Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 211913
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
310 PM EDT THU AUG 21 2014

.SYNOPSIS...A SERIES OF UPPER LEVEL DISTURBANCES WILL DIVE SOUTHEAST
INTO OUR REGION FROM THE OHIO VALLEY AND MIDWEST. A COLD FRONT
LOCATED ACROSS THE MID ATLANTIC ON FRIDAY WILL MOVE SOUTH THROUGH
THE AREA OVER THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 310 PM WEDNESDAY...

NORTHWEST FLOW CONTINUES ALOFT. THE PIEDMONT TROUGH IS SET UP OVER
THE EASTERN PIEDMONT/COASTAL PLAIN...AND AREAS TO THE WEST HAVE SEEN
MORE MIXING THAN IN THE EAST WITH MORE WESTERLY FLOW AND DRIER AIR
ALOFT.  MLCAPE RANGES FROM LESS THAN 1000 J/KG TO AS MUCH AS 2000
J/KG.   THE CUMULUS FIELD OVER THE COASTAL PLAIN IN A BIT MORE
PRONOUNCED WHERE LOW-LEVEL CONVERGENCE AND INSTABILITY OVERLAP.  TO
THE NORTHWEST...A SERIES OF UPPER DISTURBANCES ARE MOVING ACROSS
KENTUCKY/WEST VIRGINIA.  THE MEAN FLOW MAY CAUSE SOME OF THE
SCATTERED CONVECTION THAT TRIGGERS FROM THIS DISTURBANCE TO MOVE
SOUTHEAST INTO THE NORTHWEST OR NORTHERN PIEDMONT BY THIS EVENING.
HOWEVER...THE HRRR CONTINUES TO SHOW VERY LITTLE ACTIVITY THIS
AFTERNOON.   EFFECTIVE SHEAR WILL INCREASE 25-30KT ACROSS THE NORTH
THIS EVENING...SO IF ANY STORMS CAN GET GOING THERE...THEY WILL
STAND THE BEST CHANCE OF BEING STRONG TO SEVER

WITH THE LOSS OF HEATING...THE CHANCE OF SHOWERS OR STORMS WIL
SLOWLY DIMINISH...THOUGH A CHANCE MAY LINGER ACROSS THE NORTH
THROUGH MIDNIGHT AS CONVECTION OVER VIRGINIA EVOLVES.  LOWS IN THE
LOWER 70S.


.SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
AS OF 235 PM THURSDAY...

FRIDAY WILL BE ANOTHER DAY WITH NORTHWESTERLY FLOW ALOFT...SURFACE
TROUGHING IN THE EAST...AND THE POTENTIAL FOR A DISTURBANCE OR TWO
TO CROSS THE AREA.  THE MAIN DISTURBANCES IN QUESTION ARE LIKELY
ASSOCIATED WITH CONVECTION OVER THE UPPER MIDWEST...AND ARE PROGGED
TO MOVE SOUTHEAST ACROSS THE AREA LATE FRIDAY AFTERNOON.  TIMING OF
SUCH A FEATURE IS STILL TOUGH THIS FAR OUT...SO CONFIDENCE IN ITS
ADDITIONAL SUPPORT FOR AFTERNOON CONVECTION IS LOW.  DEEP MIXING IS
EXPECTED AGAIN DURING THE AFTERNOON...WHICH WILL TEMPER INSTABILITY
A LITTLE IN THE WEST WHERE DEWPOINTS SHOULD DROP BACK INTO THE MID
60S.  THERMAL PROFILES ARE RELATIVELY SIMILAR TO TODAY...SO MLCAPE
SHOULD AGAIN RANGE FROM LESS THAN 1000 J/KG IN THE WEST TO OVER 1500
J/KG IN THE EAST.  A BELT OF STRONGER WESTERLIES OVER THE CENTRAL
APPALACHIANS WILL LIKELY ENHANCE CONVECTION OVER VA...AND SOME OF
THIS ACTIVITY MAY DRIFT SOUTH INTO THE NORTHERN PORTIONS OF THE CWA
BY FRIDAY EVENING...SO WILL HAVE THE HIGHEST CHANCE POPS ACROSS THE
NORTH...WHILE AREAS IN SOUTHERN PIEDMONT MAY STAY DRY.

H85 TEMPS ARE FORECAST TO BE ABOVE 20C AGAIN FRIDAY AND WITH DEEP
MIXING RESULTS IN MID TO POSSIBLY UPPER 90S.  DEWPOINTS ARE FORECAST
TO MIX OUT A LITTLE MORE IN THE EAST THAN TODAY...THOUGH ONLY
SLIGHTLY...SO HEAT INDEX VALUES SHOULD AGAIN HOLD AROUND 100F IN THE
SOUTHEAST.

