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182
FXUS62 KRAH 311114
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
715 AM EDT THU JUL 31 2014

.SYNOPSIS...THE ATMOSPHERE ACROSS CENTRAL NC WILL BECOME VERY MOIST
AND SLIGHTLY UNSTABLE. THIS WILL LEAD TO AN UNSETTLED WEATHER PATTERN
FRIDAY...LASTING INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 310 AM THURSDAY...

RECENT TRANQUIL WEATHER PATTERN WILL BECOME INCREASINGLY UNSETTLED
THE NEXT FEW DAYS.

ISOLATED-SCATTERED SHOWERS IN THE SANDHILLS EARLY THIS MORNING
ASSOCIATED WITH WEAK LOW LEVEL MOISTURE ADVECTION COUPLED WITH AN
AREA OF LIFT ASSOCIATED WITH THE NOSE OF THE UPPER LEVEL JET. EXPECT
THESE SHOWERS TO WANE IN COVERAGE AND INTENSITY PRIOR TO DAYBREAK AS
LIFT WEAKENS THOUGH COULD SEE A REGENERATION OF SHOWER ACTIVITY
FARTHER WEST ACROSS THE SOUTHERN PIEDMONT AROUND DAYBREAK IN
ASSOCIATION WITH MODEST UPSLOPE FLOW.

MID-UPPER LEVEL FLOW WILL BACK IN RESPONSE TO A L/W TROUGH THAT DIGS
SOUTHWARD INTO THE TN VALLEY-DEEP SOUTH THROUGH FRIDAY. THIS BACKING
FLOW WILL ADVECT PLENTY OF WARM MOIST AIR RESIDING OVER TEH GULF
INTO CENTRAL NC. THIS WILL LEAD TO CONSIDERABLE CLOUDINESS OVER THE
REGION TODAY AND CONTINUING THROUGH TONIGHT.

A SERIES OF UPPER LEVEL DISTURBANCES WILL INTERACT WITH THIS
AVAILABLE MOISTURE TO CAUSE SCATTERED SHOWERS ALONG WITH A FEW T-
STORMS. FIRST SUCH DISTURBANCE BEING HANDLED WELL BY THE
ECMWF...CURRENTLY EXITING THE MS DELTA REGION AT 06Z. THIS FEATURE
SHOULD BE NEAR THE UPSTATE OF SC BY 18Z...THEN TRACK E-NE ALONG THE
NC/SC BORDER. BASED ON FAVORABLE TIMING AND DEEPER MOISTURE RESIDING
OVR THE WEST VERSUS THE EAST...WILL MAINTAIN THE CHANCE POPS THIS
AFTERNOON ACROSS THE WESTERN-SOUTHERN PIEDMONT TO SLIGHT CHANCE
ACROSS THE NE. WILL NEED TO MONITOR UPSTREAM CONDITIONS AS COULD SEE
A HIGHER SHOWER THREAT OVER THE WEST-SW THAN CURRENTLY ADVERTISED.

PRESENT INDICATIONS ARE THAT ANY STORMS THAT DEVELOP SHOULD REMAIN
BELOW SEVERE CRITERIA AS ATMOSPHERE PROJECTED TO BE RELATIVELY
STABLE FOR LATE JULY. DID NOTE THE BULK SHEAR OF 35-40KTS (PER GFS)
ACROSS THE SOUTH-SE THIS AFTERNOON-EARLY EVENING. THIS WOULD SUGGEST
SOME POTENTIAL FOR SOME ORGANIZED CONVECTION IF ENOUGH INSTABILITY
WAS ACHIEVED.

MAX TEMPS THIS AFTERNOON WILL LIKELY BE HELD DOWN A FEW DEGREES FROM
NORMAL VALUES DUE TO CONSIDERABLE CLOUD COVER. MAX TEMPS GENERALLY
IN THE MID 80S.

TONIGHT...POTENTIAL TO SEE AN INCREASE IN SHOWER
ACTIVITY...ESPECIALLY ACROSS THE WEST...AS ANOTHER UPPER LEVEL
DISTURBANCE PROJECTED TO LIFT E-NE ACROSS THE REGION. THIS OCCURS
WHILE LOW LEVEL FLOW AND ITS UPSLOPE COMPONENT INCREASES...PROVIDING
LOW LEVEL LIFT IN THE INCREASINGLY MOIST AIR MASS. PLAN TO MAINTAIN
FORECAST TREND OF INCREASING POPS OVERNIGHT...ESPECIALLY AFTER
MIDNIGHT IN THE WEST. IF MODEL TRENDS REMAIN CONSISTENT...COULD
ARGUE FOR HIGH CHANCE/LOW END LIKELY IN VICINITY OF THE YADKIN RIVER
LATE TONIGHT. MIN TEMPS 65-70.

&&

.SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
AS OF 310 AM THURSDAY...

