Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 021141
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
740 AM EDT TUE SEP 2 2014

.SYNOPSIS...AN AREA OF HIGH PRESSURE WILL EXTEND OVER THE REGION
TODAY.  A WEAK SURFACE FRONT WILL SETTLE SOUTHWARD ACROSS CENTRAL NC
ON WEDNESDAY. HIGH PRESSURE WILL BUILD BACK OVER THE AREA FOR THE
REMAINDER OF THE WORK WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 300 AM TUESDAY...

BERMUDA HIGH PRESSURE REMAINS IN CONTROL OVER THE REGION AND WILL
CREATE ANOTHER HOT AND HUMID DAY ACROSS CENTRAL NC.  THE THERMAL
RIDGE...WHERE H85 TEMPS VERIFIED AT 19C AT 00Z...WILL EXPAND ACROSS
THE PIEDMONT TODAY...AND GUIDANCE IS IN VERY GOOD AGREEMENT ON HIGHS
OF 93-97 WITH JUST ISOLATED STORMS AT BEST DURING THE AFTERNOON
HOURS. DEWPOINTS WILL AGAIN MIX OUT A LITTLE MORE IN THE WEST...WITH
HIGHER HEAT INDEX VALUES AROUND 100 DEGREES EAST OF US HWY 1.

MEANWHILE...A SHORTWAVE OVER MID-MISSISSIPPI RIVER VALLEY REGION
WILL CROSS THE UPPER OHIO VALLEY AND GREAT LAKES REGION THIS
EVENING...LEADING TO WEAK HEIGHT FALLS AS FAR SOUTH AS THE NC/VA
BORDER.  AS THE ASSOCIATED COLD FRONT SLIPS SOUTH INTO VA THIS
EVENING...MODELS INDICATE ONGOING PREFRONTAL CONVECTION CROSSING THE
MOUNTAINS AND POTENTIALLY CONTINUING INTO AT LEAST THE WESTERN AND
NORTHERN PIEDMONT BY MIDNIGHT AS PW INCREASE TO NEAR 2 INCHES.
HOWEVER... FORCING WILL MUCH WEAKER THIS FAR SOUTH AWAY FROM THE
MAIN SHORTWAVE...SO COVERAGE IS STILL A LITTLE UNCERTAIN. WEAK SHEAR
AND NOCTURNAL STABILIZATION SHOULD LIMIT THE INTENSITY OF THE
CONVECTION...BUT WITH ONLY ISOLATED STORMS EXPECTED THIS
AFTERNOON...THERE SHOULD BE SOME LINGERING INSTABILITY AS DEWPOINTS
RECOVER DURING THE EVENING.  THUS...IF CONVECTION CAN CONTINUE INTO
THE AREA...A STRONG TO SEVERE STORM MAY STILL BE POSSIBLE THIS
EVENING AND OVERNIGHT.  POPS WILL INDICATE THE INCREASING CHANCE
THROUGH THE EVENING HOURS...DECREASING WITH SOUTHERN EXTENT AFTER
MIDNIGHT.  LOWS IN THE UPPER 60S AND LOWER 70S.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
AS OF 330 AM TUESDAY...

THE WEAK FRONTAL ZONE...MAINLY JUST SURFACE TROUGH...WILL SETTLE
OVER CENTRAL ON WEDNESDAY AS ITS PRIMARY SHORTWAVE LIFTS WELL OFF TO
THE NORTHEAST.  THE AXIS OF HIGHER PW NEAR 2 INCHES WILL SHIFT SOUTH
ACROSS THE SOUTHERN TIER OF THE AREA.  WEAK WESTERLY FLOW ALOFT MAY
CONTAIN A DISTURBANCE OR TWO TO HELP TRIGGER SCATTERED SHOWERS AND
STORMS...MAINLY ALONG AND SOUTH OF THE SURFACE TROUGH WHERE MODERATE
INSTABILITY WILL DEVELOP.  THE AIRMASS WONT CHANGE MUCH ON WEDNESDAY
BUT H85 TEMPS ARE KNOCKED BACK A DEGREE OR TWO...AND ADDITIONAL
CLOUD COVER SHOULD ALSO HELP TO KEEP HIGHS IN THE LOWER 90S.
OVERNIGHT LOWS IN THE UPPER 60S AND LOWER 70S.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
AS OF 325 AM TUESDAY...

THE SUB-TROPICAL RIDGE WILL BRIEFLY EXPAND NORTHWARD...INTO THE OH
VALLEY AND MIDDLE ATLANTIC...THROUGH FRI. MEANWHILE...A MID LEVEL
SHEAR AND MOIST AXIS...THE TAIL END OF A TROUGH ALOFT FORECAST TO
CROSS THE NORTHEAST US AND SOUTHEAST CANADA...WILL REMAINS DRAPED
ACROSS THE CAROLINAS THROUGH THE MIDDLE OF THIS WEEK. MEDIUM RANGE
ENSEMBLE GUIDANCE SUGGESTS THE SUB-TROPICAL RIDGE WILL THEN WEAKEN
AND BECOME SUPPRESSED...IN PROGRESSIVE FLOW ALOFT...BY ANOTHER
TROUGH FORECAST TO CROSS THE NE US AND SE CANADA THIS WEEKEND...
BEFORE YET ANOTHER ESTABLISHMENT OF THE RIDGE ACROSS THE SOUTHEAST
THROUGH THE MIDDLE OF NEXT WEEK.

