Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 021934
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
333 PM EDT WED SEP 2 2015

.SYNOPSIS...A DISTURBANCE WILL DROP SOUTHEAST THROUGH THE AREA
TONIGHT THROUGH EARLY THURSDAY...BUT OTHERWISE DEEP HIGH PRESSURE
WILL HOLD OVER THE REGION THROUGH FRIDAY. A COLD FRONT WILL MOVE
SOUTHWARD THROUGH THE AREA LATE FRIDAY INTO SATURDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 252 PM WEDNESDAY...

ISOLATED CONVECTION HAS BEGUN OVER THE FAR NRN CWA... ROUGHLY A
COUPLE OF HOURS AHEAD OF THE TIMING SUGGESTED BY THE SPC SSEO / NSSL
WRF / 3KM NAM CONUS NEST... AND JUST ABOUT AN HOUR AHEAD OF THE NCAR
WRF ENSEMBLE. THE NCAR AND NSSL WRF ALONG WITH THE HRRR/NAM/GFS
INDICATE GREATEST COVERAGE OF STORMS OVER THE NE CWA LATE THIS
AFTERNOON THROUGH EARLY EVENING... REASONABLE CONSIDERING THAT THE
BEST DPVA WILL BE LOCATED HERE... ALONG WITH STRONG HEATING AND HIGH
INCOMING LOW-LEVEL LAPSE RATES OVER 8.5 C/KM. EFFECTIVE DEEP-LAYER
SHEAR REMAINS MARGINAL AT AROUND 25 KTS... BUT MIXED-PHASE CAPE IS
MAXIMIZED HERE AT 400 J/KG AND WITH OBSERVED DOWNDRAFT CAPE AOA 1000
J/KG... LOCALIZED ENHANCED WIND GUSTS ARE POSSIBLE IN/NEAR ANY
STORMS ESPECIALLY NORTH OF A LINE FROM RDU TO WILSON. THIS IS ALSO
SUPPORTED BY THE NCAR WRF ENSEMBLE NEIGHBORHOOD PROBABILITIES OF
STRONG SURFACE WIND GUSTS VERY LATE AFTERNOON INTO EARLY EVENING.
FOLLOWING THE TIMING OF THESE CONVECTION-ALLOWING MODELS... AND
THEIR TRENDS WHICH ARE FOR GRADUAL WEAKENING AND DECREASING COVERAGE
AS CONVECTION HEADS TO THE SSE OVER CENTRAL NC THROUGH THE
EVENING... WILL MAINTAIN POPS FROM EARLIER FORECAST UPDATE WITH ONLY
MINOR TEMPORAL CHANGES. WILL START WITH 25-45% COVERAGE (BEST NE)
THROUGH EARLY EVENING... WITH ACTIVITY DROPPING TO THE SSE THROUGH
EARLY TO MID EVENING WHILE STEADILY WEAKENING AND DECREASING IN
COVERAGE BEFORE DISSIPATING AROUND OR SOON AFTER 06Z WITH LOSS OF
HEATING / FALLING CAPE AND THE DEPARTURE OF THE POTENT MID LEVEL
WAVE NOW DROPPING THROUGH ERN WV. THERE SHOULD BE AN INITIAL PARTIAL
CLEARING BEHIND THE BROKEN/DIFFUSE CONVECTIVE BAND... BUT SCATTERED
MID CLOUDS AS WELL AS HIGH THIN CLOUDS SPREADING OFF LOWER MISS
VALLEY AND GULF CONVECTION WILL KEEP SKIES PARTLY CLOUDY
OVERNIGHT... LIMITING THE FOG THREAT DESPITE THE LIGHT WINDS. LOWS
67-72. -GIH

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
AS OF 333 PM WEDNESDAY...

THE MID LEVEL VORTICITY MAX SHOULD BE SHIFTING OFF THE NRN NC COAST
THU MORNING... ALBEIT WITH A WEAK TRAILING SHEAR AXIS EXTENDING BACK
ACROSS THE NRN CWA. THIS TRAILING VORTICITY WILL SINK SLOWLY
SOUTHWARD THROUGH THE DAY BUT REMAIN EXTENDED ACROSS THE SRN CWA
LATE THU THROUGH THU NIGHT. PW VALUES WILL HAVE FALLEN WITH A
SLIGHTLY MORE STABLE AND SUBSIDING COLUMN BEHIND THE CORE OF THE
EXITING WAVE... SO EXPECT ANY SHOWER/STORM COVERAGE TO BE FAIRLY
SMALL GIVEN THE WEAK WIND FIELD... LACK OF STRONG FORCING FOR
ASCENT... AND LIMITED CAPE. WILL RETAIN AN ISOLATED POP JUST ACROSS
THE SOUTH AND SE NEAR THE SHEAR AXIS AND WHERE LOW LEVEL DEWPOINTS
WILL LIKELY BE HIGHER. ANOTHER MUCH WEAKER WAVE WILL PUSH INTO THE
REGION FROM THE SW LATE THU INTO THU NIGHT... BUT THIS APPEAR TO
CONTRIBUTE VERY LITTLE DYNAMIC FORCING... AND WITH LACK OF HEATING
AFTER SUNSET... COVERAGE SHOULD BE ISOLATED AT BEST WITH THIS SECOND
WAVE. WILL KEEP A MENTION OF ISOLATED STORMS IN THE NE CWA THROUGH
THE EVENING... THEN TREND POPS DOWN BELOW 15% OVERNIGHT. THIS
PATTERN CORRELATES WITH THE LOCATION OF THE SREF`S HIGHER CHANCES OF
MEASURABLE PRECIP. WITH GOOD MIXING AND CONTINUED ABOVE NORMAL
THICKNESSES... EXPECT STEAMY HIGHS OF 90-95. LOWS 67-72 UNDER PARTLY
CLOUDY SKIES. -GIH

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
AS OF 315 PM WEDNESDAY...

