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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 151904
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
305 PM EDT WED MAY 15 2013

.SYNOPSIS...
A RIDGE OF HIGH PRESSURE ALOFT OVER THE SOUTHEAST WILL CONTROL THE
WEATHER ACROSS CENTRAL NC THROUGH THURSDAY. A MID AND UPPER LEVEL
AREA OF LOW PRESSURE WILL APPROACH THE AREA FROM THE WEST THURSDAY
NIGHT AND FRIDAY. A COLD FRONT WILL SLOWLY DROP SOUTH TO NEAR THE
VA/NC BORDER ON SATURDAY AND PERSIST THROUGH THE WEEKEND.

&&

.NEAR TERM /THROUGH THURSDAY NIGHT/...
AS OF 255 PM WEDNESDAY..

FOR THIS AFTERNOON AND TONIGHT....
RECENT SURFACE ANALYSIS SHOWS A 1025MB HIGH PRESSURE SYSTEM CENTERED
OFF THE SOUTHEAST COAST WITH A BROAD SOUTHWESTERLY SURFACE FLOW
ACROSS THE CAROLINAS. PERSISTENT PATCH OF ALTOCUMULUS THAT LINGERED
FOR MUCH OF THE DAY ACROSS THE NORTHERN PIEDMONT HAS GENERALLY
MELTED AWAY LEAVING BRIGHT SUNSHINE ACROSS CENTRAL NC. RAP/NAM BUFR
SOUNDINGS INDICATE A RATHER DRY AIR MASS WILL REMAIN IN PLACE ACROSS
CENTRAL NC THIS AFTERNOON. SPC MESOANALYSIS PRODUCTS CONTINUES TO
SHOW STEEP MID LAYER LAPSE RATES ACROSS NORTHERN NC...EXCEEDING
7 DEG/KM NEAR THE NC/VA BORDER. MLCAPE VALUES HAVE CLIMBED TO 1000
J/KG OR MORE ACROSS THE MOUNTAINS AND FOOTHILLS AND SOME CUMULUS IS
DEVELOPING IN THE HIGHER TERRAIN NEAR KAVL. CONVECTION ALLOWING HIGH
RES MODELS ARE UNANIMOUS IN KEEPING CENTRAL NC CONVECTION FREE THIS
AFTERNOON AND EVENING WITH SOME WRF-NMM MEMBERS SUGGESTING AN
ISOLATED SHOWER IS POSSIBLE WEST OF KCLT. WILL KEEP THE FORECAST DRY
FOR THIS AFTERNOON AND EVENING WITH MAINLY CLEAR SKIES. AFTER THE
WARMEST DAY OF THE YEAR IN MANY LOCATIONS...TEMPERATURES SHOULD ONLY
FALL INTO THE LOWER 60S OVERNIGHT.

FOR THURSDAY AND THURSDAY NIGHT...
THE RIDGE OF HIGH PRESSURE ACROSS THE SOUTHEAST FLATTENS DURING THE
PERIOD AND HEIGHTS ACROSS CENTRAL NC NUDGE DOWNWARD. A CLOSED AREA
OF LOW PRESSURE ACROSS OK TONIGHT WILL SLOWLY DRIFT EAST AND OPEN
UP. A DISTURBANCE IN THE CYCLONIC FLOW AHEAD OF THIS SYSTEM WILL
MOVE INTO CENTRAL NC ON THURSDAY AFTERNOON WITH A SECOND DISTURBANCE
LIKELY TO ROTATE THROUGH THE AREA ON THURSDAY NIGHT. AT THE SAME
TIME A COLD FRONT WILL DROP INTO THE MID ATLANTIC REGION AND LIKELY
TRIGGER SCATTERED SHOWERS AND THUNDERSTORMS IN WV AND VA DURING THE
AFTERNOON. THE AIR MASS ACROSS CENTRAL NC ON THURSDAY AFTERNOON IS
NOT TERRIBLY SUPPORTIVE OF CONVECTION WITH WEAK INSTABILITY
GENERALLY LESS THAN 500 J/KG AND A RATHER DRY AIR MASS. IT IS
POSSIBLE THAT AFTERNOON CONVECTION IN WV/VA COULD SUSTAIN ITSELF IN
A REGION OF GREATER INSTABILITY AND MOVE SOUTH INTO NORTHERN NC ON
THURSDAY EVENING. FOR NOW WILL GO WITH A DRY FORECAST FOR THURSDAY
AND INCLUDE ONLY A SLIGHT CHANCE OF A THUNDERSTORM ACROSS THE
NORTHERN HALF ON THURSDAY EVENING.

