846
FXUS64 KHUN 210549
AFDHUN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
1249 AM CDT MON SEP 21 2026
..NEW AVIATION
KEY MESSAGES
UPDATED AT 1101 PM CDT SUN SEP 20 2026
- THE COVERAGE OF SHOWERS AND THUNDERSTORMS WILL REMAIN FAIRLY
HIGH FROM THIS EVENING THROUGH TUESDAY. CONDITIONS WILL BE
FAVORABLE FOR STRONG-SEVERE THUNDERSTORMS, PARTICULARLY MONDAY
AFTERNOON/EVENING AND AGAIN ON TUESDAY AFTERNOON. LOCALLY
DAMAGING DOWNBURST WINDS, FREQUENT LIGHTNING AND HEAVY RAINFALL
WILL BE THE MAIN STORM IMPACTS.
- HOT TEMPERATURES WILL CONTINUE INTO TUESDAY, WITH HIGHS IN THE
90S ACCOMPANIED BY HEAT INDICES BETWEEN 98-104F.
- A SLIGHTLY COOLER AND DRIER AIRMASS WILL BEGIN TO ARRIVE ON
WEDNESDAY. HIGHS WILL FALL BACK INTO THE LOWER-MID 80S FROM
THURSDAY-SUNDAY, WITH LOWS IN THE MID-UPPER 50S THIS WEEKEND.
NEAR TERM
(THIS EVENING THROUGH MONDAY)
ISSUED AT 1101 PM CDT SUN SEP 20 2026
IN THE MID/UPPER-LEVELS, OUR FORECAST AREA WILL REMAIN BENEATH A
RIDGE (EXTENDING FROM THE LOWER RIO GRANDE VALLEY NORTHEASTWARD
INTO EASTERN PARTS OF THE TN VALLEY) OVERNIGHT. HOWEVER, THE RIDGE
WILL CONTINUE TO WEAKEN AS A SOUTHERN STREAM SHORTWAVE TROUGH
ADVANCES EASTWARD FROM THE SOUTHERN PLAINS INTO THE LOWER MS
VALLEY. AT THE SURFACE, A RELAXED PRESSURE GRADIENT WILL EXIST
BETWEEN A LINGERING RIDGE AXIS EXTENDING SOUTHWESTWARD INTO THE
CENTRAL GULF COAST AND A WEAKENING AREA OF LOW PRESSURE DRIFTING
EASTWARD ACROSS THE OZARKS. OUTFLOW BOUNDARY COLLISIONS AND
LIGHT/VEERING FLOW IN THE LOW-LEVELS (IN ADVANCE OF THE
APPROACHING SHORTWAVE) HAVE LIKELY HELPED TO SUSTAIN ISOLATED
THUNDERSTORMS ACROSS THE TN VALLEY THIS EVENING. ALTHOUGH REMNANT
CONVECTION OVER NORTHEASTERN AL CONTINUES TO SPREAD SOUTHWARD,
ADDITIONAL SHOWERS AND THUNDERSTORMS MAY DEVELOP LATER THIS
EVENING (AND PERSIST INTO THE EARLY MORNING HOURS ON MONDAY) IN
THE VICINITY OF ANOTHER SUBTLE CONFLUENCE AXIS IN THE WESTERN
PORTION OF THE CWFA. EVEN WITH WEAKENING LOW-LEVEL LAPSE RATES,
SUFFICIENT ELEVATED CAPE WILL EXIST WITHIN THE MOIST AIRMASS
(FEATURING PWAT VALUES OF 1.7-1.9") OVERNIGHT TO SUPPORT A RISK
FOR STRONG WIND GUSTS (UP TO 40-45 MPH) AND FREQUENT LIGHTNING
WITH THE MOST INTENSE CELLS. OTHERWISE, IT WILL BE ANOTHER PARTLY
CLOUDY, WARM AND MUGGY NIGHT, WITH LOWS RANGING FROM THE U60S/E TO
M70S/W.
