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000
FXUS62 KRAH 160659
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
257 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 SATURDAY NIGHT/...
AS OF 200 PM WEDNESDAY...

FOR FRIDAY NIGHT: THE WEAK SURFACE TROUGH IS EXPECTED TO LINGER
ACROSS CENTRAL/ERN NC INTO SC... WHILE THE PRIMARY FRONTAL ZONE
STRETCHES ACROSS MD BACK TOWARD CHICAGO. THE WEAK MID LEVEL LOW NOW
OVER NW TX WILL EASE EASTWARD ACROSS THE CAROLINAS AS A WEAK AND
SHEARING OPEN WAVE... ALTHOUGH DPVA SHOULD BE QUITE SMALL GIVEN THE
VERY LIGHT MID-LEVEL FLOW FROM THE NW. THE NOSE OF THE LOW LEVEL JET
SITS WELL WEST OVER THE LOWER-MID MISS VALLEY (NRN LA/NRN AL/WRN
TN/KY) BUT MODELS DEVELOP AFTERNOON STORMS ALL ALONG AND SOUTH OF
THE 925 MB FRONT FROM NRN IL ACROSS WV TO SE VA... WITHIN AN OVERALL
WEAK WIND FIELD AND LOW DEEP LAYER SHEAR BUT POSSESSING MODERATE
INSTABILITY (MLCAPE UP TO 1000-1500 J/KG). CURRENT CONFIGURATION OF
CONVECTION CHANCES WITH THE BEST CHANCES NEAR THE VA BORDER AND IN
THE NORTHEAST PORTIONS OF THE FORECAST AREA HANDLES THIS WELL. THE
ECMWF AND ESPECIALLY THE GFS KEEP CONVECTION GOING OVERNIGHT OVER
MUCH OF EASTERN NC NEAR THE POORLY DEFINED INTERSECTION OF THE
AFOREMENTIONED TROUGH AND WHAT LOOKS TO BE A SSW-MOVING OUTFLOW
BOUNDARY. GIVEN THE LINGERING MARGINAL ELEVATED INSTABILITY
OVERNIGHT AND PRECIP WATER OVER 150% OF NORMAL... SCATTERED
SLOW-MOVING SHOWERS AND ISOLATED STORMS IN THE EAST THROUGH THE
NIGHT HERE SEEMS REASONABLE. HIGHS 82-87 WITH THICKNESSES 15-20
METERS ABOVE NORMAL AND INCREASING CLOUD COVER. LOWS 62-66 WITH
MOSTLY CLOUDY SKIES... INCLUDING LOW STRATUS TOWARD DAYBREAK.

FOR SATURDAY/SATURDAY NIGHT: THE MID LEVEL WAVE OBSERVED OVER NV/UT
THIS MORNING IS EXPECTED TO TRACK TOWARD THE ESE TOWARD NC BY THE
WEEKEND... ALTHOUGH ITS STRENGTH ON THE MODELS MAY BE ERRONEOUSLY
ENHANCED BY CONVECTIVE FEEDBACK ALONG ITS JOURNEY. THE WEAK STEERING
FLOW OVER NC WILL STILL LIMIT THE FORCING FOR ASCENT VIA DPVA AS THE
WAVE ARRIVES LATE SATURDAY INTO SATURDAY NIGHT... AND THE WEAK LOW
LEVEL FLOW WILL CURB MASS CONVERGENCE ALONG ANY RESIDUAL ILL-DEFINED
TROUGH OR OUTFLOW. BUT DESPITE THIS AND MID LEVEL LAPSE RATES OF
JUST 5.5-6.0 C/KM... THE CONTINUED PRESENCE OF ABOVE-NORMAL PRECIP
WATER (NEAR 1.5 INCHES OR OVER 150% OF NORMAL) AND INCREASING
INFLUENCE OF LOW LEVEL CONFLUENT AND ONSHORE-DIRECTED ATLANTIC
INFLOW NECESSITATES A MENTION OF AT LEAST SCATTERED STORMS FOCUSED
IN (BUT NOT RESTRICTED TO) THE AFTERNOON/EVENING HOURS. INSTABILITY
IS IN QUESTION WITH 500-M MLCAPE OF 500-1000 J/KG ON THE ECMWF AND
1000-2000 J/KG ON THE GFS... AND IF WE DO ACHIEVE GREATER
INSTABILITY... POPS MAY NEED TO GO UP INTO THE LIKELY RANGE IN LATER
FORECASTS. HIGHS 79-85 WITH CONSIDERABLE CLOUDINESS. LOWS 62-66
UNDER CLOUDY SKIES. -GIH

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 305 PM WEDNESDAY...

