857
FXUS62 KRAH 230024
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
824 PM EDT TUE SEP 22 2026
WHAT HAS CHANGED
* DAY 1 MARGINAL SVR TSTM RISK REMOVED FROM ALL BUT THE EXTREME SW
CORNER OF OUR CWA FOR THE REST OF TODAY.
* CONTINUED MINOR DOWNWARD ADJUSTMENT TO MAXIMUM TEMPERATURES ON WED
AND THURS.
KEY MESSAGES
AS OF 225 PM TUESDAY...
1) REDUCED SVR TSTM THREAT THE REST OF TODAY, WITH LOCALIZED FLASH
FLOOD THREAT STILL A POSSIBILITY.
2) COLD AIR DAMMING WILL BRING MUCH BELOW NORMAL TEMPERATURES DURING
MID TO LATE WEEK.
DISCUSSION
AS OF 225 PM TUESDAY...
1) REDUCED SVR TSTM THREAT THE REST OF TODAY, WITH LOCALIZED FLASH
FLOOD THREAT STILL A POSSIBILITY.
A COLD FRONT JUST NORTH OF THE VIRGINIA BORDER WILL MOVE SOUTH
ACROSS CENTRAL NORTH CAROLINA TONIGHT. AHEAD OF THE FRONT, THE
ATMOSPHERE WILL REMAIN VERY MOIST AND MODERATELY UNSTABLE, WITH
LATEST MESOANALYSIS SHOWING PWATS AROUND 1.6 TO 2.0 INCHES AND
MLCAPE GENERALLY AROUND 500-1500 J/KG (HIGHEST MLCAPE SOUTHERN HALF
OF OUR CWA). HOWEVER, WIND SHEAR WILL REMAIN VERY WEAK, LIMITING
STORM ORGANIZATION AND FAVORING SLOW-MOVING STORMS. WHILE A FEW
STRONG TO MARGINALLY SEVERE STORMS (DAMAGING WINDS GUSTS THE
CONCERN) WILL STILL BE POSSIBLE ACROSS THE FAR SW PORTION OF OUR
CWA, THE GREATER CONCERN WILL BE LOCALLY HEAVY RAINFALL AND ISOLATED
FLOODING, AS SLOW STORM MOTIONS COULD ALLOW STORMS TO PRODUCE VERY
HEAVY DOWNPOURS OR REPEATEDLY MOVE OVER THE SAME AREAS. STORM
COVERAGE IS STILL EXPECTED TO INCREASE THROUGH THE REST OF THIS
AFTERNOON AS THE FRONT APPROACHES AND VARIOUS TRIGGERING MECHANISMS
CURRENTLY EXIST, SUCH AS OUTFLOWS, LOCALIZED CONVERGENT FLOW, AND
DIFFERENTIAL HEATING BOUNDARIES. ONCE WE SEE COVERAGE EXPAND, WE
EXPECT SCATTERED THUNDERSTORMS TO CONTINUE INTO THE EVENING. THE
EXACT LOCATION OF THE HEAVIEST CONVECTION REMAINS UNCERTAIN, BUT
AREAS ACROSS NORTHERN AND CENTRAL NC COULD SEE LOCALLY HIGHER
RAINFALL TOTALS WHERE STORMS TRAIN. GIVEN RECENT DRY CONDITIONS,
WIDESPREAD FLOODING IS NOT EXPECTED, THOUGH LOCALIZED FLOODING COULD
OCCUR, PARTICULARLY IN URBAN AND POOR-DRAINAGE AREAS.
THUNDERSTORMS SHOULD GRADUALLY WEAKEN DURING THE EVENING AS
INSTABILITY DECREASES; HOWEVER SHOWERS MAY BECOME WIDESPREAD
OVERNIGHT AS THE FRONT MOVES THROUGH. RAIN WILL LIKELY CONTINUE INTO
THE EARLY MORNING HOURS WEDNESDAY, ESPECIALLY ACROSS THE PIEDMONT
AND WESTERN PORTIONS OF CENTRAL NC. THROUGH WEDNESDAY MORNING, MOST
LOCATIONS SHOULD RECEIVE AROUND 0.5 TO 1.0 INCH OF RAIN, WITH
LOCALLY HIGHER AMOUNTS OF 1 TO 2 INCHES OR MORE POSSIBLE WHERE
THUNDERSTORMS REPEATEDLY DEVELOP OR MOVE OVER THE SAME AREA.
KEY MESSAGE 2... COLD AIR DAMMING WILL BRING MUCH BELOW NORMAL
TEMPERATURES DURING MID TO LATE WEEK.
