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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 171032
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
632 AM EDT FRI MAY 17 2013

.SYNOPSIS...
A COLD FRONT OVER THE OHIO VALLEY AND MID ATLANTIC WILL GRADUALLY
MOVE SOUTH INTO OUR REGION WHILE AN UPPER LEVEL LOW PRESSURE SYSTEM
MOVES IN FROM THE WEST. BOTH THE FRONT AND THE UPPER LEVEL LOW WILL
LINGER AROUND OUR AREA THROUGH THE WEEKEND INTO EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH SATURDAY/...
AS OF 310 AM FRIDAY...

TODAY:
A WEAK S/W MOVING ACROSS THE AREA NOW IS EXPECTED TO PUSH TO THE
EAST OF CENTRAL NC BY DAYBREAK... LEAVING WEAK S/W RIDING TO BUILD
OVER THE REGION TODAY. DO NOT EXPECT MUCH IF ANY SHOWER ACTIVITY
WITH THE CURRENT MID LEVEL DISTURBANCE MOVING ACROSS THE AREA GIVEN
THE TIME OF DAY AND LACK OF GOOD MOISTURE. MORE OF A CONCERN IS THE
SURFACE TROUGH ACROSS THE AREA (WHICH IS EXPECTED TO BECOME ORIENTED
MORE WEST TO EAST BY THIS AFTERNOON) ALONG WITH REMNANT OUTFLOW THAT
HAS MOVE ACROSS NORTHERN PORTIONS OF THE AREA FROM CONVECTION ACROSS
WV/VA EARLIER TODAY. MEANWHILE THE ACTUAL SURFACE FRONT (WHICH IS
STILL STALLED OUT FROM JUST SOUTH OF THE GREAT LAKES TO THE NORTHERN
MID-ATLANTIC). THIS FRONT IS EXPECTED TO FINALLY GET A PUSHED
SOUTHWARD AS SURFACE HIGH PRESSURE BUILDS SOUTHWARD OUT OF CENTRAL
CANADA. EXPECT THE FRONT SHOULD GENERALLY REMAIN TO THE NORTH AND
NORTHEAST OF THE AREA THOUGH. THUS... THINK THE AFOREMENTIONED
SURFACE TROUGH COMBINED WITH THE REMNANT OUTFLOW WILL BE THE FOCUS
FOR ANY SHOWERS AND STORMS TODAY. WRT TO PRECIP CHANCES... OVERALL
MOISTURE IS EXPECTED TO BE BETTER TODAY... WITH PW`S APPROACHING 1.5
INCHES. HOWEVER... WITH S/W RIDGING BUILDING ACROSS THE AREA
TODAY... UPPER LEVEL SUPPORT IS NOT GREAT. HI-RES MODELS ALONG WITH
THE GFS AND NAM CONTINUE TO SHOW DEVELOPMENT ACROSS THE AREA
TODAY... INVOF THE AFOREMENTIONED SURFACE TROUGH AND OUTFLOW.
THUS... WILL SHOW THE HIGHEST POP (30-40 PERCENT) CENTERED NEAR A
LINE FROM EXX TO RDU AND RWI... WITH LOW END CHANCE POPS TO THE
NORTH OF THIS LINE AND SLIGHT CHANCE ACROSS OUR FAR SOUTH. IN
ADDITION... WE MAY ALSO SEE A FEW SHOWERS/STORMS DEVELOP ALONG THE
HIGHER TERRAIN AND SLOWLY DRIFT EASTWARD INTO OUR WESTERN PIEDMONT
THIS AFTERNOON. WRT TO A SVR POTENTIAL... MLCAPE VALUES ARE EXPECTED
TO TOP OUT THIS AFTERNOON IN THE 700-1500 J/KG RANGE... BUT 0-6 KM
DEEP LAYER SHEAR WILL AGAIN BE QUITE WEAK (LESS THAN 20 KTS).
THUS... ANY SEVERE POTENTIAL WILL REMAIN QUITE LOW... WITH NOT EVEN
A 5 PERCENT MENTION FROM SPC. HIGH TEMPS TODAY WILL BE TEMPERED
ACROSS MOST OF THE AREA A BIT BY THE EXTRA MOISTURE/CLOUD COVER....
WITH THE BEST HEATING EXPECTED ACROSS THE FAR SOUTH. THUS... WILL GO
WITH HIGH TEMPS RANGING FROM THE MID 80S NORTH TO AROUND 90 SOUTH.

