-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 151758
AFDRAH

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

.SYNOPSIS...
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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.
-- End Changed Discussion --



&&

.NEAR TERM /THROUGH THURSDAY/...
AS OF 1055 AM WEDNESDAY..

LATEST SURFACE ANALYSIS SHOWS A 1024MB HIGH PRESSURE SYSTEM CENTERED
OFF THE SOUTHEAST COAST WITH A BROAD SOUTHWESTERLY SURFACE FLOW
ACROSS THE REGION. SATELLITE IMAGERY CONTINUES TO INDICATE PATCHES
OF MID LEVEL CLOUDS ASSOCIATED WITH A BATCH OF ENHANCED MOISTURE IN
THE 600-500 MB LAYER. MORNING PROXIMITY RAOBS HIGHLIGHT THE LAYER OF
MOISTURE PRODUCING THE CLOUDINESS THIS MORNING. IN ADDITION STEEP
MID LAYER LAPSE RATES >7 DEG/KM ARE NOTED NEAR KGSO ASSOCIATED WITH
AN EML ORIGINATING IN THE CENTRAL ROCKY MOUNTAINS.

MID LEVEL WARMING THIS AFTERNOON WILL KEEP A DECENT MID LEVEL CAP
THROUGHOUT MUCH OF THE DAY. THE RIDGE AXIS CENTERED OVER THE
NORTHEAST OF GULF OF MEXICO WILL PRODUCE A WESTERLY/NORTHWESTERLY
FLOW ABOVE 850MB THAT WILL GENERATE A WEAK LEE SIDE TROUGH ACROSS
THE PIEDMONT AND COASTAL PLAIN THIS AFTERNOON. THESE FEATURES
COMBINED WITH ONLY MODEST AMOUNTS OF MOISTURE SHOULD PUT THE KIBOSH
ON CONVECTION TODAY DESPITE ELEVATED CAPE VALUES > 100 J/KG.
CONVECTION ALLOWING HIGH RES MODELS ARE NEARLY UNANIMOUS IN KEEPING
CENTRAL NC CONVECTION FREE TODAY.

THE AIR MASS ACROSS CENTRAL NC HAS MODIFIED SIGNIFICANTLY DURING THE
PAST 24 HOURS WITH MORNING THICKNESSES AT KGSO AND KRNK BOTH
INCREASING 54M DURING THE 24 HOUR PERIOD ENDING AT 12Z THIS MORNING.
WITH MOSTLY SUNNY SKIES THIS AFTERNOON AND LOW LEVEL THICKNESS
VALUES CLIMBING INTO THE 1410 TO 1420 METER RANGE...HIGH SHOULD
CLIMB WELL INTO THE MID TO UPEPR 80S. DO NOT THINK WE WILL SEE
RECORD HIGH TEMPS THOUGH... GSO RECORD HIGH FOR TODAY IS 92 AND
RDU`S IS 95. -BLAES/BSD

TONIGHT:
QUITE WEATHER IS EXPECTED TO CONTINUE TONIGHT... WITH ABOVE
MENTIONED FRONTAL ZONE EXPECTED TO REMAIN TO THE NORTH OF CENTRAL NC
FROM THE OHIO VALLEY INTO THE NORTHERN MID-ATLANTIC. CLEAR SKIES
INITIALLY MAY GIVE WAY TO SOME HIGH CIRRUS ASSOCIATED WITH
CONVECTION ALONG THIS BOUNDARY TO THE NORTH. GIVEN THE INCREASE IN
LOW LEVEL MOISTURE... WARMER TEMPS TODAY AND THIS INCREASING HIGH
LEVEL CLOUD COVER EXPECT LOW TEMPS THURSDAY MORNING WILL BE IN THE
LOW TO MID 60S. HAVE TRENDED OVERNIGHT LOWS TO THE WARMER SIDE OF
GUIDANCE GIVEN THE ABOVE MENTIONED REASONS.

