-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 161033
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
633 AM EDT THU MAY 16 2013

.SYNOPSIS...
A RIDGE OF HIGH PRESSURE OVER THE SOUTHEAST WILL CONTROL THE WEATHER
ACROSS CENTRAL NC THROUGH TODAY. A MID AND UPPER LEVEL AREA OF LOW
PRESSURE WILL APPROACH THE AREA FROM THE WEST TONIGHT AND FRIDAY. A
SURFACE BOUNDARY WILL SLOWLY MOVE SOUTH OVER OUR REGION DURING THE
WEEKEND.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 255 AM THURSDAY...

TODAY:
A DAMPENING RIDGE ALOFT WILL CONTINUE TO KEEP THE BULK OF THE
SHOWERS AND STORMS TO THE WEST AND NORTH OF THE AREA AGAIN TODAY...
AS A NORTHERN STREAM MID LEVEL LOW PUSHED EASTWARD OUT OF THE GREAT
LAKES AND INTO NEW ENGLAND... ALONG WITH A WEAKENING MID LEVEL LOW
MOVING SLOWLY EASTWARD OUT OF OKLAHOMA TODAY. THE MAIN FRONTAL ZONE
NEAR OUR REGION WILL CONTINUE TO REMAIN WELL TO THE NORTH OF OUR
AREA TODAY... EXTENDING FROM THE OHIO VALLEY EASTWARD INTO THE
NORTHERN MID-ATLANTIC... WITH A WEAK LEE SIDE TROUGH OVER OUR
WESTERN PIEDMONT. EXPECT CONVECTION TO FIRE ALONG THE FRONTAL
ZONE... WHICH WILL SLOWLY SINK SOUTHWARD TODAY. WE COULD POSSIBLY
SEE A FEW SHOWERS AND STORMS DRIFT SOUTHWARD.... POSSIBLY
INTERACTING WITH A WEAK DISTURBANCE MOVING ACROSS OUR AREA IN THE
WESTERLY MID LEVEL FLOW TO PRODUCE A FEW SHOWERS AND STORMS ACROSS
OUR FAR NORTH. IN ADDITION ANY STORMS THAT DEVELOP IN THE HIGHER
TERRAIN WILL DRIFT EASTWARD IN THE FAIRLY WEAK WESTERLY FLOW ALOFT.
HOWEVER... INSTABILITY DOES NOT LOOK OVERLY IMPRESSIVE THOUGH...
WITH MLCAPE VALUES 500 TO A 1000 J/KG AT BEST... WITH 20 KTS OR LESS
OF DEEP LAYER SHEAR. THUS... WILL MAINTAIN A SLIGHT CHANCE OF
SHOWERS AND STORMS... WITH A VERY LOW SEVERE POTENTIAL. HOWEVER...
FOR THE MOST PART THINK THE ONLY CLOUDS WE WILL SEE WILL BE FROM MID
AND HIGH LEVEL DEBRIS CLOUD FROM THE SHOWERS AND STORMS TO THE WEST
AND NORTH OF CENTRAL NC. AFTERNOON LOW LEVEL THICKNESS VALUES ARE
EXPECTED TO TOP OUT IN THE 1410 TO 1416 METER RANGE ACROSS THE AREA.
GIVEN WE SHOULD START OUT WARMER TODAY... THINK THIS SHOULD OFFSET
SOME OF THE LOSS OF INCOMING SOLAR RADIATION FROM THE INCREASING
MID/UPPER LEVEL CLOUDS.... AND NOW EXPECT HIGH TEMPS THIS AFTERNOON
TO BE IN THE MID TO UPPER 80S... WITH A FEW LOCATIONS ACROSS THE
EASTERN AND SOUTHERN HALF REACHING THE 90 DEGREE MARK.

