Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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227
FXUS62 KRAH 031039
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
639 AM EDT TUE MAY 3 2016

.SYNOPSIS...
LOW PRESSURE WILL MOVE OFF THE MIDDLE ATLANTIC COAST EARLY TODAY. A
SECONDARY WAVE OF LOW PRESSURE WILL DEVELOP ALONG THE TRAILING COLD
OVER NC THIS AFTERNOON AND EVENING...BEFORE MOVING SLOWLY TO THE
COAST AND OFFSHORE LATE TONIGHT AND WED.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 400 AM TUESDAY...

AN AREA OF LOW PRESSURE NOW OVER MD WILL MOVE OFFSHORE EARLY TODAY.
A SECONDARY LOW WILL DEVELOP OVER SOUTHERN VA/CENTRAL NC ALONG A
TRAILING LEE SURFACE TROUGH AND SYNOPTIC COLD FRONT THAT WILL
STRETCH THROUGH THE WESTERN CAROLINAS THIS AFTERNOON...IN RESPONSE
TO HEIGHT FALLS /INCREASING LARGE SCALE FORCING FOR ASCENT/
ACCOMPANYING A POSITIVELY-TILTED TROUGH EVOLVING FROM SOUTHEAST
CANADA TO THE CENTRAL PLAINS.

SHOWERS AND A COUPLE OF ISOLATED MINI-SUPERCELLS OVER BOTH DILLON
AND SUMTER COUNTY SC --ON THE LEAD OUTFLOW BOUNDARY AND IN A HSLC
ENVIRONMENT CHARACTERIZED BY STRONG LOW LEVEL SHEAR /35 KTS OF 0-1
KM BULK AND 200-250 M2/S2 EFFECTIVE SRH/ AND AMIDST 35-40 KTS OF MID
LEVEL FLOW PER REGIONAL VWP DATA...WILL MOVE NORTHEAST ACROSS EAST-
CENTRAL NC DURING THE NEXT SEVERAL HOURS. ASSOCIATED MESO-VORTICES
WILL BE CAPABLE OF PRODUCING LOCALLY DAMAGING WIND GUSTS AND/OR A
WEAK TORNADO AS THEY TRACK NORTHEAST ACROSS CUMBERLAND/SAMPSON/WAYNE
COUNTIES THROUGH AROUND 11Z. A COMPOSITE OUTFLOW BOUNDARY FROM
WIDESPREAD CONVECTION FROM THE DELMARVA TO WESTERN NC WILL LIKELY
INTERCEPT THE STORMS AND SERVE AS THE NORTHERN BOUND FOR THE SEVERE
THREAT. OTHERWISE...PERSISTENT ANA-EFFECTIVE FRONTAL RAIN ON THE
COOL SIDE OF THE OUTFLOW(S)...AT TIMES MODERATE TO HEAVY...MAY LEAD
TO VERY LOCALIZED FLOODING.

ALL OF THIS ACTIVITY SHOULD MOVE NORTHEAST OF CENTRAL NC WITH THE
PASSAGE OF THE PARENT MID LEVEL DISTURBANCE NOW CROSSING EASTERN
GA/WESTERN SC...BETWEEN 12-15Z.