TONIGHT:
WITH WEAK S/W RIDGING HOLDING ON ACROSS THE AREA TONIGHT... EXPECT
ANY AFTERNOON AND EVENING SHOWERS/STORMS SHOULD DWINDLE WITH
NOCTURNAL COOLING AND RESULTANT STABILIZATION OF THE BOUNDARY LAYER.
THUS... WILL TREND POPS TO A SLIGHT CHANCE AFTER MIDNIGHT. CANNOT
RULE OUT ANY LOCALIZED AREA OF FOG AND LOW CLOUDS DEPENDING ON IF
AND WHERE ANY LOCALIZED HEAVY PRECIP FALLS TODAY. EXPECT LOW TEMPS
TONIGHT WILL AGAIN BE ABOVE NORMAL IN THE MID TO UPPER 60S.

SATURDAY:
THE WEAK MID LEVEL LOW OVER THE OZARKS THIS MORNING WILL CONTINUE
SLOWLY SHIFT EASTWARD ON SATURDAY WHILE OPENING UP AND WEAKENING...
WHILE MOVING INTO THE CENTRAL AND SOUTHERN APPALACHIANS. BOTH THE
GFS AND ECMWF DEPICT THIS DISTURBANCE SHOULD BE CLOSE ENOUGH TO THE
AREA TO SUPPORT HIGHER POPS ON SATURDAY (WITH THE NAM TRYING TO HOLD
IT OFF MORE). THUS... WILL CONTINUE TO GO WITH A WETTER SOLUTION.
MLCAPE VALUES ARE EXPECTED TO TOP OUT IN THE 1500 TO 2000 J/KG RANGE
ACROSS THE PIEDMONT. STILL DEEP LAYER SHEAR WILL REMAIN WEAK (LESS
THAN 20 KTS AGAIN)... RESULTING IN A LOW SEVERE POTENTIAL AGAIN.
HOWEVER... WE MAY HAVE A LOCALIZED FLOODING THREAT WITH THE EXPECTED
SLOW MOTION OF THE SHOWERS/STORMS AND EXPECTED GREATER COVERAGE.
THUS... WILL HIGHLIGHT THIS THREAT FOR LOCALIZED FLOODING/EXCESSIVE
RAINFALL IN THE HWO. HIGHS SATURDAY WILL BE LOWER WITH THE FRONT TO
THE NORTH TRYING TO OOZE DOWN INTO NORTHERN PORTIONS OF OUR AREA AND
GREATER COVERAGE OF SHOWERS AND STORMS. THUS WILL GO WITH UPPER 70S
NORTH TO MID 80S SOUTH. EXPECT THE BEST COVERAGE OF SHOWERS AND
STORMS WILL AGAIN BE ACROSS THE NORTHERN HALF OF THE AREA... CLOSER
TO THE BEST SURFACE CONVERGENCE. THUS.. WILL GO WITH LIKELY POPS
NORTH TO CHANCE SOUTH.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
AS OF 301 AM FRIDAY...

WET AND UNSETTLED PERIOD SETTING UP FOR CENTRAL NC WITH A
POSSIBILITY OF LOCALLY EXCESSIVE RAINFALL.

