472
FXUS64 KHUN 042317
AFDHUN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
617 PM CDT FRI SEP 4 2026
..NEW AVIATION
KEY MESSAGES
UPDATED AT 1048 AM CDT FRI SEP 4 2026
- A HEAT ADVISORY REMAINS IN EFFECT THROUGH 8 PM SATURDAY DUE TO
MAJOR TO EXTREME HEATRISK, ALONG WITH AFTERNOON HEAT INDICES
RISING UP TO 105-109 DEGREES IN PORTIONS OF THE FORECAST AREA.
- A FEW THUNDERSTORMS MAY OCCUR THIS AFTERNOON (NORTH OF THE TN
RIVER), WITH A SLIGHT INCREASE IN COVERAGE EXPECTED REGION-WIDE
ON SATURDAY AFTERNOON/EVENING. CONDITIONS WILL BE FAVORABLE
FOR LOCALLY DAMAGING WINDS, FREQUENT LIGHTNING AND HEAVY RAIN.
NEAR TERM
(REST OF TODAY AND TONIGHT)
ISSUED AT 251 PM CDT FRI SEP 4 2026
FORECAST REASONING FOR THE NEAR TERM PERIOD HAS NOT CHANGED
SIGNIFICANTLY SINCE THE UPDATE EARLIER THIS MORNING, WITH A
SCATTERED COVERAGE OF SHOWERS AND THUNDERSTORMS LIKELY TO CONTINUE
(ESPECIALLY NORTH OF THE TN RIVER) THROUGH LATE THIS AFTERNOON
(BEFORE DISSIPATING QUICKLY BETWEEN 23-0Z). HOWEVER, FOR MOST OF
THE FORECAST AREA (NOT IMPACTED BY EITHER COOLING RAINFALL,
CONVECTIVE DEBRIS CLOUDS OR RAIN-COOLED OUTFLOW AIR), DANGEROUSLY
HOT/HUMID CONDITIONS WILL PERSIST AS CURRENT HEAT INDICES ARE IN
THE 105-107F RANGE IN MANY LOCATIONS. MOSTLY CLEAR SKIES AND DRY
CONDITIONS WILL EXIST OVERNIGHT, AND AS TEMPERATURES GRADUALLY
FALL INTO THE L-M 70S, DEVELOPMENT OF PATCHY FOG MAY OCCUR IN
LOCATIONS THAT EXPERIENCE WETTING RAINFALL LATER TODAY.
PREVIOUS DISCUSSION:
OVER THE COURSE OF THE NEAR TERM PERIOD, A MID-LEVEL HIGH
(INITIALLY CENTERED ACROSS WESTERN NC) WILL WEAKEN UNDER THE
INFLUENCE OF A DEEPENING NORTHERN STREAM TROUGH DIGGING
SOUTHEASTWARD ACROSS ONTARIO. HOWEVER, HEIGHTS WILL BEGIN TO RISE
ACROSS THE CENTRAL PLAINS, AND A BROAD MID-LEVEL TROUGH WILL
CONTINUE TO RETROGRADE SLOWLY WESTWARD ACROSS THE CENTRAL/WESTERN
GULF. AT THE SURFACE, OUR FORECAST AREA WILL REMAIN WITHIN A
RELAXED PRESSURE GRADIENT BETWEEN A WEAKENING HIGH OVER THE
SOUTHERN APPALACHIANS AND A SUBTLE AREA OF LOW PRESSURE (RELATED
TO THE TROUGH TO OUR SOUTH) THAT WILL DRIFT SLOWLY NORTHWESTWARD
OVER THE NORTH-CENTRAL GULF AND ADJACENT PORTIONS OF SOUTHERN LA.
