Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 291309 RRA
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
908 AM EDT WED JUL 29 2015

.SYNOPSIS...A WEAK SURFACE TROUGH WILL REMAIN OVER CENTRAL NC TODAY
AS AN UPPER LEVEL RIDGE BRIEFLY BUILDS OVERHEAD.  A COLD FRONT WILL
APPROACH FROM THE NORTHWEST ON THURSDAY AND SINK SOUTH OF THE AREA
THROUGH THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 900 AM WEDNESDAY...

WITH REGARD TO THE REMAINDER OF THIS MORNING...THERE WILL BE LITTLE
CHANGE IN THE FORECAST OTHER THAN TO CONFINE SHOWER CHANCES TO THE
NE COASTAL PLAIN (I.E. WARREN/HALIFAX COUNTIES) THROUGH NOON. A NEW
DISCUSSION FOR THIS AFT/EVE INTO TONIGHT WILL BE POSTED EARLY THIS
AFTERNOON. -VINCENT

PRIOR DISCUSSION: NORTHWESTERLY FLOW ALOFT WILL SHIFT TO A LITTLE
MORE NORTHERLY TODAY AS THE CENTRAL US RIDGE BUILDS EAST IN RESPONSE
TO A STRONG SHORTWAVE CROSSING THE UPPER MIDWEST. WATER VAPOR
IMAGERY AND RAP H5 VORTICITY SUGGEST A COUPLE WEAK DISTURBANCES WILL
DROP SOUTH ACROSS THE AREA...BUT NEITHER APPEARS TO BE VERY STRONG
AND THERE SHOULDN`T BE MUCH IMPACT GIVEN THAT HEIGHTS BUILD ALOFT
AND INSTABILITY WILL BE WEAK.  AT THE SURFACE...A TROUGH EXTENDING
SOUTH FROM THE MID ATLANTIC STATES APPEARS TO HAVE SUNK A LITTLE
FURTHER SOUTH IN RESPONSE TO THE LAST EVENINGS CONVECTION NEAR THE
NC-VA BORDER...NOW SITUATED FROM ROUGHLY DAVIDSON COUNTY NORTHEAST
TO GRANVILLE COUNTY.  THIS COULD SERVE AS AN ADDITIONAL FOCUS FROM
SOME WIDELY SCATTERED CONVECTION...IN ADDITION TO CONVECTION OVER
THE HIGHER TERRAIN...AND RECENT RUNS OF THE HRRR HINT AT DEVELOPMENT
BY MIDDAY.  IF NOTHING FORMS ON THIS BOUNDARY AND/OR IT WASHES
OUT...THEN CONVECTION WILL BE FOCUS OVER THE NORTHWEST PIEDMONT AND
SHOULDN`T HAVE MUCH OPPORTUNITY TO MOVE EAST GIVEN WEAK NORTHERLY
STEERING FLOW.  OVERALL...THE COVERAGE OF SHOWERS/STORMS IS EXPECTED
TO BE LESS THAN THE PAST COUPLE OF DAYS.  HIGHS SHOULD BE ABLE TO
REACH THE FULL SUN POTENTIAL AS IR IMAGERY SHOWS LITTLE IN THE WAY
OF UPSTREAM CLOUD COVER TO INHIBIT HEATING.  HIGHS 88-93.

CONVECTION SHOULD SEND A LITTLE SOONER THIS EVENING WITH LOSS OF
HEATING AND NO SUPPORT FROM DISTURBANCES ALOFT.  THERE IS A
DISTURBANCE OVER SOUTHERN MICHIGAN THIS MORNING THAT IS FORECAST TO
DIVE SOUTH LATE TONIGHT AND EARLY THURSDAY...WHICH COULD CONCEIVABLY
CAUSE SOME REDEVELOPMENT OF SHOWERS...MAINLY WEST..BY EARLY THURSDAY
MORNING...BUT GUIDANCE DOESN`T SHOW MUCH ACTIVITY...SO WILL LEAVE THE
OVERNIGHT FORECAST DRY.  LOWS WILL BE IN THE LOWER 70S.

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
AS OF 400 AM WEDNESDAY...

A COLD FRONT...ATTENDANT TO AN OCCLUDED LOW WAY TO THE NORTH OVER
CENTRAL CANADA...WILL APPROACH FROM THE NORTHWEST ON THURSDAY.  THE
PREFRONTAL LEE TROUGH WILL SHARPEN IN RESPONSE TO THE APPROACHING
FRONT... BUT WITH INSTABILITY STILL EXPECTED TO BE RELATIVELY
WEAK...MODELS ARE SURPRISINGLY DRY DURING THE DAY ON THURSDAY. THERE
IS A DISTURBANCE FORECAST TO DIVE SOUTH INTO THE AREA EARLY
THURSDAY...AS MENTIONED IN THE NEAR TERM DISCUSSION...AND EVOLUTION
OF THIS FEATURE MAY BE WORTH WATCHING TO SEE IF/HOW IT COULD IMPACT
CONVECTION INITIATION ON THURSDAY.

THE FRONT WILL PUSH INTO THE AREA THURSDAY EVENING...BUT POOR
DIURNAL TIMING AND FORCING LIMITED TO JUST FRONTAL CONVERGENCE
SHOULD RESULT IN JUST SCATTERED CONVECTION AND NO WIDESPREAD SEVERE
WEATHER.

