Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 281047
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
645 AM EDT TUE JUL 28 2015

.SYNOPSIS...A SERIES OF PERTURBATIONS ALOFT INTERACTING WITH A MOIST
AND UNSTABLE AIR MASS WILL TRIGGER SCATTERED THUNDERSTORMS...MAINLY
DURING THE AFTERNOON AND EVENING HOURS...THROUGH THE REMAINDER OF
THE WORK WEEK.

&&

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

NORTHWESTERLY FLOW ALOFT CONTINUES DOWNSTREAM OF THE SOUTHERN PLAINS
CENTRAL U.S. RIDGE...WITH NUMEROUS ILL-DEFINED DISTURBANCES
STREAMING ACROSS THE CENTRAL AND SOUTHERN APPALACHIANS. MOISTURE
RECOVERY ALSO CONTINUES IN EARNEST AS PW HAS RECOVERED TO NEARLY 2
INCHES IN THE PAST 24 HOURS...WITH SOUTHEASTERLY FLOW BETWEEN A
RIDGE AXIS ALONG THE MID-ATLANTIC COAST AND AN INVERTED TROUGH OFF
THE SOUTHEAST COAST.  DEWPOINTS IN THE LOWER 70S THIS MORNING AREN`T
FORECAST DROP MUCH TODAY GIVEN WEAK BOUNDARY LAYER
FLOW/MIXING...WHICH SHOULD YIELD SLIGHTLY BETTER INSTABILITY THAN
YESTERDAY...WITH MLCAPE OF 1000-2000 J/KG PROJECTED ACROSS THE
WESTERN/NORTHERN PIEDMONT AND LESSER AMOUNTS TO THE SOUTHEAST.
DIFFERENTIAL HEATING..ALONG WITH THE AFOREMENTIONED DISTURBANCES
ALOFT AND A WEAK LEE TROUGH WILL BE THE PRIMARY TRIGGERS...WHICH
AGAIN FAVORS THE NORTHERN/WESTERN PIEDMONT FOR AFTERNOON STORMS THAT
WILL HAVE A PRIMARY THREAT OF HEAVY RAIN AND LOCALIZED FLOODING
GIVEN WEAK STEERING FLOW.  HIGHS 89-94.

PERSISTENCE WOULD SUGGEST STORMS MAY CONTINUE TO PERCOLATE ON OLD
OUTFLOW BOUNDARIES THROUGH MIDNIGHT...STAYING CONFINED TO THE
PIEDMONT.  LOWS WILL AGAIN BE IN THE LOWER 70S.

 &&

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

THE CENTRAL U.S. RIDGE WILL BE SUPPRESSED A BIT ON WEDNESDAY BY A
SHORTWAVE CROSSING THE GREAT LAKES...LEADING A LITTLE MORE NORTHERLY
FLOW ALOFT OVER OUR AREA AND LESS IN THE WAY OF UPPER DISTURBANCES
TO ENHANCE CONVECTIVE COVERAGE.  FORECAST SOUNDINGS CONTINUE TO SHOW
SLIGHTLY BETTER INSTABILITY OVER WESTERN NC AND MOST NWP FAVORS THE
WESTERN HALF OF CENTRAL NC FOR AFTERNOON CONVECTION...THOUGH
NORTHERLY STEERING FLOW MAY LIMIT THE BEST COVERAGE TO THE FAR
WESTERN PIEDMONT.  WEAK MID-LEVEL FLOW WILL CONTINUE TO LIMIT THE
SEVERE WEATHER THREAT.  HIGHS WILL BE BE WITH A DEGREE OR TWO OF
TODAY`S VALUES...89-94.  LOWS WEDNESDAY NIGHT IN THE LOWER 70S.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
AS OF 415 AM TUESDAY...

THE MODELS ARE IN GOOD AGREEMENT REGARDING THE EVOLUTION OF TWO
DOMINANT FEATURES DURING THE MEDIUM RANGE - A SUB-TROPICAL RIDGE
FORECAST TO RETROGRADE FROM THE SOUTHERN PLAINS AND MID-MS VALLEY
WEST TO THE FOUR CORNERS REGION...AND A MID-UPPER LOW FORECAST TO
LIFT FROM THE NORTHERN ROCKIES TO THE SOUTHERN TIP OF HUDSON BAY.
BOTH ARE FORECAST TO THEN BECOME ANCHORED OVER THOSE RESPECTIVE
LOCATIONS THROUGH THE PERIOD. AT THE BASE OF THE UPPER LOW OVER
HUDSON BAY...A LONGWAVE TROUGH WILL BECOME ESTABLISHED ACROSS THE
EASTERN UNITED STATES.

