838  
FXUS64 KHUN 220031  
AFDHUN  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE HUNTSVILLE AL  
731 PM CDT FRI JUL 21 2017  
   
NEAR TERM
 
(TONIGHT)  
ISSUED AT 720 PM CDT FRI JUL 21 2017  
 
TEMPERATURES HAVE FALLEN BELOW HEAT ADVISORY CRITERIA, SO THE HEAT  
ADVISORY FOR TODAY WAS ALLOWED TO EXPIRE AT 7 PM CDT. HOWEVER, A HEAT  
ADVISORY REMAINS IN EFFECT FOR TOMORROW FROM NOON TO 7 PM CDT. AN  
NPW PRODUCT WAS JUST ISSUED TO ADDRESS THE CANCELLATION OF THE FORMER  
HEAT ADVISORY, BUT ALSO CONTAINING INFORMATION FOR THE HEAT ADVISORY  
STILL IN EFFECT FOR TOMORROW.  
 
OTHERWISE, SATELLITE IMAGERY INDICATES A GENERAL DOWNTREND IN CU  
DEVELOPMENT IN THE AREA AND SHRA/TSRA IN UPSTREAM OR NEARBY  
LOCATIONS. WITHOUT ANY SIGNIFICANT TRIGGER IN PLACE IN THE REGION,  
THE DECISION WAS THUS MADE TO DROP THE ISOLATED POP FOR THE EVENING.  
FORECAST GRIDS HAVE BEEN UPDATED ALONG WITH THE HWO.  
   
SHORT TERM
 
(SATURDAY THROUGH SUNDAY)  
ISSUED AT 257 PM CDT FRI JUL 21 2017  
 
ANOTHER VERY WARM TO HOT DAY WILL END THE WEEK. THE UPPER HIGH OVER  
THE REGION WILL BREAK DOWN MORE AS MOISTURE FROM THE SOUTHERN LOW  
WEAKENS THE RIDGE. THE STRONG DAYTIME HEATING AND THIS MOISTURE AND  
RESULTING INSTABILITY WILL RESULT IN ISOLATED TO SCATTERED SHOWERS  
AND THUNDERSTORMS, ESPECIALLY TOMORROW AFTERNOON. PRECIPITABLE WATER  
AMOUNTS RISE INTO THE 1.7 TO 1.8 INCH RANGE, WITH LOCALLY HEAVY RAINS  
AND GUSTY WINDS ACCOMPANYING THE MORE SUBSTANTIAL CONVECTION. HIGH  
TEMPERATURES IN THE LOW/MID 90S, ALONG WITH DEWPOINT VALUES INTO THE  
LOW/MID 70S WILL YIELD MORE HEAT INDICES INTO THE UPPER 90S NE  
ALABAMA AND ADJACENT SOUTHERN MIDDLE TENNESSEE, TO 107-109 ACROSS  
PARTS OF NW ALABAMA. AS SUCH, ANOTHER HEAT ADVISORY WILL BE NEEDED  
FOR SATURDAY AFTERNOON.  
 
MORE CLOUDS THAN SUN ON SUNDAY, WILL BRING SOMEWHAT OF A RELIEF  
REGARDING HIGH TEMPERATURES. BETTER RAIN CHANCES ARE ALSO EXPECTED AS  
VARIOUS UPPER LEVEL SYSTEMS MOVE ACROSS THE REGION. THE NAM IN  
PARTICULAR WAS DEPICTING A POSSIBLE GRAVITY WAVE MOVING SOUTHWARD  
FROM CONVECTION TO OUR NORTH. THIS COULD BRING A GOOD CHANCE OF RAIN  
TO THE AREA TO BEGIN A NEW WEEK. PRECIP WATER AMOUNTS ARE EVEN  
HIGHER, GENERALLY OVER 2 INCHES FROM THE NAM; SOMEWHAT LOWER FROM THE  
GFS. THUS LOCALLY HEAVY RAINS AND GUSTY WINDS ARE AGAIN THE MAIN  
THREATS. SOME STORMS IN THESE SITUATIONS CAN BECOME VERY ACTIVE  
ELECTRICALLY WISE.  
   