MUCH LIKE PREVIOUS DAYS...THE ATMOSPHERE WILL THEN DESTABILIZE WITH
PARTIAL SUNSHINE --THOUGH ONLY WEAKLY TO MODERATELY SO WITH BOTH
TEMPERATURES AND DEWPOINTS A FEW DEGREES LOWER THAN PREVIOUS DAYS--
IN THE WAKE OF THE EARLY MORNING ACTIVITY. SCATTERED TO NUMEROUS
STORMS WILL SUBSEQUENTLY RE-DEVELOP OVER WEST-CENTRAL NC /ALONG THE
AFOREMENTIONED LEE SURFACE TROUGH AND/OR SYNOPTIC COLD FRONT/ THEN
MOVE EAST ACROSS CENTRAL NC THIS AFTERNOON AND EVENING. MID LEVEL
FLOW AND ASSOCIATED EFFECTIVE SHEAR WILL STEADILY INCREASE FROM THE
WEST INTO THE 40-60 KT RANGE WITH THE APPROACH OF THE AFOREMENTIONED
UPPER TROUGH. THE CHARACTER OF THE STRONG SHEAR...INDICATED BY LONG
AND STRAIGHT HODOGRAPHS FROM THE SFC TO 6 KM...WILL FAVOR SPLITTING
SUPERCELLS - ONES CAPABLE OF PRODUCING LARGE HAIL (SOME POSSIBLY
VERY LARGE) AND WESTERLY WIND GUSTS UP TO 60-70 KTS. THE GREATEST
SEVERE THREAT WILL EXIST ROUGHLY EAST OF US HIGHWAY 1...WHERE MLCAPE
WILL BE RELATIVELY MAXIMIZED IN AN AXIS OF SURFACE DEWPOINTS IN THE
MIDDLE TO UPPER 60S...VERSUS LOWER 60S OVER THE WESTERN PIEDMONT
WHERE A COMPONENT OF WESTERLY LOW LEVEL FLOW WILL OCCUR.

THE FRONTAL ZONE AND EMBEDDED WAVE OF LOW PRESSURE...AND ASSOCIATED
DEEP MOISTURE AND SHOWERS...WILL MOVE GRADUALLY EAST OVERNIGHT...
WITH JUST A LINGERING SLIGHT-LOW CHANCE OF SHOWERS EAST OF I-95 BY
WED MORNING...AND DRYING ELSEWHERE. COOLER WITH LOWS IN THE MID-
UPPER 50S.

&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
AS OF 405 AM TUESDAY...

A PAIR OF NOTABLE CURLS IN WATER VAPOR OVER OVER IOWA AND NEBRASKA
THIS MORNING WILL ELONGATE AND MOVE EAST BENEATH A DEEPER TROUGH
DEVELOPING FROM A WAVE DIVING SOUTH OUT OF CENTRAL CANADA.
THIS LEAD WAVE WILL CROSS CENTRAL NC EARLY WEDNESDAY... AND IN
RESPONSE A BROAD WAVE OF LOW PRESSURE IS FORECAST TO DEVELOP OVER
EASTERN NC WEDNESDAY AFTERNOON. DESPITE THE AIRMASS CHANGE IN THE
WAKE OF TODAYS COLD FRONT... SLIGHTLY ELEVATED DEWPOINTS IN THE
UPPER 50S IN THE COASTAL PLAIN AND WEAK LOW LEVEL MASS CONVERGENCE
BENEATH STRONG COOLING ALOFT AND 60M HEIGHT FALLS SHOULD BE ENOUGH
TO KICK OFF SOME SHOWERS AND ISOLATED STORMS...MAINLY IN THE
NORTHERN COASTAL PLAIN. THE FREEZING LEVEL WILL DROP TO AROUND 9000
FT...SO SOME SMALL HAIL CANT BE RULED OUT WITH WEAK DESTABILIZATION.
HIGHS WILL BE INT HE LOW/MID 70S...WITH FURTHER COOLING BENEATH AN
UPPER LOW THAT WILL SETTLE OVER THE CAROLINAS LATE WEEK.

ANY CONVECTION SHOULD DIE OFF AS THE UPPER FORCING DEPARTS TO THE
EAST AND NOCTURNAL COOLING SETS IN.  HOWEVER...WITH THE
AFOREMENTIONED CANADIAN SHORTWAVE DROPPING THROUGH THE MIDWEST...
SOME ADDITIONAL SHOWERS MAY DROP SOUTH THROUGH VA EARLY THURSDAY.
MAINLY INT HE LOWER 50S.


&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
AS OF 405 AM TUESDAY...

