-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 180753
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
319 AM EDT SAT MAY 18 2013

.SYNOPSIS...
AN UPPER LEVEL TROUGH WILL TRACK SLOWLY EAST ACROSS OUR REGION
THROUGH EARLY NEXT WEEK.

&&

.NEAR TERM /TODAY AND TONIGHT/...
AS OF 300 AM SATURDAY...

OVERVIEW:
A SHORTWAVE DISTURBANCE LOCATED OVER CENTRAL TN/KY AT 06Z THIS
MORNING WILL SLOWLY PROGRESS EAST INTO WESTERN NC AND EVENTUALLY
INTO CENTRAL NC TONIGHT. FURTHER UPSTREAM...A SHORTWAVE CENTERED
OVER CENTRAL ILLINOIS AT 06Z WILL TRACK SOUTHEAST TO EASTERN TN/KY
OR THE WESTERN SLOPES OF THE SOUTHERN APPALACHIANS BY 12Z SUN. IN
THE LOWER LEVELS...A WEAK FRONT EXTENDING SE FROM CENTRAL VA INTO
NORTHEAST PORTIONS OF NC WILL REMAIN NEARLY STATIONARY TODAY...
LIFTING SLOWLY NORTHWARD INTO SOUTHEAST VA AND THE DELMARVA LATE
TONIGHT AS A MOIST SOUTHERLY RETURN FLOW STRENGTHENS BETWEEN A
LOW-LEVEL RIDGE MOVING OFFSHORE THE EAST COAST AND A LOW-LEVEL
REFLECTION OF THE UPPER LEVEL DISTURBANCE APPROACHING FROM THE WEST.

PRECIP CHANCES:
EXPECT AN INCREASE CHANCE OF SHOWERS AND THUNDERSTORMS TODAY IN
COMPARISON TO PREVIOUS DAYS...THOUGH COVERAGE REMAINS DIFFICULT TO
ASCERTAIN. UPPER LEVEL FORCING WILL BE PRIMARILY ASSOC/W THE
AFOREMENTIONED DISTURBANCE APPROACHING FROM THE WEST...AND PRIMARILY
IN WESTERN PORTIONS OF THE STATE (INCLUDING THE WESTERN PIEDMONT)
LATER THIS AFT/EVE. SEVERAL MESOSCALE BOUNDARIES WERE PRESENT ACROSS
THE REGION THIS MORNING...INCLUDING OUTFLOW FROM PRIOR CONVECTION...
THE REMNANTS OF YESTERDAY`S SEABREEZE...AND A LINGERING (ALBEIT
WEAK) FRONTAL ZONE OVER NORTHEAST PORTIONS OF THE AREA. THE
INTERPLAY BETWEEN THESE REMNANT BOUNDARIES...A ROBUST SEABREEZE THIS
AFTERNOON AND DIURNAL DESTABILIZATION WILL LARGELY DETERMINE
COVERAGE IN EAST/SE PORTIONS OF THE AREA. THE BEST DIURNAL
DESTABILIZATION IS EXPECTED EAST OF HWY 1 WHERE LESS CLOUD COVER AND
BETTER LOW-LEVEL MOISTURE ARE ANTICIPATED. DESPITE WEAKER MID-LEVEL
LAPSE RATES...EXPECT MLCAPE VALUES AS HIGH AS 1000-1500 J/KG. WITH
THE ABOVE IN MIND...WILL INDICATE PRECIP CHANCES MID/LATE AFTERNOON
RANGING FROM 50-60% IN THE FAR W/NW PIEDMONT TO 30% IN THE EAST/SE.
THIS EVENING AND TONIGHT...WILL INDICATE PRECIP CHANCES RANGING FROM
60-70% WEST TO 40% EAST. 20-30 KT SOUTHWESTERLY STEERING FLOW SHOULD
KEEP CONVECTION MOVING ALONG...THOUGH LOCALLY HEAVY RAIN CAN BE
EXPECTED IN AREAS REPEATEDLY AFFECTED. DO NOT ANTICIPATE A SEVERE
THREAT THIS AFTERNOON AND EARLY EVENING GIVEN INSUFFICIENT
DEEP-LAYER SHEAR (15 KT OR LESS) AND LOW DCAPE.

