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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 161751
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
151 PM EDT THU MAY 16 2013

.SYNOPSIS...
-- Changed Discussion --
A COLD FRONT OVER THE OHIO VALLEY AND MID ATLANTIC WILL GRADUALLY
MOVE SOUTH INTO THE REGION...AS UPPER LEVEL LOW PRESSURE MOVES IN
FROM THE WEST. BOTH THE FRONT AND THE UPPER LEVEL LOW WILL LINGER
AROUND THE REGION THROUGH THE WEEKEND...AND INTO EARLY NEXT WEEK.
THIS WILL RESULT IN UNSETTLED WEATHER AT LEAST THROUGH TUESDAY.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 1040 AM THURSDAY...

TODAY:
MOISTURE INCREASES ALOFT AHEAD OF A MODESTLY-STRONG MID-LEVEL
SHORTWAVE READILY APPARENT ON WATER VAPOR IMAGERY MOVING ACROSS
NORTHERN ALABAMA. MOSTLY HIGH CLOUDS HAVE ALREADY DRIFTED OVER PARTS
OF CENTRAL NORTH CAROLINA AS OF MID MORNING AND MID-LEVEL MOISTURE
FORECASTS FOR THE REST OF THE DAY...ALONG WITH BUFR SOUNDINGS...
SUGGEST THERE WILL BE NUMEROUS AREAS OF HIGH CLOUDS ACROSS A LARGE
PART OF CENTRAL NORTH CAROLINA. FOR MOST LOCATIONS...THE DAY SHOULD
AVERAGE PARTLY SUNNY...BUT THERE WILL BE MOSTLY CLOUDY PERIODS AT
TIMES. THIS WILL HAVE AN EFFECT ON TEMPERATURES...AND OPTED TO LOWER
MAXES A DEGREE OR TWO ON AVERAGE ACROSS THE AREA. THE 12Z KGSO
SOUNDING WAS DRY AND STABLE TO DEEP CONVECTION...WITH CONSIDERABLE
CIN. BUFR SOUNDINGS FROM BOTH THE NAM AND GFS...ALONG WITH SOUNDINGS
FROM THE RUC...SHOW MOISTURE INCREASING OR APPARENT ABOVE 500MB.
REDUCED ALREADY LOW POPS SOME THROUGH MOST OF THE DAY...BELOW SLIGHT
CHANCE. HIGHS MAINLY 85 TO 90 UNDER A WEST WIND THAT WILL HAVE A FEW
GUSTS IN THE TEENS KNOTS.

TONIGHT:
INSTABILITY INCREASES TO THE NORTH AND WEST LATE THIS AFTERNOON INTO
THIS EVENING...AND 850MB THETA-E AND PRECIPITABLE WATER VALUES ALSO
INCREASE FROM THE WEST AND NORTH...WITH THE LATTER INCREASING FROM
JUST ABOVE A HALF-INCH THIS MORNING TO NEARLY 1.5 INCHES AS WE
APPROACH 06Z. INSTABILITY WILL BE GREATER TO OUR NORTH CLOSER TO THE
SURFACE AND 850MB BOUNDARIES...AND INCREASING FROM THE WEST
ASSOCIATED WITH THE SHORTWAVE THAT BOTH THE LATEST NAM AND RUC
FORECAST MOVING INTO THE WESTERN PIEDMONT AROUND SUNSET. MODEST
500MB HEIGHT FALLS SPREAD EAST...AND BUFR SOUNDINGS FROM BOTH THE
NAM AND GFS SHOW LAPSE RATES ABOVE 800MB STEEPENING DURING THE
EVENING. THE BUFR SOUNDINGS STILL SHOW DECENT CIN IN THE LOWER
LEVELS...BUT MODEST FORCING FROM THE MID-LEVEL SHORTWAVE IN
COMBINATION WITH STEEPENING MID-LEVEL LAPSE RATES AND INCREASING
MOISTURE COULD PROVIDE FOR AN ISOLATED-TO-WIDELY SCATTERED SHOWER OR
THUNDERSTORM THIS EVENING THROUGH THE OVERNIGHT HOURS. IF ANY SHOWER
OR THUNDERSTORM WOULD OCCUR...TAKING THE CONSENSUS OF WRF GUIDANCE...
QPF AND LIFT...IT WOULD BE MORE LIKELY WEST OF A LINE FROM ABOUT
KIXA TO KAFP BEFORE MIDNIGHT...WITH SOME OCCURRENCE TOWARD KRWI AND
KGSB DURING THE OVERNIGHT HOURS. THE LATEST GFS NOTES SCATTERED QPF
THOUGH MOS GUIDANCE POPS ARE LOW...AND THINK COVERAGE SHOULD BE
LIMITED. 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 /18Z THURSDAY THROUGH TUESDAY/...
-- Changed Discussion --
AS OF 150 PM THURSDAY...

VFR CONDITIONS WILL PREVAIL THROUGH THE 18Z VALID TAF PERIOD. AN
ISOLATED SHOWER OR THUNDERSTORM IS POSSIBLE OVERNIGHT...MAINLY AFTER
00Z AND AWAY FROM KFAY. A STRAY SHOWER OR THUNDERSTORM MAY REMAIN
AWAY FROM VICINITY OF KRWI UNTIL THE LATE NIGHT HOURS. WINDS AT KFAY
SHOULD RETAIN A WESTERLY COMPONENT...WHILE ELSEWHERE SURFACE
WINDS...WHILE LIGHT...SHOULD VEER TO AT LEAST NORTHERLY OVER TIME
BEFORE BACKING QUICKLY TO SOUTHWEST TOWARD THE END AND JUST AFTER
THE 18Z VALID TAF PERIOD.

BEYOND THE 18Z VALID TAF PERIOD...AS A COLD FRONT APPROACHES FROM
THE NORTH...AND AN UPPER-LEVEL LOW APPROACHES FROM THE WEST...THE
CHANCES FOR UNSETTLED WEATHER INCREASE. ISOLATED-TO-SCATTERED
SHOWERS AND THUNDERSTORMS ARE POSSIBLE FRIDAY AFTERNOON AND FRIDAY
NIGHT...WITH SCATTERED-TO-NUMEROUS SHOWERS AND THUNDERSTORMS OVER
THE WEEKEND. SCATTERED SHOWERS AND THUNDERSTORMS SHOULD CONTINUE
EARLY NEXT WEEK. OUTSIDE OF SHOWERS AND THUNDERSTORMS...THE CHANCE
FOR LATE NIGHT AND EARLY MORNING LOW CLOUDS AND FOG INCREASES INTO
THE WEEKEND IN A MOIST AIR MASS.
-- End Changed Discussion --

&&

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

&&

$$

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