657
FXUS62 KRAH 210555
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
155 AM EDT FRI SEP 21 2018
SYNOPSIS
SURFACE HIGH PRESSURE WILL EXTEND INTO THE REGION FROM THE NORTHEAST
THROUGH FRIDAY. A COLD FRONT WILL MOVE SOUTH INTO VA ON SATURDAY
NIGHT AND SUNDAY, THEN STALL OVER OUR AREA ON MONDAY.
NEAR TERM /OVERNIGHT/
AS OF 940 PM THURSDAY...
00Z UPPER AIR ANALYSIS REVEALS A STRONG AREA OF HIGH PRESSURE ALOFT
OVER THE CAROLINAS WITH A SFC RIDGE STRETCHING BASICALLY SOUTH-NORTH
OVER THE COASTAL PLAIN. THIS SET UP WILL MAINTAIN WARM AND DRY
CONDITIONS ACROSS CENTRAL NC OVERNIGHT.
THE POSITION/ORIENTATION OF THE SFC RIDGE WILL PERMIT A LIGHT SLY
RETURN FLOW OVER THE WESTERN PIEDMONT. THIS FLOW MAY LEAD TO THE
FORMATION BY DAYBREAK OF A LAYER OF LOW CLOUDS. ELSEWHERE PATCHY MID
LEVEL CLOUDS MAY OCCUR, ALONG WITH POCKETS OF FOG. CANNOT RULE OUT
THE POSSIBILITY OF LOCALLY DENSE FOG IN A FEW SPOTS, THOUGH
CURRENTLY DO NO THINK THAT A DENSE FOG ADVISORY WILL BE NEEDED DUE
TO THE EXPECTED LIMITED COVERAGE.
OVERNIGHT TEMPERATURES GENERALLY IN THE MID-UPPER 60S.
SHORT TERM /FRIDAY THROUGH SATURDAY/
AS OF 220PM THURSDAY...
DEEP LAYER RIDGING WILL PEAK OVER THE AREA FRIDAY MORNING,
SHIFTING SLOWLY EAST THROUGH FRIDAY NIGHT AND SATURDAY. THE EARLY
MORNING STRATUS/FOG WILL BURN OFF QUICKLY, EXCEPT IN THE NW PIEDMONT
WHERE THE STRATUS WILL GRADUALLY LIFT OUT BY LATE MORNING LEAVING
PARTLY SUNNY SKIES. OTHER THAN AN ISOLATED (20 PERCENT CHANCE)
SHOWER OR AFTERNOON THUNDERSTORM (MAINLY NW) ON FRIDAY
AFTERNOON/EARLY EVENING, EXPECT PARTLY SUNNY SKIES AND LESS THAN A
15 PERCENT CHANCE OF A SHOWER ELSEWHERE. HIGHS ARE FORECAST TO BACK
OFF A FEW DEGREES DUE TO THE INCREASE IN THE LIGHT E-SE FLOW
TEMPERING CONDITIONS. EXPECT MOSTLY MID 80S FOR HIGHS. LOWS FRIDAY
NIGHT WITH PARTLY CLOUDY SKIES WILL BE IN THE UPPER 60S TO LOWER
70S.
SATURDAY, THERE IS A CHANCE OF MAINLY AFTERNOON AND EVENING
THUNDERSTORMS ACROSS THE NORTHERN PIEDMONT AS A COLD FRONT
APPROACHES FROM WVA/VA LATE IN THE DAY. THE LOW LEVEL WINDS WILL
BECOME S TO SW WITH A RETURN FLOW AS HIGH PRESSURE SHIFTS OFFSHORE.
THIS WILL LEAD TO HIGHS IN THE MID 80S TO AROUND 90 (SANDHILLS).
LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/
AS OF 400 PM THURSDAY...
THE LONG TERM LOOKS TO BE CHARACTERIZED BY MOSTLY ABOVE NORMAL
TEMPERATURES AND PRECIPITATION WITH THE LATEST RUNS OF THE GEFS
AND GEPS SHOWING MOSTLY ABOVE NORMAL HEIGHT ANOMALIES.
THE LONG TERM WILL OPEN UP WITH A SURFACE COLD FRONT NEAR THE
NC/ VA BORDER WITH A POTENTIAL COLD AIR DAMMING SITUATION
SETTING UP. DURING THE DAY SUNDAY THE COLD FRONT WILL SLOWLY SAG
SOUTH AND WASH OUT AS A WEAK SHORTWAVE MOVES INTO WESTERN NORTH
CAROLINA. BY SUNDAY EVENING, THE GFS, ECMWF, NAM, AND CMC ALL
HAVE THE FRONT THROUGH THE TRIAD. AS THE FRONT PASSES, PWATS
WILL REMAIN ONLY AROUND 1.3" WITH INSTABILITY RATHER LACKING.