THE LEADING EDGE OF THE SURFACE COLD FRONT, CURRENTLY DRAPED FROM
NEAR RICHMOND SOUTHWEST TO NEAR THE VA/NC BORDER AND BACK NORTHWEST
TO JUST SOUTHWEST OF BLACKSBURG, VA. THIS FRONT HAS MOVED LITTLE
OVER THE PAST 24 HOURS SINCE THE STRONG AREA OF HIGH PRESSURE
REMAINS ELONGATED WEST-EAST AS IT SLIDES INTO SOUTHERN QUEBEC. THIS
IS EXPECTED TO CHANGE TONIGHT AS UPPER DIVERGENCE OVERSPREADS A
BROAD AREA OF LOW PRESSURE OFF THE CAROLINA COAST, AND AS IT
DEEPENS, STRENGTHENING NORTH-NORTHEASTLY FLOW WILL PULL THE COLD
FRONT, LATER TO BE DEEMED THE CAD FRONT, EQUATORWARD AND INTO THE
CAROLINAS BY WED MORNING. MOIST ISENTROPIC ASCENT IN THE 295-305K
LAYER WILL PROVIDE DIABATIC SUPPORT TO LOCK IN THE CAD, ESPECIALLY
ALONG AND NORTH OF THE FAVORED I-85 CORRIDOR WHERE PERSISTENT LOW
CLOUDS AND DRIZZLE IS LIKELY THROUGH WED NIGHT. PERIODS OF MODERATE
RAIN APPEARS LIKELY WED EVENING INTO THE OVERNIGHT PERIOD AS A
CONSOLIDATED SHORTWAVE TROUGH EJECTS ACROSS THE SOUTHERN
APPALACHIANS BEFORE CLOSING OFF OVER THE VA/NC PIEDMONT BY THURS
MORNING.
CAD EROSION IS ALWAYS DIFFICULT TO FORECAST, BUT A FAVORABLE SETUP
FOR DISPERSION IS EXPECTED THURS INTO FRI WITH AN AREA OF LOW
PRESSURE DEEPENING OVER THE WESTERN ATLANTIC AS IT SHIFTS NORTHWARD
WITH TIME. ALTHOUGH LOCAL RESEARCH SUGGESTS CAD DISPERSION SHOULD
BEGIN ONCE THE LOW REACHES THE LATITUDE OF THE VA/NC, WHICH SHOULD
OCCUR BY WED NIGHT, THE REINFORCING SHORTWAVE CLOSING OVER THE
WESTERN PIEDMONT SHOULD CONTINUE TO PROVIDE LIFT AND SUPPORT LOW
OVERCAST AND DRIZZLE THROUGHOUT THE DAY ON THURS. HOWEVER, AS THE
AREA OF LOW PRESSURE CONTINUES TO DEEPEN THURS AFTERNOON, ANOTHER
SURGE OF SLIGHTLY COOLER BUT SIGNIFICANTLY DRIER AIR SHOULD ERODE
THE CLASSIC CAD PATTERN FROM NE TO SW THURS NIGHT INTO FRI. BELOW
NORMAL TEMPERATURES WILL PERSIST INTO THE WEEKEND AS CONTINUED
PERTURBATIONS ROTATING AROUND THE BACKSIDE OF THE CLOSED LOW JUST
OFF THE NORTHEAST COAST WILL SUPPORT PERSISTENT NORTHERLY FLOW OVER
THE MID-ATLANTIC, ALTHOUGH LIKELY GRADUALLY MODERATING WITH TIME AS
LOW-LVL THICKNESSES STEADILY RISE.
AVIATION /00Z WEDNESDAY THROUGH SUNDAY/
AS OF 820 PM TUESDAY...
A BACKDOOR COLD FRONT AND ASSOCIATED LEADING EDGE OF BOTH GUSTY NELY
SURFACE WINDS AND MVFR-IFR CEILINGS, AND ALSO THE NRN BOUND OF
SHOWERS/STORMS, WAS ANALYZED AT 00Z FROM NEAR GSB TO HFF. THIS
BOUNDARY WILL CONTINUE TO MOVE SOUTH AND PAST FAY IN THE NEXT COUPLE
OF HOURS. WHILE POST-FRONTAL CEILINGS MAY INITIALLY HOVER AROUND
1000 FT, THEY ARE EXPECTED TO LOWER THROUGH IFR RANGE AND BE
ACCOMPANIED BY PERIODS OF LIGHT RAIN LATER TONIGHT THROUGH WED
NIGHT, AS A MID/UPR-LEVEL TROUGH PIVOTS OVERHEAD AND DEEPENS LIFT
AND SATURATION WITHIN A DEVELOPING COLD AIR DAMMING AIRMASS OVER
CNTL NC.
OUTLOOK: WIDESPREAD STRATUS WITH AT LEAST SUB-VFR CONDITIONS ARE
EXPECTED THROUGH THURSDAY. CONDITIONS WILL IMPROVE ON FRIDAY AND
SATURDAY AS VFR CONDITIONS ARRIVE.
RAH WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...NP/AS
AVIATION...MWS/NP
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