-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 241910
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
310 PM EDT THU JUL 24 2014

.SYNOPSIS...
A COLD FRONT WILL MOVE SOUTHWARD INTO SOUTHERN VIRGINIA LATE THIS
AFTERNOON...PROGRESS INTO CENTRAL NORTH CAROLINA TONIGHT...THEN
STALL NEAR THE SOUTH CAROLINA BORDER ON FRIDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 245 PM THURSDAY...

THOUGH MID-LEVEL LAPSE RATES REMAIN WEAK AT ~5.5 C/KM...A VERY
MOIST BOUNDARY LAYER ALONG WITH STRONG INSOLATION WILL YIELD
MODERATE DIURNAL DESTABILIZATION TODAY WITH MLCAPE VALUES GENERALLY
RANGING FROM 1000-2000 J/KG...HIGHEST IN THE EAST WHERE LOW-LEVEL
MOISTURE AND SUNSHINE ARE MOST ABUNDANT AND LOWEST WEST. MODERATE
INSTABILITY AND LITTLE OR NO CIN ALLOWED CONVECTION TO DEVELOP IN
VICINITY OF THE PRE-FRONTAL SFC TROUGH OVER THE COASTAL PLAIN
EARLIER THIS MORNING (12-16Z)...CREATING AN EFFECTIVE FRONTAL ZONE
ORIENTED ROUGHLY WEST-EAST ALONG OR NEAR HWY 64. AS OF 18Z...
DISSIPATING CLOUD COVER FROM PRIOR CONVECTION HAS ALLOWED FULL
HEATING /INSOLATION/ FOR SEVERAL HOURS OVER THE NORTHERN AND WESTERN
PIEDMONT...SIGNIFICANTLY WEAKENING THE EFFECTIVE FRONT. HOWEVER...
CONVECTION PERSISTS OVER THE COASTAL PLAIN...AND THE EFFECTIVE FRONT
PERSISTS EAST OF THE TRIANGLE. THE PRESENCE OF THE AFOREMENTIONED
`EFFECTIVE FRONT` CONTINUES TO INCREASE UNCERTAINTY WITH REGARD TO
THE CONVECTIVE FORECAST THROUGH THIS EVENING.

WITH THE ABOVE IN MIND...CONFIDENCE IS TOO LOW TO PROVIDE MORE
SPECIFIC DETAILS ABOUT CONVECTIVE COVERAGE AND EVOLUTION THIS
AFT/EVE. HOWEVER...FORECAST REASONING REMAINS THE SAME. GIVEN
CYCLONIC FLOW ALOFT (CYCLONIC SHEAR VORTICITY AND DPVA ASSOC/W SMALL
AMPLITUDE SHORTWAVES)...A SFC-925 MB TROUGH SINKING SOUTHWARD INTO
THE REGION NEAR PEAK HEATING...ABUNDANT MOISTURE...AND MODERATE
INSTABILITY...EXPECT ABOVE NORMAL CHANCES FOR CONVECTION LATE THIS
AFT THROUGH THIS EVENING...WITH CONVECTION POSSIBLY PERSISTING
THROUGH SUNRISE FRIDAY MORNING SOUTH AND EAST OF THE TRIANGLE.

SEVERE THREAT: DEEP LAYER SHEAR ON THE ORDER OF 25-35 KT WILL
SUPPORT MULTICELL CLUSTERS AND PERHAPS AN ISOLD SUPERCELL THIS
AFT/EVE. EXPECT A POTENTIAL FOR A FEW SEVERE STORMS WITH A PRIMARY
THREAT OF DAMAGING WINDS...PRIMARILY SOUTH OF HWY 64 WHERE DCAPE
VALUES BEGIN TO INCREASE ABOVE 500 J/KG...APPROACHING 1000 J/KG
NEAR THE SC BORDER. DIME TO QUARTER SIZE HAIL WILL ALSO BE
POSSIBLE WITH ANY ROBUST UPDRAFTS. THOUGH WEAK MID-LEVEL LAPSE
RATES WILL REDUCE THE POTENTIAL FOR HAIL > 1.00 IN...LARGE HAIL UP
TO THE SIZE OF GOLFBALLS WOULD BE POSSIBLE IN ANY ROBUST UPDRAFT
THAT ACQUIRES ROTATION...ESP SOUTH OF HWY 64 WHERE MLCAPE VALUES
WILL APPROACH 2000-2500 J/KG DURING PEAK HEATING. -VINCENT

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
-- Changed Discussion --
AS OF 305 PM THURSDAY...

