547
FXUS62 KRAH 201040
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
640 AM EDT SUN SEP 20 2026
WHAT HAS CHANGED
* NO MAJOR CHANGES.
KEY MESSAGES
AS OF 200 AM SUNDAY...
1) ISOLATED STRONG TO SEVERE STORMS, CAPABLE OF DAMAGING STRAIGHT-
LINE WINDS AND TORRENTIAL RAINFALL WILL BE POSSIBLE MONDAY AND
TUESDAY.
2) CLASSIC COLD-AIR DAMMING PATTERN WILL LIKELY DEVELOP BY MID-WEEK
AND BRING WELL-BELOW NORMAL TEMPERATURES INTO THE WEEKEND.
DISCUSSION
AS OF 200 AM SUNDAY...
KEY MESSAGE 1... ISOLATED STRONG TO SEVERE STORMS, CAPABLE OF
DAMAGING STRAIGHT-LINE WINDS AND TORRENTIAL RAINFALL WILL BE
POSSIBLE MONDAY AND TUESDAY.
A WEAK WAVE OF LOW PRESSURE IS EXPECTED TO RIPPLE ALONG STATIONARY
FRONT DRAPED ACROSS THE MID-MS VALLEY INTO THE OHIO VALLEY TODAY AND
EVENTUALLY OFF THE NJ COAST BY MON MORNING. THE DEPARTURE OF THE
SURFACE LOW AND STRONG HIGH PRESSURE SLIDING EASTWARD INTO SOUTHERN
ONTARIO/QUEBEC WILL COMBINE TO PUSH THE LEADING EDGE OF A COLD FRONT
THROUGH VA BY MON MORNING. SOUTH OF THIS BOUNDARY, A HOT AND HUMID
AIR MASS WILL BE IN PLACE AS SURFACE TEMPERATURES RISE INTO THE
UPPER 80S TO LOW 90S WITH PEAK HEATING SURFACE DEW POINTS IN THE
UPPER 60S TO AROUND 70. THIS SHOULD RESULT IN A 1500-2500 J/KG OF
MLCAPE TO DEVELOP, GREATEST ALONG AND JUST SOUTH OF THE LOCATION OF
THE SURFACE BOUNDARY, AND SUPPORT DEEP CONVECTION TO DEVELOP IN THE
VICINITY OF THE SURFACE CONVERGENCE MON AFTERNOON.
MODERATE INSTABILITY, PWAT VALUES ABOVE THE 90TH PERCENTILE PER
GSO/MHX RAOB CLIMATOLOGY, AND STEEPENING LOW-LVL LAPSE RATES > 8.5
C/KM WILL SUPPORT WATER-LOADED DOWNBURSTS BRINGING A PRIMARY CONCERN
FOR DAMAGING STRAIGHT-LINE WINDS. WEAK DEEP-LAYER WIND SHEAR WILL
LIMIT STORM ORGANIZATION/LONGEVITY PROVIDING MAINLY AN ISOLATED
SEVERE WIND THREAT; ALTHOUGH IF UPDRAFTS CAN ORGANIZE AROUND A
COMMON COLD-POOL, MORE SCATTERED INSTANCES OF STRONG WINDS MAY BE
POSSIBLE (40-60 MPH). SLOW STORM MOTIONS, WELL-ABOVE NORMAL PWAT,
AND A WARM CLOUD-LAYER AROUND 10 KFT WILL ALSO SUPPORT EFFICIENT
RAINFALL PRODUCING STORMS WHICH MAY CAUSE LOCALIZED URBAN FLOODING
CONCERNS.
THE SURFACE COLD FRONT WILL LIKELY CONTINUE TO SLOWLY OOZE SOUTH,
ASSISTED BY CONVECTIVE OUTFLOW FROM MON AFTERNOON/EVENING
CONVECTION, AND PROVIDE A VERY SIMILAR SETUP FOR TUES BUT CLOSER TO
THE NC/SC BORDER. ALTHOUGH SHOWERS/STORMS WILL STILL BE POSSIBLE
NORTH OF THE BOUNDARY, LIMITED AND ELEVATED INSTABILITY SHOULD
REDUCE THE THREAT FOR BOTH SEVERE AND FLOODING.
KEY MESSAGE 2... CLASSIC COLD-AIR DAMMING PATTERN WILL LIKELY
DEVELOP BY MID-WEEK AND BRING WELL-BELOW NORMAL TEMPERATURES INTO
THE WEEKEND.
CENTRAL NC WILL LIKELY BE ON THE SOUTHERN PERIPHERY OF THE MORE
CLASSIC CAD SETUP WITH THE REX-BLOCKING CONFIGURATION OVER THE GREAT
LAKES AND OHIO VALLEY AS OPPOSED TO INTO THE TN VALLEY AND
SOUTHEAST. ADDITIONALLY, ALTHOUGH THE SURFACE HIGH PRESSURE IS
STRONG (>1030 MB), IT IS A BIT FAR NORTH (CLOSER TO 50 N LATITUDE)
AND ELONGATED EAST-WEST TO PROVIDE A CAD ONSET FROM THE SURFACE HIGH
ALONE. THIS CONFIGURATION WILL LIKELY GREATLY DEPEND ON A SURFACE
LOW TO DEVELOP AND DEEPEN OVER THE WESTERN ATLANTIC TO PULL THE
FRONT EQUATORWARD AS WELL AS LOW-PREDICTABILITY CONVECTIVELY INDUCED
MCVS FROM UPSTREAM CONVECTION TO PROVIDE THE DIABATIC COMPONENT TO
LOCK IN THE CAD ON TUES TO PERSIST INTO WED AND THURS; ESPECIALLY
WITH THE LACK OF ANY LOW-LVL WAA OVER NC.
FROM A TEMPERATURE STANDPOINT, ENSEMBLE GUIDANCE DOES SUPPORT THE
ONSET OF A CAD REGIME OVER THE AREA WITH SURFACE RIDING EXTENDING
DOWN THROUGH THE CAROLINAS AND PERSISTENT NORTHERLY FLOW IN ITS WAKE
AND PROVIDING WELL BELOW-NORMAL TEMPERATURES TO THE REGION. THE
UNCERTAINTY COMES FROM THE PRECIPITATION AMOUNTS WE WILL PRODUCE
FROM THIS PATTERN WITH MUCH OF THE SYNOPTIC FORCING REMAINING IN THE
VIRGINIAS BEFORE TRANSFERRING TO THE SURFACE LOW DEEPENING OFF THE
MID-ATLANTIC COAST, AS WELL AS ITS PROXIMITY TO THE COAST WHEN THE
LOW DOES DEVELOP.
AVIATION /12Z SUNDAY THROUGH THURSDAY/
AS OF 640 AM SUNDAY...
THROUGH 12Z MONDAY: GENERALLY VFR CONDITIONS ARE EXPECTED UNDER WEAK
HIGH PRESSURE DURING THE TAF PERIOD. THERE IS A CHANCE OF AN
ISOLATED AFTERNOON OR EVENING THUNDERSTORM LATER TODAY, BUT MAINLY
IN THE GSO/INT AREA.
OUTLOOK: A COLD FRONT APPROACHING MONDAY WILL BRING A BETTER CHANCE
OF SHOWERS AND STORMS TO THE ENTIRE AREA. UNSETTLED WEATHER MAY
PERSIST UNDER A CAD-REGIME DEVELOPING TUESDAY-WEDNESDAY, WHERE
PERIODS OF SUB-VFR STRATUS AND FOG MAY EXIST INTO LATE WEEK.
RAH WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...AS
AVIATION...NP
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