233
FXUS62 KRAH 211928
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
328 PM EDT MON SEP 21 2026
WHAT HAS CHANGED
* FURTHER DECREASED TEMPERATURES WITHIN THE CAD REGIME, ESPECIALLY
ACROSS THE PIEDMONT, ON TUESDAY THROUGH THURSDAY.
KEY MESSAGES
AS OF 325 PM MONDAY...
1) POTENTIAL FOR STRONG STORMS WITH HEAVY DOWNPOURS TODAY ACROSS
MAINLY THE NORTH.
2) ADDITIONAL LOCALIZED HEAVY RAIN POSSIBLE AREAWIDE ON TUESDAY.
3) COLD AIR DAMMING WILL BRING MUCH BELOW NORMAL TEMPERATURES DURING
MID TO LATE WEEK.
DISCUSSION
AS OF 325 PM MONDAY...
KEY MESSAGE 1... POTENTIAL FOR STRONG STORMS WITH HEAVY DOWNPOURS
TODAY ACROSS MAINLY THE NORTH.
A COLD FRONT IS CURRENTLY ANALYZED OVER SOUTHERN VA, WITH COOL NE
FLOW AND LOW STRATUS TO ITS NORTH. AHEAD OF THE FRONT, HEATING AND
DESTABILIZATION HAVE OCCURRED, WITH WIDESPREAD TEMPERATURES IN THE
UPPER-80S TO LOWER-90S ACROSS CENTRAL NC AND MLCAPE IN THE 1000-2000
J/KG RANGE, HIGHEST OVER THE NW PIEDMONT. SCATTERED CUMULUS HAS
BEGUN TO DEVELOP, WITH A FEW ISOLATED SHOWERS ALREADY POPPING UP
OVER PARTS OF THE NORTHERN AND WESTERN PIEDMONT. THE DEEPER
CONVECTION IS LOCATED ALONG A CONVERGENCE AXIS OVER WESTERN VA/NC AS
A SHORTWAVE APPROACHES FROM WESTERN KY.
HIGH-RES MODELS ARE IN GOOD AGREEMENT THAT CONVECTION WILL CONTINUE
TO EXPAND THIS AFTERNOON, THOUGH HOW FAR SE IT MAKES BEFORE
NOCTURNAL STABILIZATION IS STILL UNCERTAIN AS LATEST RUNS OF THE
HRRR AND NAMNEST KEEP THE HEAVIEST RAIN JUST NORTH OF OUR CWA. WHERE
STORMS DO OCCUR, LOCALLY EXCESSIVE RAINFALL WILL BE POSSIBLE, WITH
THE GREATEST THREAT NEAR THE NC/VA BORDER. 12Z HREF LPMM INDICATES
POTENTIAL FOR ISOLATED 1-3"+ AMOUNTS IN THOSE AREAS, WHICH MAKES
SENSE GIVEN ABOVE-NORMAL PW VALUES OF 1.6-2 INCHES AND VERY WEAK
FLOW AND SHEAR (0-6KM MEAN WINDS ONLY AROUND 5 KTS) RESULTING IN
VERY SLOW-MOVING STORMS AND POSSIBLE MERGING AND TRAINING OF CELLS.
GIVEN DRY ANTECEDENT CONDITIONS, THINK ANY FLASH FLOODING WOULD BE
ISOLATED AND MAINLY LIMITED TO URBAN AREAS.
AS FOR THE SEVERE THREAT, SPC HAS AREAS FROM RDU NORTH AND WEST IN A
MARGINAL (LEVEL 1 OF 5) RISK TODAY. THE MAIN THREAT IS DAMAGING
WINDS GIVEN STEEP LOW-LEVEL LAPSE RATES AND DCAPE AS HIGH AS 900
J/KG OVER THE NW PIEDMONT. ANY SEVERE THREAT SHOULD DIMINISH AFTER
DARK.
