Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 201420
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1015 AM EDT WED AUG 20 2014

.SYNOPSIS...A SERIES OF UPPER LEVEL DISTURBANCES IN NORTHWEST FLOW
ALOFT WILL CROSS THE REGION THIS WEEK.  A BACK DOOR COLD FRONT IS
FORECAST TO SLIP INTO THE AREA OVER THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1015 AM WEDNESDAY...

THE OVER ALL WEATHER PATTERN STILL CONSISTS OF RELATIVELY WEAK
NORTHWESTERLY FLOW ALOFT AND A BROAD TROUGH AT THE SURFACE.  IS
SLOWLY ERODING THIS MORNING...THOUGH AREAS NORTH OF HWY 64 ARE STILL
ENSHROUDED IN STRATUS.  UPSTREAM...AN UPPER LEVEL TROUGH MOVING
THROUGH THE CENTRAL APPALACHIANS IS AIDING A BROKEN LINE OF SHOWERS
AND STORMS...WHICH HAS ACTUALLY HELD TOGETHER PRETTY WELL ON THE
SOUTHERN END NEAR THE BLUE RIDGE.  THE WEAK VORT LOBE WITH THIS
TROUGH WILL CROSS THE CWA THIS AFTERNOON. LINGERING STRATUS WILL
DELAY BETTER DESTABILIZATION...BUT RADAR TRENDS SUGGEST THE SHOWERS
AND STORMS MAY HOLD TOGETHER THROUGH AT LEAST THE TRIAD AREA
INITIALLY.  WITH ADDITIONAL HEATING...FORECAST SOUNDINGS GIVE 1000-
1500 J/KG MLCAPE THIS AFTERNOON...THOUGH THE NAM/GFS VALUES ARE VERY
SENSITIVE TO HIGHER/LOWER DEWPOINTS.  IN FACT...THE NAM FORECAST
SOUNDINGS AT KINT/KGSO HAVE A DEWPOINT OF 70F AND MLCAPE OVER 2000
J/KG THIS AFTERNOON. THIS SEEMS OVERDONE GIVEN SREF CONSENSUS.  ALSO
ACCOMPANYING THE AFOREMENTIONED SHORTWAVE IS A RIBBON OF EFFECTIVE
DEEP SHEAR OF UP TO 30KT...SO IF CONVECTION CAN REINTENSIFY OVER THE
PIEDMONT BY EARLY AFTERNOON...A FEW STRONG TO SEVERE STORM CLUSTERS
COULD BE POSSIBLE. WILL INCREASE POPS OVER THE NORTHWEST PIEDMONT
THROUGH MIDDAY...WITH A CHANCE ACROSS THE NORTH THIS AFTERNOON AND A
SLIGHT CHANCE ACROSS THE SOUTH. HIGHS IN THE UPPER 80S TO LOWER 90S.
LOWS TONIGHT IN THE UPPER 60S TO LOWER 70S.

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
AS OF 245 AM WEDNESDAY...

LITTLE CHANGE ON THE SYNOPTIC PATTERN ON THURSDAY. CENTRAL NC WILL
REMAIN POISED TO SEE VORT DISTURBANCES EMBEDDED IN THE NW FLOW ALOFT
AS THE UPPER LOW OVER THE GREAT LAKES WEAKENS THROUGH THE DAY AS IT
MOVES EAST INTO THE NE US. AT THIS TIME...CAN NOT FIND A DISCERNIBLE
FEATURE THAT WOULD SUPPORT MORE THAN ISOLATED SLIGHT CHANCE POPS
THURSDAY/THURSDAY NIGHT...IN FACT...500MB HEIGHTS ACTUALLY INCREASE
OVER THE AREA ON THURSDAY...WITH ASSOCIATED SUBSIDENCE/WARMING ALOFT
POSSIBLY SUPPRESSING CONVECTION TO A POINT WHERE IT COULD END UP
BEING ONE OF THE LEAST CONVECTIVELY ACTIVE DAYS OF THE WEEK.

AS FAR AS TEMPERATURES...BOTH THE EC AND GFS INDICATE H8
TEMPERATURES WILL WARM TO 22C...WHICH SHOULD SUPPORT HIGHS THURSDAY
SOLIDLY IN THE MID 90S. LOWS THURSDAY NIGHT IN THE LOWER 70S.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
AS OF 245 AM WEDNESDAY...