TEMPERATURES:
SOMEWHAT CHALLENGING...DEPENDING PRIMARILY ON CLOUD COVER AND
PRECIP. WILL INDICATE HIGHS RANGING FROM THE MID 80S E/SE (HIGHEST
EAST OF HWY 1/SOUTH OF HWY 64) TO UPPER 70S AND LOWER 80S IN THE FAR
W/NW PIEDMONT WHERE CLOUD COVER WILL BE MORE PERVASIVE. -VINCENT

&&

.SHORT TERM /SUNDAY AND SUNDAY NIGHT/...
AS OF 315 AM SATURDAY...

THE ADDITIONAL SHORTWAVE ENERGY APPROACHING THE APPALACHIANS LATE
TONIGHT WILL PROGRESS INTO CENTRAL NC SUNDAY AFTERNOON INTO SUNDAY
NIGHT...SLOWLY DEAMPLIFYING ALONG THE WAY. A MOIST LOW-LEVEL
SOUTHERLY RETURN FLOW WILL PERSIST...WITH AN OVERALL MOIST COLUMN IN
PLACE GIVEN PLENTIFUL MID/UPPER LEVEL MOISTURE ALONG AND AHEAD OF
THE DISTURBANCE APPROACHING TODAY/TONIGHT AND THE SECONDARY
DISTURBANCE SUN/SUN NIGHT. AS A RESULT...EXPECT MORE WIDESPREAD
CLOUD COVER AND LESS DIURNAL DESTABILIZATION THAN TODAY WITH MLCAPE
VALUES NO HIGHER THAN 500-1000 J/KG. HOWEVER...GIVEN DEEP MOISTURE
AND UPPER LEVEL FORCING OVER THE REGION IN THE FORM OF WEAK DPVA...
EXPECT GREATER CONVECTIVE COVERAGE THAN TODAY...AND WILL INDICATE
PRECIP CHANCES RANGING FROM 70-80% WEST/NW TO 50% FAR EAST/SE WHERE
THE RELATIVE BETTER UPPER LEVEL FORCING ASSOC/W THE SECONDARY
SHORTWAVE SHOULD LAG SOMEWHAT BEHIND PEAK HEATING IN ADDITION TO
WEAKENING WITH TIME. THE BEST OVERALL PRECIP CHANCES ARE EXPECTED
DURING THE MID/LATE AFTERNOON THROUGH EARLY EVENING...WITH A GENERAL
DECREASE IN COVERAGE SUN NIGHT IN ASSOC/W NOCTURNAL STABILIZATION...
THOUGH PRECIP CHANCES WILL REMAIN HIGHER THAN AVERAGE (40-50%) GIVEN
A CONTINUED MOIST AIRMASS IN THE PRESENCE OF WEAK/SLOW MOVING
SHORTWAVE ENERGY ALOFT. EXPECT COOLER HIGHS THAN TODAY...RANGING
FROM THE UPPER 70S IN THE N/NW PIEDMONT TO LOWER 80S SE COASTAL
PLAIN. ONCE AGAIN...DO NOT ANTICIPATE A SEVERE THREAT GIVEN VERY
WEAK DEEP-LAYER SHEAR AND LOW DCAPE. -VINCENT

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
-- Changed Discussion --
AS OF 245 AM SATURDAY...

THE UNSETTLED PERIOD IS EXPECTED TO CONTINUE INTO THE UPCOMING WEEK.
THE AFOREMENTIONED MID/UPPER TROUGH IS FORECAST TO LINGER OVER OUR
REGION MONDAY INTO MONDAY NIGHT. SHOWERS AND THUNDERSTORMS ARE
EXPECTED AGAIN MONDAY... ESPECIALLY DURING THE AFTERNOON AND EVENING
HOURS. LOCALLY HEAVY RAIN SHOULD CONTINUE TO BE A THREAT WITH
LOCALLY 1+ INCHES LIKELY. THE HIGHEST POP SHOULD GRADUALLY SHIFT
EASTWARD WITH TIME... WITH THE HIGHEST POP MONDAY AFTERNOON AND
EVENING LIKELY TO BE IN THE CENTRAL AND EASTERN ZONES. HIGHS SHOULD
REACH NEAR 80... BUT CONVECTION WILL PUT A LID ON TEMPS BY EARLY
AFTERNOON.

