Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 200645
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
245 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 245 AM WEDNESDAY...

W-NW FLOW ALOFT BETWEEN THE UPPER LEVEL RIDGE BUILDING FROM THE
WESTERN GULF OF MEXICO INTO THE NRN PLAINS AND THE PERSISTENT MID-
LEVEL CYCLONE MOVING SLOWLY EASTWARD THROUGH THE GREAT LAKES WILL
PERSIST THROUGH THE PERIOD. VORTICITY LOBE EMBEDDED WITHIN THE
BROADER TROUGH OVER THE NORTHERN/NE CONUS WILL TRAVERSE THE MID-
ATLANTIC REGION...ONCE AGAIN DURING PEAK HEATING...BETWEEN 18 TO
03Z. WEAK DPVA COUPLED WITH SEASONABLY MOIST AIRMASS AND UNSTABLE
AIR WILL SUPPORT ISOLATED TO WIDELY SCATTERED POPS...WITH BEST
CHANCE ACROSS THE NORTHERN TIER INVOF THE BETTER UPPER SUPPORT.

CONVECTIVE PARAMETERS ARE NEARLY IDENTICAL TO TUESDAY(WEAK SHEAR
20KTS OR LESS AND ML CAPE 1200 TO 1500 J/KG)...RESULTING A LOW/NON-
ZERO SEVERE THREAT. HIGHS IN THE 89 TO 94. LOWS 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 /06Z WEDNESDAY THROUGH SUNDAY/...
AS OF 110 AM WEDNESDAY...

SKIES HAVE CLEARED OFF THIS EVENING. AREA METARS ARE ALREADY
REPORTING 2 TO 3 DEGREE DEWPOINT DEPRESSIONS. COMBINED WITH LIGHT
WINDS...THIS ALLOW FOR THE DEVELOPMENT OF MOSTLY MVFR FOG. NORTHERN
COASTAL PLAIN/NORTHEAST PIEDMONT(KRWI AND KRDU)COULD ALSO SEE SOME
STRATUS ADVECT INTO THE AREA AS N-NELY FLOW DEVELOPS. EXPECT
CONDITIONS TO IMPROVE TO VFR BETWEEN 14-15Z.

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.

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



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