MID-UPPER LEVEL FLOW BACKS IN RESPONSE TO
THE DIGGING L/W TROUGH OVER THE TN VALLEY/DEEP SOUTH. THIS PLACES
CENTRAL NC IN THE FAVORABLE RIGHT ENTRANCE REGION OF UPPER JET PLUS
TAPS ABUNDANT MOISTURE RESIDING OVER THE GULF. A RATHER POTENT VORT
MAX CURRENTLY ASSOCIATED WITH CONVECTION ACROSS THE SOUTHERN
PLAINS/RED RIVER VALLEY PROJECTED TO CROSS OUR REGION FRIDAY. LIFT
ASSOCIATED WITH THIS FEATURE ALONG WITH JET DYNAMICS AND AVAILABLE
DEEP MOISTURE SUGGEST LIKELY POPS FOR FRIDAY-FRIDAY EVENING. LOCALLY
HEAVY RAIN MAY OCCUR ACROSS THE WEST WHERE TRAINING OF
SHOWERS/STORMS APPEARS MORE PROBABLE. CONVECTIVE PARAMETERS OVER THE
SANDHILLS AND COASTAL PLAIN ARE A BIT MORE SUPPORTIVE OF AN ISOLATED
SEVERE STORM AS MLCAPE APPROACHES 1000J/KG AND BULK SHEAR 40-50KTS
NOTED.

CONSIDERABLE CLOUDINESSS AND NUMEROUS SHOWERS-STORMS SHOULD HOLD
TEMPS DOWN SEVERAL DEGREES BELOW NORMAL. MAX TEMPS WILL LIKELY NOT
BREAK 80 DEGREES OVER PARTS OF THE PIEDMONT. MAX TEMPS FRIDAY MID
70S NW TO LOWER 80S SE. IF SHOWER COVERAGE TURNS OUT TO BE MORE
SCATTERED THAN NUMEROUS...THEN MAX TEMPS MAY END UP BEING 3-4
DEGREES WARMER.

ANTICIPATE A BRIEF LULL IN CONVECTIVE ACTIVITY SOMETIME FRIDAY NIGHT
AS ONE VORT MAX LIFTS OUT OF THE REGION BUT ANOTHER FOLLOWS BEHIND
IT...BUT DIFFICULT TO SAY FOR CERTAIN IF/WHEN THIS OCCURS. PLAN TO
SHOW A GRADUAL DECREASE IN POPS FRIDAY NIGHT WITH CHANCE POPS (40
PERCENT) FOR MOST LOCATIONS AFTER MIDNIGHT. MIN TEMPS 65-70.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
AS OF 310 AM THURSDAY...

EARLY IN THIS LONG-TERM PERIOD...A SOUTHWEST FLOW ALOFT IS FORECAST
OVER CENTRAL NORTH CAROLINA WITH A SERIES OF MID-LEVEL SHORTWAVES
MOVING THROUGH THE AREA AHEAD OF A TROUGH AXIS EXTENDING FROM THE
GREAT LAKES THROUGH THE OHIO AND TENNESSEE VALLEYS. WHILE THERE ARE
TIMING DIFFERENCES...THE LONG-TERM GUIDANCE IS FAIRLY CONSISTENT IN
LIFTING THE TROUGH NORTH BY EARLY NEXT WEEK WITH A MODEST INCREASE
IN HEIGHTS ALOFT...ALTHOUGH A WEAK SOUTHWEST FLOW ALOFT TENDS TO
PERSIST OVER CENTRAL NORTH CAROLINA AHEAD OF A WEAKNESS IN THE MID-
LEVEL HEIGHTS TO OUR SOUTHWEST IN VICINITY OF MISSISSIPPI AND
ALABAMA. EXTENDING TO THE NORTHEAST OF THIS WEAK LOW ALOFT MAY BE A
SHEAR AXIS NEAR OR OVER CENTRAL NORTH CAROLINA AT LEAST THROUGH
EARLY NEXT WEEK.

ON SATURDAY...THE NAM MOVES THE SURFACE FRONT FARTHER INLAND THAN
THE GFS AND ECMWF...SUCH AS THAT FORMER MODEL HAS MUCH HIGHER QPF
TOWARD THE TRIAD THAN THE OTHERS. NEVERTHELESS...MOS GUIDANCE POPS
ARE HIGH THROUGHOUT CENTRAL NORTH CAROLINA SATURDAY...AND GIVEN THE
INLAND PROGRESSION OF THE FRONT...MID-LEVEL WAVES MOVING THROUGH THE
AREA IN THE SOUTHWEST FLOW...AND AMPLE MOISTURE...WILL CONTINUE WITH
THE LIKELY CHANCES FOR SHOWERS ALONG WITH SCATTERED THUNDERSTORMS.
INSTABILITY ON THE NAM AND ECMWF IS NOT AS GREAT AS ON THE GFS...
WHICH ACTUALLY PAINTS A SOMEWHAT CONCERNING PICTURE SATURDAY WITH
SURFACE-BASED CAPE NEAR 1000J/KG...0-3KM HELICITY NEAR 100M2/S2...
AND SHEAR IN THE 20S KNOTS. AS LCL HEIGHTS SHOULD BE LOW GIVEN THE
DEGREE OF LOW-LEVEL MOISTURE...DEPENDING ON THE INSTABILITY A
ROTATING CELL OR TWO IN VICINITY OF THE SURFACE FRONT WOULD BE A
POSSIBILITY IF THE GFS VERIFIES. FOR NOW WILL FOCUS ON THE RAINFALL
BUT TRENDS WILL NEED TO BE MONITORED. BASIN-AVERAGE RAINFALL AMOUNTS
LATE IN THE WEEK INTO THE WEEKEND COULD BE AROUND 1.5 INCHES.