ALTHOUGH THE GREATEST SPATIAL CONCENTRATION OF SHOWERS AND
THUNDERSTORMS TODAY IN OUR GENERAL REGION SHOULD OCCUR WITHIN A
ZONE OF ENHANCED LOW-LEVEL MOISTURE ADVECTION TO THE EAST OF THE
TROUGH (ACROSS LA, SOUTHERN PORTIONS OF MS/AL/GA, AND NORTH FL) A
DIFFUSE STREAMLINE CONFLUENCE AXIS ACROSS THE TN VALLEY WILL
LIKELY INITIATE DEVELOPMENT OF AT LEAST A FEW CONVECTIVE CELLS IN
OUR REGION (BEGINNING IN THE 17-19Z TIMEFRAME). HOWEVER, WITH THIS
FEATURE EXPECTED TO LIFT SLOWLY NORTHWARD FROM AN INITIAL
POSITION ALONG THE AL-TN BORDER, WE WILL ONLY INCLUDE A LOW
(10-20%) POP FOR LOCATIONS NORTH OF THE TN RIVER. REGARDLESS OF
STORM COVERAGE, STEEP LOW-LEVEL LAPSE RATES, MLCAPE IN THE
2000-2500 J/KG RANGE AND FAVORABLE DCAPE VALUES OF 1200-1400 J/KG
SUGGEST THAT LOCALLY DAMAGING WET DOWNBURST WINDS AND FREQUENT
LIGHTNING MAY OCCUR GIVEN PWAT VALUES IN THE 1.7-1.9" RANGE. FOR
THE VAST MAJORITY OF THE REGION (THAT WILL NOT EXPERIENCE ANY
CONVECTIVE IMPACTS), IT WILL BE ANOTHER HOT/HUMID DAY FEATURING
HIGHS IN THE 95-100F RANGE IN THE VALLEY AND 90-95F IN ELEVATED
TERRAIN. EVEN ACCOUNTING FOR DIURNAL MIXING LOWERING DEWPOINTS
INTO THE U60S-L70S, HI WILL STILL REACH 103-107F IN OUTLYING AREAS
AND 107-109F IN URBAN LOCATIONS, AND A HEAT ADVISORY REMAINS IN
EFFECT.
WITH NO EVIDENCE OF EITHER A LOW OR MID-LEVEL SOURCE OF LIFT, WE
EXPECT ANY AFTERNOON CONVECTION THAT MANAGES TO DEVELOP IN OUR
REGION TO QUICKLY DISSIPATE AROUND OR SHORTLY BEFORE 0Z, WITH
MOSTLY CLEAR SKIES AND DRY CONDITIONS ANTICIPATED THIS EVENING AND
OVERNIGHT. LOW TEMPERATURES WILL ONCE AGAIN BE IN THE L-M 70S,
WITH BRIEF DEVELOPMENT OF PATCHY FOG DURING THE PREDAWN HOURS IN
VALLEYS AND NEAR LARGE WATER SOURCES.
SHORT TERM
(SATURDAY THROUGH SUNDAY NIGHT)
ISSUED AT 1048 AM CDT FRI SEP 4 2026
LATEST GLOBAL MODEL CONSENSUS SUGGESTS THAT NORTHERLY FLOW ALOFT
WILL BECOME ESTABLISHED ACROSS THE TN VALLEY DURING THE SHORT TERM
PERIOD, AS OUR REGION WILL BE SITUATED BETWEEN AN AMPLIFYING
RIDGE ACROSS THE GREAT PLAINS AND AN AMPLIFYING TROUGH THAT WILL
SHIFT SLOWLY EASTWARD INTO THE WESTERN NORTH ATLANTIC. WITH LESS
NEGATIVE INFLUENCE FROM A WEAK MID-LEVEL SUBSIDENCE INVERSION, THE
ENVIRONMENT WILL BECOME MORE FAVORABLE FOR THE DEVELOPMENT OF
AFTERNOON SHOWERS AND THUNDERSTORMS REGION-WIDE TOMORROW (BUT
PARTICULARLY IN REGIONS OF FAVORABLE OROGRAPHIC ASCENT ACROSS
NORTHEAST AL/SOUTHERN MIDDLE TN). STRONGER CONVECTIVE UPDRAFTS
WILL ONCE AGAIN BE ABLE TO TAKE ADVANTAGE OF FAVORABLE
THERMODYNAMIC PROFILES (SIMILAR TO THOSE FROM TODAY) TO YIELD A
RISK FOR LOCALLY DAMAGING WINDS, FREQUENT LIGHTNING AND HEAVY
RAINFALL.
