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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 150657
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
300 AM EDT WED MAY 15 2013

.SYNOPSIS...
-- Changed Discussion --
AN AREA OF HIGH PRESSURE WILL EXTEND ACROSS THE CAROLINAS THROUGH
THURSDAY. AN AREA OF LOW PRESSURE WILL APPROACH FROM THE WEST FRIDAY
AND AFFECT OUR WEATHER THROUGH THE WEEKEND.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
AS OF 1030 PM TUESDAY...

REMAINDER OF TONIGHT...
LATEST SURFACE ANALYSIS SHOWS SURFACE HIGH PRESSURE CENTERED OFF THE
SOUTHEAST COAST AND AN EASTWARD ADVANCING WARM FRONT ACROSS THE OHIO
VALLEY. THE 00Z UPPER AIR ANALYSIS SHOWS AN IMPRESSIVE WARM AIR
ADVECTION PATTERN ACROSS THE WESTERN GREAT LAKES WHICH IS SHIFTING
INTO THE OHIO VALLEY. SATELLITE IMAGERY SHOWS A BROAD BAND OF MID
LEVEL CLOUDINESS ASSOCIATED WITH THE WARM FRONT IN A REGION OF
ENHANCED FLOW AND MOISTURE AT 500 MB AND ISENTROPIC LIFT CENTERED
AROUND THE 305K SURFACE. PATCHES OF SCT-BKN ALTO LEVEL CLOUDINESS
THIS EVENING ACROSS EASTERN VA/NC SHOULD GRADUALLY SHIFT EAST AS THE
MID LEVEL RIDGE EXTENDS INTO THE REGION. ALSO OF NOTE WILL BE A
STRENGTHENING LOW LEVEL JET AFTER MIDNIGHT. NAM/RAP BUFR SOUNDINGS
NOTE 35-40KTS OF WIND AROUND 09Z IN THE 1500-2000FT LAYER.

SENSIBLE WEATHER TONIGHT SHOULD FEATURE A DECREASE IN CLOUDINESS
ACROSS THE EAST WITH MAINLY CLEAR SKIES EXPECTED ACROSS CENTRAL NC
OVERNIGHT. A SOUTHWEST WIND WILL STIR FOR MOST OF THE NIGHT AT 5-10
MPH. A MODIFIED AIRMASS AND A LIGHT BREEZE WILL RESULT IN LOW
TEMPERATURES ON WEDNESDAY MORNING THAT ARE MUCH WARMER THAT TUESDAY
MORNING. LOWS SHOULD RANGE IN THE LOWER 50S IN MOST LOCATIONS. -BLAES

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 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

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
-- Changed Discussion --
AS OF 300 AM WEDNESDAY...

THURSDAY NIGHT...BROAD UPPER LEVEL RIDGE OVER THE SE U.S.
DISSIPATES...ALLOWING A WEAKENING AREA OF LOW PRESSURE TO TRAVERSE
EAST FROM THE TN VALLEY. THIS WEATHER FEATURE WILL INCREASE/THICKEN
MID-HIGH LEVEL CLOUD COVER AND ALSO AID TO MAINTAIN A LIGHT SLY FLOW
AT THE SURFACE. THIS WILL RESULT IN A MILD NIGHT WITH MIN TEMPS
LOW-MID 60S.

FRIDAY...A S/W ROTATING THROUGH THE BASE OF AN UPPER LEVEL TROUGH
OVER EASTERN CANADA-NEW ENGLAND WILL PROPEL A SURFACE BOUNDARY
ACROSS VA FRIDAY AFTERNOON-EVENING. THIS BOUNDARY WILL ENCOUNTER A
SLIGHT-MODERATELY UNSTABLE AIR MASS WITH ENOUGH MOISTURE TO SUPPORT
THE DEVELOPMENT OF SCATTERED STRONG CONVECTION. OUTFLOW ASSOCIATED
WITH THESE STORMS WILL DRIFT SWD INTO OUR FAR NORTHERN COUNTIES LATE
FRIDAY AFTERNOON-FRIDAY EVENING. WHILE AIR MASS WILL NOT BE AS
FAVORABLE FOR CONVECTIVE DEVELOPMENT AS TO THE NORTH...MODEL RH
CROSS SECTIONS AND CONVECTIVE PARAMETERS POINT TO AN AIR MASS OVER
THE PIEDMONT/NORTHERN COASTAL PLAIN CAPABLE OF SUSTAINING SCATTERED
CONVECTION THROUGH MID EVENING.