TONIGHT:
ANY SHOWERS AND STORMS WHICH ARE ABLE TO DEVELOP AND/OR MOVE INTO
THE AREA FROM THE NORTH TODAY... ARE EXPECTED TO GENERALLY DISSIPATE
WITH THE LOSS OF DAYTIME HEATING. HOWEVER... SOME OF THE LATEST
HIRES MODELS NOW SHOW A FEW ISOLATED SHOWERS OVERNIGHT TONIGHT. THE
LATEST GFS ALSO SHOWS ANOTHER WEAK DISTURBANCE ALOFT... EMANATING
FROM THE SHOWERS AND STORMS CURRENTLY ACROSS OK/TX... MOVING ACROSS
OUR REGION OVERNIGHT. THIS MAY HELP TO SUPPORT AN ISOLATED
SHOWER/STORM OR TWO... BUT CONFIDENCE IS NOT HIGH ENOUGH TO ADD ANY
MENTION TO THE FORECAST AT THIS TIME... GIVEN THE POOR DIURNAL
TIMING AND RESULTANT LACK OF INSTABILITY. LOWS FRIDAY MORNING LOOK
TO BE ON THE WARM SIDE AGAIN... IN THE 62-67 DEGREE RANGE.

FRIDAY:
MAIN WEAK MID LEVEL TROUGH AXIS (WHICH IS FROM THE CURRENT WEAK MID
LEVEL LOW OVER OKLAHOMA NOW) WILL MOVE INTO THE SOUTHEAST U.S...
WHILE THE COLD FRONT TO THE NORTH OF THE AREA IS EXPECTED TO PUSH
SOUTH/SOUTHWESTWARD IN BACKDOOR FASHION A SURFACE HIGH PRESSURE
BUILDS SOUTHWARD OUT OF CENTRAL CANADA BEHIND THE SLOW EXITING
NORTHERN STREAM MID LEVEL LOW (PUSHING TO THE EAST OF NEW ENGLAND BY
00Z SATURDAY). EXPECT THE FRONT WILL APPROACH OUR FAR NORTHEASTERN
REACHES BY 00Z SATURDAY.. EXPECT THE BEST CHANCE OF SHOWERS AND
STORMS WILL BE INVOF THE FRONTAL ZONE. MLCAPE VALUES ON FRIDAY
AFTERNOON ARE EXPECTED TO BE IN THE 700 TO 1500 J/KG RANGE... WITH
0-6 KM DEEP LAYER SHEAR AGAIN EXPECTED TO BE QUITE WEAK... LESS THAN
20 KTS. THUS... NOT OVERLY EXCITED ABOUT A SEVERE THREAT. WILL
CONTINUE TO MENTION HIGH CHANCE POPS ACROSS OUR FAR NORTHEAST TO
SLIGHT CHANCE ACROSS SOUTHERN CENTRAL NC (BEST CHANCE OF SHOWERS AND
STORMS WILL BE FROM THE AFTERNOON INTO THE EVENING... WHEN
INSTABILITY WILL BE MAXIMIZED). GIVEN THE ADDED CLOUD COVER FROM THE
EXPECTED CONVECTION ACROSS THE NORTH... WILL SHOW HIGH TEMPS RANGING
FROM THE MID 80S NORTH TO UPPER 80S TO AROUND 90 SOUTH.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
AS OF 312 AM THURSDAY...

FRIDAY NIGHT...STILL SOME UNCERTAINTY AS TO THE EXTENT OF SCATTERED
CONVECTION THAT IS EXPECTED FRIDAY EVENING ACROSS CENTRAL NC. BASED
ON PROBABLE POSITION OF SFC BOUNDARY ACROSS THE NE COUNTIES AND A
WEAK SHEAR AXIS ALOFT OVER WESTERN-SOUTH CENTRAL NC...EXPECT BEST
CHANCE FOR CONVECTION AFTER SUNSET TO OCCUR NORTH AND EAST OF RDU.
EXPECT COVERAGE TO BECOME ISOLATED BY LATE EVENING THROUGH THE
OVERNIGHT. MIN TEMPS GENERALLY IN THE MID 60S.