ALTHOUGH THE NUMBER OF SHOWERS AND THUNDERSTORMS DURING THE
EARLY-MID AFTERNOON HOURS WILL LIKELY REMAIN FAIRLY LOW
(WARRANTING A CONTINUATION OF THE HEAT ADVISORY THROUGH 8 PM), IT
APPEARS AS IF COVERAGE WILL INCREASE FROM NE-TO-SW DURING THE LATE
AFTERNOON AND EVENING HOURS AS EXTENSIVE CONVECTIVE OUTFLOW
(ORIGINATING FROM MULTIPLE SMALL CLUSTERS OF THUNDERSTORMS
TRACKING SOUTHEASTWARD FROM THE LOWER GREAT LAKES/OH VALLEY INTO
THE SOUTHERN MID-ATLANTIC STATES) BEGINS TO PROPAGATE
SOUTHWESTWARD INTO THE TN VALLEY. EVEN WITH A NOCTURNALLY
STABILIZING BOUNDARY LAYER DURING THE EVENING HOURS, CONDITIONS
WILL REMAIN FAVORABLE FOR GUSTY OUTFLOW WINDS, FREQUENT LIGHTNING
AND LOCALLY HEAVY RAINFALL UNTIL STORMS DISSIPATE AROUND OR
SHORTLY AFTER MIDNIGHT.
IN THE WAKE OF THE OUTFLOW BOUNDARY, LIGHT NNE WINDS WILL BEGIN
TO ADVECT A DRIER AIRMASS INTO THE REGION, WITH NO PRECIPITATION
IS EXPECTED FOR THE REMAINDER OF THE SHORT TERM PERIOD. DRY
ADVECTION IS EXPECTED TO CONTINUE ON SUNDAY (WHEN DEWPOINTS MAY
FALL INTO THE L-M 60S) AND SUNDAY NIGHT, WHEN DEWPOINTS MAY FALL
INTO THE U50S AS A BACKDOOR COLD FRONT (MARKING THE LEADING EDGE
OF A CANADIAN AIRMASS CENTERED ACROSS SOUTHERN ONTARIO/QUEBEC)
ARRIVES. AT THIS POINT, WE WILL NOT PLAN TO EXTEND THE HEAT
ADVISORY, AS APPARENT TEMPERATURES IN THIS SCENARIO WOULD IMPROVE
BY THE SECOND HALF OF THE WEEKEND.
LONG TERM
(MONDAY THROUGH THURSDAY)
ISSUED AT 931 PM CDT THU SEP 3 2026
THE UPPER LEVEL RIDGE IS FORECAST TO SLIGHT SHIFT TO THE WEST THE
BEGIN THE WEEK, ALLOWING RELATIVELY (KEY WORD HERE) COOLER
TEMPERATURES TO SETTLE OVER THE TN VALLEY. HIGH TEMPERATURES WILL
STILL BE IN THE LOW 90S WITH OVERNIGHT LOWS IN THE MID 60S TO LOW
70S AS MODERATE (LEVEL 2 OF 4) HEAT IMPACTS CONTINUE THROUGH THE
WEEK. AS THE RIDGE SHIFTS BACK EASTWARD, TEMPERATURES WILL
GRADUALLY CLIMB BACK INTO THE MID 90S BY THE END OF THE WEEK WITH
DIURNAL HEATING CONTRIBUTING TO LOW CHANCES (20% OR LESS) OF
THUNDERSTORM DEVELOPMENT EACH DAY. ONE THING TO WATCH WILL BE
WHERE SFC HIGH PRESSURE SETS UP ALONG THE APPALACHIANS AND WHETHER
OR NOT NE AL AND SOUTHERN MIDDLE TN EXPERIENCE CAD (COLD USED
LOOSELY). IF THIS IS THE CASE, INCREASED POPS MAY BE NECESSARY AS
DIFFERENTIAL HEATING BOUNDARIES BEGIN TO SET UP ALONG NORTH
CENTRAL AL. AS FAR AS HEAT HEADLINES GO, WILL LIKELY NOT NEED
ANYTHING PAST SUNDAY AS HEAT INDICES DROP TO AROUND 100 DEGREES.
AVIATION
(00Z TAFS)
ISSUED AT 617 PM CDT FRI SEP 4 2026
VFR CONDITIONS ARE FORECAST OVERNIGHT INTO SATURDAY MORNING.
SATURDAY AFTERNOON INTO THE EVENING, A PROB30 GROUP WAS ADDED AT
BOTH SITES INTO MVFR DUE TO LOW THUNDERSTORM CHANCES POTENTIALLY
CAUSING LOWERED VISIBILITIES AND CEILINGS.
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...70
SHORT TERM....70
LONG TERM....AMP
AVIATION...HC
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