-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 170708
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
308 AM EDT MON JUN 17 2013

.SYNOPSIS...
A COLD FRONT WILL APPROACH FROM THE NORTHWEST TODAY AND ACROSS OUR
REGION LATE TUESDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
AS OF 940 PM SUNDAY...

RELATIVELY BENIGN CONVECTION HAS BEEN MOVING WEST TO EAST ACROSS
KY/WV/VA THIS EVENING...WITHIN A ZONE OF PREFRONTAL CONVERGENCE AND
DEEP MOISTURE.  FURTHER SOUTH OVER THE LOWER TENNESSEE
VALLEY...WHERE DAYTIME INSTABILITY STILL LINGERS...A MORE WELL
DEFINED CLUSTER OF STORMS IS CURRENTLY MOVING ACROSS NORTHERN GA AND
AND INTO FAR WESTERN NC. THESE TWO AREAS WILL GRADUALLY POSE A
THREAT TO THE NORTHERN AND WESTERN PORTIONS OF CENTRAL NC THROUGH
MONDAY.  TONIGHT...FORCING WILL BE WEAK AS THE MOIST/CONVERGENCE
AXIS..WHERE PW VALUES AT 1.5-2"...SLOWLY SHIFTS SOUTHEASTWARD TOWARD
THE AREA.  THE AFOREMENTIONED CLUSTER OF STORMS APPROACHING WESTERN
NC SHOULD WEAKEN AS IT ENCOUNTERS MORE HOSTILE AIR EAST OF THE
MOUNTAINS...BUT THE LINGERING OUTFLOW COULD ALSO SERVE AS A CATALYST
FOR SHOWERS IF IT DRIFTS ALL THE WAY INTO THE SOUTHERN/WESTERN
PIEDMONT.  BASED ON CURRENT RADAR TRENDS AND LATEST HRRR DATA...HAVE
PUSHED CHANCE POPS BACK UNTIL AFTER 08Z.   OTHERWISE...TEMPS WILL
REMAIN RATHER MILD..FALLING INTO THE UPPER 60S AS CLOUDS STEADILY
INCREASE. -BLS

MONDAY...THE MID-LEVEL SHORTWAVE IS FORECAST TO MOVE THROUGH CENTRAL
NORTH CAROLINA...LEAVING SOME SUBSIDENCE IN ITS WAKE LATE IN THE
DAY...MAINLY TOWARD THE TRIAD. THE NAM IS WEAKER WITH ITS
MIXED-LAYER CAPE...500-1000J/KG COMPARED TO THE 1000-1500J/KG OF THE
GFS. BOTH MODELS SHOW ONLY LIMITED DOWNDRAFT CAPE...MAINLY 200J/KG
OR LESS...UNDER WEAK 0-3KM SHEAR IN THE RANGE OF 15KT. 1000-500MB
LAPSE RATES ARE WEAK AS WELL...TO ABOUT 6C/KM BASED ON THE HIGHER
GFS. AS THE DISTURBANCE PASSES THROUGH WITH A WEAK SURFACE TROUGH IN
PLACE...WILL ESSENTIALLY CARRY HIGH CHANCE POPS FOR THE DAY...
CONFINING THOSE POPS MAINLY TO THE AFTERNOON IN THE FAR SOUTHEAST.
ANTICIPATING MORE CLOUDS...HAVE LOWERED MAXES FOR MONDAY TO THE
LOWER TO MID 80S.

MONDAY NIGHT...BOTH THE NAM AND THE GFS FORECAST SOME SUBSIDENCE
BEHIND THE MID-LEVEL SHORTWAVE...PARTICULARLY FROM THE TRIANGLE
NORTHWEST AND NORTH OVERNIGHT. THIS MAY RESULT IN CHANCES FOR
PRECIPITATION BECOMING LIMITED IN THOSE AREAS. FARTHER
SOUTH...HIGHER MOISTURE AND INSTABILITY PERSISTS OVERNIGHT...WITH
ANOTHER MID-LEVEL SHORTWAVE SKIRTING THE AREA TO THE SOUTH. IF THIS
VERIFIES...CHANCES FOR SHOWERS AND ISOLATED THUNDERSTORMS COULD
LINGER INTO THE OVERNIGHT HOURS...ESPECIALLY ACROSS THE SANDHILLS
AND SOUTHERN COASTAL PLAIN. FOR THIS FORECAST...WILL SHOW A
DIMINISHING TREND TO PRECIPITATION CHANCES...ONLY SLIGHT CHANCE IN
THE TRIAD OVERNIGHT WITH CHANCES MAINLY ALONG AND SOUTH OF U.S. 64.
ONCE AGAIN...OVERNIGHT LOWS SHOULD BE WARM...WITHIN A DEGREE OR
THREE OF 70.
-- End Changed Discussion --

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
-- Changed Discussion --
AS OF 240 AM MONDAY...

