Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 010034
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
834 PM EDT THU JUL 31 2014

.SYNOPSIS...A PROLONGED PERIOD OF UNSETTLED WEATHER CAN BE EXPECTED
THROUGH EARLY NEXT WEEK AS AN UPPER LEVEL TROUGH SLOWLY APPROACHES
THE REGION FROM THE WEST.

&&

.NEAR TERM /OVERNIGHT/...
AS OF 830 PM THURSDAY...

CYCLONIC FLOW ALOFT WILL PREVAIL OVER THE REGION THROUGH TONIGHT.
UPPER LEVEL FORCING WILL BE PRESENT IN THE FORM OF CYCLONIC SHEAR
VORTICITY IN ADDITION TO POCKETS OF MORE CONCENTRATED DPVA ATTENDANT
TRANSIENT SMALL AMPLITUDE DISTURBANCES IN CYCLONIC FLOW ALOFT. AT
THE SAME TIME...SOUTHEASTERLY RETURN FLOW WILL ADVECT RICH LOW-LEVEL
MOISTURE INTO THE REGION...WITH 925 MB DEWPOINTS OF 18-19C IN
COASTAL SC (23Z SPC MESO) ADVECTING INTO UPSTATE SC AND WESTERN NC
OVERNIGHT. ALTHOUGH WEAK MID-LEVEL LAPSE RATES (5.0-5.5 C/KM) WILL
PERSIST OVER THE REGION...RICH LOW-LEVEL MOISTURE/WARM ADVECTION
WILL MAINTAIN 500-1000 J/KG OF MUCAPE OVERNIGHT...IN THE FORM OF
ELEVATED INSTABILITY ATOP A SHALLOW RAIN-COOLED AIRMASS IN THE
LOWEST 25-50 MB. WITH THE ABOVE IN MIND...EXPECT STRATIFORM RAIN
WITH EMBEDDED ELEVATED CONVECTION TO PERSIST ALONG/WEST OF HWY 1
OVERNIGHT...PERHAPS INCREASING IN COVERAGE AND INTENSITY OVER THE
FAR WESTERN PIEDMONT AND FOOTHILLS AFTER MIDNIGHT VIA LOW-LEVEL
MOISTURE POOLING ALONG/EAST THE CREST OF THE APPALACHIANS AND
OROGRAPHIC ASCENT IN PROXIMITY THEREOF. EXPECT LOWS DRIVEN LARGELY
BY CLOUDS/PRECIP (EVAP COOLING)...IN THE MID/UPPER 60S.

GIVEN THE PRESENCE OF LOWER/UPPER LEVEL FORCING...AS MUCH AS 500-
1000 J/KG MUCAPE...AND ~40 KNOTS OF DEEP LAYER SHEAR...IT IS
POSSIBLE THAT ISOLATED UPDRAFTS COULD ACQUIRE MID-LEVEL ROTATION AND
BRIEFLY EXHIBIT SUPERCELLULAR CHARACTERISTICS (I.E. SPLITTING/
DEVIANT MOTION) IN THE FAR WESTERN PIEDMONT/FOOTHILLS. GIVEN THE
ELEVATED NATURE OF ANY CONVECTION AND THE PRESENCE OF EXTREMELY
MARGINAL MID-LEVEL LAPSE RATES...DO NOT ANTICIPATE A POTENTIAL FOR
SEVERE WEATHER. -VINCENT

&&

.SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
AS OF 300 PM THURSDAY...

ON FRIDAY THE UPPER TROUGH WILL CONTINUE TO HOVER WEST OF THE AREA.
AT THE SURFACE...THERE WILL BE STRONG SURFACE CONVERGENCE OVER
CENTRAL NC AS DISTURBANCES MOVE THROUGH THE TROUGH ACROSS THE
WESTERN PIEDMONT AND AT THE SAME TIME A SEPARATE PLUME OF MOISTURE
WILL APPROACH CENTRAL NC FROM THE SSE. THE ONSLAUGHT OF MOISTURE
WILL BEGIN IN EARNEST AS PRECIPITABLE WATER VALUES CLIMB OVER 2
INCHES ACROSS THE AREA. MODEL FORECAST SOUNDINGS AS SEEN IN BUFKIT
ARE VERY WET FROM TOP TO BOTTOM BUT THERE STILL REMAINS A QUESTION
OF HOW MUCH INSTABILITY WILL BE PRESENT. THE NAM IS VERY BULLISH AND
THE GFS NOT AS MUCH BUT THEY BOTH AGREE THAT THE SOUTHEAST WILL
CARRY THE MOST CAPE. PLENTY OF FORCING WILL BE PRESENT WITH 30-40
KTS OF BULK SHEAR ACROSS THE EAST AND POTENTIALLY SOME DECENT 0-3 KM
HELICITY VALUES. SPC OUTLOOK NOT CALLING FOR A SLIGHT RISK AT THIS
POINT BUT WOULD NOT BE SURPRISED TO SEE A FEW STRONGER OR ROTATING
CELLS IN THE SOUTHEAST FRIDAY AFTERNOON. ALL THIS ASIDE THE MAIN
STORY WILL STILL BE THE RAINFALL WITH A HALF OF AN INCH TO AN INCH
(LOCALLY HIGHER) EXPECTED ACROSS THE AREA WITH HEAVIER TOTALS IN
MORE CONVECTIVE CELLS IN THE EAST. MAX TEMPS IN THE UPPER 70S TO
LOWER 80S NW TO SE.