FOR SUNDAY/SUNDAY NIGHT: THE WEAK WAVE WILL CONTINUE TO MEANDER TO
THE SE ACROSS THE CAROLINAS SUNDAY... ALTHOUGH IT WILL BE EMBEDDED
WITHIN A LARGE RIDGE EXTENDING FROM THE GREAT LAKES DOWN TO THE
INTERIOR SOUTHEAST... WHILE BROAD TROUGHING SITS OVER THE WESTERN
CONUS. THE GFS RETAINS A STRONGER MID LEVEL WAVE AND AS SUCH FORMS A
POTENT INVERTED TROUGH OVER ERN NC INTO CENTRAL SC WITH A WEDGE-LIKE
NNE SURFACE FLOW PATTERN OVER THE WRN PIEDMONT... WHEREAS THE ECMWF
WITH ITS WEAKER WAVE DEPICTS A LARGE SURFACE HIGH CENTERED OFF NEW
ENGLAND EXTENDING SOUTHWARD JUST OFF THE EAST COAST WITH A BROAD
SOUTHEASTERLY ATLANTIC INFLOW AND NO SUCH TROUGHING FEATURE. BOTH
HAVE BEEN CONSISTENT BUT SUSPECT THE GFS MAY BE ADVERSELY AFFECTED
BY GRIDSCALE FEEDBACK AND THUS LOWERING SURFACE PRESSURES TOO
MUCH... SO WILL LEAN TOWARD THE ECMWF. THIS FAVORS A MORE
LOW-LEVEL-STEERED INFLUX OF A TROPICAL-LIKE AIR MASS INTO NC
SUNDAY... SUGGESTING GOOD COVERAGE OF LOW-BASED SHOWERS AND A FEW
STORMS (PARTICULARLY IN THE WEST WHERE UPSLOPE FLOW MAY AUGMENT RAIN
COVERAGE) BUT WITH SOME HOLES IN THE CLOUD COVER. HIGHS 77-83 AND
LOWS 64-67.

FOR MONDAY THROUGH WEDNESDAY: AGAIN FOLLOWING THE ECMWF... THE
SURFACE HIGH OFF THE NORTHEAST COAST STARTS TO DRIFT SOUTHWARD...
PUSHED BY MID LEVEL TROUGHING LOCATED TO ITS EAST... WHILE THE MID
LEVEL ANTICYCLONE BECOMES CENTERED OVER THE REGION. THIS RESULTS IN
ANOTHER DAY OF WARM TEMPS ALOFT AND LONG-FETCH SOUTHEAST LOW LEVEL
FLOW INTO NC... AND ANOTHER DAY OF AT LEAST SCATTERED SHOWERS AND A
FEW STORMS WITH MORE CLOUDS THAN SUNSHINE. AS THE OFFSHORE SURFACE
HIGH DRIFTS FURTHER SOUTHWARD... LOW LEVEL FLOW OVER NC WILL WEAKEN
AND VEER TO BE MORE FROM A SOUTHERLY DIRECTION... AND THIS MORE
OVER-LAND DIRECTION AND CONTINUED WARM MID-LEVEL TEMPS SHOULD LEAD
TO REDUCED SHOWERS/STORM COVERAGE ON TUESDAY INTO WEDNESDAY... WITH
A BIT MORE SUNSHINE AND HIGHS REBOUNDING BACK ABOVE NORMAL. MID
LEVEL HEIGHTS WILL CONTINUE TO FALL WITH A CYCLONE CENTER FORMING
OVER THE MIDWEST... AND THIS IS PROJECTED TO BE SLOW TO DRIFT TO THE
SSE OVER THE MID MISS VALLEY... WHICH SHOULD KEEP ITS ASSOCIATED
COLD FRONT (AND FRONTAL PRECIP) WELL TO OUR NORTHWEST THROUGH
WEDNESDAY. WILL KEEP POPS NEAR OR BELOW CLIMATOLOGY ON WEDNESDAY AS
WELL... WITH TEMPS ABOUT A CATEGORY ABOVE NORMAL. -GIH

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
AS OF 140 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
WILL CONTINUE TO EXTEND INTO OUR REGION AND GENERALLY CONTROL OUR
WEATHER. THIS WILL RESULT IN GENERALLY DRY CONDITIONS AGAIN TODAY...
WITH A SLIGHT CHANCE OF AN AFTERNOON AND/OR EVENING SHOWER AND/OR
STORM ACROSS OUR WESTERN AND NORTHERN TAF SITES
(KGSO/KINT/KRDU/KRWI). HOWEVER... PROBABILITIES REMAIN TOO LOW TO
INCLUDE ANY MENTION IN THE TAFS AT THIS TIME. OTHERWISE... LIGHT
SOUTH TO SOUTHWESTERLY WINDS TO 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 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.

&&

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

&&

$$

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