657
FXUS64 KHUN 171041
AFDHUN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
541 AM CDT THU SEP 17 2026
..NEW AVIATION
KEY MESSAGES
UPDATED AT 207 AM CDT THU SEP 17 2026
- A HEAT ADVISORY IS IN EFFECT THROUGH 8 PM SATURDAY ACROSS ALL
OF SOUTHERN MIDDLE TENNESSEE AND NORTHERN ALABAMA.
- NWS HEAT RISK HIGHLIGHTS MODERATE (LEVEL 2/4) TO MAJOR (LEVEL
3/4) HEAT IMPACTS THROUGH THE WEEKEND ACROSS THE TENNESSEE
VALLEY. LOCALIZED EXTREME (LEVEL 4/4) IMPACTS MAY OCCUR IN
URBANIZED AREAS.
NEAR TERM
(TODAY)
ISSUED AT 207 AM CDT THU SEP 17 2026
MODERATE (LEVEL 2/4) TO MAJOR (LEVEL 3/4) HEAT IMPACTS WILL
CONTINUE TODAY ACROSS THE TENNESSEE VALLEY AS A STRONG AREA OF
HIGH PRESSURE AND ITS SUBSEQUENT "HEAT DOME" UNDERNEATH IT REMAINS
IN PLACE. MOSTLY SUNNY CONDITIONS AND LIGHT SOUTHERLY WINDS WILL
PUSH HIGH TEMPERATURES INTO THE MID TO UPPER 90S IN MOST LOCATIONS
AGAIN THIS AFTERNOON. COMBINED WITH DEWPOINTS IN THE UPPER 60S TO
LOWER 70S, THIS WILL PUSH PEAK HEAT INDEX VALUES TO AROUND 105
DEGREES BY THIS AFTERNOON ONCE AGAIN. AS WE'VE BEEN HIGHLIGHTING
FOR THE PAST SEVERAL DAYS, THIS WILL POSE A DANGER FOR HEAT
RELATED ILLNESS ESPECIALLY FOR THOSE THAT ARE ESPECIALLY SENSITIVE
TO THE HEAT OR WITHOUT PROPER COOLING AND HYDRATION. PLEASE
PRACTICE COMMON SENSE HEAT SAFETY, ESPECIALLY IF YOU HAVE OUTDOOR
PLANS! A HEAT ADVISORY REMAINS IN EFFECT THROUGH 8 PM SATURDAY.
SHORT TERM
(THURSDAY NIGHT THROUGH SATURDAY NIGHT)
ISSUED AT 1020 PM CDT WED SEP 16 2026
THROUGHOUT THE SHORT TERM PERIOD, A WEAKENING SUBTROPICAL HIGH IN
THE MID-LEVELS WILL REMAIN CENTERED OVER THE ARKLATEX AS A
DEVELOPING UPPER LOW TRAVELS WEST-SOUTHWESTWARD ACROSS THE FL
PENINSULA AND INTO THE EASTERN GULF. THIS CONFIGURATION WILL
SUSTAIN N-NE FLOW ALOFT OF 10-20 KNOTS, ALTHOUGH GRADUAL
MOISTENING OF THE LOWER TROPOSPHERIC COLUMN WILL SUPPORT A MINOR
INCREASE IN PWAT AS WE PROGRESS THROUGH THE PERIOD (WITH VALUES
RISING BACK TO 1.6-1.7" EARLY THIS WEEKEND).
LATEST GUIDANCE STILL SUGGESTS THAT A CANADIAN SURFACE HIGH WILL
TRANSLATE SOUTHEASTWARD ACROSS OT AND INTO SOUTHERN QC FROM
THURSDAY NIGHT-FRIDAY NIGHT, WITH A COLD FRONT EDGING SLOWLY
SOUTHWESTWARD BETWEEN THE LOWER GREAT LAKES AND OH VALLEY. IT
STILL APPEARS AS IF A PREFRONTAL WIND SHIFT AXIS WILL INITIATE
AFTERNOON CONVECTION FROM THE OH VALLEY INTO THE SOUTHERN MID-
ATLANTIC STATES ON FRIDAY, WITH A GREATER COVERAGE OF TERRAIN-
INDUCED THUNDERSTORMS ACROSS THE SOUTHERN APPALACHIANS, AS WELL.
STORM COVERAGE WILL LIKELY BE A BIT HIGHER ACROSS OUR CWFA
(PARTICULARLY THE EASTERN HALF) DURING THE AFTERNOON AND EVENING
HOURS DUE TO THE DIMINISHING INFLUENCE OF THE SUBTROPICAL RIDGE.