THURSDAY:
THURSDAY STILL LOOKS TO REMAIN DRY AS WELL THROUGH MOST OF IF NOT
ALL OF THE DAY. ONE DIFFERENCE FROM TODAY WILL BE THE AMOUNT OF MID
AND HIGH CLOUDS MOVING ACROSS OUR AREA FROM SHOWERS AND STORMS
ASSOCIATED WITH THE STALLED FRONTAL ZONE TO THE NORTH OF OUR AREA.
GIVEN THIS AND THE MID LEVEL RIDGE DAMPENING AND BEGINNING TO SHIFT
TO THE EAST OF THE AREA WE MAY ACTUALLY SEE HIGH TEMPS A FEW DEGREES
COOLER ON THURSDAY. AFTERNOON LOW LEVEL THICKNESS VALUES ARE AROUND
5 TO 10 METERS LOWER AS WELL. THIS STILL YIELD HIGH TEMPS IN THE MID
TO UPPER 80S... GENERALLY A DEGREE OR TWO COOLER ACROSS ALL
LOCATIONS EXCEPT THE FAR EASTERN REACHES OF CENTRAL NC. THE BEST
CHANCE FOR ANY SHOWERS AND STORMS ON THURSDAY LOOKS TO BE LATE IN
THE DAY ACROSS THE FAR NORTH... ASSOCIATED WITH OUTFLOW DRIVER
SHOWERS AND STORMS. CONFIDENCE IS NOT HIGH THAT WE WILL SEE MUCH IF
ANY PRECIP THROUGH. THUS... WILL JUST GO WITH A SLIGHT CHANCE OF
SHOWERS AND STORMS ACROSS OUR FAR NORTH...GENERALLY ALONG AND NORTH
OF KRDU... WITH ANY SVR THREAT REMAINING LOW GIVE THE LACK OF
SUFFICIENT DEEP LAYER SHEAR AND WEAK INSTABILITY.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
AS OF 300 AM WEDNESDAY...

THURSDAY NIGHT...BROAD UPPER LEVEL RIDGE OVER THE SE U.S.
DISSIPATES...ALLOWING A WEAKENING AREA OF LOW PRESSURE TO TRAVERSE
EAST FROM THE TN VALLEY. THIS WEATHER FEATURE WILL INCREASE/THICKEN
MID-HIGH LEVEL CLOUD COVER AND ALSO AID TO MAINTAIN A LIGHT SLY FLOW
AT THE SURFACE. THIS WILL RESULT IN A MILD NIGHT WITH MIN TEMPS
LOW-MID 60S.

FRIDAY...A S/W ROTATING THROUGH THE BASE OF AN UPPER LEVEL TROUGH
OVER EASTERN CANADA-NEW ENGLAND WILL PROPEL A SURFACE BOUNDARY
ACROSS VA FRIDAY AFTERNOON-EVENING. THIS BOUNDARY WILL ENCOUNTER A
SLIGHT-MODERATELY UNSTABLE AIR MASS WITH ENOUGH MOISTURE TO SUPPORT
THE DEVELOPMENT OF SCATTERED STRONG CONVECTION. OUTFLOW ASSOCIATED
WITH THESE STORMS WILL DRIFT SWD INTO OUR FAR NORTHERN COUNTIES LATE
FRIDAY AFTERNOON-FRIDAY EVENING. WHILE AIR MASS WILL NOT BE AS
FAVORABLE FOR CONVECTIVE DEVELOPMENT AS TO THE NORTH...MODEL RH
CROSS SECTIONS AND CONVECTIVE PARAMETERS POINT TO AN AIR MASS OVER
THE PIEDMONT/NORTHERN COASTAL PLAIN CAPABLE OF SUSTAINING SCATTERED
CONVECTION THROUGH MID EVENING.

WHILE LOW LEVEL LAPSE RATES PROJECTED TO BE NEAR 9 DEG C/KM...MID
LEVEL LAPSE RATES NO HIGHER THAN 6 DEG C/KM. IN ADDITION...WIND
FIELD RATHER WEAK. WHILE A STRONG STORM CANNOT BE RULED OUT NEAR THE
VA BORDER LATE IN THE DAY-EARLY EVENING...NOT ANTICIPATING MUCH IN
THE WAY OF SEVERE STORMS. PLAN TO MAINTAIN CHANCE POPS ACROSS
THE REGION WITH HIGHEST POPS (NEAR 40 PERCENT) ACROSS THE FAR
NORTH-NE BUT DID DELAY ONSET OF HIGHER POPS UNTIL LATE IN THE
AFTERNOON (5 PM OR LATER). SINCE LATER ARRIVAL OF SCATTERED
CONVECTION EXPECTED...AFTERNOON HEATING SHOULD WARM TEMPS INTO THE
MID-UPPER 80S.

FRIDAY NIGHT...SCATTERED CONVECTION ACROSS THE NORTH EARLY IN THE
PERIOD WILL MOVE SEWD AND WEAKEN WITH TIME. MAY SEE CONVECTION MAKE
IT AS FAR SOUTH AS ASHEBORO-FAYETTEVILLE BEFORE DISSIPATING LATE.
DEEPER MOISTURE ACROSS THE FAR N-NE IN PROXIMITY TO THE SWD DRIFTING
SFC BOUNDARY SUGGEST A THREAT OF A SHOWER OR TWO OVERNIGHT TO THE
NORTH-NE OF RDU. MIN TEMPS IN THE LOW-MID 60S.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
AS OF 300 AM WEDNESDAY...

THIS PERIOD WILL START OUT A BIT UNSETTLED THEN SLOWLY IMPROVE EARLY
NEXT WEEK.

