

MANY VIRGINIANS WILL REMEMBER THE MULTIPLE ICE STORMS DURING THE
1993-94 WINTER. SEVERAL OF THESE STORMS WERE ACCOMPANIED BY VERY
COLD TEMPERATURES...WHICH INHIBITED THE MELTING OF THE ICE 
AND PROLONGED RECOVERY EFFORTS.

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. VIRGINIA'S 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 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.

BY KEEPING ABREAST OF THE LATEST FORECASTS THROUGH NOAA WEATHER
RADIO OR YOUR LOCAL TV AND RADIO STATIONS...YOU WILL BE BETTER
PREPARED TO HANDLE WINTER'S WEATHER ELEMENTS...WHATEVER THEY MAY
BE!

ADDITIONAL INFORMATION ON WINTER WEATHER PREPAREDNESS CAN BE
OBTAINED ON-LINE THROUGH THE VIRGINIA DEPARTMENT OF EMERGENCY
MANAGEMENT HOME PAGE AT:

WWW.VAEMERGENCY.COM/THREATS/WINTER/INDEX.CFM

IN ADDITION...THE READY VIRGINIA WEB SITE HAS BEEN DEVELOPED 
TO AID VIRGINIANS IN THEIR OVERALL DISASTER PREPAREDNESS:

WWW.READYVIRGINIA.GOV...ENGLISH VERSION/
WWW.LISTOVIRGINIA.GOV...SPANISH VERSION/

UP-TO-DATE WEATHER INFORMATION IS ALSO AVAILABLE ON-LINE FROM THE
NATIONAL WEATHER SERVICE AT: WWW.WEATHER.GOV/BLACKSBURG.

THE NATIONAL WEATHER SERVICE WINTER WEATHER AWARENESS HOME PAGE IS:
WWW.NWS.NOAA.GOV/OM/WINTER/INDEX.SHTML