Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 281503
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1105 AM EDT TUE JUL 28 2015

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

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1105 AM TUESDAY...

JUST MINOR TWEAKS REQUIRED TO THE NEAR TERM FORECAST. NAMELY TO
RAISE MAX TEMPS A DEGREE OR TWO ACROSS THE EAST AND SOUTH
SECTIONS...AND TO CONCENTRATE THE HIGHEST POPS (30-40%) ACROSS THE
WESTERN-NW PIEDMONT.

12Z UPPER AIR ANALYSIS DEPICTS A HIGHLY AMPLIFIED RIDGE EXTENDING
FROM THE SOUTHERN PLAINS INTO THE GREAT LAKES. THIS YIELDS A NWLY
MID-UPPER LEVEL FLOW OVER CENTRAL NC. WATER VAPOR IMAGERY SUGGEST A
FEW VORT MAXIMA CIRCULATING AROUND THE RIDGE OVER THE LOWER OH AND
EASTERN TN VALLEYS. PER TRAJECTORIES...THESE SYSTEMS SHOULD REMAIN
WEST OF OUR AREA THIS AFTERNOON AND TONIGHT.

IN THE LOWER LEVELS...A WEAK SFC TROUGH WAS POSITIONED OVER THE FAR
NW PIEDMONT INTO SOUTH CENTRAL VA. CONFLUENCE ALONG THIS FEATURE WAS
VERY WEAK. MESO-ANALYSIS INDICATES A NARROW RIBBON OF HIGHER
MOISTURE/MODEST INSTABILITY IN VICINITY OF THIS FEATURE. THIS
APPEARS TO BE THE FAVORED REGION FOR CONVECTIVE INITIATION LATER
TODAY. DIFFICULT TO DISCERN ANY TRIGGER MECHANISM ALOFT. THUS
BELIEVE BULK OF CONVECTION WILL BE INITIATED BY AFTERNOON HEATING.
THUS EXPECT ONLY ISOLATED COVERAGE ALONG AND EAST OF HIGHWAY 1 WITH
A SLIGHTLY BETTER COVERAGE ANTICIPATED IN VICINITY OF THE YADKIN
RIVER VALLEY AND THE FAR NW PIEDMONT. MAY NEED TO RE-EVALUATE POP
FOR THE TRIAD REGION AS 40-50% MAY BE TOO HIGH.

STRONG HEATING THIS MORNING HAS PUSHED TEMPS WELL INTO THE 80S BY
MID-LATE MORNING. IN EXPECTATION OF ISOLATED CONVECTION...THE
SOUTHERN PIEDMONT AND SANDHILLS SHOULD REACH THE LOW-MID 90S WITH
NEAR/LOWER 90S EXPECTED ELSEWHERE. -WSS

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 /15Z TUESDAY THROUGH SATURDAY/...
AS OF 1105 AM TUESDAY...

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 INCLUDING 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...WSS/22
SHORT TERM...22
LONG TERM...26
AVIATION...22


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