WHILE LOW LEVEL LAPSE RATES PROJECTED TO BE NEAR 9 DEG C/KM...MID
LEVEL LAPSE RATES NO HIGHER THAN 6 DEG C/KM. IN ADDITION...WIND
FIELD RATHER WEAK. WHILE A STRONG STORM CANNOT BE RULED OUT NEAR THE
VA BORDER LATE IN THE DAY-EARLY EVENING...NOT ANTICIPATING MUCH IN
THE WAY OF SEVERE STORMS. PLAN TO MAINTAIN CHANCE POPS ACROSS
THE REGION WITH HIGHEST POPS (NEAR 40 PERCENT) ACROSS THE FAR
NORTH-NE BUT DID DELAY ONSET OF HIGHER POPS UNTIL LATE IN THE
AFTERNOON (5 PM OR LATER). SINCE LATER ARRIVAL OF SCATTERED
CONVECTION EXPECTED...AFTERNOON HEATING SHOULD WARM TEMPS INTO THE
MID-UPPER 80S.

FRIDAY NIGHT...SCATTERED CONVECTION ACROSS THE NORTH EARLY IN THE
PERIOD WILL MOVE SEWD AND WEAKEN WITH TIME. MAY SEE CONVECTION MAKE
IT AS FAR SOUTH AS ASHEBORO-FAYETTEVILLE BEFORE DISSIPATING LATE.
DEEPER MOISTURE ACROSS THE FAR N-NE IN PROXIMITY TO THE SWD DRIFTING
SFC BOUNDARY SUGGEST A THREAT OF A SHOWER OR TWO OVERNIGHT TO THE
NORTH-NE OF RDU. MIN TEMPS IN THE LOW-MID 60S.
-- End Changed Discussion --

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
-- Changed Discussion --
AS OF 300 AM WEDNESDAY...

THIS PERIOD WILL START OUT A BIT UNSETTLED THEN SLOWLY IMPROVE EARLY
NEXT WEEK.

THE L/W TROUGH OVER NEW ENGLAND-EASTERN CANADA FRIDAY LIFTS E-NE
SATURDAY INTO SUNDAY...CAUSING AN UPPER LEVEL RIDGE TO EXPAND NE
FROM THE LOWER MS VALLEY INTO NEW ENGLAND. MEANWHILE A SERIES OF
UPPER LEVEL DISTURBANCES OVER THE MID MS VALLEY-LOWER OH VALLEY GET
CAUGHT UNDERNEATH THIS EXPANDING RIDGE AND DRIFT SEWD TOWARD THE
CAROLINAS. THESE PERTURBATIONS INTERACTING WITH A THE MODERATELY
MOIST AND SLIGHTLY UNSTABLE AIR MASS WILL AID TO TRIGGER SCATTERED
CONVECTION...ESPECIALLY IN THE AFTERNOON AND EVENING HOURS. EXPECT
SCATTERED CONVECTION TO BE MORE CONCENTRATED AREAWIDE SATURDAY
AFTERNOON DUE TO THE PRESENCE OF THE OLD SURFACE BOUNDARY WHICH WILL
SERVE AS A FOCUS FOR MOISTURE CONVERGENCE AND CONVECTION INITIATION.
SIMILAR TO YESTERDAY...ECMWF HAS THIS FEATURE FARTHER SOUTH
(SANDHILLS-SOUTHERN PIEDMONT) COMPARED TO THE GFS (NORTHERN
PIEDMONT-NORTHERN COASTAL PLAIN). CONVECTIVE PARAMETERS SUGGEST
ENOUGH INSTABILITY (MLCAPE 1000J/KG); SBCAPE 2000-3000 J/KG  TO
SUPPORT A FEW STRONG STORMS THOUGH WIND PROFILE SUGGEST SEVERE
POTENTIAL WEAK. WILL FAVOR THE MORE NORTHWARD GFS PLACEMENT AN D
HAVE THE HIGHEST POPS ACROSS THE NORTH (35-42 PERCENT) VERSUS SOUTH
(27-30 PERCENT). EXPECT CONSIDERABLE CLOUDINESS SATURDAY ALONG WITH
A SHOWER OR TWO IN THE MORNING...WITH SCATTERED CONVECTION BECOMING
MORE PROMINENT BY EARLY AFTERNOON. THIS SUGGEST MAXIMUM TEMPS
SATURDAY A FEW DEGREES COOLER COMPARED TO FRIDAY...ESPECIALLY ACROSS
THE NORTH. HIGH TEMPS SATURDAY...NEAR 80 NORTH TO MID 80S SOUTH.

