-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 141911
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
311 PM EDT TUE MAY 14 2013

.SYNOPSIS...
AN UPPER LEVEL RIDGE WILL BUILD OVER THE CAROLINAS FROM THE WEST
THROUGH WEDNESDAY.

&&

.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
-- Changed Discussion --
AS OF 300 PM TUESDAY...

THROUGH TONIGHT:
THE SYNOPTIC PATTERN OVER THE CAROLINAS WILL BE CHARACTERIZED BY
RISING HEIGHTS AND NW FLOW ALOFT AS AN UPPER LEVEL TROUGH PROGRESSES
FURTHER OFFSHORE THE MID-ATLANTIC AND AN AMPLIFYING UPSTREAM RIDGE
BUILDS EAST TOWARD THE SOUTHERN APPALACHIANS. THOUGH SOME MID-LEVEL
MOISTURE COULD ADVECT INTO THE CAROLINAS THIS AFTERNOON THROUGH
TONIGHT IN NW FLOW ALOFT...DRY/STABLE CONDITIONS WILL PRECLUDE THE
POSSIBILITY OF PRECIP. EXPECT HIGHS SEVERAL DEGREES WARMER THAN
YESTERDAY IN ASSOC/W RISING THICKNESSES...RANGING FROM 69-74F...
WARMEST IN THE SANDHILLS AND SOUTHWEST PIEDMONT. DUE TO AIRMASS
MODIFICATION AND A TIGHTENING PRESSURE GRADIENT /SOUTHWEST BREEZE/
IN ADVANCE OF A LOW PRESSURE SYSTEM TRACKING EAST THROUGH THE GREAT
LAKES...LOWS TONIGHT SHOULD BE MUCH WARMER THAN THIS MORNING...
RANGING FROM THE UPPER 40S IN RURAL AND LOW-LYING AREAS SHELTERED
FROM ANY BREEZE TO LOWER/MID 50S ELSEWHERE.

WEDNESDAY AND WEDNESDAY NIGHT:
AN UPPER LEVEL RIDGE BUILDING TOWARD THE SOUTHERN APPALACHIANS TODAY
WILL CONTINUE TO BUILD EAST INTO THE SOUTHEAST/CAROLINAS WED AND WED
NIGHT...THE THE NORTHERN PERIPHERY OF THE RIDGE WILL FLATTEN
SIGNIFICANTLY FROM THE CAROLINAS NORTHWARD AS POTENT SHORTWAVE
ENERGY TRACKS EAST THROUGH THE GREAT LAKES. AS A RESULT...WESTERLY
FLOW ALOFT WILL PREVAIL IN THIS PERIOD. A MARKEDLY WARMER MID-LEVEL
AIRMASS /EML/ WILL SURGE INTO THE REGION FROM THE W/NW TONIGHT...
FOLLOWED BY A MARKEDLY WARMER LOW-LEVEL AIRMASS BY LATE WED MORNING.
FOR EXAMPLE...THE H85 TEMP VIA THE 12Z GSO SOUNDING TODAY WAS
2C...AND IS THE H85 TEMP IS EXPECTED TO BE IN VICINITY OF 17C BY 12Z
WED. THE NET RESULT WILL BE NOTICEABLY WARMER TEMPS ALMOST 10F ABOVE
NORMAL WITH HIGHS IN THE UPPER 80S...IN STARK CONTRAST TO THE RECORD
LOW TEMPS OBSERVED THIS MORNING (I.E. 39F AT RDU AND 40F AT GSO).
LOW-LEVEL MOISTURE WILL INCREASE FROM THE W/SW THROUGHOUT THE
DAY...WITH 925 MB DEWPOINTS IN VICINITY OF 12C AND SFC DEWPOINTS
NEAR 60F WED AFTERNOON. THE AFOREMENTIONED MOISTURE ALONG WITH VERY
STEEP MID-LEVEL LAPSE RATES WILL CONTRIBUTE TO PERHAPS 750-1500 J/KG
MLCAPE DURING PEAK HEATING (~21Z)...MOST UNSTABLE IN THE WESTERN
PIEDMONT. HOWEVER...AN OTHERWISE DRY AIRMASS AND STRONG H85 CAP
(THOUGH DIURNALLY WEAKENING) SHOULD PRECLUDE THE POSSIBILITY OF
ISOLD CONVECTION GIVEN LITTLE IN THE WAY OF FORCING. 12Z HIGH-RES
WRF NMM SIM REF OUTPUT DOES INDICATE VERY ISOLD CONVECTION
DEVELOPING IN FAR SOUTHWEST NC LATE WED AFTERNOON...MOVING EASTWARD
TOWARD CHARLOTTE BY SUNSET...AND THIS CANNOT BE COMPLETELY RULED OUT
GIVEN A POTENTIAL FOR SMALL AMPLITUDE DISTURBANCES IN WESTERLY FLOW
ALOFT DURING THE LATE AFTERNOON AND EARLY EVENING. HOWEVER...THE
PROB OF THIS OCCURRING IS TOO LOW TO MENTION IN THE FORECAST AT THIS
TIME. IF ISOLD CONVECTION DOES DEVELOP...VERY HIGH (BORDERLINE
EXTREME) DCAPE VALUES ~1500 J/KG WOULD CERTAINLY SUPPORT A POTENTIAL
FOR STRONG TO DAMAGING WINDS. THOUGH DEEP-LAYER SHEAR IS EXPECTED TO
BE INSUFFICIENT TO SUPPORT ANY TYPE OF ORGANIZED CONVECTION...
ORGANIZATION ASSOC/W OUTFLOW WOULD BE POSSIBLE GIVEN THE
THERMODYNAMIC ENVIRONMENT IN PLACE...CONDITIONAL UPON CONVECTIVE
INITIATION IN THE FIRST PLACE. EXPECT LOWS WED NIGHT MUCH WARMER IN
THE LOWER 60S. -VINCENT
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
AS OF 145 PM TUESDAY...