HIGHS THURSDAY HAVE THE POTENTIAL TO REACH THE LOW TO MID 90S ACROSS THE
ENTIRE AREA AS THE 850MB THERMAL RIDGE SHIFTS OVER THE AREA AHEAD OF
THE FRONT AND 850MB TEMPS REACH 19-20C.  SOME HIGH CLOUDS ASSOCIATED
WITH THE FRONTAL ZONE WILL SPREAD ACROSS THE AREA BUT CURRENTLY DO
NOT LOOK WIDESPREAD OR THICK ENOUGH TO IMPACT HIGHS.  LOWS THURSDAY
NIGHT WILL BE MOSTLY IN THE LOW TO MID 70S...ESPECIALLY INT HE
SOUTHEAST WHERE THE FRONT WILL ONLY SLOW REACH BY FRIDAY MORNING.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
AS OF 410 AM WEDNESDAY...

FORECAST RATIONALE REMAINS GENERALLY UNCHANGED FROM PREVIOUS DAYS.
THE MODELS REMAIN IN GOOD AGREEMENT REGARDING THE PERSISTENCE OF AN
EASTERN CONUS TROUGH FORECAST TO DEVELOP DURING THE NEAR AND SHORT
TERM...COINCIDENT WITH THE RETROGRESSION OF A SUB-TROPICAL RIDGE
FROM THE SOUTHERN PLAINS AND MID-MS VALLEY WEST TO THE FOUR CORNERS
REGION.

MEANWHILE IN THE LOW LEVELS...THE MODELS AGREE THAT A COLD FRONT
RELATED TO A POTENT  UPPER LOW OVER SOUTHERN MANITOBA THIS MORNING
WILL BE INVOF THE I-95 CORRIDOR FRI MORNING...THEN DRIFT SOUTHEAST
THROUGH THE COASTAL PLAIN THROUGH THE MIDDAY-AFTERNOON HOURS. THIS
GRADUALLY DIFFUSING BOUNDARY WILL BE THE FOCUS FOR SHOWERS AND
STORMS CENTERED OVER THE EASTERN CAROLINAS FRI-SUN...WHILE A DRIER
AIR MASS BOTH AT THE SURFACE AND ALOFT SETTLES ACROSS THE WESTERN...
AND MUCH OF THE CENTRAL PART...OF NC. AS THE PREVIOUS SHIFT
NOTED...ANY NORTHWESTWARD SHIFT IN THE FRONTAL POSITION AND
ASSOCIATED AXIS OF TROPICAL MOISTURE --CHARACTERIZED BY PRECIPITABLE
WATER VALUES AOA TWO INCHES-- WOULD RESULT IN A WETTER WEEKEND FOR
PARTICULARLY EAST-CENTRAL NC.

THOUGH MODEL SPREAD INCREASES BY THE EARLY-MIDDLE OF NEXT WEEK...THE
MODELS TO VARYING DEGREES HAVE HINTED THAT THE TROPICAL MOISTURE
MAY GET DRAWN NORTH/INCORPORATED INTO THE LONGWAVE TROUGH BY LATE
SUN-MON...AT WHICH TIME THE PROBABILITY OF SHOWERS AND STORMS ARE
MORE LIKELY TO INCREASE THROUGHOUT CENTRAL NC.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
AS OF 640 AM WEDNESDAY...

DENSE FOG THIS AT KINT THIS MORNING IS VERY ISOLATED AND WILL
IMPROVE QUICKLY...WITH VFR CONDITIONS LIKELY TO RETURN BY 13Z.
ELSEWHERE...SOME SCATTERED SHOWERS HAVE DEVELOPED NORTH OF KRDU/KRWI
AND ARE DRIFTING SLOWLY TO THE EAST-NORTHEAST...GENERALLY AWAY FROM
THE TERMINALS.  SOME ADDITIONAL SHOWERS MAY DEVELOP IN THE NEXT
COUPLE HOURS...BUT THE IMPACTS OF THE SHOWERS SHOULD BE LIMITED AND
VFR CONDITIONS SHOULD PREVAIL.

AN UPPER LEVEL RIDGE WILL BRIEFLY BUILD OVER THE REGION TODAY AND
MAY LIMIT STORM COVERAGE MORE SO THAN IN PRIOR DAYS.  AS SUCH...WILL
NOT MENTION THUNDER IN THE CURRENT TAF...BUT CHANCES WILL BE
GREATEST AT KGSO AND KINT ONCE AGAIN.  STRATUS IS POSSIBLE AGAIN
TONIGHT...AND CONFIDENCE IS A LITTLE HIGHER THAN IN PAST NIGHTS
GIVEN A SLIGHTLY STRONGER WIND JUST ABOVE THE SURFACE AND A BETTER
AGREEMENT ON AMONG MODELS...WITH THE BEST CHANCE FROM KFAY TO KRWI.

OUTLOOK...A COLD FRONT WILL APPROACH FROM THE NORTHWEST ON
THURSDAY...WITH SOME PREFRONTAL CONVECTION POSSIBLE THURSDAY
AFTERNOON.  THE FRONT WILL THEN PUSH THROUGH THE AREA THURSDAY NIGHT
AND SETTLE SOUTH OF THE AREA ON FRIDAY.  IF THIS FRONT DOES PUSH ALL
THE WAY THROUGH THE AREA...THEN VFR CONDITIONS WILL BE MUCH MORE
LIKELY FOR THE UPCOMING WEEKEND.

&&

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

&&

$$

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


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