HOWEVER, THIS WILL BE CONTINGENT ON A SOURCE OF LOW-LEVEL ASCENT
(LIKELY A COMBINATION OF CONVECTIVE OUTFLOW AND TOPOGRAPHY).
SHOULD STRONGER UPDRAFTS MANAGE TO DEVELOP IN OUR REGION, THE
THERMODYNAMIC ENVIRONMENT FRIDAY AFTERNOON WILL SUPPORT LOCALLY
DAMAGING DOWNBURST WINDS, ALONG WITH FREQUENT LIGHTNING.
AS THE WEAKENING CANADIAN SURFACE HIGH SHIFTS EASTWARD ACROSS NEW
ENGLAND ON SATURDAY/SATURDAY NIGHT, MINOR PRESSURE RISES IN THE
LEE OF THE SOUTHERN APPALACHIANS WILL INDUCE LIGHT SSE FLOW ACROSS
OUR REGION, WITH SCATTERED DIURNAL CONVECTION AND A SIMILAR RISK
FOR LOCALLY DAMAGING DOWNBURST WINDS ON SATURDAY (AND CONTINUING
INTO SATURDAY EVENING) EXPECTED TO BE FOCUSED ALONG THE INTERFACE
OF THIS REGIME. AFTERNOON HIGHS AND OVERNIGHT LOWS WILL EXHIBIT
LITTLE FLUCTUATION THROUGH THE SHORT TERM PERIOD, AND IN ORDER TO
HIGHLIGHT HEAT RISK VALUES IN THE LEVEL 2/4 TO 3/4 RANGE, WE WILL
MAINTAIN A HEAT ADVISORY THROUGH 8 PM SATURDAY.
LONG TERM
(SUNDAY THROUGH WEDNESDAY)
ISSUED AT 1020 PM CDT WED SEP 16 2026
EXTENDED RANGE MODEL DATA SUGGESTS THAT LIGHT S-SW FLOW IN THE
LOW-LEVELS WILL EXIST ACROSS THE REGION FROM SUNDAY INTO MONDAY,
AS A WEAK AREA OF LOW PRESSURE TRACKS EAST-NORTHEASTWARD FROM THE
OZARKS INTO NORTHERN PARTS OF THE TN VALLEY. THIS WILL SUSTAIN A
WARM AND INCREASINGLY MOIST AIRMASS, WITH HIGHS REMAINING IN THE
M-U 90S (IN LOWER ELEVATIONS) AND AN ISOLATED-WIDELY SCATTERED
COVERAGE OF MAINLY AFTERNOON/EARLY EVENING SHOWERS AND
THUNDERSTORMS. DURING THE TIMEFRAME FROM MONDAY NIGHT INTO
TUESDAY, THE WEAKENING AREA OF LOW PRESSURE TO OUR NORTH WILL
EVOLVE INTO A FRONTAL WAVE AS IT LIFTS FURTHER NORTHEASTWARD INTO
THE UPPER OH VALLEY, WITH A GENERAL INCREASE IN THE SPATIAL
COVERAGE OF SHOWERS AND THUNDERSTORMS ANTICIPATED BOTH PERIODS AS
THE TRAILING COLD FRONT DRIFTS SOUTHEASTWARD. WHETHER OR NOT THE
FRONT CONTINUES TO ADVANCE SOUTHEASTWARD (AND BRINGS OUR FORECAST
AREA A SLIGHTLY COOLER/DRIER AIRMASS ON TUESDAY NIGHT/WEDNESDAY)
REMAINS UP FOR DEBATE, AND WILL LIKELY BE DEPENDENT ON
AMPLIFICATION OF AN UPPER-LEVEL TROUGH TO OUR NORTH. REGARDLESS,
WE WILL ADVERTISE SLIGHTLY COOLER HIGH TEMPS (U80S-L90S) BY
WEDNESDAY.
AVIATION
(12Z TAFS)
ISSUED AT 541 AM CDT THU SEP 17 2026
VFR CONDITIONS WILL PREVAIL THROUGH THE PERIOD, WITH LIGHT WINDS
AND A MOSTLY CLEAR SKY.
HUN WATCHES/WARNINGS/ADVISORIES
AL...HEAT ADVISORY UNTIL 8 PM CDT SATURDAY FOR ALZ001>010-016.
TN...HEAT ADVISORY UNTIL 8 PM CDT SATURDAY FOR TNZ076-096-097.
NEAR TERM...AMP
SHORT TERM....70
LONG TERM....70
AVIATION...AMP.24
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