SATURDAY THROUGH SUNDAY...
UNSETTLED WEATHER ANTICIPATED FOR THE WEEKEND. WHILE THE ENTIRE
WEEKEND WILL NOT BE A WASH-OUT...IT DOES APPEAR THAT CONVECTION WILL
BE NUMEROUS ENOUGH TO ALTER OUTDOOR PLANS DURING THE AFTERNOON-EARLY
EVENING HOURS.  REMNANTS OF THE UPPER LOW...CURRENTLY CROSSING THE
SOUTHERN PLAINS...WILL APPROACH CENTRAL NC FROM THE TN VALLEY.
MEANWHILE A WEAK SFC BOUNDARY WILL DRIFT SWD AND STALL OVER CENTRAL
NC. THE AIR MASS ACROSS THE CAROLINAS WILL BE QUITE MOIST FOR LATE
SPRING AS PRECIPITABLE WATER VALUES WILL BE INT HE 1.5-1.7 INCHES
RANGE. HEATING OF THIS AIR MASS WILL YIELD SBCAPE VALUES
2000-3000J/KG WITH MLCAPE PROJECTED TO BE CLOSE TO 1500 J/KG. THIS
SUGGEST A MARGINAL THREAT FOR PULSE-TYPE SEVERE STORMS SATURDAY
AFTERNOON THOUGH A WEAK WIND PROFILE WILL LIMIT THE EXTENT OF
STRONG-SEVERE STORMS. MAY SEE MORE OF A HEAVY RAIN THREAT RATHER
THAN DAMAGING WINDS FROM THE STORMS AS THE SHOWERS AND STORMS WILL
BE SLOW-MOVING DUE TO THE WEAK STEERING CURRENTS.

DUE TO MODEL CONSISTENCY...HAVE RAISED POPS SLIGHTLY WITH LIKELY
POPS SATURDAY AFTERNOON-EVENING ACROSS THE NORTH AND SOLID CHANCE
POPS ACROSS THE SOUTH. SEVERE THREAT MARGINAL AT BEST SO WILL NOT
MENTION IN THE HAZARDOUS WEATHER OUTLOOK AT THIS TIME. MAX TEMPS
SATURDAY HIGHLY DEPENDENT ON WHETHER ANY BREAKS IN THE OVERCAST
DEVELOP. THIS POSSIBILITY SEEMS MORE LIKELY SOUTH VERSUS NORTH. PLAN
TO MAINTAIN PREVIOUS FORECAST OF NEAR 80 NORTH TO MID 80S SOUTH.

PRESENCE OF MID-UPPER LEVEL TROUGH/SHEAR AXIS TO OUR WEST-SW COUPLED
WITH A STALLED SFC BOUNDARY AND A VERY MOIST AIR MASS SUGGEST THAT
SCATTERED SHOWERS-ISOLATED THUNDER WILL LIKELY CONTINUE WELL INTO
SATURDAY NIGHT. PLAN TO HAVE HIGH CHANCE POPS ACROSS THE WEST HALF.
MIN TEMPS IN THE MID 60S.

SUNDAY...MODEL DIFFERENCES MENTIONED IN WEDNESDAY AFTERNOON
DISCUSSION PERSIST IN THE LATEST MODEL RUN WITH THE GFS AMPLIFYING
THE SFC BOUNDARY AS A RESULT OF HIGH PRESSURE NOSING INTO THE REGION
CAD STYLE WHILE ECMWF HAS A WEAKER SFC BOUNDARY GRADUALLY WASHING
OUR OVER OUR REGION. FAVOR ECMWF BUT CANNOT TOTALLY RULE OUT THE
GFS. STILL WITH MID-UPPER LEVEL TROUGH IMMEDIATELY TO OUR WEST-SW
AND A MOIST UNSTABLE AIR MASS IN PLACE (PRECIPITABLE WATER VALUES
APPROACHING 1.75 INCHES)...EXPECT ANOTHER ROUND OF SHOWERS AND
STORMS SUNDAY AFTERNOON-EVENING...ESPECIALLY IN THE WEST WHERE MODEL
GUIDANCE HAS FAVORED LOW LEVEL CONVERGENCE IN THIS REGION.  MAX
TEMPS SUNDAY AGAIN DEPENDENT UPON WHETHER ANY BREAKS DEVELOP IN
OVERCAST. EXPECT A MORE SOLID DECK OF OVERCAST WHICH WILL LEAD TO
SLIGHTLY COOLER (BUT RATHER HUMID) CONDITIONS SUNDAY. MAX TEMPS
UPPER 70S NORTH TO LOWER 80S SOUTH.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
AS OF 324 AM THURSDAY...