LATEST MODEL GUIDANCE SUGGESTS THAT THE PREVIOUSLY MENTIONED MID-
LEVEL SHORTWAVE TROUGH WILL GRADUALLY DECAY AS IT TRANSLATES
SLOWLY EASTWARD TOMORROW, BUT SHOULD CONTRIBUTE TO A MINOR
INCREASE IN WSW FLOW ALOFT TO 10-20 KNOTS. AS THIS OCCURS, THE
WEAKENING SURFACE LOW WILL GRADUALLY OPEN INTO A TROUGH AS IT
DRIFTS EASTWARD OVER WESTERN TN. FORECAST SOUNDINGS SUGGEST THAT
CONVECTIVE TEMPERATURES WILL BE BREACHED IN THE 17-19Z TIMEFRAME
AS TEMPERATURES ASCEND INTO THE L-M 90S AND THIS SHOULD ALLOW
THUNDERSTORMS TO INITIALLY DEVELOP IN ZONES OF OROGRAPHIC LIFT
BEFORE ADDITIONAL CONVECTIVE DEVELOPMENT RAPIDLY OCCURS IN THE
VICINITY OF PREEXISTING MESOSCALE BOUNDARIES (AS WELL AS IN THE
VICINITY OF THE SURFACE TROUGH TO OUR NORTHWEST). ASIDE FROM A
MORE PRONOUNCED WESTERLY STEERING FLOW, LITTLE TO NO CHANGE IS
ANTICIPATED IN THE GENERAL KINEMATIC OR THERMODYNAMIC ENVIRONMENT
TOMORROW. THUS, WE EXPECT MLCAPE IN THE 2000-2500 J/KG RANGE
(COUPLED WITH RICH MOISTURE AND STEEP LOW-LEVEL LAPSE RATES) TO
SUPPORT A CONTINUED RISK FOR LOCALLY DAMAGING DOWNBURSTS, FREQUENT
LIGHTNING AND HEAVY RAINFALL.
SHORT TERM
(MONDAY NIGHT THROUGH WEDNESDAY NIGHT)
ISSUED AT 1101 PM CDT SUN SEP 20 2026
OVER THE COURSE OF THE EXTENDED PERIOD, A WEAKENING MID/UPPER-
LEVEL CYCLONE WILL SHIFT SLOWLY EAST-SOUTHEASTWARD FROM THE
NORTHERN PLAINS INTO THE CENTRAL APPALACHIANS (TO THE SOUTH OF A
BLOCKING 500-MB RIDGE ACROSS ONTARIO). ALTHOUGH WSW FLOW ALOFT OF
10-20 KNOTS WILL PERSIST MONDAY NIGHT, THIS PATTERN EVOLUTION WILL
FORCE WINDS ALOFT TO VEER TO WNW AND GRADUALLY STRENGTHEN
BEGINNING ON TUESDAY, WITH NNW FLOW ALOFT OF 30-40 KNOTS PREDICTED
TO BE ESTABLISHED BY THE END OF THE PERIOD. IN THE LOW-LEVELS, A
SURFACE TROUGH IS EXPECTED TO LIE FROM NORTHERN MS INTO WV AT THE
BEGINNING OF THE PERIOD, AND THIS FEATURE (ALONG WITH MULTIPLE
MESOSCALE BOUNDARY COLLISIONS) WILL LIKELY HELP TO SUSTAIN A
FAIRLY WIDESPREAD COVERAGE OF SHOWERS AND THUNDERSTORMS REGION-
WIDE MONDAY EVENING, WITH REDEVELOPMENT OF THUNDERSTORMS ON
TUESDAY EXPECTED TO BE FOCUSED TO THE EAST OF THE TROUGH AXIS. DUE
TO LITTLE CHANGE IN THE FAVORABLE THERMODYNAMIC ENVIRONMENT, THE
RISK FOR LOCALLY DAMAGING WIND GUSTS WILL PERSIST MONDAY EVENING
AND TUESDAY (WITH A SLIGHTLY GREATER POTENTIAL FOR STORM
ORGANIZATION INTO MULTICELL CLUSTERS ON TUESDAY DUE TO THE
INCREASE IN FLOW ALOFT).