A SERIES OF DISTURBANCES ALOFT...WHICH HAVE TRENDED WEAKER IN NWP
GUIDANCE DURING THE PAST FEW DAYS AND WHOSE TIMING IS UNCERTAIN
GIVEN THE PROBABILITY OF BEING MODULATED BY UPSTREAM
CONVECTION...WILL MIGRATE THROUGH THE BASE OF A BROAD TROUGH ALOFT
EAST OF THE ROCKIES...AND ACROSS THE CENTRAL APPALACHIANS/NC THROUGH
WED. MEANWHILE AT THE SURFACE...A PRE-FRONTAL TROUGH OVER THE MIDDLE
ATLANTIC REGION THIS MORNING WILL STRENGTHEN THROUGH TUE...THEN BE
OVERTAKEN BY A COLD FRONT THAT WILL SETTLE SLOWLY SOUTHWARD FROM THE
MASON DIXON LINE TUE EVENING TO THE NC/SC LINE BY WED EVENING.

PRECIPITABLE WATER VALUES WILL CONSEQUENTLY REMAIN ABOVE
AVERAGE...BETWEEN 1.5 AND 1.8 INCHES... UNTIL FRONTAL PASSAGE. THE
DEEP MOISTURE AND ASSOCIATED UNINHIBITED CONDITIONAL INSTABILITY...
WHICH IS FORECAST TO MAXIMIZE IN THE 1000-1500 J/KG EACH
AFTERNOON...WILL SUPPORT NUMEROUS TO WIDESPREAD THUNDERSTORMS...WITH
COVERAGE DIMINISHING WITH NOCTURNAL COOLING TUE NIGHT...AND THEN
FROM NORTH TO SOUTH WITH THE FRONTAL PASSAGE ON WED. GIVEN THE
EXPECTATION OF WEAKER DISTURBANCES THAN PREVIOUSLY INDICATED...NOTED
ABOVE...MID LEVEL FLOW AND ASSOCIATED BULK SHEAR VALUES ARE NOW
FORECAST TO PEAK ONLY IN THE 20-25 KT RANGE...HIGHEST WED. AS
SUCH...ALREADY MINIMAL SEVERE POTENTIAL WILL BE FURTHER MUTED UNLESS
POCKETS OF STRONGER INSOLATION AND MODERATE INSTABILITY ARE
REALIZED...IN WHICH CASE A FEW STRONG-MARGINALLY SEVERE WET
MICROBURSTS WOULD BE PROBABLE. A MORE LIKELY SCENARIO REMAINS A
THREAT OF DOWNPOURS AND LOCALIZED FLOODING IN TRAINING
CONVECTION...OWING TO WSW MEAN FLOW ALIGNED PARALLEL TO THE MYRIAD
OF UNDERLYING SURFACE BOUNDARIES (TROUGH/EFFECTIVE FRONT-OUTFLOW
/ACTUAL FRONT...AND TO BACKBUILDING INDICATED BY SMALL FORECAST
CORFIDI VECTORS. ANY SUCH FLOODING WILL NOT BE WIDESPREAD...AND
INSTEAD CONFINED MOST LIKELY TO URBAN AREAS SINCE THE ANDREA-SOAKED
SOIL HAS DRIED IN THE PAST WEEK TO 10 DAYS...AND RESULTANT FLASH
FLOOD GUIDANCE VALUES HAVE INCREASED...INTO THE 2.5 TO 3 INCH RANGE
FOR ONE HOUR FOR EXAMPLE.

PROVIDED THERE ARE AT LEAST A FEW BREAKS IN OTHERWISE MOSTLY CLOUDY
SKIES AND CONVECTION...TEMPERATURES SHOULD CLIMB INTO THE LOWER TO
MIDDLE 80S...WARMEST SANDHILLS TUE. OTHERWISE...UPPER 70S WOULD BE
PROBABLE (IE. IN AREAS THAT EXPERIENCE MORE FREQUENT SHOWERS AND
STORMS). LOWS TUE NIGHT MOSTLY IN THE UPPER 60S...TO AROUND 70
DEGREES SOUTH...COOLING A CATEGORY TO TWO IN COOLER POST-FRONTAL NE
FLOW WED NIGHT.
-- End Changed Discussion --