FOR THURSDAY/THURSDAY NIGHT: ABOVE-NORMAL WARMTH PERSISTS WITH BROAD
RIDGING ALOFT AND A MILD WSW LOW LEVEL FLOW INTO NC. THE MID-UPPER
LEVEL LOW OVER THE DESERT SOUTHWEST AND NW MEXICO WILL SLOG SLOWLY
EASTWARD THROUGH THE SOUTHERN PLAINS AND MID MISS VALLEY THROUGH
THURSDAY NIGHT... EMBEDDED WITHIN A VERY WEAK STEERING FLOW
PATTERN... BEFORE DISSIPATING OVER THE MID SOUTH. A ROUGHLY
WEST-EAST ORIENTED SYNOPTIC FRONT ACROSS THE OHIO VALLEY WILL DIP
SOUTHWARD TOWARD THE NC/VA BORDER (PUSHED BY A MID LEVEL LOW MOVING
EAST ACROSS THE ST LAWRENCE VALLEY) WHILE SURFACE TROUGHING DEVELOPS
THROUGH THE NC PIEDMONT. WITH LOW DEEP-LAYER SHEAR (UNDER 20 KTS)...
LIMITED LOW LEVEL MOISTURE INFLUX INTO CENTRAL NC (850 MB WINDS STAY
LARGELY FROM THE WEST)... AND SUPPRESSION OF THE BETTER INSTABILITY
(1000-2000 J/KG) TO OUR NORTH NEAR THE FRONT OVER VA... THIS TROUGH
SHOULD NOT BE TOO CONVECTIVELY ACTIVE OVER CENTRAL NC. BUT THE
INCREASING SURFACE DEW POINTS AND WARM TEMPS DO WARRANT A MENTION OF
ISOLATED WEAKLY-FORCED STORMS FROM VERY LATE AFTERNOON THROUGH THE
EVENING. THICKNESSES WILL REMAIN ABOUT 20 METERS ABOVE NORMAL
ALTHOUGH HEATING WILL BE TEMPERED SOMEWHAT BY REMNANT MID CLOUDS
FROM UPSTREAM CONVECTION. HIGHS 86-90. EXPECT A MILD NIGHT WITH LOWS
62-66.