THE L/W TROUGH OVER NEW ENGLAND-EASTERN CANADA FRIDAY LIFTS E-NE
SATURDAY INTO SUNDAY...CAUSING AN UPPER LEVEL RIDGE TO EXPAND NE
FROM THE LOWER MS VALLEY INTO NEW ENGLAND. MEANWHILE A SERIES OF
UPPER LEVEL DISTURBANCES OVER THE MID MS VALLEY-LOWER OH VALLEY GET
CAUGHT UNDERNEATH THIS EXPANDING RIDGE AND DRIFT SEWD TOWARD THE
CAROLINAS. THESE PERTURBATIONS INTERACTING WITH A THE MODERATELY
MOIST AND SLIGHTLY UNSTABLE AIR MASS WILL AID TO TRIGGER SCATTERED
CONVECTION...ESPECIALLY IN THE AFTERNOON AND EVENING HOURS. EXPECT
SCATTERED CONVECTION TO BE MORE CONCENTRATED AREAWIDE SATURDAY
AFTERNOON DUE TO THE PRESENCE OF THE OLD SURFACE BOUNDARY WHICH WILL
SERVE AS A FOCUS FOR MOISTURE CONVERGENCE AND CONVECTION INITIATION.
SIMILAR TO YESTERDAY...ECMWF HAS THIS FEATURE FARTHER SOUTH
(SANDHILLS-SOUTHERN PIEDMONT) COMPARED TO THE GFS (NORTHERN
PIEDMONT-NORTHERN COASTAL PLAIN). CONVECTIVE PARAMETERS SUGGEST
ENOUGH INSTABILITY (MLCAPE 1000J/KG); SBCAPE 2000-3000 J/KG  TO
SUPPORT A FEW STRONG STORMS THOUGH WIND PROFILE SUGGEST SEVERE
POTENTIAL WEAK. WILL FAVOR THE MORE NORTHWARD GFS PLACEMENT AN D
HAVE THE HIGHEST POPS ACROSS THE NORTH (35-42 PERCENT) VERSUS SOUTH
(27-30 PERCENT). EXPECT CONSIDERABLE CLOUDINESS SATURDAY ALONG WITH
A SHOWER OR TWO IN THE MORNING...WITH SCATTERED CONVECTION BECOMING
MORE PROMINENT BY EARLY AFTERNOON. THIS SUGGEST MAXIMUM TEMPS
SATURDAY A FEW DEGREES COOLER COMPARED TO FRIDAY...ESPECIALLY ACROSS
THE NORTH. HIGH TEMPS SATURDAY...NEAR 80 NORTH TO MID 80S SOUTH.

ON SUNDAY...BEST CHANCES FOR AFTERNOON CONVECTION APPEAR TO BE IN
THE WEST CLOSER TO BETTER UPPER SUPPORT COMPARED TO THE EAST. SFC
BOUNDARY DIMINISHES WITH TIME. THUS EXPECT COVERAGE SUNDAY TO BE A
LITTLE LESS COMPARED TO THE SATURDAY. THIS WILL LEAD TO WARMER
TEMPS. MAX TEMPS SUNDAY LOW-MID 80S.

MID-UPPER LEVEL SHEAR AXES ASSOCIATED WITH THE WEEKEND UPPER LEVEL
DISTURBANCES GRADUALLY WEAKEN AND LIFT NEWD MONDAY INTO TUESDAY. AN
AREA OF HIGH PRESSURE WILL BECOME ANCHORED OFFSHORE AND EXTEND WEST
INTO THE SE U.S./FL PENINSULA. MEANWHILE A DEEP UPPER LEVEL LOW WILL
LIFT NEWD ACROSS THE CENTRAL PLAINS INTO THE UPPER MIDWEST. THIS
PATTERN RESEMBLES AN EARLY SUMMER SCENARIO AND EXPECT COMPARABLE
CONDITIONS ACROSS CENTRAL NC. OVERNIGHT TEMPS IN THE 60S FOLLOWED BY
AFTERNOON TEMPS IN THE 80-85 DEGREE RANGE. A MARGINALLY
MOIST/SLIGHTLY UNSTABLE AIR MASS WILL SUPPORT ISOLATED TO SCATTERED
AFTERNOON CONVECTION WITH BULK OF ACTIVITY DIMINISHING AT SUNSET.
AIR MASS DRIES OUT A BIT BY TUESDAY SUGGESTING A DECREASE IN
CONVECTIVE COVERAGE.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
-- Changed Discussion --
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
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&&

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

&&

$$

SYNOPSIS...BLAES
NEAR TERM...BLAES/BSD
SHORT TERM...WSS
LONG TERM...WSS
AVIATION...BLAES