SATURDAY NIGHT INTO SUNDAY...MODELS IN GOOD CONSENSUS WITH AN UPPER
LEVEL LOW OVER THE LOWER OH VALLEY SATURDAY EVENING DRIFTING  SLOWLY
SEWD INTO EASTERN KY BY SUNDAY AFTERNOON. MEANWHILE A STALLED SFC
BOUNDARY WILL STRETCH WEST-TO-EAST IN VICINITY OF THE NC/VA BORDER.
THE APPROACH OF THE UPPER LEVEL LOW WILL INCREASE LOW LEVEL SLY
FLOW...MADE EVIDENT BY 850MB FLOW INCREASING FROM 15 KTS SATURDAY
EVENING TO 25-30KTS BY SUNDAY EVENING. THIS FLOW WILL PUMP MOISTURE
OFF THE ATLANTIC AND EASTERN GULF INTO THE CAROLINAS...INCREASING
PRECIPITABLE WATER VALUES TO AS HIGH AS 1.75 INCHES BY SUNDAY
EVENING. THE UPPER LEVEL LOW WILL ALSO INCREASE MID-UPPER DIVERGENCE
OVER THE REGION. THUS THE COMBINATION OF INCREASING LOW LEVEL
CONVERGENCE...INCREASING DIVERGENCE ALOFT...AND A VERY MOIST AIR
MASS WILL SUSTAIN SCATTERED SHOWERS ACROSS THE REGION SATURDAY
NIGHT...MAINLY NORTH AND WEST...AND LEAD TO THE DEVELOPMENT OF
NUMEROUS SHOWERS AND A FEW T-STORMS SUNDAY AFTERNOON-SUNDAY NIGHT.
WILL MAINTAIN LIKELY POPS ACROSS THE NORTH HALF FOR NORTH WITH SOLID
CHANCE POPS SOUTH-SOUTHEAST. MAX TEMPS SUNDAY WILL BE AFFECTED BY
OVERCAST SKIES AND NUMEROUS SHOWERS. MAX TEMPS LOWER 80S
SOUTH-SOUTHEAST TO THE UPPER 70S NORTH.

SUNDAY NIGHT THROUGH MONDAY NIGHT...UPPER LEVEL LOW SLOWLY OPENS UP
AND DRIFTS EAST ACROSS THE FORECAST AREA DURING THIS TIME.
ASSOCIATED MID LEVEL TROUGH WILL ALSO DRIFT EAST WITH TIME BUT HELP
TO FOCUS MOST OF THE SHOWERS AND SCATTERED T-STORMS ALONG AND EAST
OF HIGHWAY 1 BY MONDAY AFTERNOON. STALLED SFC BOUNDARY IN VICINITY
OF THE VA BORDER WILL CONTINUE TO SERVE AS A FOCUS FOR LOW LEVEL
CONVERGENCE AND MOISTURE POOLING. THUS STILL FAVOR HIGHER POPS
(LIKELY) ACROSS THE NORTH-NORTHEAST THIS PERIOD...TRENDING TO HIGH
CHANCE OR LOW END LIKELY SOUTH. MONDAY MAX TEMPS AGAIN HAMPERED BY
EXTENSIVE CLOUDINESS AND SCATTERED-NUMEROUS SHOWERS. MAX TEMPS UPPER
70S/NEAR 80 NORTH TO LOWER 80S SOUTH. MIN TEMPS MID 60S.

PRESENCE OF THE STALLED SFC BOUNDARY ACROSS THE NORTH WILL AID TO
FOCUS MOST OF THE SHOWER DEVELOPMENT. WITH PRECIP WATER VALUES
AROUND 1.6-1.75 INCHES LATE SATURDAY THROUGH MONDAY NIGHT...SHOWERS
AND STORMS WILL BE EFFICIENT RAIN PRODUCERS. HPC HAS AN AREA OF THE
NC PIEDMONT AND SOUTHERN VA OUTLINED FOR THE POSSIBILITY OF
EXCESSIVE RAINFALL WITH AMOUNTS IN EXCESS OF 3 INCHES (EQUIVALENT TO
A MONTHS WORTH OF RAIN) POSSIBLE NEAR THE VIRGINIA BORDER LATE
SATURDAY THROUGH MONDAY EVENING. CURRENTLY...WENT A BIT MORE
CONSERVATIVE AND HAVE STORM TOTAL PRECIP AMOUNTS 2-2.5 INCHES IN
THIS REGION. HOWEVER THIS SET-UP USUALLY LEAD TO LOCALLY EXCESSIVE
RAINFALL SO COULD SEE HIGHER AMOUNTS IN THIS REGION. PLAN TO MENTION
THREAT FOR LOCALLY EXCESSIVE RAINFALL IN THE HAZARDOUS WEATHER
OUTLOOK.

&&

.LONG TERM /TUESDAY THROUGH THURSDAY/...
AS OF 301 AM FRIDAY...