DUE TO THE ABOVE, HAVE KEPT POPS IN THE CHANCE CATEGORY. DURING
THE DAY MONDAY ISENTROPIC UPGLIDE ALONG WITH UPSLOPE FLOW LOOKS
TO FAVOR HIGHER POPS. CONDENSATION PRESSURE DEFICITS ALSO AT
THIS TIME DO START TO LOWER.
PWATS THROUGH THE REMAINDER OF THE EXTENDED REMAIN AROUND 1.70"
WITH MID-LEVEL RIDGING SLOWLY BEGINNING TO BREAK DOWN. WEDNESDAY
INTO THURSDAY A PATTERN CHANGE WILL BEGIN TO DEVELOP ACROSS THE
UNITED STATES WITH A LONG WAVE TROUGH BEGINNING TO SETUP.
WEDNESDAY INTO THURSDAY A SHORTWAVE WILL EJECT NORTHEAST WITH A
WEAK COLD FRONT CROSSING THE ZONES THURSDAY. THE LATEST RUN OF
THE ECMWF HAS THE FRONT STALLING NORTH OF THE AREA IN VIRGINIA,
WHILE THE GFS AND CMC HAVE THE FRONT WASHING OUT ACROSS THE
VIRGINIA/ NORTH CAROLINA BORDER. THURSDAY INTO FRIDAY OF NEXT
WEEK A MORE POTENT SHORTWAVE WILL TRAVERSE THROUGH THE LONG WAVE
TROUGH AS THE GROUP VELOCITY OF THE LONG WAVE SLOWS. THIS
LIKELY MEANS OUR FIRST FALL COLD FRONT WILL PROBABLY CROSS AT
THE END OF NEXT WEEK.
AVIATION /06Z FRIDAY THROUGH TUESDAY/
AS OF 155 AM FRIDAY...
MVFR TO LOW-END VFR CEILINGS ARE EXPECTED ACROSS THE AREA OVERNIGHT,
WITH THE LOWEST CEILINGS MORE LIKELY IN PROXIMITY OF THE TRIAD
TERMINALS. OTHERWISE, THIS CLOUD COVER SHOULD LIMIT FOG DEVELOPMENT
OVERNIGHT, WITH THE EXCEPTION FOR FOG PRONE AREA LIKE KRWI. THE BULK
OF THE LOW CLOUDS WILL LIFT AND SCATTER OUT BETWEEN 12Z-15Z, THOUGH
MAY LINGER UNTIL 16Z IN VICINITY OF THE TRIAD. OUTSIDE OF SOME
ISOLATED CONVECTION INVOF THE TRIAD TERMINALS THIS AFTERNOON, EXPECT
VFR CONDITIONS THROUGH THE REMAINDER OF THE TAF PERIOD.
LOW-LEVEL FLOW VEERS AROUND TO A MORE SWLY COMPONENT FRIDAY NIGHT,
AHEAD OF A COLD FRONT APPROACHING FROM THE NORTH. THIS SHOULD RESULT
IN LOWER PROBABILITIES FOR SUB-VFR CONDITIONS IN FOG AND/OR STRATUS
SATURDAY MORNING. A BACK-DOOR COLD FRONT WILL PUSH SOUTH INTO THE
AREA LATE SATURDAY AND INTO SUNDAY. OWING TO THE APPROACH OF THE
FRONT, THE CHANCE OF SHOWERS AND STORMS WILL INCREASE ACROSS THE
AREA, ESPECIALLY ACROSS THE NORTHERN TERMINALS SATURDAY AFTERNOON AND
SATURDAY NIGHT. ADDITIONALLY, A PROLONGED PERIOD OF SUB-VFR CEILINGS
ASSOCIATED WITH COLD AIR DAMMING EAST OF THE MTNS LOOKS INCREASINGLY
LIKELY SUNDAY, LINGERING INTO EARLY NEXT WEEK.
RAH WATCHES/WARNINGS/ADVISORIES
NONE.
SYNOPSIS...BADGETT/CBL
NEAR TERM...WSS
SHORT TERM...BADGETT
LONG TERM...HAINES
AVIATION...CBL
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