THE MAIN PLAYER IN THE WEATHER PATTERN FOR THE LONG TERM WILL BE A
1026 MB SURFACE HIGH PRESSURE SYSTEM OVER NEW ENGLAND THAT WILL PUSH
A BACKDOOR COLD FRONT THROUGH THE AREA ON FRIDAY NIGHT AND SET UP A
WEDGE FRONT THAT IN PATTERN WILL BE REMINISCENT OF A COLD AIR
DAMMING SCENARIO BUT WITHOUT THE ISENTROPIC LIFT THAT WE USUALLY SEE
CONTRIBUTING TO MORE STRATIFORM RAIN ACROSS THE TRIAD. THE FEATURE
THROUGH WILL CAUSE LOW CLOUDS TO SPREAD ACROSS MUCH OF THE AREA ON
SATURDAY AND BRING IN MUCH COOLER HIGH TEMPERATURES (LOW TO MID 80S).

AS THE WEEKEND CONTINUES...A VERY WEAK LOW OFF OF THE FLORIDA COAST
WILL ATTEMPT TO HELP FORM AN INVERTED TROUGH ALONG THE CAROLINA
COAST BUT THE STRENGTH OF THIS FEATURE REMAINS UNCERTAIN AT THIS
TIME. CURRENT MODEL RUNS SUGGEST THAT THIS FEATURE MAY REMAIN FAIRLY
WEAK BUT IT WILL CERTAINLY CAUSE AN UPTICK IN POPS ACROSS EASTERN
PORTIONS OF THE CWA...PARTICULARLY SUNDAY AND MONDAY AFTERNOONS
DURING PEAK HEATING WITH PSEUDO WEDGE FRONT BOUNDARY HELPING TO
INITIATE CONVECTION. THE EXACT LOCATION OF THIS BOUNDARY IS TO BE
DETERMINED AND THUS THE AFTERNOON FORECAST REMAINS FAIRLY LOW
CONFIDENCE BUT GENERAL TRENDS SUGGEST THAT RAIN WILL BE MORE LIKELY
FURTHER EAST.

ON TUESDAY THE SURFACE HIGH BREAKS DOWN AND TEMPERATURES WILL START
A SLOW WARMING TREND INTO THE MID TO UPPER 80S BY MID WEEK. THE MAIN
THREAT FOR PRECIPITATION WILL BE WITH A FEW SHORTWAVES ALONG THE
SOUTH CAROLINA COAST WHICH MAY PROVIDE SOME FORCING FOR DIURNAL
SHOWERS OR STORMS BOTH DAYS.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
AS OF 145 PM WEDNESDAY...

HIGH CONFIDENCE IN VFR CONDITIONS HOLDING THROUGH MID AFTERNOON
THU... ALTHOUGH THERE WILL BE ONE BRIEF PERIOD OF EXCEPTION. THE
PASSAGE OF AN UPPER LEVEL DISTURBANCE FROM NW TO SE THROUGH THE
REGION LATE TODAY THROUGH THIS EVENING WILL BRING SCATTERED
STORMS... MOST LIKELY TO AFFECT RWI AND PERHAPS RDU... WITH INT/GSO
SEEING A SLIGHTLY LOWER CHANCE OF STORMS AND FAY SEEING THE LEAST
CHANCE. THE PRIMARY WINDOW OF STORM POTENTIAL WILL BE 21Z-01Z AT
INT/GSO/RDU/RWI. A SHORT PERIOD OF GUSTY WINDS AND MVFR TO IFR
CONDITIONS CAN BE EXPECTED IN AND NEAR ANY STORMS... ALTHOUGH
COVERAGE WILL BE SMALL AND DURATION LESS THAN AN HOUR AT ANY GIVEN
LOCATION. OTHERWISE... ANY CIGS ARE LIKELY TO BE ABOVE 6K FT AGL.
LIGHT AND VARIABLE SURFACE WINDS WILL BECOME PREDOMINANTLY FROM THE
NE OR NORTH TONIGHT BUT REMAIN LIGHT THROUGH THU.

LOOKING BEYOND 18Z THU... VFR CONDITIONS LIKELY TO HOLD. THE CHANCE
OF SHOWERS AND STORMS INCREASES LATE FRI INTO FRI NIGHT IN
ASSOCIATION WITH A COLD FRONT PASSAGE... FOLLOWED BY A LOWER CHANCE
SAT AFTERNOON. SUB-VFR LOW CLOUDS AND FOG POSSIBLE LATE FRI NIGHT /
EARLY SAT MORNING... AND AGAIN LATE SAT NIGHT / EARLY SUN MORNING
WITH A LOW LEVEL FLOW FROM THE EAST OR NE BEHIND THE FRONT DRAWING
ATLANTIC MOISTURE INTO THE AREA. -GIH

&&

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

&&

$$

SYNOPSIS...HARTFIELD
NEAR TERM...HARTFIELD
SHORT TERM...HARTFIELD
LONG TERM...ELLIS
AVIATION...HARTFIELD


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