ON SUNDAY...BEST CHANCES FOR AFTERNOON CONVECTION APPEAR TO BE IN
THE WEST CLOSER TO BETTER UPPER SUPPORT COMPARED TO THE EAST. SFC
BOUNDARY DIMINISHES WITH TIME. THUS EXPECT COVERAGE SUNDAY TO BE A
LITTLE LESS COMPARED TO THE SATURDAY. THIS WILL LEAD TO WARMER
TEMPS. MAX TEMPS SUNDAY LOW-MID 80S.

MID-UPPER LEVEL SHEAR AXES ASSOCIATED WITH THE WEEKEND UPPER LEVEL
DISTURBANCES GRADUALLY WEAKEN AND LIFT NEWD MONDAY INTO TUESDAY. AN
AREA OF HIGH PRESSURE WILL BECOME ANCHORED OFFSHORE AND EXTEND WEST
INTO THE SE U.S./FL PENINSULA. MEANWHILE A DEEP UPPER LEVEL LOW WILL
LIFT NEWD ACROSS THE CENTRAL PLAINS INTO THE UPPER MIDWEST. THIS
PATTERN RESEMBLES AN EARLY SUMMER SCENARIO AND EXPECT COMPARABLE
CONDITIONS ACROSS CENTRAL NC. OVERNIGHT TEMPS IN THE 60S FOLLOWED BY
AFTERNOON TEMPS IN THE 80-85 DEGREE RANGE. A MARGINALLY
MOIST/SLIGHTLY UNSTABLE AIR MASS WILL SUPPORT ISOLATED TO SCATTERED
AFTERNOON CONVECTION WITH BULK OF ACTIVITY DIMINISHING AT SUNSET.
AIR MASS DRIES OUT A BIT BY TUESDAY SUGGESTING A DECREASE IN
CONVECTIVE COVERAGE.
-- End Changed Discussion --

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
AS OF 145 AM WEDNESDAY...

24-HR TAF PERIOD...
HIGH CONFIDENCE OF VFR CONDITIONS THROUGH THE TAF PERIOD... BUT A
PERIOD OF MARGINAL LOW LEVEL WIND SHEAR IS POSSIBLE DURING GENERALLY
THE PRE-DAWN HOURS OF THIS MORNING.

SURFACE HIGH PRESSURE LOCATED OFFSHORE AND HIGH PRESSURE ALOFT OVER
THE REGION WILL RESULT IN VFR CONDITIONS FOR THE 24 HOUR TAF
PERIOD... WITH GENERALLY DRY CONDITIONS EXPECTED (VERY VERY SMALL
CHANCE OF AN AFTERNOON SHOWER OR STORM). HOWEVER... A SOUTHWESTERLY
LOW LEVEL JET WILL STRENGTHEN THIS MORNING WITH WINDS INCREASING TO
35-40KTS DOWN TO AROUND 1500 FT. SURFACE WIND SPEED ARE EXPECTED TO
INCREASE AS WELL INTO THE 6 TO 11 KT RANGE DURING THE PRE-DAWN
HOURS. THIS WILL RESULT IN MARGINAL LLWS CRITERIA. HOWEVER...
CONFIDENCE IS NOT HIGH ENOUGH TO REMOVE LLWS FROM THE TAFS AT THIS
TIME. THAT BEGIN SAID... WILL SHOW LLWS CONDITIONS ENDING FASTER
THAN THE PREVIOUS FORECAST INDICATED. NOW EXPECT LLWS CONDITIONS
SHOULD END AS WE BEGIN TO MIX SHORTLY AFTER 12Z. EXPECT SUSTAINED
WINDS TO INCREASE INTO THE 12 TO 15 KT RANGE AFTER SUNRISE... WITH
GUSTS OF UP TO 19-22 KTS POSSIBLE THROUGH THE LATE AFTERNOON INTO
THE EARLY EVENING... BEFORE DIURNAL MIXING ENDS WITH THE LOSS OF
DAYTIME HEATING. HOWEVER... STILL EXPECT SUSTAINED WIND SPEEDS WILL
BE AROUND 6 TO 10 KTS RANGE AFTER SUNSET TONIGHT.

LOOKING FURTHER AHEAD...
GENERALLY FAIR WEATHER IS EXPECTED FOR THE MAJORITY OF THE LONGER
TERM BUT THERE IS THE POTENTIAL OF DIURNAL MAINLY AFTERNOON AND
EVENING SHOWERS AND STORMS THURSDAY THROUGH SUNDAY...WITH SUB-VFR
CONDITIONS POSSIBLE IN SCT SHOWERS AND THUNDERSTORM AND POSSIBLE
PRE-DAWN SUB-VFR CONDITIONS IN THE FORM OF LOW STRATUS AND/OR FOG.

&&

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

&&

$$

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