TUESDAY THROUGH WEDNESDAY...WEAK SUBSIDENCE BEHIND THE EXITING
MID/UPPER LEVEL TROUGH WILL AID TO DRY OUT THE AIR MASS. A SLIGHTLY
MORE STABLE AND DRIER AIR MASS WILL LEAD TO FEWER SHOWERS AND STORMS
IN THE AFTERNOON. IN ADDITION...THIS WILL LEAD TO WARMER AFTERNOON
TEMPS. WILL MAINTAIN A SLIGHT CHANCE POP EVERYWHERE TO COVER THREAT
OF AFTERNOON CONVECTION WHILE MAX TEMPS WILL BE REFLECTIVE OF THE
EARLY SUMMER PATTERN IN THE LOW-MID 80S.

BY THURSDAY...GFS MUCH MORE AGGRESSIVE WITH ITS EWD MOVEMENT OF A
S/W TROUGH AND ASSOCIATED SFC FRONT INTO THE MID ATLANTIC AND
CAROLINAS. ECMWF MUCH SLOWER WITH BEST UPPER SUPPORT OVER THE GREAT
LAKES AND LOWER OH VALLEY. FAVOR THE SLOWER ECMWF AT THIS TIME.
THUS...WILL LOWER POPS THURSDAY FROM PREVIOUS FORECAST WITH SLIGHT
CHANCE OF AFTERNOON CONVECTION AND HIGHS TEMPS SOLIDLY IN THE MID
80S. MIN TEMPS THROUGH THE PERIOD MAINLY IN THE MID 60S.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
AS OF 630 AM FRIDAY...

MAINLY VFR CONDITIONS WILL PREVAIL THROUGH THE 12Z TAF PERIOD. THE
POSSIBLE EXCEPTION WILL RESULT FROM SCATTERED SHOWERS AND STORMS
FOCUSED ALONG A SURFACE PRESSURE TROUGH/REMNANT OUTFLOW THIS
AFTERNOON FROM TRIAD TERMINALS TO KRDU AND KRWI AND POSSIBLY SOME
LOW STRATUS AND/OR FOG IN THE PRE-DAWN HOURS OF SATURDAY. WILL KEEP
ONLY VICINITY SHOWERS MENTIONED IN THE TAFS FROM THIS AFTERNOON INTO
THE EVENING... GIVEN BOTH THE TIMING AND COVERAGE UNCERTAINTY WITH
ANY SHOWERS AND STORMS. WILL GO WITH A LIGHT AND VARIABLE WIND
ACROSS THE THE NORTHERN TAF SITES... WITH MORE OF A SOUTHWESTERLY
WIND AT KFAY THROUGH EARLY AFTERNOON... BEFORE OUTFLOW FROM SHOWERS
AND STORMS TO THE NORTH MAY RESULT IN VARIABLE WINDS FOR KFAY AS
WELL. EXPECT THE BULK OF THE PRECIP TO DISSIPATE AND DWINDLE IN
COVERAGE LATE THIS EVENING WITH THE LOSS OF DAYTIME HEATING. WE MAY
SEE SOME PATCHY FOG AND/OR LOW STRATUS DEVELOP TONIGHT ACROSS THE
AREA. HOWEVER... WILL NOT MENTION ANY RESTRICTIONS IN THE TAFS AT
THIS TIME GIVEN THE SUB-VFR CONDITIONS WILL BE DRIVEN BY WHERE THE
RAIN FALLS AND THE AMOUNT OF MID AND HIGH LEVEL CLOUD COVER
STREAMING INTO THE AREA FROM THE WEST.

LOOKING AHEAD: AS A COLD FRONT APPROACHES FROM THE NORTH...AND AN
UPPER-LEVEL LOW APPROACHES FROM THE WEST...THE CHANCES FOR UNSETTLED
WEATHER INCREASE. SCATTERED-TO-NUMEROUS SHOWERS AND THUNDERSTORMS
ARE EXPECTED OVER THE WEEKEND. SCATTERED SHOWERS AND THUNDERSTORMS
SHOULD CONTINUE EARLY NEXT WEEK AS WELL. THE CHANCE FOR LATE NIGHT
AND EARLY MORNING LOW CLOUDS AND FOG WILL INCREASE INTO THE WEEKEND
AND EARLY NEXT WEEK IN A MOIST AIR MASS AS WELL.
-- End Changed Discussion --

&&

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

&&

$$

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