EXPECT MID AND HIGH CLOUDINESS TO INCREASE ON THURSDAY RESULTING IN
PARTLY CLOUDY SKIES BY AFTERNOON. AFTERNOON LOW LEVEL THICKNESS
VALUES ON THURSDAY ARE ACTUALLY A FEW METERS COOLER THAN TODAY. THE
AXIS OF WARMEST CONDITIONS WHICH WAS LOCATED OVER WESTERN NC ON
WEDNESDAY SHIFTS EAST INTO THE COASTAL PLAIN ON THURSDAY. MOS
GUIDANCE IS ACTUALLY DEPICTING MAXES THAT ARE ROUGHLY A DEGREE
WARMER THAN WHAT THEY FORECASTED FOR WEDNESDAY. WHILE SOME HIGH/MID
LEVEL CLOUDINESS IS EXPECTED...STILL FEEL THAT THERE WILL BE
SUFFICIENT INSOLATION FOR MAXES TO WARM TO VALUES SIMILAR TO
WEDNESDAY WITH THE WARMEST TEMPS FLIP FLOPPED FROM WEST TO EAST.
WILL GO WITH HIGHS OF 85 NORTHWEST TO 90 NORTHEAST. MID AND HIGH
CLOUDINESS WILL CONTINUE TO THICKEN ON THURSDAY NIGHT AND A LIGHT
STIRRING OF SOUTHERLY WIND WILL RESULT IN A MILD NIGHT WITH LOWS IN
THE 60 TO 65 RANGE. -BLAES
&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 200 PM WEDNESDAY...

FOR FRIDAY/FRIDAY NIGHT: THE WEAK SURFACE TROUGH IS EXPECTED TO
LINGER ACROSS CENTRAL/ERN NC INTO SC... WHILE THE PRIMARY FRONTAL
ZONE STRETCHES ACROSS MD BACK TOWARD CHICAGO. THE WEAK MID LEVEL LOW
NOW OVER NW TX WILL EASE EASTWARD ACROSS THE CAROLINAS AS A WEAK AND
SHEARING OPEN WAVE... ALTHOUGH DPVA SHOULD BE QUITE SMALL GIVEN THE
VERY LIGHT MID-LEVEL FLOW FROM THE NW. THE NOSE OF THE LOW LEVEL JET
SITS WELL WEST OVER THE LOWER-MID MISS VALLEY (NRN LA/NRN AL/WRN
TN/KY) BUT MODELS DEVELOP AFTERNOON STORMS ALL ALONG AND SOUTH OF
THE 925 MB FRONT FROM NRN IL ACROSS WV TO SE VA... WITHIN AN OVERALL
WEAK WIND FIELD AND LOW DEEP LAYER SHEAR BUT POSSESSING MODERATE
INSTABILITY (MLCAPE UP TO 1000-1500 J/KG). CURRENT CONFIGURATION OF
CONVECTION CHANCES WITH THE BEST CHANCES NEAR THE VA BORDER AND IN
THE NORTHEAST PORTIONS OF THE FORECAST AREA HANDLES THIS WELL. THE
ECMWF AND ESPECIALLY THE GFS KEEP CONVECTION GOING OVERNIGHT OVER
MUCH OF EASTERN NC NEAR THE POORLY DEFINED INTERSECTION OF THE
AFOREMENTIONED TROUGH AND WHAT LOOKS TO BE A SSW-MOVING OUTFLOW
BOUNDARY. GIVEN THE LINGERING MARGINAL ELEVATED INSTABILITY
OVERNIGHT AND PRECIP WATER OVER 150% OF NORMAL... SCATTERED
SLOW-MOVING SHOWERS AND ISOLATED STORMS IN THE EAST THROUGH THE
NIGHT HERE SEEMS REASONABLE. HIGHS 82-87 WITH THICKNESSES 15-20
METERS ABOVE NORMAL AND INCREASING CLOUD COVER. LOWS 62-66 WITH
MOSTLY CLOUDY SKIES... INCLUDING LOW STRATUS TOWARD DAYBREAK.