FRIDAY AND FRIDAY NIGHT....THE MAIN UPPER TROUGH AXIS WILL MOVE EAST
OF THE AREA BY FRIDAY MORNING...WHILE THE ASSOCIATED RELATIVELY WEAK
COLD FRONT SLIPS SOUTH AND STALLS NEAR THE NC/SC BORDER.  HIGH
PRESSURE WILL BUILD QUICKLY ACROSS VA DURING THE DAY...WITH DRIER
MID-LEVEL AIR OVER MOST OF CENTRAL NC. THE AIRMASS DOESNT CHANGE
MUCH BEHIND THE FRONT...WITH DEWPOINTS ONLY DROPPING INTO THE MID
60S TO THE NORTHWEST AND HOVERING NEAR 70S IN THE SOUTH.  WEAK
INSTABILITY AND LEVEL CONVERGENCE IN THE VICINITY OF WHAT IS LEFT OF
THE FRONT MAY PRODUCE SOME VERY ISOLATED CONVECTION NEAR THE SC
BORDER.  HIGHS WILL BE IN THE MID 80S.  WEAK HIGH PRESSURE WILL BE
OFF THE VA COAST BY FRIDAY NIGHT...AND A LIGHT SOUTHEASTERLY RETURN
FLOW MAY PRODUCE SOME FOG AND LOW CLOUDS SATURDAY MORNING...SHOWN
MOST AGGRESSIVELY BY THE NAM.  LOWS IN THE MID/UPPER 60S.

SATURDAY AND SATURDAY NIGHT...A WEAK UPPER DISTURBANCE...POSSIBLY
EMANATING FROM CONVECTION NORTH OF THE SOUTHERN PLAINS RIDGE...WILL
SWING ACROSS THE AREA ON SATURDAY.  CURRENTLY...MODELS SHOW THE WAVE
DEAMPLIFYING AS IT CROSSES THE MOUNTAINS...AND THE EARLY DAY TIMING
WOULD ALSO BE UNFAVORABLE FOR CONVECTIVE INITIATION.  MOST OF
CENTRAL NC WILL REMAIN DRY...WITH THE EXCEPTION BEING THE FAR
SOUTHEAST CWA WHERE THE SEABREEZE MAY MAKE A RUN DURING THE
AFTERNOON.  WEST-SOUTHWESTERLY LOW-LEVEL FLOW WILL PROMOTE DEEPER
MIXING AND A WARMER DAY WITH HIGHS LIKELY IN THE LOWER 90S.  LOWS
SAT NIGHT WILL BE WARMER AS WELL IN THE LOWER 70S.
-- End Changed Discussion --

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
AS OF 305 PM THURSDAY...

