Special Weather Statement, NWS Columbia, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
219 PM EDT WED JUL 17 2013

.SYNOPSIS...
HIGH PRESSURE RIDGE ACROSS THE MIDWEST WILL DOMINATE THE WEATHER
ACROSS THE REGION FOR THE NEXT COUPLE OF DAYS. SCATTERED AFTERNOON
AND EVENING SHOWERS AND THUNDERSTORMS ARE EXPECTED THROUGH THE
REMAINDER OF THE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
CONVECTION ALREADY DEVELOPING IN A STRONGLY UNSTABLE ENVIRONMENT
WITH LIFTED INDEX VALUES AROUND -8C. SHEAR IS NOT VERY STRONG AND
EXPECT STORMS TO BECOME OUTFLOW DOMINATED WHILE SOME ORGANIZATION
IS POSSIBLE ASSOCIATED WITH A WEAK SHORTWAVE ROTATING AROUND THE
UPPER RIDGE. WILL CONTINUE WITH HIGH CHANCE POPS THROUGH THE
AFTERNOON INTO THIS EVENING...AND AN ISOLATED SEVERE STORM CANNOT
BE RULED OUT. TEMPERATURES THIS AFTERNOON CURRENTLY IN THE 90S
ACROSS THE AREA AND WILL REMAIN SO OUTSIDE OF THUNDERSTORMS WHERE
TEMPERATURES LIKELY WILL FALL INTO THE MID 70S.