THE LONG TERM PERIOD WILL BE CHARACTERIZED BY A BUILDING UPPER RIDGE
ACROSS THE MISSISSIPPI RIVER VALLEY WITH AN UPPER TROUGH/CLOSED LOW
OFF THE NORTHEAST COAST...LEAVING CENTRAL NC UNDER A NORTHWESTERLY
UPPER FLOW REGIME. DIFFERENCES REMAIN AMONG THE MODELS WITH RESPECT
TO THE EVOLUTION OF THE UPPER AIR PATTERN...ESPECIALLY BY EARLY NEXT
WEEK. REGARDLESS...GIVEN THAT MUCH OF OUR PRECIP CHANCES WILL HINGE
ON DISTURBANCES ALOFT WITHIN THE NORTHWEST FLOW AND THAT THE PRECISE
TIMING OF ANY SUCH DISTURBANCES THIS FAR OUT IS NEARLY IMPOSSIBLE...
CONFIDENCE IN THE EXACT DETAILS OF PRECIP CHANCES ARE RATHER LOW.

AS A SHORTWAVE TROUGH TRACKS OFF THE NORTHEASTERN US COAST (AND
EVENTUALLY TRANSITIONS INTO A CLOSED LOW/DEEP TROUGH JUST OFF THE
EAST COAST THROUGH EARLY NEXT WEEK)...A BACKDOOR COLD FRONT WILL BE
PUSHED THROUGH THE AREA FRIDAY. THIS SHOULD LEAD TO SOLID CHANCE
POPS. MODELS HAVE BACKED OFF ON DRIER AIR FILTERING IN BEHIND THE
FRONT AND THEREFORE PRECIP CHANCES WILL REMAIN IN THE FORECAST
THROUGH AT LEAST EARLY NEXT WEEK GIVEN THE PERSISTENT NORTHWEST FLOW
REGIME AND SUBSEQUENT "TRAIN" OF DISTURBANCES ALOFT TRACKING ACROSS
THE AREA. THERE ARE SOME INDICATIONS THAT THE UPPER RIDGE MAY BUILD
FAR ENOUGH EAST BY THE VERY END OF THE LONG TERM PERIOD WHICH WOULD
RESULT IN DECREASING PRECIP CHANCES.

TEMPS ON FRIDAY ARE EXPECTED TO BE IN THE LOW TO MID 90S...WITH
SLIGHTLY "COOLER" TEMPS FOR THE WEEKEND AND EARLY NEXT WEEK AS
HEIGHTS FALL WHILE THE DEEP UPPER TROUGH BUILDS DOWN THE WESTERN
ATLANTIC...WITH MAINLY 80S EXPECTED. TEMPS MAY BEGIN TO REBOUND SOME
BY TUESDAY IF THE UPPER RIDGE DOES INDEED START TO BUILD EAST.
OVERNIGHT LOWS WILL GENERALLY IN THE UPPER 60S TO LOWER 70S
THROUGHOUT THE PERIOD. &&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
AS OF 720 AM WEDNESDAY...

RAP SOUNDINGS SUGGEST FOG/STRATUS ACROSS THE NORTHEAST PIEDMONT AND
NORTHERN COASTAL PLAIN WILL DISSIPATE BETWEEN 13-15Z. SHORTWAVE
DISTURBANCES TRAVERSING THE REGION WILL ONCE AGAIN FUEL ISOLATED TO
SCATTERED CONVECTION THIS AFTERNOON/EVENING... WITH THE HIGHEST
PROBABILITY ACROSS THE NORTHERN TAF SITES. HOWEVER... CONFIDENCE IS
NOT HIGH ENOUGH TO INCLUDE ANY MENTION OF CONVECTION IN THE TAFS AT
THIS TIME. WILL FOLLOW PERSISTENCE WRT FOG TONIGHT...DEVELOPING
ACROSS THE AREA BETWEEN 06 TO 12Z.

OUTLOOK... EARLY MORNING STRATUS/FOG...ALONG WITH AFTERNOON SHOWERS
AND STORMS WILL BE POSSIBLE EACH DAY THIS WEEK INTO THE WEEKEND.

&&

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

&&

$$

SYNOPSIS...BLS
NEAR TERM...CBL/BLS
SHORT TERM...CBL
LONG TERM...KRD
AVIATION...CBL/BLS



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