DEPENDING ON HOW MUCH CONVECTION THERE IS TO THE NORTH FRIDAY
EVENING...THERE IS THE POTENTIAL FOR A WEAK EFFECTIVE FRONT INTO THE
NORTHERN COASTAL PLAIN FRIDAY NIGHT...NECESSITATING POPS THROUGH THE
OVERNIGHT HOURS.  LOWS IN THE UPPER 60S TO LOWER 70S.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
AS OF 145 PM THURSDAY...

THE LONG TERM PERIOD REMAINS CHARACTERIZED BY A BUILDING UPPER RIDGE
ACROSS THE MISSISSIPPI RIVER VALLEY WITH A DEEPENING UPPER TROUGH OFF
THE EAST COAST...RESULTING IN A NORTHWEST UPPER FLOW REGIME ACROSS
CENTRAL NORTH CAROLINA. AT THE SURFACE...A BACKDOOR COLD FRONT WILL MOVE
SOUTH THROUGH THE AREA ON SATURDAY. DEEP MOISTURE WILL REMAIN ENTRENCHED
OVER THE REGION THROUGH THE FIRST HALF OF THE WEEKEND. AS SUCH...THE
BEST CHANCE OF PRECIPITATION WILL BE ON SATURDAY GIVEN THE SURFACE
BOUNDARY AND POTENTIAL ADDITIONAL SUPPORT FROM DISTURBANCES ALOFT
WITHIN THE NORTHWEST FLOW.

THE UPPER TROF AXIS SHIFTS FURTHER OFFSHORE...ALLOWING DRIER AIR TO
SURGE SOUTH AT THE MID LEVELS...WITH DEEPER MOISTURE SUPPRESSED SOUTHWEST
OF THE AREA SUNDAY THROUGH THE MIDDLE OF NEXT WEEK. THE UPPER RIDGE WILL
SHIFT EAST TO FURTHER AID IN DAMPENING CONVECTION AS WELL...SO PRECIP
CHANCES WILL BE MINIMAL FROM MONDAY THROUGH THURSDAY.

LOW LEVEL THICKNESS VALUES WILL GRADUALLY FALL THROUGH EARLY NEXT
WEEK AS THE UPPER TROUGH DEEPENS DOWN THE WESTERN ATLANTIC. IN
ADDITION...NORTHEASTERLY SURFACE FLOW WILL PERSIST AS HIGH PRESSURE
RIDGES INTO THE AREA FROM THE NORTHEAST. ALL OF THIS WILL RESULT IN
BELOW NORMAL TEMPS...WITH MID 80S TO NEAR 90 DEGREES ON SATURDAY
FALLING INTO THE UPPER 70S TO LOW/MID 80S SUNDAY THROUGH TUESDAY.
TEMPS WILL BEGIN TO MODERATE WEDNESDAY INTO THURSDAY AS THE UPPER
RIDGE SHIFTS EAST. OVERNIGHT LOWS THIS WEEKEND WILL BE IN THE UPPER 60S
TO LOWER 70S...WITH MID TO UPPER 60S MONDAY MORNING AND FOR THE
REMAINDER OF THE WEEK.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
AS OF 200 PM THURSDAY...

VFR CONDITIONS ACROSS CENTRAL NC THIS AFTERNOON WITH A GENERALLY
LIGHT WESTERLY WIND.  A COUPLE WEAK DISTURBANCES WITHIN THE
NORTHWESTERLY FLOW ALOFT WILL CROSS THE APPALACHIANS THIS
EVENING...BUT THERE IS RELATIVELY LOW CONFIDENCE IN WHETHER OR NOT
ADDITIONAL SHOWERS AND STORMS WILL BE ABLE TO MOVE EAST INTO THE
PIEDMONT THIS AFTERNOON.  TO THE EAST...WHERE INSTABILITY IS
GREATEST...SOME WEAK CONVERGENCE MAY SUPPORT STORMS OVER THE COASTAL
PLAIN...MOSTLY FROM KFAY TO KRWI AND EAST.  HOWEVER...CONFIDENCE IS
TOO LOW FOR MENTION IN THE CURRENT TAF.

MOST OF ANY CONVECTION WILL DIE DOWN AFTER SUNSET...THOUGH MODELS
SHOW THE POTENTIAL FOR SOME ADDITIONAL STORMS MOVING THROUGH SOUTHERN
VA TO TRACK INTO THE NORTHERN COASTAL PLAIN OVERNIGHT.  FOG AND
STRATUS SHOULD AGAIN BE ISOLATED AND MOSTLY MVFR.

OUTLOOK... A BACKDOOR COLD FRONT WILL MOVE INTO THE AREA OVER THE
WEEKEND...BRINGING A PERIOD OF UNSETTLED WEATHER AND ADVERSE
AVIATION CONDITIONS.  DRIER WEATHER IS EXPECTED NEXT WEEK.

&&

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

&&

$$

SYNOPSIS...BLAES
NEAR TERM...BLS
SHORT TERM...BLS
LONG TERM...MLM
AVIATION...BLS



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