LONG TERM
 
(SUNDAY NIGHT THROUGH THURSDAY)  
ISSUED AT 257 PM CDT FRI JUL 21 2017  
 
STRONG SHORTWAVE TROUGH WILL PUSH SOUTHWARD ACROSS THE MISSISSIPPI  
VALLEY ON MONDAY. THIS WILL HELP SLIDE A COLD FRONT, ALBEIT A WEAK  
FRONT, TOWARD THE REGION. EXPECT SCATTERED TO NUMEROUS SHOWERS AND  
THUNDERSTORMS ACROSS THE REGION ON MONDAY INTO MONDAY EVENING. GIVEN  
THE RATHER ROBUST HEAT/MOISTURE IN PLACE ALONG WITH THE ENHANCED  
UPWARD VERTICAL MOTION/FORCING WITH THE UPPER LEVEL SYSTEM AND A FEW  
STRONG STORMS ARE POSSIBLE.FORECAST SOUNDINGS FROM THE GFS INDICATE  
FAIRLY STEEP LOW LEVEL LAPSE RATES (AS YOU WOULD EXPECT IN THIS  
REGIME) AND DCAPE POTENTIAL APPROACHING 1 KJ/KG.  
 
ON TUESDAY, THE SOUTHERN STREAM EXTENSION OF THE TROUGH MAY ATTEMPT  
TO CUT OFF KEEPING THE WEATHER SOMEWHAT UNSETTLED ACROSS THE LOWER  
TENNESSEE VALLEY AND GULF COAST REGION. THE 12Z GFS IS SLIGHTLY  
FURTHER SOUTH WITH THIS FEATURE BUT IT'S FAIRLY WELL DEFINED IN ALL  
OF THE EXTENDED GUIDANCE. THUS, WILL MAINTAIN CHANCE POPS THROUGH THE  
TUESDAY-WEDNESDAY TIME FRAME. AGAIN, A FEW STRONG STORMS WILL BE  
POSSIBLE ON TUESDAY.  
 
FLOW BECOMES NORTHWESTERLY LATER IN THE WORK WEEK AS THE UPPER LEVEL  
RIDGE IS ESTABLISHED ONCE AGAIN ACROSS THE PLAINS. THIS SHOULD KEEP  
THE WORST OF THE HEAT TO OUR WEST AND AT LEAST MAINTAIN A LOW THREAT  
OF STORMS THROUGH THE PERIOD.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)  
ISSUED AT 630 PM CDT FRI JUL 21 2017  
 
VFR CONDITIONS ARE LIKELY TO PREVAIL AT KHSV/KMSL TAF SITES OVER THE  
NEXT 24 HOURS. THE ONLY CAVEAT IS THE THREAT FOR SCTD SHRA/TSRA  
DEVELOPMENT IN THE REGION TOMORROW AFTERNOON. THE BEST CHANCE FOR  
ACTIVITY IS TO THE SOUTH OF THE AREA, NEVERTHELESS A PROB30 GROUP IS  
WARRANTED IN TAFS FOR THE 18-00Z PERIOD.  
 

 
   
HUN WATCHES/WARNINGS/ADVISORIES
 
 
AL...HEAT ADVISORY FROM NOON TO 7 PM CDT SATURDAY FOR ALZ001>007.  
 
TN...HEAT ADVISORY FROM NOON TO 7 PM CDT SATURDAY FOR TNZ076-096.  
 

 
 

 
 
NEAR TERM...KDW  
SHORT TERM...RSB  
LONG TERM...15  
AVIATION...KDW  
 
FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE  
AT WEATHER.GOV/HUNTSVILLE.  
 
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