SUNDAY THROUGH MONDAY NIGHT... A STRONG SHORTWAVE MOVING SOUTHEAST
OUT OF THE CANADIAN ROCKIES ON SUNDAY WILL BEGIN THE AMPLIFICATION
OF THE LONGWAVE PATTERN HEADING INTO NEXT WEEK.  CONVECTION PASSING
TO OUR NORTH ACROSS VA MAY BLEED SOUTH INTO MAINLY THE NORTHERN
PORTIONS OF THE AREA...PARTICULARLY SUNDAY EVENING BASED ON CURRENT
PROGS.  HOWEVER THE MAIN FORCING TO IMPACT CENTRAL NC WILL COME
MONDAY WHEN MODELS SHOW ADDITIONAL ENERGY...ACCOMPANIED BY STRONG
HEIGHT FALLS AND A BELT OF ENHANCED WESTERLIES...SWINGING ACROSS THE
AREA.  GIVEN THAT TEMPS ARE EXPECTED TO BE WELL INTO THE MID 90S ON
SUNDAY AND AT LEAST THE LOWER 90S ON MONDAY...INSTABILITY SHOULD BE
FAVORABLE AHEAD OF THE FRONT.  WHILE THERE IS STILL SOME UNCERTAINTY
AS TO HOW MUCH OVERLAP THERE WILL BE BETWEEN THE BEST INSTABILITY
AND STRONGEST SHEAR...THE SETUP LOOKS PRETTY GOOD FOR SEVERE WEATHER
AT DAY 5 IN LATE JULY.

TUESDAY THROUGH THURSDAY... MEDIUM RANGE ENSEMBLES SHOW AN
UNSEASONABLY DEEP UPPER TROUGH DEVELOPING OVER THE EASTERN US BY MID
WEEK WITH AN UPPER LOW CENTERED JUST SOUTH OF THE HUDSON BAY.  GIVEN
THAT BOTH THE GFS AND ECMWF SHOW THE SYNOPTIC FRONT REACHING THE
GULF OF MEXICO... CONFIDENCE IS HIGH THAT TEMPS WILL BE BELOW NORMAL
MUCH OF NEXT WEEK.  LOW-LEVEL THICKNESSES ARE PROGGED TO DIP BELOW
1390M...WHICH SUGGESTS HIGHS IN THE LOW/MID 90S AND LOWS IN THE
LOW/MID60S... POSSIBLY TOUCHING THE UPPER 50S IN THE COOLEST SPOTS.
THE AIRMASS CHANGE WILL ALSO BRING LOWER HUMIDITY...AND WITH
DEWPOINTS DROPPING INTO THE 50S THE CHANCES OF SHOWERS OR STORMS
WILL BE RELATIVELY LOW UNTIL RETURN FLOW DEVELOPS LATER IN THE WEEK.
-- End Changed Discussion --

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
AS OF 1145 AM THURSDAY...

AREAS OF MVFR CEILINGS ASSOCIATED WITH A VERY MOIST LOW-LEVEL
AIRMASS WILL PERSIST INTO EARLY/MID AFTERNOON OVER CENTRAL NC...
ESPECIALLY IN OR NEAR LOCATIONS AFFECTED BY CONVECTION. SCATTERED
TO NUMEROUS SHOWERS AND THUNDERSTORMS WILL LIKELY EFFECT ALL
TERMINALS FOR A PERIOD OF AT LEAST SEVERAL HOURS THIS AFTERNOON
THROUGH TONIGHT AS A COLD FRONT MOVES SOUTHWARD INTO THE AREA.
WINDS WILL BECOME VARIABLE AS THE FRONT APPROACHES FROM THE NORTH
THIS AFT/EVE AND WILL REMAIN LIGHT AT 5-10 KT (OUTSIDE OF
CONVECTION).

LOOKING AHEAD: AT THIS TIME...VFR CONDITIONS ARE EXPECTED ON
FRIDAY AS THE FRONT STALLS OUT JUST S/SE OF CENTRAL NC...THOUGH
SOME OF THE LATEST MODEL GUIDANCE SUGGESTS THAT THE FRONT MAY
REMAIN CLOSE ENOUGH FOR SUB-VFR CEILINGS AND/OR A POTENTIAL FOR
SHOWERS AND THUNDERSTORMS TO PERSIST. A PERSISTENT PATTERN OF
TROUGHING OVER THE EASTERN CONUS WILL RESULT IN AN ABOVE NORMAL
CHANCE FOR CONVECTION THROUGH EARLY NEXT WEEK...WITH NUMEROUS
THUNDERSTORMS POSSIBLE DURING THE AFTERNOON AND EVENING HOURS EACH
DAY. -VINCENT

&&

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

&&

$$

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