133  
FXUS64 KHUN 190017  
AFDHUN  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE HUNTSVILLE AL  
717 PM CDT SAT AUG 18 2018  
   
NEAR TERM
 
(TONIGHT)  
ISSUED AT 716 PM CDT SAT AUG 18 2018  
 
HAVE MADE SOME MINOR ADJUSTMENTS TO POPS THIS EVENING AND TONIGHT.  
RADARS CURRENTLY DETECT JUST A FEW SHOWERS IN SOUTHERN PORTIONS OF  
OUR FORECAST AREA (SOUTH OF MOULTON TO GUNTERSVILLE). THE SHOWER BAND  
BETWEEN LYNCHBURG AND NASHVILLE IN SOUTHERN MIDDLE TN ARE SLOWLY  
DRIFTING SOUTHEAST. THE WEAK CONVERGENCE ZONE ALONG AND NEAR THE I-40  
CORRIDOR HAS LITTLE TO NO DEVELOPMENT WEST-SOUTHWEST OF NASHVILLE.  
HAVE CONFIGURED POPS THIS EVENING TO BETTER FIT THESE CONVERGENCE  
ZONES, BUT CONFIDENCE IN OVERNIGHT WEATHER IS RATHER LOW. THE HRRR  
RUNS ARE SHOWING ISOLATED-SCATTERED DEVELOPMENT, BUT EXACT LOCATIONS  
ARE STILL SUCH THAT I WILL KEEP THE POP AT A CHANCE LEVEL. LOWER  
CLOUDS ARE LIKELY TO DEVELOP AS WELL GIVEN THE VERY MOIST LOWER 2KM  
PER THE 00Z OHX SOUNDING.  
 
   
SHORT TERM
 
(SUNDAY THROUGH MONDAY)  
ISSUED AT 225 PM CDT SAT AUG 18 2018  
 
A POTENTIAL WET PATTERN REMAINS IN PLACE ON SUNDAY AS A SURFACE  
BOUNDARY STALLED NORTH OF THE REGION DRIFTS NORTH AS A WARM FRONT.  
AGAIN, A CAVEAT REMAINS THE SOUTH TO NORTH MOISTURE GRADIENT, WHICH  
WOULD AGAIN FAVOR CENTRAL AL FOR BETTER COVERAGE OF SHOWERS/STORMS AS  
OPPOSED TO N. AL AND S. MIDDLE TN. AS SUCH, ON AVERAGE, HAVE UNDER  
CUT SUPERBLEND POPS A BIT FOR TOMORROW. STILL CANNOT RULE OUT SOME  
SCATTERED SHOWERS DURING THE AFTERNOON TOMORROW GIVEN A SOUTHERLY  
COMPONENT TO THE FLOW REGIME AND A SURFACE BOUNDARY NEAR OUR NORTHERN  
BORDER.  
 
AS WE HEAD INTO MONDAY, EXPECT DEEPER SOUTHERLY FLOW TO DEVELOP AHEAD  
OF AN APPROACHING COLD FRONT, PROGGED TO SHIFT THROUGH THE REGION  
LATER THIS WEEK. ADDITIONALLY, THERE WILL BE SOME MID/UPPER LEVEL  
SUPPORT FOR MORE ORGANIZED THUNDERSTORMS, SO WE CANNOT RULE OUT THE  
POTENTIAL A STRONG STORM OR TWO FOR MONDAY AFTERNOON/EVENING. PARTLY  
TO MOSTLY CLOUDY CONDITIONS THROUGH THE PERIOD WILL KEEP TEMPS MAXED  
IN THE MID TO UPPER 80S EACH AFTERNOON.  
   
LONG TERM
 
(MONDAY NIGHT THROUGH FRIDAY)  
ISSUED AT 225 PM CDT SAT AUG 18 2018  
 
A MID-LEVEL TROUGH, LOCATED ACROSS SOUTHEASTERN IA/NORTHEASTERN MO  
AT THE BEGINNING OF THE EXTENDED PERIOD, IS PREDICTED TO DEEPEN AND  
LIFT EAST-NORTHEASTWARD INTO THE EASTERN GREAT LAKES BY 00Z  
WEDNESDAY. DOWNSTREAM WEST-SOUTHWESTERLY FLOW AND ATTENDANT LOWER-  
TROPOSPHERIC WAA WILL STRENGTHEN ACROSS THE TN VALLEY ON MONDAY  
NIGHT, SUPPORTING A FAIRLY WIDESPREAD COVERAGE OF NOCTURNAL  
CONVECTION IN THE VERY MOIST AIRMASS (PWATS IN THE 1.9-2.1 INCH  
RANGE). ALTHOUGH LIGHTNING AND LOCALLY HEAVY RAINFALL WILL BE THE  
PRIMARY THREATS WITH THIS ACTIVITY, INCREASING DEEP-LAYER SHEAR MAY  
SUPPORT SOME STORM ORGANIZATION AND A THREAT FOR STRONG WIND GUSTS  
WITH THE MOST INTENSE CELLS.  
 
