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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 220719
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
319 AM EDT WED MAY 22 2013

.SYNOPSIS...
BERMUDA HIGH PRESSURE WILL EXTEND INTO THE MIDDLE ATLANTIC TODAY. A
SURFACE PRESSURE TROUGH WILL DEVELOP IN THE LEE OF THE APPALACHIANS
THURSDAY...FOLLOWED BY THE PASSAGE OF A COLD FRONT THURSDAY NIGHT.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
AS OF 315 AM WEDNESDAY...

THE MID LEVEL TROUGH THAT HAS PROMOTED NUMEROUS TO WIDESPREAD
DOWNPOURS IN RECENT DAYS IS NO LONGER DISCERNIBLE IN REGIONAL VWP
DATA. BERMUDA HIGH PRESSURE WILL CONSEQUENTLY BRIEFLY EXERT THE
DOMINANT INFLUENCE TO WEATHER CONDITIONS OVER CENTRAL NC TODAY...SO
CONVECTIVE COVERAGE SHOULD BE MUCH LESS THAN PREVIOUS DAYS...AND
FOCUSED BY THE SEA BREEZE AND OTHER SMALLER SCALE/LOWER
PREDICTABILITY DIFFERENTIAL HEATING OR REMNANT OUTFLOW BOUNDARIES.
A BLANKET 20-30 PERCENT POP IS ACCORDINGLY WARRANTED...WITH RELATIVE
HIGHEST CHANCES ASSOCIATED WITH THE SEA BREEZE OVER THE COASTAL
PLAIN AND EASTERN SANDHILLS AND PIEDMONT. DESPITE WHAT SOME OF THE
NWP GUIDANCE WOULD SUGGEST...IT SEEMS IMPROBABLE THAT ANY
MOUNTAIN-INDUCED CONVECTION WOULD AFFECT THE WESTERN
PIEDMONT...OWING TO SOUTH TO SOUTH SOUTHWESTERLY STEERING FLOW THAT
WOULD HOLD STORM MOTIONS/PROPAGATION WEST OF THE YADKIN RIVER. HIGHS
SIMILAR TO THOSE OF TUESDAY...GENERALLY IN THE MIDDLE 80S.

HEIGHT FALLS IN ASSOCIATION WITH THE COMPLEX TROUGH ALOFT
APPROACHING FROM THE CENTRAL CONUS...ON THE ORDER OF 20-30 METERS AT
H5...WILL SPREAD EASTWARD ACROSS CENTRAL NC TONIGHT. WHILE THESE
HEIGHT FALLS ARE APT TO SUPPORT A BAND OF PRE-FRONTAL SHOWERS AND
STORMS FROM THE TN VALLEY TO THE APPALACHIANS BY THIS EVENING...IT
SEEMS PROBABLE THAT THIS CONVECTION WILL WEAKEN CONSIDERABLY AS IT
EMERGES INTO AN INCREASINGLY STABLE...NOCTURNALLY-COOLED BOUNDARY
LAYER IN THE LEE OF THE MOUNTAINS - A SOLUTION DEPICTED WELL BY THE
00Z SPC NMM. AS SUCH...WILL INDICATE A HIGH CHANCE OF MAINLY
LEFT-OVER SHOWERS INTO THE SOUTHERN AND WESTERN PIEDMONT AFTER 11
PM...TAPERING TO SLIGHT CHANCE RANGE AROUND THE TRIANGLE AREA...TO
DRY ROUGHLY EAST OF I-95. A CONTINUED VERY MOIST AIR MASS WILL
RESULT IN ADDITIONAL LOW STRATUS DEVELOPMENT THROUGH THU MORNING...
WITH PERSISTENCE LOWS IN THE MIDDLE 60S.
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
AS OF 308 AM WEDNESDAY...

COLD FRONT WILL CROSS THE AREA... ENTERING THE STATE FROM THE WEST
THURSDAY EVENING... AND WILL REACH THE COAST BY 12Z FRIDAY.
THUNDERSTORMS WILL DEVELOP IN THE MOIST AIRMASS IN ADVANCE OF THE
FRONT THURSDAY... AND MODEST INSTABILITY OF 500-1000 J/KG MLCAPE AND
0-6 KM BULK SHEAR VALUES OF 25 KTS WILL SUPPORT A FEW MULTICELL
CLUSTERS. BEST UPPER LEVEL FORCING REMAINS NORTH OF THE AREA... AND
WITH THE STRONGEST LOW LEVEL FORCING ASSOCIATED WITH THE FRONT NOT
MAKING IT THROUGH THE AREA UNTIL LATE THURSDAY... SEVERE POTENTIAL
IS LOW. HIGHS LOW TO MID 80S... LOWS IN THE 60S.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
AS OF 305 AM WEDNESDAY...

BEHIND THE FRONT... NORTHWESTERLY FLOW WILL USHER IN A MUCH DRIER
AIRMASS... AND PRECIPITATION WILL END FROM WEST TO EAST EARLY
FRIDAY. TEMPERATURES WILL BE SEVERAL DEGREES BELOW NORMAL THROUGH
THE WEEKEND... WITH HIGHS IN THE 70S. COOLEST LOWS FRIDAY NIGHT...
IN THE UPPER 40S TO LOW 50S... THEN LOW TO MID 50S SATURDAY NIGHT.

MOISTURE WILL INCREASE AGAIN ON MONDAY AS THE FLOW BECOMES MORE
SOUTHERLY... WITH PWAT VALUES AGAIN CLIMBING TO NEAR 1.5 INCHES.
GUIDANCE INDICATES A WARM FRONT WILL BE IN THE VICINITY OF THE
MIDATLANTIC MONDAY EVENING INTO TUESDAY... AND TEMPERATURES TUESDAY
WILL REBOUND TO NEAR NORMAL... UPPER 70S TO LOW 80S. DEPENDING ON
THE LOCATION OF THE FRONT... ISENTROPICALLY DRIVEN SHOWERS ARE
POSSIBLE... AND WILL CONTINUE WITH SLIGHT CHANCE POPS.

&&

.AVIATION /06Z WEDNESDAY THROUGH SATURDAY/...
AS OF 240 AM WEDNESDAY...

A CONTINUED VERY MOIST AIR MASS WILL RESULT IN A HIGH CHANCE OF
LIFR-IFR CEILINGS THIS MORNING. THESE CEILINGS WILL LIFT AND SCATTER
TO VFR WITH HEATING THROUGH MIDDAY. HEATING OF THE MOIST AIR MASS
WILL ALSO CAUSE WIDELY SCATTERED SHOWERS AND STORMS TO DEVELOP THIS
AFTERNOON...BUT WITH LESSER COVERAGE VERSUS PREVIOUS DAYS OWING TO
THE WEAKENING AND DEPARTURE OF A LIFT-INDUCING TROUGH THAT RESIDED
OVER THE AREA DURING RECENT DAYS. UNTIL A COLD FRONT SWEEPS
ACROSS CENTRAL NC THU NIGHT...THE CONTINUED VERY MOIST REGIME WILL
PROMOTE ADDITIONAL LOW STRATUS DEVELOPMENT TONIGHT...AND A CONTINUED
THREAT OF MAINLY AFTERNOON SHOWERS AND STORMS. VFR CONDITIONS WILL
OTHERWISE PREVAIL IN CANADIAN HIGH PRESSURE THROUGH THE WEEKEND.

&&

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

&&

$$

SYNOPSIS...MWS
NEAR TERM...MWS
SHORT TERM...SEC
LONG TERM...SEC
AVIATION...MWS