FOR FRIDAY/FRIDAY NIGHT: THE WEAK SURFACE TROUGH IS EXPECTED TO
LINGER OVER SC AND ERN NC WHILE THE PRIMARY FRONTAL ZONE HOLDS
ACROSS PA BACK TOWARD CHICAGO/MN. WHILE DEEP LAYER SHEAR STAYS VERY
LOW AS DOES MODEL-PROJECTED MLCAPE... MID LEVEL PERTURBATIONS
INDUCED BY UPSTREAM CONVECTION OVER THE MIDWEST WILL BE POISED TO
TRACK SOUTHEAST ACROSS THE SOUTHERN APPALACHIANS AND CAROLINAS/VA
FRIDAY/FRIDAY NIGHT... WHICH MAY HELP KICK OFF SOME DISORGANIZED
STORMS PARTICULARLY IF THE REALIZED INSTABILITY IS STRONGER THAN THE
MODELS ARE INDICATING. WILL RETAIN CHANCE POPS... FOCUSED ON MID
AFTERNOON THROUGH MID EVENING BUT WITH A LOWER CHANCE LINGERING
AFTER SUNDOWN. HIGHS 82-87 AND LOWS 61-66. -GIH

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
AS OF 300 PM TUESDAY...

SATURDAY/SUNDAY: THE WEEKEND WILL FEATURE A MID LEVEL LOW OVER MAINE
INTO SE CANADA AND A WEAK BUT AMPLIFIED TROUGH EXTENDING FROM MT TO
NM... HEADING INTO THE PLAINS. STEERING FLOW REMAINS VERY WEAK AND
ILL-DEFINED OVER THE GULF STATES/SOUTHEAST/CAROLINAS BUT WILL BE
GENERALLY FROM THE NW. AS HEIGHTS FALL UPSTREAM WITH A DEEPENING LOW
OVER THE MIDWEST... BOTH THE OPERATIONAL GFS AND ECMWF SHOW A SMALL
VORTICITY MAX (LIKELY A CONVECTIVELY-INSTIGATED FEATURE) OVER IL
SATURDAY MORNING... AND THEY TAKE THIS SLOWLY SE THROUGH THE
CAROLINAS BY SUNDAY. THIS FEATURE WILL BE EMBEDDED WITHIN OVERALL
LONGWAVE RIDGING OVER THE EASTERN CONUS... AND AS SURFACE RIDGING
STRENGTHENS OFF THE EAST COAST (PER THE ECMWF)... THE STRENGTHENING
LOW LEVEL FLOW FROM THE SOUTHEAST AND SOUTH (ATLANTIC- AND
GULF-SOURCE) AHEAD OF THE PLAINS TROUGH WILL SPREAD EASTWARD INTO
THE CAROLINAS. WE SHOULD SEE INCREASING CHANCES FOR SHOWERS/STORMS
EVEN OUTSIDE OF THE DIURNALLY-FAVORED HOURS FROM MID AFTERNOON
THROUGH MID EVENING. ADDITIONAL DYNAMIC SUPPORT WITH THE WEAK
PERTURBATION ON TOP OF THE AFTERNOON INSTABILITY SHOULD YIELD BETTER
COVERAGE SUNDAY COMPARED TO SATURDAY... HOWEVER THE DETAILS ARE
TOUGH TO PIN DOWN THIS FAR OUT ESPECIALLY WITH SUCH A WEAK FLOW
REGIME. THICKNESSES SIT AT OR JUST ABOVE NORMAL WITH PARTLY TO
MOSTLY CLOUDY SKIES... SUGGESTING HIGHS IN THE UPPER 70S TO MID
80S... AND LOWS IN THE 60S.