BY TUESDAY AND WEDNESDAY... A SUBTROPICAL RIDGE WILL TRY TO BUILD
WESTWARD FROM THE WESTERN ATLANTIC AS THE MID/UPPER TROUGH WEAKENS.
IT APPEARS THAT SOME DRYING WILL GRADUALLY WORK INTO OUR REGION IN
THE MID AND UPPER LEVELS. HOWEVER... IT APPEARS THAT THERE WILL BE
PLENTY OF LOW LEVEL MOISTURE TO WORK WITH (DEW POINTS WELL INTO THE
60S) TO SUPPORT WIDELY SCATTERED TO SCATTERED DIURNALLY DRIVEN
SHOWERS AND THUNDERSTORMS BOTH DAYS. HOWEVER... A PRONOUNCED
REDUCTION IN COVERAGE OF CONVECTION IS EXPECTED BOTH DAYS WHEN
COMPARED TO SUNDAY AND MONDAY. HIGHS WILL REBOUND BACK INTO THE MID
80S (UPPER 80S SANDHILLS). LOWS WILL BE WARM AND HUMID... 65-70.

THURSDAY AND FRIDAY... AN INCREASE IN SHOWERS AND THUNDERSTORMS IS
EXPECTED AGAIN AS ANOTHER MID/UPPER TROUGH APPROACHES FROM THE WEST.
HOWEVER... THE MAIN COLD FRONT IS PROJECTED TO REMAIN WEST OF THE
APPALACHIANS UNTIL SATURDAY WHEN IT MAY MAKE A RUN AT CENTRAL NC.
THEREFORE... WE WILL CONTINUE TO SHOW A GRADUAL INCREASE IN
DIURNALLY DRIVEN CONVECTION THURSDAY INTO SATURDAY... KEEPING POP IN
THE "CHANCE" CATEGORY. LOWS WILL CONTINUE WARM AND HUMID (65-70).
HIGHS IN THE 80S ARE EXPECTED... WITH SOME MINIMAL COOLING SATURDAY
BACK INTO THE UPPER 70S TO MID 80S.
-- End Changed Discussion --

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
AS OF 145 AM SATURDAY...

24-HR TAF PERIOD:
A POTENTIAL FOR MVFR FOG WILL EXIST BETWEEN 08-12Z THIS MORNING...
PRIMARILY AT THE INT/GSO/RWI TERMINALS WHERE RECENT SHOWER ACTIVITY
HAS RESULTED IN RELATIVELY LOW TEMP/DPT SPREADS AS OF 05Z.
ELSEWHERE...SCT/BKN MID-LEVEL CLOUD COVER AND RELATIVELY HIGHER
TEMP/DPT SPREADS SHOULD PRECLUDE FOG FORMATION. OTHERWISE...
ANTICIPATE VFR CONDITIONS TO GENERALLY PREVAIL THROUGH MID
AFTERNOON. BY LATE AFTERNOON AND EVENING...EXPECT AN INCREASING
CHANCE FOR ISOLD TO SCT SHOWERS AND STORMS...ESP AT THE INT/GSO/
RDU/RWI TERMINALS...OR ALONG AND NORTH OF HWY 64.

LOOKING AHEAD:
A SLOW MOVING UPPER LEVEL DISTURBANCE APPROACHING THE REGION WILL
RESULT IN AN INCREASING CHANCE FOR SCATTERED TO WIDESPREAD SHOWERS/
STORMS AND ASSOCIATED SUB-VFR CONDITIONS SAT NIGHT THROUGH EARLY
NEXT WEEK...WITH THE BEST OVERALL CHANCE DURING THE AFTERNOON AND
EVENING HOURS EACH DAY. -VINCENT


&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SYNOPSIS...VINCENT
NEAR TERM...VINCENT
SHORT TERM...VINCENT
LONG TERM...BADGETT
AVIATION...VINCENT