CONVECTION SHOULD WANE AFTER SUNSET WITH THE LOSS OF HEATING
WHILE DEBRIS CLOUDS COULD LIMIT THE AMOUNT OF COOLING EARLY IN THE
NIGHT. SOME DRIER AIR ALOFT NOTED ON THE WATER VAPOR IMAGERY COULD
SET UP THE POTENTIAL FOR SOME EARLY MORNING FOG...MAYBE
DENSE...BUT TOO MUCH UNCERTAINTY TO FORECAST WITH CONFIDENCE AT
THIS POINT. OVERNIGHT LOWS GENERALLY IN THE LOWER 70S.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
UPPER RIDGE IS EXPECTED TO WEAKEN BY THURSDAY NIGHT AS HEIGHTS
FALL ACROSS THE REGION. ALTHOUGH AIRMASS WILL BECOME
MODERATELY/STRONGLY UNSTABLE THURSDAY AND FRIDAY...MODELS NOT
SHOWING MUCH IN THE WAY OF DISTURBANCES MOVING ACROSS THE REGION.
AT THE SURFACE...MODELS DO SHOW A WEAK SURFACE TROUGH. MODELS
SHOW UPPER TROUGH DEVELOPING ACROSS THE REGION BY FRIDAY NIGHT.
PWAT VALUES A BIT LOWER THAN PREVIOUS DAYS AROUND 1.7-1.8 INCHES.
BUT STILL HIGH ENOUGH TO GO 20-30 PERCENT CHANCE DIURNAL
CONVECTIVE ACTIVITY. DECIDED TO LIMIT MAINLY DURING AFTERNOON AND
EVENING HOURS WITH NOT MUCH AFTER MIDNIGHT. ATMOSPHERE SHOULD
BECOME UNSTABLE WITH STRONG SURFACE HEATING IN THE AFTERNOON
HOURS. NAM LIS -5 IN THE AFTERNOON EACH DAY. CAPES OVER 2500 J/KG
THURSDAY AFTERNOON AND OVER 3000 J/KG FRIDAY AFTERNOON. STRONG LOW
LEVEL LAPSE RATES MAY SUPPORT AFTERNOON/EVENING CONVECTIVE
ACTIVITY. SPC HAS REGION IN GENERAL THUNDERSTORM AREA THURSDAY AND
FRIDAY. IN ADDITION... MODELS INDICATE AN INCREASE IN SURFACE
BOUNDARIES FROM CONVECTIVE OUTFLOW BOUNDARIES TO LOW LEVEL
CONVERGENCE TO POSSIBLE SEA BREEZE INTERACTIONS THAT MAY LEAD TO
AN INCREASE IN POPS. WITH MORE SUN THAN CLOUDS...WILL SHOW A BIT
OF AN INCREASE IN HIGH TEMPERATURES...LOWER 90S THURSDAY AND
MIDDLE 90S FRIDAY. OVERNIGHT LOWS IN THE LOWER TO MIDDLE 70S.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
MEDIUM RANGE MODELS IN GOOD AGREEMENT. BOTH GFS AND ECMWF SHOW
UPPER TROUGH DISPLACING UPPER RIDGE IN EASTERN CONUS SATURDAY AND
CONTINUING THROUGH TUESDAY. THEN...UPPER TROUGH STRENGTHENS SOME
BY WEDNESDAY. THIS WEATHER PATTERN IS EXPECTED TO PULL A COLD
FRONT IN THE GREAT LAKES AREA SATURDAY TO THE CAROLINAS MONDAY
AND TUESDAY. THE FRONT SHOULD STALL IN THE VICINITY OF THE REGION
BY WEDNESDAY. THE WEATHER IS EXPECTED TO BE UNSETTLED AS THE
UPPER TROUGH PICKS UP SOME TROPICAL MOISTURE FROM THE SOUTH
BY SUNDAY WITH PWATS RUNNING AROUND 2 INCHES OR JUST ABOVE THROUGH
TUESDAY. THEN...WEDNESDAY IS A BIT DRIER WITH PWATS AROUND 1.8
INCHES. GENERALLY LIKED MOS GUIDANCE POPS. DECIDED TO TREND POPS
IN A DIURNAL NATURE WITH 40-60 PERCENT DAYTIME AND EARLY EVENING
POPS SATURDAY THROUGH TUESDAY. WILL LOWER TO 20-30 PERCENT
OVERNIGHT. WEDNESDAY SHOULD BE A BIT DRIER AND MORE SUMMER-LIKE
WITH 20-30 DAY AND NIGHT-TIME POPS. AGREE WITH MOS TEMPERATURE
GUIDANCE...HIGHS AROUND 90 SATURDAY AND SUNDAY AHEAD OF THE
COLD FRONT...AND HIGHS IN THE UPPER 80S MONDAY THROUGH WEDNESDAY.
NIGHT-TIME LOWS IN THE LOWER TO MIDDLE 70S SATURDAY AND SUNDAY
NIGHTS...THEN MAINLY THE LOWER 70S MONDAY AND TUESDAY NIGHTS.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
CONVECTION ALREADY DEVELOPING IN AN UNSTABLE ATMOSPHERE WITH SOME
SHOWERS NEAR CAE/CUB. IFR VSBYS POSSIBLE IN SHOWERS AND
THUNDERSTORMS 18Z-02Z ACROSS THE REGION THOUGH AGS/DNL LIKELY WILL
NOT SEE MUCH UNTIL AFTER 20Z. GENERALLY NORTHWEST TO NORTHERLY
ENVIRONMENTAL WINDS THROUGH 06Z BEFORE WINDS BECOME CALM TO LIGHT
AND VARIABLE. SOME DRIER AIR IS MOVING OVER THE AREA ALOFT AND MAY
SET UP A SCENARIO FOR FOG DEVELOPMENT LATE TONIGHT. WILL FORECAST
MVFR VISIBILITIES AFTER 10Z BUT NOT GOING AS LOW AS LAMP GUIDANCE
SUGGESTS...THOUGH THE POSSIBILITY OF DENSE FOG DOES EXIST WITH
ABUNDANT LOW LEVEL MOISTURE AND DRIER AIR ALOFT.

EXTENDED AVIATION OUTLOOK...RESTRICTIONS POSSIBLE EACH DAY IN MAINLY
AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS AS WELL AS LATE
NIGHT/EARLY MORNING FOG/STRATUS.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
GA...NONE.
&&

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