KEY MESSAGE 2... ADDITIONAL LOCALIZED HEAVY RAIN POSSIBLE AREAWIDE
ON TUESDAY.
CENTRAL NC WILL LIKELY BE POSITIONED BETWEEN THE LEADING EDGE OF THE
SYNOPTIC COLD FRONT IN VA, LATER TO BE ESTABLISHED AS THE CAD FRONT,
AND CONVECTIVE OUTFLOW AND/OR DIFF HEATING BOUNDARY FROM MON/MON
NIGHT CONVECTION. A MODERATELY UNSTABLE AIR MASS WITH WEAK SHEAR,
TALL SKINNY CAPE, ABOVE NORMAL PWAT, AND AN APPROACHING SHORTWAVE
TROUGH FROM THE OHIO VALLEY INTO THE SOUTHERN APPALACHIANS WILL ALL
FAVOR AN INCREASE IN CONVECTIVE COVERAGE WITH SLOW MOVING STORMS,
THAT MAY PERSIST INTO THE OVERNIGHT PERIOD, CAPABLE OF TORRENTIAL
RAINFALL AND INCREASED FLOODING RISK (LEVEL 2 OUT OF 4 FROM WPC
EXCESSIVE RAINFALL OUTLOOK).
KEY MESSAGE 3... COLD AIR DAMMING WILL BRING MUCH BELOW NORMAL
TEMPERATURES DURING MID TO LATE WEEK.
AS THE SURFACE FRONT SETTLES S OF NC, CONFIDENCE IS HIGH IN THE
DEVELOPMENT OF A ROBUST, CLASSICAL COLD AIR DAMMING EVENT THIS WEEK.
WITH AN EARLY-WEEK REX BLOCK IN PLACE OVER THE UPPER MIDWEST AND
MANITOBA/ONTARIO, MID LEVEL ENERGY WILL UNDERCUT THE BLOCKING HIGH,
CROSSING IN/OH BEFORE DEEPENING TO A LOW OVER THE MID ATLANTIC
REGION DURING THE MID-LATE WEEK. THIS WILL KEEP THE SURFACE FRONTAL
ZONE PINNED TO OUR S AND SE, WITH STEADY ADVECTION OF COOL AND LOW-
DEWPOINT SURFACE AIR FROM A FAIRLY STRONG AND ANCHORED SURFACE HIGH
CENTERED OVER QUEBEC. THIS HIGH WILL WEAKEN AS IT SLOWLY RETROGRADES
TO THE WSW LATE THU INTO FRI, DRIFTING INTO THE N GREAT LAKES AND S
ONTARIO IN RESPONSE TO WHAT IS EXPECTED TO BE STRONG COASTAL
CYCLOGENESIS JUST OFF THE MID ATLANTIC AND NORTHEAST COAST BY
FRI/SAT, BUT THE CIRCULATION AROUND SUCH A LOW ALONE SHOULD MAINTAIN
THE WEDGE REGIME AND LOW LEVEL CAA THROUGH AT LEAST FRI, DESPITE THE
LIKELIHOOD OF FURTHER DRYING ALOFT POTENTIALLY ERODING MUCH OF THE
CAD STRATUS BY LATE IN THE DAY.
