862
FXUS62 KRAH 211006
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
605 AM EDT MON SEP 21 2026
WHAT HAS CHANGED
* CONFIDENCE IN UPCOMING COLD AIR DAMMING EVENT HAS INCREASED.
KEY MESSAGES
AS OF 245 AM MONDAY...
1) POTENTIAL FOR STRONG STORMS WITH HEAVY DOWNPOURS TODAY AND
ADDITIONAL LOCALIZED HEAVY RAIN ON TUESDAY.
2) COLD AIR DAMMING WILL BRING MUCH BELOW NORMAL TEMPERATURES DURING
MID TO LATE WEEK.
DISCUSSION
AS OF 245 AM MONDAY...
KEY MESSAGE 1... POTENTIAL FOR STRONG STORMS WITH HEAVY DOWNPOURS
TODAY AND ADDITIONAL LOCALIZED HEAVY RAIN ON TUESDAY.
A COLD FRONT WILL BE THE PRIMARY DRIVER FOR THE AFOREMENTIONED
WEATHER AND HAZARDS TODAY AND TUESDAY. THAT FRONT WILL DRIFT SOUTH
TOWARD AND ACROSS THE MOUNTAINS LATER TODAY. MOSTLY SUNNY CONDITIONS
THIS MORNING WILL GIVE WAY TO INCREASING CLOUDS AND SCATTERED
SHOWERS AND THUNDERSTORMS THIS AFTERNOON AND EARLY EVENING, WITH THE
HIGHEST COVERAGE IN OUR CWA NEAR THE VA/NC BORDER WHERE A LINGERING
OUTFLOW BOUNDARY AND PRE-FRONTAL CONVERGENCE ZONE MAY SET UP.
DESPITE STRONGER SHEAR REMAINING TO OUR NORTH, ADEQUATE HEATING AND
MOISTURE AHEAD OF THE FRONT WILL RESULT IN MODERATE INSTABILITY AND
THUS COULD SUPPORT A FEW STRONG TO SEVERE STORMS WITH DAMAGING WIND
GUSTS THE PRIMARY THREAT. MOST OF THIS ACTIVITY SHOULD BE CONFINED
TO AREAS WEST OF US-1. HEAVY RAINFALL COULD ALSO PRODUCE LOCALIZED
FLASH FLOODING, ESPECIALLY IN AND AROUND THE TRIAD WHERE URBAN AREAS
MAY BE MORE VULNERABLE TO EXCESSIVE RAINFALL.
THE FRONT WILL PUSH SOUTH ACROSS NC TUESDAY, PLACING OUR AREA ON THE
COOLER SIDE OF THE BOUNDARY AND LARGELY ENDING THE SEVERE WEATHER
THREAT FOR TUESDAY. HOWEVER, RAIN WILL LIKELY CONTINUE WITH LOCALLY
HIGH RAINFALL RATES POSSIBLE ALONG THE FRONT. THE ENTIRE AREA
REMAINS UNDER A MARGINAL RISK (LEVEL 1 OF 4) FOR EXCESSIVE RAINFALL
WITH THE GREATEST CONCERN TUESDAY AFTERNOON. LOCALIZED FLOODING WILL
BE POSSIBLE WHERE HEAVIER OR REPEATED RAINFALL OCCURS.
KEY MESSAGE 2... 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 /12Z MONDAY THROUGH FRIDAY/
AS OF 605 AM MONDAY...
THROUGH 12Z TUESDAY: VERY LOCALIZED MVFR FLT CONDITIONS ATTM DUE TO
PATCHY FOG, OTHERWISE LOOK FOR VFR CONDITIONS AFTER 12Z AND UNTIL
SCATTERED SHOWERS AND TSTMS MOVE ACROSS CENTRAL NC LATER TODAY
BETWEEN 21Z AND 02Z. WITH THOSE STORMS, FLT CONDITIONS WILL BE
TEMPORARILY REDUCED TO IFR ALONG WITH ERRATIC AND GUSTY SFC WINDS.
LOCATIONS FROM RDU NORTH AND WEST ARE MOST LIKELY TO SEE THESE
STORMS, WITH KFAY AND KRWI LESS LIKELY. AFTER THE STORMS END, LOOK
FOR CIGS TO DECREASE TONIGHT WITH COOL MOIST NE LOW LEVEL FLOW
SETTING UP.
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.
RAH WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...NP/HARTFIELD
AVIATION...NP
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