&&

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

THU THROUGH FRI: BELOW AVERAGE TEMPERATURES - GENERALLY IN THE LOWER
TO MIDDLE 80S - IN WEAK POST-FRONTAL HIGH PRESSURE AND ASSOCIATED NE
TO EAST LOW LEVEL FLOW AND STABILITY...WILL THEN PREVAIL THROUGH THE
END OF THE WEEK. WILL ACCORDINGLY MAINTAIN THE FLAVOR OF PREVIOUS
GENERALLY DRY FORECASTS FOR THU-FRI...EXCEPT FOR THE SLIGHTEST OF
CHANCES ALONG THE FAR SOUTHERN AND WESTERN TIER...WHERE BOUNDARY
LAYER MOISTURE WOULD SUPPORT A LATE DAY SHOWER OR STORM. EVEN THAT
SLIGHT CHANCE MAY BE OVERDONE GIVEN AN APPARENT LACK OF TRIGGER
AMIDST DIVERGENT ANTICYCLONIC FLOW WITHIN THE AFOREMENTIONED SURFACE
RIDGE AXIS.

THIS WEEKEND: A SHALLOW UPPER LOW WILL HAVE DRIFTED INTO THE
SOUTHEAST STATES BY THE START OF THE WEEKEND...BUT INSTEAD OF
LIFTING TOWARD THE EAST COAST...GUIDANCE SUGGESTS THIS FEATURE WILL
MOVE WESTWARD AROUND THE SOUTHERN PERIPHERY OF A DEVELOPING
MID-UPPER RIDGE FROM THE SOUTHERN PLAINS TO THE MIDDLE ATLANTIC
REGION. AS SUCH...TEMPERATURES...AND HUMIDITY LEVELS WILL GRADUALLY
INCREASE IN INCREASINGLY SE TO SOUTHERLY RETURN FLOW. THE INCREASING
WARMTH AND HUMIDITY WILL ALSO SUPPORT A SLIGHT UPTICK IN PROBABILITY
OF PRECIPITATION...THOUGH STILL BELOW CLIMATOLOGICAL VALUES IN THE
20TH PERCENTILE GIVEN THE AFOREMENTIONED EXPANSION OF RIDGING
ALOFT...AND LACK OF LOW LEVEL FOCI OTHER THAN PERHAPS THE SEA
BREEZE.
-- End Changed Discussion --

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
AS OF 140 AM MONDAY...

WARM...MOIST...BUT WEAKLY FORCED ENVIRONMENT WILL REMAIN OVER
CENTRAL NC THIS TAF PERIOD. CONDITIONS WILL REMAIN VFR THROUGH THE
PERIOD OUTSIDE OF CONVECTION.

EXPECT A GRADUAL INCREASE THIS MORNING IN MID LEVEL CLOUDINESS
ACROSS THE NORTHERN TIER OF THE AREA. WEAK FORCING FROM OVERNIGHT
CONVECTION IN WESTERN TN AND NORTHERN GA WILL BE MIGRATING INTO THE
WESTERN PIEDMONT THIS MORNING...WITH SCATTERED SHOWERS AT INT/GSO
AFTER SUNRISE...PERHAPS MID MORNING FURTHER EAST...RDU AND RWI.
DECENT INSTABILITY WILL SUPPORT MORE WIDESPREAD SHOWERS AND WIDELY
SCATTERED THUNDER THIS AFTERNOON...TSRA COVERAGE AND CONFIDENCE IN
TIMING/PLACEMENT PRECLUDE TAF INCLUSION AT THIS TIME. EXPECT A LULL
OVERNIGHT ALTHOUGH SCATTERED SHOWERS ARE EXPECTED. WINDS WILL BE
SOUTH TO SOUTHWEST AT LESS THAN 10KT.

ADDITIONAL DISTURBANCES WILL BE CROSSING THE AREA ALONG WITH A WEAK
COLD FRONT TUESDAY INTO WEDNESDAY...WITH PERIODS OF SHOWERS AND
STORMS PRODUCING SUB-VFR CONDITIONS. VFR CONDITIONS ARE
GENERALLY EXPECTED FROM THURSDAY ONWARD... OUTSIDE OF POSSIBLY SOME
EARLY MORNING STRATUS AND OR FOG DURING THE PRE-DAWN HOURS OF EACH
MORNING.

&&

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

&&

$$

SYNOPSIS...MLM
NEAR TERM...DJF/BLS
SHORT TERM...MWS
LONG TERM...MWS
AVIATION...MLM