GENERAL WEATHER TREND EARLY NEXT WEEK WILL BE CONVECTIVE COVERAGE
BECOME LESS WITH EACH PASSING DAY AS UPPER LEVEL SUPPORT WEAKENS AND
THE AIR MASS GRADUALLY DRIES OUT.

WHILE MODEL GUIDANCE DIVERGE ON SUNDAY IN ITS DEPICTION OF SFC
FEATURES...MODEL GUIDANCE IN GENERAL CONSENSUS BY MONDAY WITH ITS
SFC DEPICTION OF AN INVERTED SFC TROUGH SW-NE ACROSS CENTRAL NC
WHILE SUPPORT ALOFT SUPPLIED BY THE EVER LINGERING MID-UPPER LEVEL
ROUGH WHICH EDGES CLOSER TO OUR REGION MONDAY. EXPECT ANOTHER ROUND
OF SCATTERED SHOWERS/T-STORMS MONDAY AFTERNOON-EVENING. DEPENDENT
UPON WHAT HAPPENS THIS WEEKEND...THIS ROUND OF CONVECTION MAY LEAD
TO ISOLATED RUN-OFF PROBLEMS LEADING TO MINOR FLOODING AS PRECIP
WATER VALUES MONDAY AFTERNOON STILL IN THE 1.5-1.75 INCH RANGE. MAX
TEMPS AGAIN DEPENDENT ON EXTENT OF BREAKS IN OVERCAST. MA X TEMPS
NEAR 80-LOWER 80S.

TUESDAY THROUGH WEDNESDAY WILL LIKELY SEE A MORE NOTABLE DECREASE IN
CONVECTIVE COVERAGE IN THE AFTERNOON-EVENING AS AIR MASS GRADUALLY
DRIES OUT AND UPPER LEVEL SUPPORT WEAKENS/DIMINISHES. WITH A BETTER
OPPORTUNITY FOR PARTIAL SUN...AFTERNOON TEMPS IN THE LOW-MID 80S
SHOULD OCCUR.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
-- Changed Discussion --
AS OF 630 AM THURSDAY...

24-HR TAF PERIOD:
VFR CONDITIONS ARE GENERALLY EXPECTED TO CONTINUE FOR THE 24 HOUR
TAF PERIOD... AS HIGH PRESSURE TO THE EAST AND SOUTH OF THE AREA
CONTINUES TO EXTEND INTO OUR REGION AND WILL GENERALLY KEEPS CENTRAL
NC DRY. HOWEVER... WE WILL HAVE A SLIGHT CHANCE OF AN AFTERNOON
AND/OR EVENING SHOWER AND/OR STORM ACROSS OUR WESTERN AND NORTHERN
TAF SITES (KGSO/KINT/KRDU/KRWI). PROBABILITIES REMAIN TOO LOW TO
INCLUDE ANY MENTION IN THE TAFS AT THIS TIME THOUGH. OTHERWISE...
LIGHT SOUTHWESTERLY WINDS WILL INCREASE BY MID MORNING INTO THE 10
TO 15 KT RANGE.... WITH POSSIBLY A FEW GUSTS INTO THE TEENS KTS BY
AFTERNOON. WINDS WILL DECREASE AGAIN WITH SUNSET AND THE LOSS OF
DIURNAL MIXING... INTO THE 4 TO 9 KT RANGE OUT OF THE SOUTHWEST.

LOOKING AHEAD:
VFR CONDITIONS SHOULD LARGELY PREVAIL INTO THE WEEKEND. HOWEVER...
EXPECT AN INCREASING POTENTIAL FOR DIURNAL SHOWERS AND STORMS FRIDAY
THROUGH THE WEEKEND...WITH SUB-VFR CONDITIONS POSSIBLE IN
ASSOCIATION WITH ISOLD TO SCT SHOWERS AND THUNDERSTORMS...PRIMARILY
DURING THE LATE AFTERNOON AND EVENING...AND A CHANCE OF FOG OR LOW
CEILINGS DURING THE EARLY MORNING HOURS...PRIMARILY SUN/MON.
-- End Changed Discussion --

&&

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

&&

$$

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