CHANCES FOR RAIN WILL CONTINUE THROUGH FRIDAY NIGHT WITH THE EAST
EXPECTED TO SEE MORE OF THE ACTIVITY MAINLY IN THE FORM OF SHOWERS
AS CONDITIONS BECOME SLIGHTLY MORE STABLE OVERNIGHT. FOG AND/OR LOW
STRATUS SHOULD BE PREVALENT ACROSS THE AREA BEFORE DAYBREAK ON
SATURDAY. LOWS 65-70 DEGREES.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
AS OF 300 PM THURSDAY...

...AN UNSETTLED AND ACTIVE PERIOD THROUGH AT LEAST THE WEEKEND WITH
SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS WITH LOCALLY HEAVY
RAIN...

A BROAD UPPER LEVEL TROUGH PERSISTS JUST WEST OF THE APPALACHIANS
INTO EARLY NEXT WEEK. AT THE SAME TIME A SURFACE TROUGH SETS UP
ACROSS EASTERN NC WITH A FLOW OF DEEP MOISTURE MOVING ACROSS THE
AREA. THIS WILL RESULT IN A PERIOD OF UNSETTLED WEATHER AND THE
POTENTIAL FOR SOME SIGNIFICANT RAIN. THE TROUGH WEAKENS EARLY TO
MIDDLE PORTION OF NEXT WEEK AS PART OF IT LIFTS ACROSS NEW ENGLAND
AND ANOTHER PORTION BREAKS OFF OVER THE LOWER MISSISSIPPI VALLEY.
THIS RESULTS IN A DECREASE IN PRECIPITATION COVERAGE AND A WARMING
TEMPERATURES TO NEAR OR OR JUST ABOVE AVERAGE TOWARD THE MIDDLE OF
THE WEEK.

GUIDANCE SUGGESTS THAT ONE SHORT WAVE TROUGH WILL BE DEPARTING THE
REGION EARLY SATURDAY MORNING WITH ANOTHER WAVE POISED TO MOVE
ACROSS THE AREA SATURDAY NIGHT...BUT TRYING TO TIME THESE FEATURES
TOO PRECISELY IS FOOLHARDY. IN ADDITION... GUIDANCE VARIES WITH THE
INLAND PROGRESSION OF THE COASTAL TROUGH. THE END RESULT THOUGH
SHOULD BE A FAIRLY ACTIVE CONVECTIVE PATTERN SATURDAY WITH THE BULK
OF THE SHOWERS AND THUNDERSTORMS OCCURRING DURING THE AFTERNOON
THROUGH THE EVENING INTO THE EARLY OVERNIGHT HOURS. THE NAM
GENERATES A LOT MORE PRECIPITATION THAN THE GFS/ECMWF DURING THE DAY
AND IS ACCORDINGLY COOLER AND MORE STABLE THAN THE GFS WHICH
GENERATES MLCAPE VALUES UP TO 1000-1500 J/KG ACROSS THE EASTERN
PIEDMONT AND COASTAL PLAIN. IT WILL BE DIFFICULT GETTING A BETTER
READ ON THE INSTABILITY UNTIL A BETTER UNDERSTANDING OF THE
EVOLUTION OF THE DIURNAL CONVECTIVE CYCLE ON FRIDAY IS COMPLETE.
GREATER CONFIDENCE IS IN THE AMOUNT OF SHEAR WITH THE GFS NOTING
STRONGER DEEP LAYER FLOW WITH BULK SHEAR VALUES OF 20-30KTS WHICH
WOULD SUPPORT SOME STORM ORGANIZATION. THE NAM HAS WEAKER
FLOW...AROUND 20KTS OR SO WITH THE SREF ENSEMBLE DISTRIBUTION SPREAD
FROM 20-30 KTS. THE GREATEST SHEAR SHOULD BE LOCATED FROM THE TRIAD
NORTH AND WEST WITH THE GREAT INSTABILITY TO THE SOUTHEAST. STILL
ANY STORM ELEMENTS THAT DEVELOP NEAR THE SURFACE BOUNDARY WILL NEED
TO BE MONITORED. FOR NOW THE MOST LIKELY THREAT IS FROM EFFICIENT
RAIN MAKING STORMS THAT REPEATEDLY TRACK OVER THE SAME LOCATION
RESULTING IN POTENTIAL FLOODING ISSUES.

