National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 190021
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
821 PM EDT SAT MAY 18 2013

.SYNOPSIS...
-- Changed Discussion --
A STATIONARY FRONT OVER CENTRAL NC WILL RETREAT NORTHWARD INTO VA ON
SUNDAY. MEANWHILE...AN UPPER LEVEL TROUGH WILL TRACK SLOWLY EAST
ACROSS THE CAROLINAS THROUGH EARLY NEXT WEEK.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH SUNDAY NIGHT/...
AS OF 300 PM SATURDAY...

OVERVIEW:
BROAD MID-LEVEL TROUGH EXTENDING FROM CENTRAL ILLINOIS SOUTHEASTWARD
INTO THE SOUTHERN APPALACHIANS WILL MOVE VERY SLOWLY EASTWARD OVER
THE NEXT 60-72 HOURS...MOVING OVERHEAD ON SUNDAY BEFORE FINALLY
SLIDING OFFSHORE LATE MONDAY.  IN THE LOWER LEVELS...A WEAK SURFACE
FRONT WILL SAG SOUTHWARD ACROSS THE NORTHERN HALF OF THE STATE
TODAY....AND WILL LIFT NORTHWARD INTO SOUTHEAST VA AND THE DELMARVA
LATE TONIGHT/EARLY SUNDAY. PWATS WILL STEADILY RISE THROUGH THE
WEEKEND DUE TO THE PROLONGED SOUTHERLY MOISTURE FEED ALONG AND AHEAD
OF THE TROUGH...WITH A POOL OF 1.6-1.8" PWATS (2 STANDARD DEVIATIONS
ABOVE NORMAL)BECOMING CENTERED OVER THE CAROLINAS.

FOR THE REMAINDER OF THE AFTERNOON THROUGH TONIGHT...
THERE WILL NOT BE A SHORTAGE OF FORCING MECHANISMS WITH THE
INTERACTION OF BOTH SYNOPTIC AND MESOSCALE FEATURES MAKING FOR
UNSETTLED WEATHER CONDITIONS THROUGH THE PERIOD. THE STALLED FRONTAL
BOUNDARY COUPLED WITH SUPPORT FROM THE LEAD S/W DISTURBANCE EMBEDDED
IN THE MID-LEVEL TROUGH WILL RESULT IN PERIODS OF SHOWERS AND
THUNDERSTORMS ...DIURNALLY ENHANCED AND AIDED BY SEVERAL MESOSCALE
BOUNDARIES PRESENT ACROSS THE REGION THIS MORNING...INCLUDING
OUTFLOWS FROM LAST NIGHT`S CONVECTION... THE REMNANTS OF YESTERDAY`S
SEABREEZE...AND EXPECTATIONS OF ANOTHER ROBUST SEABREEZE THIS
AFTERNOON.

THE BEST DIURNAL DESTABILIZATION IS EXPECTED EAST OF HWY 1 WHERE
LESS CLOUD COVER AND BETTER LOW-LEVEL MOISTURE ARE ANTICIPATED.
EXPECT MLCAPE VALUES AS HIGH AS 1000-1200 J/KG. HOWEVER WEAK SHEAR
OF 20KTS OF LESS SUGGESTS DISORGANIZED/PULSE STORMS THAT WILL
QUICKLY WEAKEN BY THE EVENING AS THE BOUNDARY LAYER STABILIZES.
INSTEAD...THE PRIMARY THREAT COULD BE FROM LOCALLY HEAVY
RAINFALL...WITH AS MUCH AS 2 INCHES POSSIBLE ESPECIALLY INVOF OF THE
STALLED FRONTAL ZONE WHICH WOULD BE CONDUCIVE FOR TRAINING OF STORMS.
MODELS SHOW THE LEAD S/W DISTURBANCE REALLY SHEARING APART
APART...WHILE THE SFC FRONT BEGINS TO RETREAT NORTHWARD AS A WARM
FRONT. WILL MAINTAIN SCATTERED SHOWERS OVERNIGHT WITH HIGHEST POPS
IN THE WEST AS THE MID-LEVEL TROUGH AXIS PROGRESSES EASTWARD INTO
THE MOUNTAINS. LOWS TONIGHT GENERALLY IN THE MID 60S.