THE RESULT WILL BE MULTIPLE DAYS OF HIGH TEMPS 10-15 DEG F BELOW
NORMAL, INCLUDING HIGHS FROM THE TRIANGLE TO THE N AND W IN THE 60S
TO AROUND 70 EACH DAY WED THROUGH FRI. THESE TEMPS WILL BE FURTHER
HELD DOWN BY COPIOUS CLOUD COVER AND WIDESPREAD OVERRUNNING RAIN,
DRIVEN IN LARGE PART BY MOIST ISENTROPIC UPGLIDE FOCUSED AT 295K-
305K FROM WED MORNING THROUGH THU NIGHT. IN ADDITION TO THE COOL
DAYS, WE'RE LIKELY TO SEE A FEW NIGHTTIME LOWS IN THE 40S NEAR THE
VA BORDER THU NIGHT THROUGH SAT NIGHT. RAIN CHANCES ARE EXPECTED TO
DWINDLE FRI AND REMAIN LOW INTO THE WEEKEND, AS LOW-LEVEL STABILITY
DECREASES WITH THE WEAKENING AND RETROGRADING SURFACE RIDGE. BUT THE
POTENTIAL FOR A BAGGY MID LEVEL TROUGH OR SHEAR AXIS HOLDING ACROSS
THE REGION ALONG WITH A PERSISTENT LOW LEVEL FLOW FROM THE N OR NNW
AROUND THE COASTAL LOW SHOULD RESULT IN HIGHS REMAINING AT LEAST A
CATEGORY BELOW NORMAL SAT/SUN. GIVEN THAT WE'VE SEEN ABOVE TO MUCH
ABOVE-NORMAL TEMPS FOR ALL BUT A COUPLE OF DAYS SO FAR THIS MONTH,
SEVERAL DAYS OF BELOW TO MUCH-BELOW NORMAL TEMPS WILL BE A WELCOME
RESPITE FOR MANY.
AVIATION /18Z MONDAY THROUGH SATURDAY/
AS OF 230 PM MONDAY...
THROUGH 18Z TUESDAY: A COLD FRONT IS CURRENTLY DRAPED ACROSS
SOUTHERN VA, KEEPING THE MVFR STRATUS PINNED TO OUR NORTH. IN THE
WARM AND UNSTABLE AIR MASS AHEAD OF IT OVER CENTRAL NC, VISIBLE
SATELLITE SHOWS SCATTERED CUMULUS BEGINNING TO DEVELOP, WITH A FEW
SHOWERS ALREADY POPPING UP OVER THE NORTHERN AND WESTERN PIEDMONT.
SHOWERS AND STORMS ARE EXPECTED TO INCREASE IN COVERAGE LATER THIS
AFTERNOON ACROSS MAINLY THE NORTHERN PIEDMONT, WITH THE BEST CHANCE
FROM ABOUT 21Z TO 02Z. PRECIPITATION CHANCES ARE GREATEST AT
INT/GSO, FOLLOWED BY RDU, THEN RWI, AND LASTLY FAY. BRIEF MVFR OR
IFR CONDITIONS AND GUSTY ERRATIC WINDS WILL BE POSSIBLE WITH ANY
STORMS.
EXPECT WIDESPREAD IFR/LIFR CEILINGS AND MVFR/IFR VISIBILITIES TO
SPREAD IN FROM NORTH TO SOUTH OVERNIGHT TONIGHT AS COOL MOIST NE
FLOW SETS IN BEHIND THE FRONT. ISOLATED SHOWERS OR LIGHT
RAIN/DRIZZLE COULD ALSO LINGER INTO THE OVERNIGHT HOURS ACROSS THE
FAR NORTH. WHILE VISIBILITIES WILL IMPROVE THROUGH THE MORNING,
CEILINGS WILL BE SLOW TO LIFT, REACHING MVFR IN MOST PLACES BY LATE
MORNING OR EARLY AFTERNOON, BUT LIKELY REMAINING IFR AT INT/GSO
THROUGH THE END OF THE TAF PERIOD.
OUTLOOK: UNSETTLED WEATHER MAY PERSIST UNDER A CAD-REGIME DEVELOPING
TUESDAY-WEDNESDAY, WHERE PERIODS OF SUB-VFR STRATUS AND FOG MAY
EXIST INTO LATE WEEK, ESPECIALLY EACH EARLY MORNING. DRY WEATHER AND
VFR SHOULD RETURN ONCE THE CAD ERODES, BY FRIDAY OR SATURDAY.
RAH WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...DANCO/AVS/HARTFIELD
AVIATION...DANCO
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