FOR MONDAY/TUESDAY: THE AFOREMENTIONED WEAK DISTURBANCE IS EXPECTED
TO CULMINATE IN A WEAK LOW OVER OR JUST OFF FL... WHILE THE
AMPLIFYING EASTERN CONUS RIDGE AXIS SHIFTS SLOWLY EASTWARD TO THE
COAST. THE MIDWEST MID LEVEL LOW GETS INCREASINGLY MIRED WITH A
HUDSON BAY VORTEX WHICH HELPS NUDGE THE MIDWEST LOW SLOWLY EASTWARD
TOWARD THE GREAT LAKES BY TUESDAY. THE WEAK/MEANDERING MEAN FLOW
OVER THE MIDATLANTIC REGION WILL BECOME VERY GRADUALLY OVERTAKEN BY
THE TROUGH APPROACHING FROM THE WEST AND ITS PRECEDING STRENGTHENING
SOUTHWEST FLOW... ALTHOUGH THIS SHOULD STAY FAR ENOUGH TO OUR WEST
THROUGH TUESDAY TO BE OF LITTLE IMMEDIATE CONCERN... AND MID LEVEL
HEIGHTS OVER NC SHOULD STAY ABOVE NORMAL. UNDERCUTTING THIS RIDGE
WILL BE THE SOUTHEASTERLY LOW LEVEL FLOW AROUND THE OFFSHORE SURFACE
HIGH... WHICH SHOULD KEEP AT LEAST A SMALL DAILY RISK OF SHOWERS IN
NC... ALTHOUGH THE ECMWF AND ITS STRONGER MID LEVEL RIDGE CENTERED
JUST OFF NC... WEAKER MID LEVEL LAPSE RATES... AND SLIGHTLY WEAKER
LOW LEVEL FLOW FAVORS LITTLE COVERAGE. FOR NOW WILL KEEP POPS ON THE
LOW SIDE... GENERALLY UNDER 30 PERCENT... FOR MONDAY/TUESDAY. WILL
KEEP TEMPS CLOSE TO SEASONAL NORMALS... HIGHS WITHIN A FEW DEGREES
OF 80... WITH LOWS IN THE UPPER 50S TO LOWER 60S. -GIH

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
-- Changed Discussion --
AS OF 200 PM TUESDAY...

24-HR TAF PERIOD:
VFR CONDITIONS WILL RULE THROUGH THE TAF PERIOD AS AN UPPER LEVEL
RIDGE BUILDS EAST ACROSS THE CAROLINAS. LOW-LEVEL WINDS WILL
INCREASE MARKEDLY TONIGHT AS THE MSLP GRADIENT TIGHTENS BETWEEN
LOW PRESSURE OVER THE GREAT LAKES AND HIGH PRESSURE OFF THE SE
COAST. A SOUTHWESTERLY LLJ OF 30-40 KT AS LOW DOWN AS 1500-2000 FT
AGL IS EXPECTED TO DEVELOP BY MIDNIGHT. AT THIS TIME...ENOUGH MIXING
IS EXPECTED TO BE PRESENT TO PRECLUDE LOW LEVEL WIND SHEAR CRITERIA
FROM BEING MET. LIGHT AND VARIABLE WINDS THIS AFTERNOON AND EVENING
WILL BECOME SOUTHWEST AT 5-10 KT OVERNIGHT...STRENGTHENING TO 13-17
KT SUSTAINED WITH GUSTS AS HIGH AS 20-25 KT BY EARLY WED AFT...OR
15-18Z WED.

LOOKING AHEAD:
VFR CONDITIONS SHOULD LARGELY PREVAIL INTO THE WEEKEND. HOWEVER...
EXPECT AN INCREASING POTENTIAL FOR DIURNAL CONVECTION THURSDAY
THROUGH SUNDAY...WITH SUB-VFR CONDITIONS POSSIBLE IN ASSOCIATION
WITH ISOLD TO SCT SHOWERS AND STORMS...PRIMARILY DURING THE AFT/EVE
HOURS. -VINCENT
-- End Changed Discussion --

&&

.CLIMATE...

RALEIGH: A NEW RECORD LOW OF 39F WAS SET AT RDU THIS MORNING.
THE PREVIOUS RECORD LOW WAS 43 DEGREES RECORDED ON MAY 14 1997.

GREENSBORO: THE RECORD LOW OF 40F WAS TIED AT GSO THIS MORNING.
THE PREVIOUS RECORD LOW OF 40 DEGREES WAS SET ON MAY 14 1941.

&&

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

&&

$$

SYNOPSIS...VINCENT
NEAR TERM...VINCENT
SHORT TERM...HARTFIELD
LONG TERM...HARTFIELD
AVIATION...VINCENT
CLIMATE...VINCENT