SUNDAY AND SUNDAY NIGHT:
A LOT OF SIMILARITIES BETWEEN TODAY AND SUNDAY...MINUS THE STALLED
SURFACE FRONT WHICH WILL BE WELL NORTH OF THE AREA. CONVECTIVE
COVERAGE SUNDAY MORNING SHOULD INITIALLY BE GREATEST IN THE WEST WITH
THE ENCROACHING REMNANTS OF THE MID-LEVEL TROUGH...AND SHOULD
GRADUALLY SPREAD EAST THROUGH THE LATE AFTERNOON AND THROUGH THE
OVERNIGHT HOURS...PEAKING DURING DAYTIME HEATING. WITH THE UPPER
TROUGH DIRECTLY OVERHEAD...CONVECTION SHOULD BE ABLE TO BETTER
SUSTAIN ITSELF SUNDAY NIGHT WITH DECENT COVERAGE EXPECTED THROUGH
THE OVERNIGHT HOURS.

MODELS ACTUALLY SUGGEST LESS INSTABILITY ON SUNDAY..HINDERED PERHAPS
BY MORE ROBUST CLOUD COVER AND RAIN CHANCES EARLIER IN THE DAY WITH
MLCAPE VALUES OF 500-1000 J/KG. GIVEN CONTINUED WEAK SHEAR OF 15KTS
OF LESS...EXPECT DISORGANIZED PULSE STORMS TO RENDER A NON-ZERO
SEVERE THREAT. A HEAVY RAIN/MINOR FLOODING THREAT WILL NEED TO BE
MONITORED IN INSTANCES OF TRAINING CELLS OVER URBAN OR POOR DRAINAGE
AREAS.

TEMPERATURES AGAIN WILL DEPEND PRIMARILY ON CLOUD COVER AND PRECIP.
HIGHS RANGING FROM THE MID 80S E/SE (HIGHEST EAST OF HWY 1/SOUTH OF
HWY 64) TO MID 70S W/NW PIEDMONT WHERE CLOUD COVER WILL BE MORE
PERVASIVE. LOWS IN THE MID 60S.

&&

.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
AS OF 245 PM SATURDAY...

WITH THE MID/UPPER TROUGH STILL LINGERING OVER THE REGION ON
MONDAY...THE INCREASED SHOWER AND THUNDERSTORM ACTIVITY IS EXPECTED
TO PERSIST FOR AT LEAST ONE MORE DAY. THE TROUGH AXIS WILL SLOWLY
SHIFT EASTWARD DURING THE DAY AND INTO THE OVERNIGHT HOURS...WHICH
SHOULD GRADUALLY SHIFT THE BEST PRECIP CHANCES EASTWARD.
THEREFORE...THE HIGHEST POPS WILL BE FOCUSED ACROSS THE CENTRAL AND
EASTERN PORTIONS OF THE FORECAST AREA. GOOD DEEP LAYER MOISTURE WILL
STILL BE IN PLACE ACROSS THE REGION...ESPECIALLY ACROSS THE
EAST...WHERE PWAT VALUES ARE PROGGED TO BE NEAR 1.75 INCHES. AS A
RESULT...LOCALLY HEAVY RAINFALL WILL BE POSSIBLE ONCE AGAIN AND WITH
THE EXPECTED AMOUNT OF PRECIP EXPECTED TO PRECEDE THE RAINFALL ON
MONDAY...SOME MINOR FLOODING...MAINLY IN POOR DRAINAGE AND URBAN
AREA WILL BE POSSIBLE. WITH ALL OF THE CLOUDS AND PRECIP ACROSS THE
AREA...HIGHS SHOULD BE HELD DOWN SOMEWHAT...WITH GENERALLY LOWER 80S
EXPECTED.

PRECIP CHANCES SHOULD GRADUALLY DECREASE MONDAY NIGHT AS THE
MID/UPPER LEVEL TROUGH AXIS SHIFTS EAST OF THE AREA. REGARDLESS...
CLOUD COVER SHOULD REMAIN FAIRLY EXTENSIVE THROUGHOUT THE OVERNIGHT
HOURS...KEEPING OVERNIGHT LOWS MOSTLY IN THE MID/UPPER 60S.


.LONG TERM /TUESDAY THROUGH SATURDAY/...
AS OF 245 PM SATURDAY...