ACTIVE WEATHER CONTINUES ON SUNDAY AS MULTIPLE SHORT WAVE TROUGHS
APPROACH THE REGION WITH A VERY MOIST AIR MASS IN PLACE. THE RESULT
SHOULD BE AN ACTIVE CONVECTIVE DAY ONCE AGAIN WITH LIKELY POPS
WARRANTED AND THE GREATEST PRECIPITATION COVERAGE ACROSS THE EASTERN
PORTION OF THE FORECAST AREA. INSTABILITY PARAMETERS ARE WEAKER THAN
SUNDAY WITH MID LEVEL LAPSE RATES PROGGED TO BE MORE THAN 0.5 C DEG
LESS AS THE MID LEVELS WARM SOMEWHAT WITH THE DEPARTING TROUGH.

THE PATTERN TRANSITIONS INTO A MORE TYPICAL SUMMERTIME APPEARANCE ON
ON MONDAY AND ESPECIALLY TUESDAY THROUGH WEDNESDAY AS THE UPPER
TROUGH WEAKENS AND THE UPPER FLOW BECOMES NOTICEABLY MORE WESTERLY.
RAIN CHANCES ACCORDINGLY DROP DURING THE EARLY TO MID WEEK
PERIOD...ESPECIALLY DURING THE A-TYPICAL DIURNAL HOURS. LOW CHANCE
TO SLIGHT CHANCE POPS WILL BE INCLUDED IN THE FORECAST FOR PRIMARILY
THE AFTERNOON AND EVENING HOURS.

TEMPERATURES AT THE BEGINNING OF THE LONG TERM WILL BE QUITE COOL AS
DICTATED BY THE COOL AIR MASS WITH MORNING 1000-850MB THICKNESSES
VALUES IN THE 1385-1395 RANGE ALONG WITH LOTS OF CLOUDS AND
PRECIPITATION. HIGHS ON SATURDAY AND SUNDAY SHOULD RANGE IN THE
UPPER 70S IN THE NORTHWEST PIEDMONT TO LOWER 80S IN THE SOUTHERN
COASTAL PLAIN. HIGHS WILL MODERATE BEGINNING TUESDAY AND WARM INTO
THE UPPER 80S TO AROUND 90 BY THURSDAY. -BLAES

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
AS OF 830 PM THURSDAY...

24-HR TAF PERIOD: EXPECT DETERIORATING CONDITIONS AT ALL TERMINALS
OVERNIGHT AS LOW-LEVEL MOISTURE INCREASES IN THE PRESENCE OF
CYCLONIC FLOW ALOFT. EXPECT WIDESPREAD RAIN AND A POSSIBILITY FOR
EMBEDDED THUNDERSTORMS ALONG/WEST OF THE HWY 1 CORRIDOR
(INT/GSO/RDU) OVERNIGHT...GRADUALLY EXPANDING EAST OF THE I-95
CORRIDOR (FAY/RWI) FRI MORNING. CEILINGS ARE EXPECTED TO FALL INTO
THE IFR/MVFR CATEGORY (500-1500 FT AGL) FROM WEST-EAST BETWEEN 07-
12Z...GRADUALLY INCREASING TO 1000-2000 FT AGL BY 15-18Z FRI WITH
SHOWERS AND THUNDERSTORMS LIKELY AT ALL TERMINALS DURING THE
AFTERNOON...ESP AT RDU/FAY/RWI.

LOOKING AHEAD: ADVERSE AVIATION CONDITIONS SIMILAR TO THOSE EXPECTED
OVERNIGHT/FRIDAY ARE ANTICIPATED TO PERSIST THROUGH THE WEEKEND AND
PERHAPS INTO EARLY NEXT WEEK AS AN UPPER LEVEL TROUGH SLOWLY
APPROACHES THE REGION FROM THE WEST. -VINCENT

&&

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

&&

$$

SYNOPSIS...VINCENT
NEAR TERM...VINCENT
SHORT TERM...ELLIS
LONG TERM...BLAES
AVIATION...VINCENT



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