FOR SATURDAY/SATURDAY NIGHT: THE MID LEVEL WAVE OBSERVED OVER NV/UT
THIS MORNING IS EXPECTED TO TRACK TOWARD THE ESE TOWARD NC BY THE
WEEKEND... ALTHOUGH ITS STRENGTH ON THE MODELS MAY BE ERRONEOUSLY
ENHANCED BY CONVECTIVE FEEDBACK ALONG ITS JOURNEY. THE WEAK STEERING
FLOW OVER NC WILL STILL LIMIT THE FORCING FOR ASCENT VIA DPVA AS THE
WAVE ARRIVES LATE SATURDAY INTO SATURDAY NIGHT... AND THE WEAK LOW
LEVEL FLOW WILL CURB MASS CONVERGENCE ALONG ANY RESIDUAL ILL-DEFINED
TROUGH OR OUTFLOW. BUT DESPITE THIS AND MID LEVEL LAPSE RATES OF
JUST 5.5-6.0 C/KM... THE CONTINUED PRESENCE OF ABOVE-NORMAL PRECIP
WATER (NEAR 1.5 INCHES OR OVER 150% OF NORMAL) AND INCREASING
INFLUENCE OF LOW LEVEL CONFLUENT AND ONSHORE-DIRECTED ATLANTIC
INFLOW NECESSITATES A MENTION OF AT LEAST SCATTERED STORMS FOCUSED
IN (BUT NOT RESTRICTED TO) THE AFTERNOON/EVENING HOURS. INSTABILITY
IS IN QUESTION WITH 500-M MLCAPE OF 500-1000 J/KG ON THE ECMWF AND
1000-2000 J/KG ON THE GFS... AND IF WE DO ACHIEVE GREATER
INSTABILITY... POPS MAY NEED TO GO UP INTO THE LIKELY RANGE IN LATER
FORECASTS. HIGHS 79-85 WITH CONSIDERABLE CLOUDINESS. LOWS 62-66
UNDER CLOUDY SKIES. -GIH

&&

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

FOR SUNDAY/SUNDAY NIGHT: THE WEAK WAVE WILL CONTINUE TO MEANDER TO
THE SE ACROSS THE CAROLINAS SUNDAY... ALTHOUGH IT WILL BE EMBEDDED
WITHIN A LARGE RIDGE EXTENDING FROM THE GREAT LAKES DOWN TO THE
INTERIOR SOUTHEAST... WHILE BROAD TROUGHING SITS OVER THE WESTERN
CONUS. THE GFS RETAINS A STRONGER MID LEVEL WAVE AND AS SUCH FORMS A
POTENT INVERTED TROUGH OVER ERN NC INTO CENTRAL SC WITH A WEDGE-LIKE
NNE SURFACE FLOW PATTERN OVER THE WRN PIEDMONT... WHEREAS THE ECMWF
WITH ITS WEAKER WAVE DEPICTS A LARGE SURFACE HIGH CENTERED OFF NEW
ENGLAND EXTENDING SOUTHWARD JUST OFF THE EAST COAST WITH A BROAD
SOUTHEASTERLY ATLANTIC INFLOW AND NO SUCH TROUGHING FEATURE. BOTH
HAVE BEEN CONSISTENT BUT SUSPECT THE GFS MAY BE ADVERSELY AFFECTED
BY GRIDSCALE FEEDBACK AND THUS LOWERING SURFACE PRESSURES TOO
MUCH... SO WILL LEAN TOWARD THE ECMWF. THIS FAVORS A MORE
LOW-LEVEL-STEERED INFLUX OF A TROPICAL-LIKE AIR MASS INTO NC
SUNDAY... SUGGESTING GOOD COVERAGE OF LOW-BASED SHOWERS AND A FEW
STORMS (PARTICULARLY IN THE WEST WHERE UPSLOPE FLOW MAY AUGMENT RAIN
COVERAGE) BUT WITH SOME HOLES IN THE CLOUD COVER. HIGHS 77-83 AND
LOWS 64-67.