WHILE THE SURFACE TROUGH SLOWLY WEAKENS...ITS POSITION RELATIVE TO
CENTRAL NORTH CAROLINA FOR NOW DEMONSTRATES LITTLE CHANGE THROUGH
THE REST OF THE LONG-TERM PERIOD. GOOD CHANCES FOR SHOWERS AND AT
LEAST ISOLATED THUNDERSTORMS CONTINUE INTO SUNDAY...THEN AS THE MID-
LEVEL TROUGH LIFTS NORTH AND HEIGHTS INCREASE MODESTLY ALOFT...
CHANCES FOR SHOWERS AND THUNDERSTORMS SHOULD START TO TAKE ON MORE
OF A TYPICAL DIURNAL NATURE...AIDED BY WEAK SURFACE CONVERGENCE...
LINGERING MOISTURE...AND A LIKELY SHEAR AXIS NEARBY OR OVERHEAD. THE
PRECIPITATION CHANCES FOR MONDAY THROUGH WEDNESDAY WILL TEND TO BE
LOWEST IN THE NORTHWEST PIEDMONT AND HIGHEST TOWARD THE INTERSTATE
95 CORRIDOR...THE LATTER WHERE THE DEEPER MOISTURE AND BETTER
INSTABILITY SHOULD BE EACH DAY. WHILE THE ECMWF REALLY TRENDS TOWARD
A TYPICAL DIURNAL PATTERN OF CHANCES DURING THE DAY AND VIRTUALLY
DRY OVERNIGHT...THE LATEST GFS FORECASTS PERIODIC WAVES MOVING
SOUTHWEST-TO-NORTHEAST ALONG THE WEAK SURFACE BOUNDARY WHICH KEEPS
SOME CHANCES EVEN INTO THE OVERNIGHT HOURS. FOR NOW...WILL FORECAST
FOR EARLY NEXT WEEK LOWER POPS OVERNIGHT BUT ONLY SHOW BELOW SLIGHT
CHANCE POPS IN THE NORTHWEST PIEDMONT OVERNIGHT TUESDAY WHEN BOTH
THE GFS AND THE ECMWF AGREE IN A RELATIVE MINIMUM OF PRECIPITATION
THERE THEN.

1000-850MB THICKNESSES AND EXPECTED CLOUD COVER WILL RESULT IN HIGHS
LEANING TOWARD THE COOLER END OF GUIDANCE...AND IN MANY CASES A
LITTLE BELOW. SOME OF THE BIAS-CORRECTED GUIDANCE HAS BEEN DOING
WELL OF LATE AND WILL LEAN TOWARD THOSE WHICH ARE CONSISTENTLY ON
THE COOL END OF GUIDANCE. SOME AREAS COULD START TO RETURN CLOSE TO
90 BY WEDNESDAY.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
AS OF 715 AM THURSDAY...

POCKETS OF MVFR/IFR FOG WILL LIFT/DISSIPATE PRIOR TO 14Z. OTHERWISE
EXPECT CONSIDERABLE CLOUDINESS TODAY THOUGH CLOUD BASES WILL REMAIN
VFR. SURFACE WINDS WILL BE LIGHT (6KTS OR LESS) AND VARIABLE.

THERE WILL BE ISOLATED TO SCATTERED SHOWERS AND POSSIBLY A
THUNDERSTORM THIS AFTERNOON DUE TO SURFACE HEATING AND A MARGINALLY
MOIST AIR MASS. THE HIGHEST THREAT FOR THIS SCATTERED CONVECTION
WILL BE SOUTH OF THE TRIAD TERMINALS AND WEST OF KFAY.

FOR TONIGHT INTO MONDAY...EXPECT PERIODS OF ADVERSE AVIATION WEATHER
CONDITIONS TO BEGIN LATER TONIGHT AS THE ATMOSPHERE OVER CENTRAL NC
BECOMES INCREASINGLY MOIST AND UNSTABLE. A SERIES OF UPPER LEVEL
DISTURBANCE WILL TRAVERSE THE REGION THROUGH MONDAY...CAUSING
SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS. IN ADDITION...THERE
WILL BE AN INCREASED PROBABILITY FOR PROLONGED MVFR-IFR CEILINGS.

&&

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

&&

$$

SYNOPSIS...WSS
NEAR TERM...WSS
SHORT TERM...WSS
LONG TERM...DJF
AVIATION...WSS




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