DURING THE PERIOD FROM TUESDAY NIGHT-WEDNESDAY NIGHT, THERE ARE
INDICATIONS THAT THE SURFACE TROUGH WILL BEGIN TO SHIFT SLOWLY
EASTWARD ACROSS THE REGION. HOWEVER, THE SPEED AT WHICH THIS
OCCURS IS UNCERTAIN, AS ITS EASTWARD MOTION WILL LIKELY BE
RETARDED BY A STRENGTHENING SURFACE ANTICYCLONE ACROSS SOUTHERN
QUEBEC AND RELATED COLD AIR DAMMING TO THE EAST OF THE
CENTRAL/SOUTHERN APPALACHIANS. THE MOST LIKELY SCENARIO AT THIS
POINT IS FOR THE TROUGH AXIS TO DRIFT VERY SLOWLY EASTWARD,
USHERING A SLIGHTLY COOLER/DRIER AIRMASS (FEATURING DEWPOINTS IN
THE U50S-M60S) INTO THE NORTHWEST PORTION OF THE CWFA, WHILE A
MOIST AIRMASS (FEATURING DEWPOINTS IN THE U60S-L70S) REMAINS IN
PLACE ACROSS THE SOUTHEAST. ALTHOUGH A FEW SHOWERS WILL BE
POSSIBLE TO THE EAST OF THE TROUGH AXIS (PARTICULARLY DURING THE
DAY WEDNESDAY), STRENGTHENING NNW FLOW ALOFT WILL USHER A DRIER
MID/UPPER-LEVEL AIRMASS INTO THE REGION, AND CONDITIONS WILL
BECOME LESS FAVORABLE FOR THUNDERSTORMS. AFTER INITIALLY DROPPING
BACK INTO THE U80S-L90S ON TUESDAY, HIGHS ON WEDNESDAY SHOULD
MERELY REACH THE M-U 80S. OVERNIGHT LOWS WILL FALL INTO THE L-M
60S BY THURSDAY MORNING.
LONG TERM
(THURSDAY THROUGH SUNDAY)
ISSUED AT 1101 PM CDT SUN SEP 20 2026
GLOBAL MODELS SUGGEST THAT A WEAK MID/UPPER-LEVEL LOW (INITIALLY
ACROSS THE CENTRAL APPALACHIANS) WILL PHASE WITH A SMALLER
DISTURBANCE TO ITS EAST LATER THIS WEEK TO FORM A DEEP LOW THAT
WILL SIT OFF THE NORTHERN MID-ATLANTIC COAST THIS WEEKEND. THIS
WILL ENSURE A CONTINUATION OF DRY NNW FLOW ALOFT ACROSS THE TN
VALLEY FOR MUCH OF THE PERIOD, BEFORE THIS REGIME WEAKENS SATURDAY
AND SUNDAY. WITH INDICATIONS THAT LOW-LEVEL CONFLUENCE ACROSS
WILL PROGRESSIVELY DIMINISH ON THURSDAY/FRIDAY, THE RISK FOR
SHOWERS IN THE EAST WILL CONTINUE TO FALL AS LIGHT N-NE FLOW
ADVECTS A DRIER AIRMASS INTO THE REGION FROM A HIGH ACROSS
SOUTHEASTERN CANADA. HIGHS WILL BE IN THE L-M 80S, WITH OVERNIGHT
LOWS DROPPING INTO THE M-U 50S THIS WEEKEND (WHEN DEWPOINTS COULD
DROP INTO THE 40S).
AVIATION
(06Z TAFS)
ISSUED AT 1249 AM CDT MON SEP 21 2026
THERE HAVE BEEN NO SIGNIFICANT CHANGES TO PREVIOUS AVIATION
FORECAST REASONING, AS OUTFLOW BOUNDARY COLLISIONS AND WEAK
FORCING FOR ASCENT AHEAD OF AN APPROACHING SHORTWAVE TROUGH WILL
CONTINUE TO SUSTAIN ISOLATED-WIDELY SCATTERED SHRA/TSRA THROUGH
THE EARLY MORNING HOURS. HOWEVER, AT THIS POINT, IMPACTS APPEAR
MOST LIKELY TO OCCUR AT MSL, WHERE A 1-HR TEMPO GROUP HAS BEEN
INCLUDED FOR THE BEGINNING OF THE TAF PERIOD. OTHERWISE, WE EXPECT
VFR CONDITIONS TO PERSIST (FEATURING FEW-SCT AC AND BKN CI, WITH
A LGT SSE WIND). A GREATER COVERAGE OF THUNDERSTORMS IS STILL
ANTICIPATED LATER THIS AFTN/EVENING, AND PROB30 GROUPS HAVE BEEN
INTRODUCED BTWN 18-22Z AND 22-4Z TO ACCOUNT FOR THIS. HOWEVER,
ASIDE FROM CONVECTIVE IMPACTS, VFR CONDITIONS WILL EXIST WITH A
LGT SSW WIND.
HUN WATCHES/WARNINGS/ADVISORIES
AL...NONE.
TN...NONE.
NEAR TERM...70/DD
SHORT TERM...70/DD
LONG TERM...70/DD
AVIATION...70/DD
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