A STRONG SHORTWAVE OVER MANITOBA THIS MORNING WILL DIVE SOUTH
THROUGH THE MIDWEST WEDNESDAY AND CUT OFF OVER THE CAROLINAS ON
THURSDAY...DEEPENING 3 TO 4 STD BELOW NORMAL THURSDAY AFTERNOON AS
AN OMEGA BLOCK DEVELOPS OVER THE CONUS. STRONG HEIGHT FALLS AND A
PERSISTENT AREA OF LOW PRESSURE/TROUGHING OVER NC SHOULD AGAIN
PROMOTE THE DEVELOPMENT OF SHOWERS... SOME OF WHICH COULD PRODUCE A
LITTLE GRAUPEL.  H10-H85 THICKNESSES DIPPING TO AROUND 1340M SUPPORTS
HIGHS IN THE MID 60S TO AROUND 70S ON THURSDAY...WHICH IS
INCREASINGLY SUPPORTED BY MEDIUM RANGE GUIDANCE. THE CHANCE OF
SCATTERED SHOWERS WILL CONTINUE FRIDAY AND DECREASE RAPIDLY INTO THE
WEEKEND AS THE UPPER LOW BEGINS TO FILL AND MOVE EAST.  RIDGING
ALOFT WILL SHIFT EAST TOWARD THE REGION AND ALLOW FOR A WARMING
TRENDING THROUGH THE WEEKEND AND INTO NEXT WEEK.  THE GFS AND ECMWF
THEN INDICATE A SHORTWAVE DIVING SOUTHEAST OUT OF CANADA...WHICH
ULTIMATELY WEAKENS THE RIDGE AND ALLOWS A COLD FRONT TO APPROACH NC
FROM THE NORTHWEST LATE SUNDAY AND MONDAY.  GIVEN THE EXPECTED
STRENGTH OF THE RIDGE...CONFIDENCE IN THE FRONT MOVING TO OUR
LATITUDE IS A LITTLE LOW AT THIS POINT AND THE FORECAST WILL REMAIN
DRY.

&&

.AVIATION /11Z TUESDAY THROUGH SATURDAY/...
AS OF 630 AM TUESDAY...

AN AREA OF WIDESPREAD SHOWERS...AND ISOLATED STORMS OVER EASTERN NC--
FORCED IN PART BY A MID LEVEL DISTURBANCE OVER NORTHERN SC-- WILL
LIFT NORTHEAST AND OUT OF CENTRAL NC...WITH A RETURN TO DRY VFR
CONDITIONS...BETWEEN 12-16Z.

MUCH LIKE PREVIOUS DAYS...THE ATMOSPHERE WILL DESTABILIZE WITH
PARTIAL SUNSHINE IN THE WAKE OF THE EARLY MORNING ACTIVITY...AND
CONSEQUENTLY SET THE STAGE FOR THE RE-DEVELOPMENT OF SCATTERED TO
NUMEROUS STORMS THAT WILL CROSS CENTRAL NC THIS AFTERNOON AND
EVENING. LARGE HAIL...INCLUDING SOME POSSIBLY VERY LARGE...AND
WESTERLY WIND GUSTS UP TO 60-70 KTS --IN SPLITTING SUPERCELLS-- WILL
POSE AN ADDED RISK BEYOND TYPICAL SUB-VFR CONDITIONS IN SHRA/TSRA.
DESPITE THE LIKELIHOOD OF OCCURRENCE OF SUCH STORMS AND CONDITIONS
OVER NC...THE ASSOCIATED PROBABILITY OF SUCH OCCURRENCES AT ANY GIVEN
POINT/TAF SITE IS TOO LOW TO INCLUDE IN THE TAFS...AT LEAST UNTIL
STORMS ULTIMATELY DEVELOP.

MULTIPLE SLOW-MOVING WAVES OF LOW PRESSURE ARE FORECAST TO DEVELOP
IN THE VICINITY OF THE MIDDLE ATLANTIC COAST MID TO LATE WEEK...WITH
ASSOCIATED SUB-VFR CEILINGS AND SHOWERS/STORMS THAT WILL GROW IN
COVERAGE AND INTENSITY WITH HEATING EACH AFTERNOON - ESPECIALLY AT
EASTERN TAF SITES.

&&

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

&&

$$
SYNOPSIS...26
NEAR TERM...26
SHORT TERM...22
LONG TERM...22
AVIATION...26



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