SOME WEAK SHORTWAVE RIDGING WILL START TO BUILD OVER THE AREA
TUESDAY AND WEDNESDAY...WHILE AT THE SURFACE...THE BERMUDA HIGH WILL
START TO RIDGE WESTWARD INTO THE CAROLINAS. ALL OF THIS WILL
TRANSLATE TO A DECREASE IN PRECIP COVERAGE FOR THE MIDDLE OF THE
WEEK. ALSO CONTRIBUTING TO THIS WILL BE SOME SLIGHT MID LEVEL
DRYING...ALTHOUGH SUFFICIENT MOISTURE SHOULD REMAIN IN PLACE OVER
THE REGION...WITH PWAT VALUES HOVERING NEAR 1.5 INCHES OR SO.
THEREFORE...AM EXPECTING SCATTERED DIURNALLY DRIVEN PRECIP EACH DAY.
WITH MORE IN THE WAY OF BREAKS IN THE CLOUD COVER AND LESS PRECIP
COVERAGE...TEMPS SHOULD BE ABLE TO REBOUND NICELY INTO THE MID/UPPER
80S.

SHOWER AND THUNDERSTORM COVERAGE SHOULD BEGIN TO INCREASE ONCE AGAIN
BY THE END OF THE WEEK WITH THE APPROACH OF OUR NEXT MID/UPPER LEVEL
TROUGH AND ASSOCIATED COLD FRONT. THERE IS STILL SOME DISAGREEMENT
WITH THE TIMING OF THE COLD FRONTAL PASSAGE...BUT FOR NOW WILL GO
WITH AN LATE FRIDAY NIGHT/EARLY SATURDAY MORNING PASSAGE.
THEREFORE...WILL SHOW HIGHEST POPS THURSDAY AND FRIDAY/FRIDAY NIGHT
(BUT WILL STILL GO NO HIGHER THAN CHANCE UNTIL BETTER AGREEMENT IS
REACHED)...WITH POPS DECREASING FROM WEST TO EAST ON SATURDAY. WITH
INCREASED PRECIP CHANCES/CLOUDS ON THURSDAY AND FRIDAY...TEMPS WILL
MOSTLY BE IN THE LOW/MID 80S...WITH SLIGHTLY COOLER TEMPS EXPECTED
ON SATURDAY.

&&

.AVIATION /00Z SUNDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
AS OF 820 PM SATURDAY...

SHOWERS AND ISOLATED THUNDERSTORMS WILL BE FOCUSED BY A STATIONARY
FRONT AND MULTITUDE OF THUNDERSTORM OUTFLOW BOUNDARIES...PRIMARILY
AT KGSO/KRDU/KFAY FOR THE NEXT SEVERAL HOURS. INITIALLY VFR
CONDITIONS OUTSIDE OF CONVECTION WILL BECOME MVFR-IFR DUE TO
LOWERING/DEVELOPING CEILINGS - LOWEST WEST (KINT/KGSO) - OVERNIGHT.
THE LOW CLOUDS WILL GRADUALLY LIFT AND SCATTER THROUGH MVFR
RANGE...TO VFR BETWEEN 3000-4000 FT...SUNDAY AFTERNOON. THE SLOW
APPROACH OF A LIFT-INDUCING AND MOISTURE-FOCUSING TROUGH ALOFT FROM
THE WEST WILL ALSO PROMOTE THE OCCURRENCE OF SCATTERED SHOWERS AND
ISOLATED STORMS OVERNIGHT...BECOMING NUMEROUS AGAIN WITH HEATING ON
SUNDAY. DESPITE THE EXPECTED COVERAGE OF SHOWERS AND STORMS...
CONFIDENCE OF OCCURRENCE AT ANY PARTICULAR TERMINAL IS TOO LOW TO
INCLUDE A MULTI-HOUR PREVAILING CONDITION OF SUCH BEYOND THE NEXT
SEVERAL HOURS...AND HAVE ELECTED TO CONVEY THE THREAT WITH VICINITY
SHOWERS THROUGHOUT THE TAF PERIOD.  -MWS

LOOKING AHEAD: A SLOW MOVING UPPER LEVEL TROUGH MOVING THROUGH THE
REGION WILL RESULT IN UNSETTLED CONDITIONS WITH NUMEROUS TO
WIDESPREAD SHOWERS AND STORMS THROUGH MONDAY. DRIER CONDITIONS BY
TUESDAY WITH MOSTLY DIURNAL RAIN CHANCES WITH THE THREAT OF MORNING
FOG/STRATUS.  -CBL
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...MWS
NEAR TERM...CBL
SHORT TERM...KRR
LONG TERM...KRR
AVIATION...MWS/CBL