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City of Columbia - Homeland Security Dept.
Friday February 12th, 2010 :: 07:36 a.m. CST

Advisory

Predicted 3-5 inches of snow midlands. Begin 4-6pm thru evening.

The distribution of this message is authorized by Interim Director Randy Martin

The weather is rapidly changing, and increasing our potential for snow.
Current predictions from the Weather Channel is calling for 3-5 inches for the midlands

NATIONAL WEATHER SERVICE COLUMBIA SC
642 AM EST FRI FEB 12 2010

.SYNOPSIS...
AN AREA OF LOW PRESSURE WILL MOVE EAST ACROSS THE GULF OF MEXICO
TODAY...THEN ACROSS CENTRAL FLORIDA AND INTO THE ATLANTIC BY EARLY
SATURDAY. THIS WILL BRING WINTER WEATHER TO THE REGION...FOLLOWED
BY COOL HIGH PRESSURE OVER THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
HAVE UPGRADED WINTER STORM WATCH TO WINTER STORM WARNING FOR LATE
AFTERNOON INTO TONIGHT...AND GONE WITH A WINTER STORM WATCH FOR
NORTHERN MIDLANDS.

STRONG SHORTWAVE OVER EAST TEXAS IS PHASING WITH SOME ENERGY
DROPPING INTO THE NORTHERN MISSISSIPPI VALLEY AND IS EXPECTED TO
CONTINUE MOVING EAST TODAY. A SURFACE LOW HAS DEVELOPED IN THE
WESTERN GULF OF MEXICO AND WILL TRACK EASTWARD AND CROSS CENTRAL
FLORIDA INTO THE WESTERN ATLANTIC BY THIS EVENING. AS THE
SHORTWAVE APPROACHES...SUFFICIENT ATMOSPHERIC MOISTURE WILL ADVENT
OVER THE REGION AND RESULT IN PRECIPITATION MOVING SOUTHWEST TO
NORTHEAST ACROSS THE FORECAST AREA THIS AFTERNOON.

THERMAL ANALYSIS THROUGH LOOKING AT SOUNDINGS AND CROSS SECTIONS
REVEALS THAT THE DOMINANT PRECIPITATION TYPE WILL LIKELY BE
SNOW...ALTHOUGH THERE COULD BE SOME RAIN INITIALLY OR A RAIN SNOW
MIX. DUE TO DRY AIR IN PLACE OVER THE AREA...ONCE PRECIPITATION
BEGINS THE LOWER ATMOSPHERE WILL COOL TO THE WETBULB TEMPERATURE
AND RESULT IN A BELOW FREEZING SOUNDING...WITH THE EXCEPTION OF A
SHALLOW WARM LAYER AT THE SURFACE. PRECIPITATION SHOULD QUICKLY
CHANGEOVER TO SNOW WITHIN AN HOUR OR TWO AFTER IT BEGINS. THERE
IS SUFFICIENT MOISTURE WITHIN THE OPTIMAL SNOW GROWTH REGION FOR
SEVERAL HOURS...ALSO COINCIDING WITH UPWARD VERTICAL
MOTION...WHICH WILL RESULT IN ACCUMULATING SNOWFALL BEGINNING MID
AFTERNOON IN THE CSRA AND OVERSPREADING THE FORECAST AREA BY THIS
EVENING.

THE MAIN CHALLENGE WILL BE THE AMOUNT OF QPF THAT WILL FALL AND
HOW FAR NORTH THE EDGE OF THE SIGNIFICANT ACCUMULATIONS WILL BE.
MODEL FORECASTS HAVE INCREASED THE AMOUNT OF QPF ACROSS THE
FORECAST AREA AND ARE IN GOOD AGREEMENT GIVING ANYWHERE BETWEEN A
QUARTER AND A HALF INCH. THE AREAS WITH HIGHEST CONFIDENCE IN
SIGNIFICANT SNOW ACCUMULATION WILL BE ALONG AND SOUTH OF A
FLORENCE TO GREENWOOD LINE AND THIS AREA HAS BEEN UPGRADED TO A
WINTER STORM WARNING. THE NORTHERN MIDLANDS COULD BE ON THE EDGE
OF THE BETTER QPF AND FORCING AND DUE TO THE LOWER
CONFIDENCE...HAVE DECIDED TO GO WITH A WATCH THERE AND LET THE
DAYSHIFT EVALUATE HOW THE STORM IS DEVELOPING AND DECIDE THEN
WHETHER TO UPGRADE TO A WARNING OR IF AN ADVISORY WILL SUFFICE.

THE TIME FRAME FOR THE HEAVIEST SNOWFALL LOOKS TO BE DURING THE
22Z TO 06Z PERIOD WHERE THE BEST DYNAMICS COINCIDE WITH THE BEST
THERMAL PROFILES. INITIALLY THE GROUND TEMPERATURES IN THE 40S
WILL COUNTERACT THE SNOWFALL AND PREVENT MUCH
ACCUMULATION...ESPECIALLY ON ROADWAYS...BUT AS THE SNOW FALLS AND
TEMPERATURES DROP DURING THE EARLY EVENING HOURS...SNOW WILL
ACCUMULATE.

TEMPERATURES WILL STRUGGLE TO RISE MUCH TODAY GIVEN THE INCREASING
AND THICKENING CLOUD COVER AND WHEN THE PRECIPITATION
BEGINS...TEMPERATURES WILL BEGIN TO FALL A BIT DUE TO EVAPORATIVE
COOLING. THEREFORE HAVE GONE BELOW GUIDANCE FOR MAX TEMPERATURES.

THE DEEPER MOISTURE AND ASSOCIATED FORCING SHIFT EAST OF THE
FORECAST AREA AFTER 06Z AND COOLER DRIER AIR WILL WORK IN FROM
THE WEST...ALLOWING OVERNIGHT LOWS TO DROP INTO THE 20S. MOISTURE
AND SNOW ON THE ROADWAYS WILL BECOME A PROBLEM LATE TONIGHT INTO
SATURDAY MORNING WITH THE FALLING TEMPERATURES.

Address/Location
City of Columbia - Homeland Security Dept.
1225 Lady St
Columbia, SC 29201

Contact
Emergency: 9-1-1
Non-emergencies: 803-545-3391

Verna York
Homeland Security
vbyork@columbiasc.net
803-545-3391

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