THE EBB AND FLOW OF THE PATTERN ALOFT...AND ASSOCIATED PERIODIC
RELAXATION OF THE SUB-TROPICAL RIDGE...WILL ALLOW A SFC COLD FRONT
TO SETTLE INTO THE CAROLINAS SUN-MON. THE FAVORED ECMWF ENSEMBLE
MEAN SOLUTION SUGGESTS THE FRONT WILL SETTLE SOUTH THROUGH CENTRAL
NC SUN AND SUN NIGHT...THEN STALL INVOF THE EASTERN CAROLINAS/
ADJACENT GULF STREAM WATERS...AS IT MEETS RESISTANCE FROM RENEWED
SUB-TROPICAL RIDGING EXPANDING FROM THE SW ATLANTIC TO THE GOM EARLY
NEXT WEEK.

THU: THE PRESENCE OF THE AFOREMENTIONED MID LEVEL SHEAR/MOIST AXIS
THROUGH THU WILL PROVIDE FOR A DEEPLY MOIST ENVIRONMENT...ONE
CHARACTERIZED BY PWAT VALUES BETWEEN ONE AND THREE QUARTERS AND TWO
INCHES...WHICH SHOULD SUPPORT SHOWER AND THUNDERSTORM GROWTH IN A
MODERATELY UNSTABLE AND WEAKLY INHIBITED REGIME OVER OUR REGION.
WITH CONSIDERABLE MID AND HIGH CLOUDS ACCOMPANYING THE SHEAR AXIS
ALOFT...AND CONVECTION...TEMPERATURES ARE APT TO CLIMB SHORT OF WHAT
CONTINUED WARM H85 TEMPS OF AROUND 18C WOULD SUPPORT - HIGHS AROUND
90. IF MORE SUNSHINE WERE REALIZED...HIGHS WOULD BE A CATEGORY
WARMER.  FRI-SAT NIGHT: A PATTERN OF WEAK SYNOPTIC-SCALE ASCENT

FRI-SAT NIGHT...AHEAD OF THE AFOREMENTIONED COLD FRONT...WILL THEN
FAVOR NEAR CLIMO PROBABILITIES OF DIURNALLY; PIEDMONT TROUGH, AND
SEA BREEZE-DRIVEN CONVECTION...WITH HIGHS EDGING INTO THE LOWER 90S
BENEATH THE BRIEFLY BUILDING SUB-TROPICAL RIDGE.

SUN-MON: THE BEST CHANCE OF SHOWERS AND STORMS DURING THE LONG TERM
PERIOD WILL ACCOMPANY THE ARRIVAL/PASSAGE OF THE COLD FRONT SUN-SUN
NIGHT...WITH LESSENING PROBABILITIES/DRYING FROM NW TO SE...ON MON.
COOLER INVOF AND BEHIND THE FRONT...WITH HIGHS GENERALLY IN THE
LOWER TO MIDDLE 80S.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
AS OF 740 AM TUESDAY...

STRATUS HAS SPREAD INLAND FROM THE KILM AREA TOWARD KCTZ...AND MAY
REACH KFAY BEFORE SCATTERING OUT BY 14Z.  HAVE INCLUDED A TEMPO THE
LIFR CEILINGS AT KFAY.  OTHERWISE...JUST A FEW LOCATIONS ARE
REPORTING MVFR VSBY...WHICH WILL RAPIDLY IMPROVE TO VFR...AND VFR
WILL PREVAIL THROUGH MUCH OF THE TAF PERIOD.  MODELS ARE INDICATING
THAT CONVECTION UPSTREAM OF THE MOUNTAINS...AS WELL AS CONVECTION
THAT FORMS ALONG THE  EAST SLOPES OF THE MOUNTAINS...WILL MOVE EAST
INTO THE PIEDMONT THIS EVENING AHEAD OF A WEAK FRONTAL ZONE TO
SETTLE INTO THE AREA OVERNIGHT.  CONFIDENCE IS STILL BELOW AVERAGE
AT THIS TIME...BUT THE BEST TIME FRAME FOR A SHOWER OR STORM AND
LOCALIZED IMPACTS WOULD ROUGHLY BE BETWEEN 23Z AND 05Z FROM WEST TO
EAST.  LATER...AS THE FRONTAL ZONE SLIPS INTO THE AREA FROM THE
NORTH...LIGHT WINDS AND LITTLE CHANGE IN LOW-LEVEL MOISTURE MAY LEAD
TO SOME PATCHY FOG/STRATUS PRIOR TO 12Z.

OUTLOOK...TYPICAL SUMMERTIME CONDITIONS ARE EXPECTED TO PERSIST
THROUGH THE PERIOD...FEATURING DIURNAL CONVECTION EACH
AFTERNOON/EVENING AND PATCHY FOG/LOW CLOUDS DURING THE PRE-DAWN
MORNING HOURS.

&&

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

&&

$$

SYNOPSIS...WSS
NEAR TERM...BLS
SHORT TERM...BLS
LONG TERM...MWS
AVIATION...KRD/BLS


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