FOR MONDAY THROUGH WEDNESDAY: AGAIN FOLLOWING THE ECMWF... THE
SURFACE HIGH OFF THE NORTHEAST COAST STARTS TO DRIFT SOUTHWARD...
PUSHED BY MID LEVEL TROUGHING LOCATED TO ITS EAST... WHILE THE MID
LEVEL ANTICYCLONE BECOMES CENTERED OVER THE REGION. THIS RESULTS IN
ANOTHER DAY OF WARM TEMPS ALOFT AND LONG-FETCH SOUTHEAST LOW LEVEL
FLOW INTO NC... AND ANOTHER DAY OF AT LEAST SCATTERED SHOWERS AND A
FEW STORMS WITH MORE CLOUDS THAN SUNSHINE. AS THE OFFSHORE SURFACE
HIGH DRIFTS FURTHER SOUTHWARD... LOW LEVEL FLOW OVER NC WILL WEAKEN
AND VEER TO BE MORE FROM A SOUTHERLY DIRECTION... AND THIS MORE
OVER-LAND DIRECTION AND CONTINUED WARM MID-LEVEL TEMPS SHOULD LEAD
TO REDUCED SHOWERS/STORM COVERAGE ON TUESDAY INTO WEDNESDAY... WITH
A BIT MORE SUNSHINE AND HIGHS REBOUNDING BACK ABOVE NORMAL. MID
LEVEL HEIGHTS WILL CONTINUE TO FALL WITH A CYCLONE CENTER FORMING
OVER THE MIDWEST... AND THIS IS PROJECTED TO BE SLOW TO DRIFT TO THE
SSE OVER THE MID MISS VALLEY... WHICH SHOULD KEEP ITS ASSOCIATED
COLD FRONT (AND FRONTAL PRECIP) WELL TO OUR NORTHWEST THROUGH
WEDNESDAY. WILL KEEP POPS NEAR OR BELOW CLIMATOLOGY ON WEDNESDAY AS
WELL... WITH TEMPS ABOUT A CATEGORY ABOVE NORMAL. -GIH
-- End Changed Discussion --

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
AS OF 155 PM WEDNESDAY...

24-HR TAF PERIOD...
HIGH CONFIDENCE OF VFR CONDITIONS THROUGH THE TAF PERIOD.

SURFACE HIGH PRESSURE LOCATED OFFS THE SOUTHEAST AND A WEAK RIDGE OF
HIGH PRESSURE ALOFT WILL RESULT IN A PERIOD OF FAIR WEATHER AND VFR
CONDITIONS THROUGH THE 24 HOUR TAF PERIOD. SKIES SHOULD REMAIN CLEAR
OTHER THAN SOME SCT ALTOCUMULUS CLOUDS THIS AFTERNOON AND A FEW
PATCHES OF CIRRUS ON THURSDAY. SOUTHWEST WINDS AT AROUND 10KTS WITH
GUSTS UP TO 18KTS TODAY WILL RELAX THIS EVENING AT AROUND 7KTS OR
LESS. WEST TO SOUTHWESTERLY WINDS AT AROUND 10KTS ARE EXPECTED ON
THURSDAY.

LOOKING FURTHER AHEAD...
A STATIONARY FRONT WILL DROP SOUTH INTO THE MID ATLANTIC AND NORTH
CAROLINA THROUGH MUCH OF THE EXTENDED PERIOD RESULTING IN THE
POTENTIAL FOR SCATTERED SHOWERS AND THUNDERSTORMS WITH SUB-VFR
CONDITIONS POSSIBLE. THE GREATEST THREAT OF CONVECTION WILL BE
DURING THE AFTERNOON AND EVENING AND ESPECIALLY ON SATURDAY AND
SUNDAY. PRE-DAWN SUB-VFR CONDITIONS IN THE FORM OF LOW STRATUS
AND/OR FOG IS ALSO POSSIBLE DURING THE WEEKEND AND INTO MONDAY.
-BLAES

&&

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

&&

$$

SYNOPSIS...BLAES
NEAR TERM...BLAES
SHORT TERM...HARTFIELD
LONG TERM...HARTFIELD
AVIATION...BLAES