EXTENDED RANGE GUIDANCE FROM THE GLOBAL MODELS INDICATES THAT THE  
TRAILING MID-LEVEL TROUGH AXIS AND SURFACE COLD FRONT WILL CROSS THE  
FORECAST AREA AFTER SUNRISE ON TUESDAY MORNING, WITH LINGERING  
SHOWERS AND THUNDERSTORMS EXPECTED TO END RATHER QUICKLY ACROSS THE  
SOUTHEASTERN ZONES. HOWEVER, FOR MUCH OF THE MID-WEEK PERIOD, THE  
REGION WILL REMAIN BENEATH A NORTHWEST FLOW ALOFT ALONG THE  
NORTHEASTERN PERIPHERY OF A LARGE SUBTROPICAL HIGH CENTERED ACROSS  
EASTERN NM/WESTERN TX. SEVERAL WEAK DISTURBANCES TRAVELING  
SOUTHEASTWARD IN THE NORTHWEST FLOW ALOFT MAY PROVIDE SUFFICIENT LIFT  
FOR THE GENERATION OF ISOLATED-WIDELY SCATTERED SHOWERS ON TUESDAY  
NIGHT/WEDNESDAY, BEFORE ATMOSPHERIC MOISTURE BECOMES DEPLETED BY  
PERSISTENT NORTHERLY FLOW AT THE SURFACE FROM WEDNESDAY NIGHT-  
THURSDAY NIGHT. MAX TEMPS WILL RANGE FROM THE LOWER 80S IN THE  
ELEVATED TERRAIN OF THE NORTHEAST, TO THE M-U 80S ELSEWHERE. LOWS  
WILL RESPOND MORE EFFECTIVELY TO THE SOUTHWARD ADVECTION OF DRIER  
AIR, WITH LOWER 60S EXPECTED ON THURSDAY/FRIDAY MORNINGS.  
 
LOW-LEVEL SOUTHEASTERLY FLOW WILL BECOME REESTABLISHED ACROSS THE  
CWFA ON FRIDAY-SATURDAY, AS A SURFACE RIDGE BUILDS SOUTHWARD IN THE  
LEE OF THE APPALACHIANS. THIS SHOULD ALLOW FOR AT LEAST SOME RETURN  
OF DEEPER MOISTURE, WITH SCATTERED AFTERNOON CONVECTION POSSIBLE BOTH  
DAYS.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)  
ISSUED AT 529 PM CDT SAT AUG 18 2018  
 
A WEAK FRONT IN TN WILL DROP SOUTH INTO NORTH AL PRODUCING ISOLATED  
TO SCATTERED THUNDERSTORMS OVERNIGHT. HOWEVER, CONFIDENCE IS TOO LOW  
TO INCLUDE AT EITHER KMSL OR KHSV AT THIS TIME. SCATTERED TO BROKEN  
CLOUDS AT ~050AGL ARE EXPECTED AT TIMES THIS EVENING BEFORE LOWER  
CLOUDS AND IFR CONDITIONS (CEILINGS OF ~005-008AGL) DEVELOP BY 06Z.  
THESE CLOUDS WILL SLOWLY LIFT TO ~025AGL BY 15Z, THEN LIFT AND  
POSSIBLY SCATTER OUT BY MIDDAY SUNDAY. HOWEVER, SCATTERED SHOWERS AND  
THUNDERSTORMS WILL REMAIN POSSIBLE, AND MAY NEED TO ADD TO THE  
FORECAST WHEN IT BECOMES MORE CERTAIN AT OUR TERMINALS.  
 

 
   
HUN WATCHES/WARNINGS/ADVISORIES
 
 
AL...NONE.  
TN...NONE.  

 
 

 
 
NEAR TERM...17  
SHORT TERM...BARRON  
LONG TERM...70/DD  
AVIATION...17  
 
FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE  
AT WEATHER.GOV/HUNTSVILLE.  
 
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