MEANWHILE IN THE LOW LEVELS...A COLD FRONT RELATED TO THE
PROGRESSION OF THE AFOREMENTIONED UPPER LOW/TROUGH AXIS ACROSS THE
GREAT LAKES/TOWARD HUDSON BAY WILL SETTLE EAST OF THE APPALACHIANS
LATE THU-FRI...THOUGH OVERNIGHT DIURNAL TIMING OF THE FRONTAL
PASSAGE IN CENTRAL NC SUGGESTS COVERAGE OF ASSOCIATED SHOWERS AND
STORMS SHOULD BE SCATTERED AT BEST...WITH THE RELATIVELY GREATER
COVERAGE OVER THE NORTHERN AND NW PIEDMONT DURING THE EVENING. THE
MODELS INDICATE THE FRONT --AND PLUME OF DEEP TROPICAL MOISTURE
CHARACTERIZED BY PRECIPITABLE WATER VALUES AOA TWO INCHES-- WILL
THEN BECOME QUASI-STATIONARY OVER THE SOUTHEAST US...WHILE A
SECONDARY FRONT APPROACHES FROM THE NORTH AND SETTLES INTO THE
MIDDLE ATLANTIC STATES EARLY-MID NEXT WEEK.

DESPITE RELATIVELY GOOD AGREEMENT IN THESE MASS FIELDS...THERE
REMAINS MIXED SIGNALS REGARDING THE PROBABILITY OF PRECIPITATION
OVER CENTRAL NC FRI THROUGH EARLY NEXT WEEK. THE OVERALL
CONFIGURATION OF A TROUGH ALOFT IN THE EASTERN US WOULD SUPPORT
ABOVE AVERAGE CHANCES OF PRECIPITATION...BUT THE SUPPRESSION OF THE
LOW LEVEL FRONTAL ZONE JUST TO THE SOUTHEAST OF CENTRAL NC WOULD
FOCUS THE BRUNT OF THE SHOWERS AND STORMS OVER THE SOUTHEASTERN PART
OF THE STATE. WITH THIS IN MIND...HAVE CUT BACK (BY ABOUT 25%) WPC
POP...WHICH YIELDS GENERALLY SLIGHT TO CHANCE POP...HIGHEST
SOUTHEAST AND MAXIMIZED DURING THE AFTERNOON AND EVENING...WITH THE
EXPECTATION THAT NORTHERN AND NW PIEDMONT LOCATIONS MAY ULTIMATELY
SEE VERY LITTLE RAINFALL...IF ANY...FRI-SAT. THE MODELS INDICATE THE
THE TROPICAL MOISTURE LURKING OVER THE SOUTHEAST MAY THEN GET DRAWN
NORTH AND ENTRAINED INTO THE LARGER SCALE TROUGH BY SUN-MON...AT
WHICH TIME THE PROBABILITY OF SHOWERS AND STORMS ARE EXPECTED TO
INCREASE THROUGHOUT CENTRAL NC.

&&


.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
AS OF 645 AM TUESDAY...

SUB-VFR VSBYS AT KRWI WILL QUICKLY IMPROVE THIS MRONING AND VFR
CONDITIONS WILL PREVAIL FOR MUCH OF THE TAF PERIOD.  A FEW WEAK
DISTURBANCES IN THE NORTHWESTERLY FLOW ALOFT COMBINED WITH
INCREASING MOISTURE AND INSTABILITY WILL TRIGGER SCATTERED STORMS
THIS AFTERNOON.  WHILE AN ISOLATED STORM CANNOT BE RULED OUT AT ANY
TAF SITE...MODEL GUIDANCE AND THE OVERALL WEATHER PATTERN SUPPORT A
HIGHER PROBABILITY...AND THUS INCLUSIONG IN THE TAF...AT KGSO AND
KINT FOR THIS AFTERNOON.  OTHERWISE...SOME AREAS OF SUB-VFR VSBYS
WILL BE POSSIBLE AGAIN LATE TONIGHT...WITH THE HIGHEST CONFIDENCE AT
THE OFTEN FOG PLAGUED TERMINAL AT KRWI.

OUTLOOK: EARLY MORNING STRATUS AND/OR FOG WILL BE POSSIBLE WEDNESDAY
AND THURSDAY WITH AFTERNOON STORMS...MAINLY WEST...EACH DAY.  A COLD
FRONT WILL THEN MOVE INTO THE AREA ON FRIDAY...POTENTIALLY STALLING
OVER EASTERN NC THIS WEEKEND.

&&

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

&&

$$

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



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