907  
FXUS64 KHUN 220859  
AFDHUN  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE HUNTSVILLE AL  
359 AM CDT SUN OCT 22 2017  
   
NEAR TERM
 
(TODAY)  
ISSUED AT 359 AM CDT SUN OCT 22 2017  
 
AN UPPER-LEVEL TROUGH WILL QUICKLY MOVE FROM THE SOUTHERN PLAINS INTO  
THE LOWER MISSISSIPPI VALLEY TODAY, PUSHING A COLD FRONT TOWARD THE  
TENNESSEE VALLEY. AS THIS TROUGH AMPLIFIES, SOUTHWEST FLOW WILL  
ADVECT GULF MOISTURE INTO THE REGION AS CAN BE NOTED BY PWATS  
CLIMBING TO NEAR 2" BY THIS AFTERNOON ON MODEL SOUNDINGS AT  
KMSL/KHSV. AHEAD OF THIS FRONT, SHOWERS AND THUNDERSTORMS WILL  
DEVELOP ALONG A PRE-FRONTAL TROUGH. THIS AREA OF SHOWERS AND STORMS  
CAN CURRENTLY BE SEEN ALONG THE MISSISSIPPI DELTA REGION OF LA/MS.  
THESE SHOWERS AND STORMS WILL ADVANCE NE WITH TIME TOWARD THE MS/AL  
BORDER AND EVENTUALLY FILL NORTHWARD AND SHIFT INTO NORTHWEST ALABAMA  
BY LATE THIS MORNING INTO THE EARLY AFTERNOON. THEN, THIS ACTIVITY  
WILL SLOW MOVE EAST ACROSS THE REGION FROM THE MID AFTERNOON AND INTO  
THE EARLY EVENING. SOME BREAKS IN THE CLOUD COVER (ESPECIALLY EAST  
OF I-65), MAY ALLOW FOR SOME MODEST INSTABILITY TO DEVELOP. THUS, DO  
THINK WE WILL SEE SOME ISOLATED THUNDERSTORMS (PERHAPS EVEN A STRONG  
STORM) IN THE AFTERNOON AND EVENING. HOWEVER, GIVEN THE  
AFOREMENTIONED MOISTURE IN PLACE, THE MAIN IMPACT GOING INTO THIS  
EVENING WILL BE THE THREAT FOR LOCALLY HEAVY RAINFALL.  
   
SHORT TERM
 
(TONIGHT THROUGH TUESDAY)  
ISSUED AT 359 AM CDT SUN OCT 22 2017  
 
COVERAGE OF SHOWERS AND STORMS WILL INCREASE AHEAD OF A COLD FRONT  
TONIGHT INTO MONDAY AS A 40-50 KT LLJ RAMPS UP LATER THIS EVENING  
ACROSS THE TN/OH RIVER VALLEYS. THE ORIENTATION OF THIS LLJ WOULD  
PLACE MUCH OF NORTHERN/CENTRAL ALABAMA IN THE RIGHT ENTRANCE REGION  
OF THE JET, ENHANCING THE LIFT AND POTENTIAL FOR DEEPER CONVECTION.  
THINK COVERAGE WILL PEAK ACROSS THE REGION DURING THIS TIME PERIOD  
BETWEEN 03-09Z TONIGHT, WITH LINGERING CHANCES FOR SUSTAINED HEAVY  
PRECIPITATION OVER NE ALABAMA THROUGH 12-15Z AS THE UPPER-TROUGH  
MOVES INTO MIDDLE TN AND NORTHERN AL AND NEGATIVELY TILTS. CURRENTLY  
FAVORING THE FASTER ECMWF AND NAM SOLUTIONS -- THOUGH MODELS ARE IN  
MUCH BETTER AGREEMENT ON TIMING COMPARED TO LAST NIGHT. HAVE  
CATEGORICAL POPS OVER THE ENTIRE REGION THIS EVENING AND OVERNIGHT,  
BEFORE TAPERING THEM OFF EARLY THIS MORNING (RATHER QUICKLY OVER NW  
ALABAMA) FROM WEST TO EAST. THOUGH WE HAVE BEEN DRY OF LATE, THE  
THREAT FOR FLOODING WILL EXIST -- MAINLY DUE TO EXCESSIVE RAINFALL  
FROM TRAINING, ESPECIALLY IN NORTHEAST ALABAMA.  
 
THINK WE'LL SEE SOME LINGERING SCATTERED SHOWERS IN AREAS EAST OF  
I-65 FOR MOST OF THE DAY ON MONDAY, ALONG WITH A MOSTLY CLOUDY SKY --  
SO WENT MORE PESSIMISTIC THERE. HOWEVER, DRIER WILL MOVE IN BEHIND  
THE FRONT AND SCOUR OUT THE MOISTURE MONDAY NIGHT, PUTTING AN END TO  
PRECIPITATION CHANCES. SOME CLOUDS IN THE EASTERN ZONES MAY BE A  
LITTLE STUBBORN TO ERODE OVERNIGHT MONDAY, BUT MOSTLY CLEAR  
CONDITIONS ARE EXPECTED BY TUESDAY MORNING AND THE COOL, DRY AUTUMN  
AIR MASS TAKES HOLD.  
 
PRIMARY NOTICEABLE CHANGE WILL BE THE AIR MASS AND TEMPERATURES,  
WHICH WILL DROP INTO THE MID TO UPPER 60S ON MONDAY AND STRUGGLE TO  
CLIMB MUCH ABOVE 60 DEGREES ON TUESDAY.  
   
LONG TERM
 
(TUESDAY NIGHT THROUGH SATURDAY)  
ISSUED AT 359 AM CDT SUN OCT 22 2017  
 
AN UPPER-LEVEL TROUGH WILL DIVE INTO THE SOUTHEAST AND FILTER IN  
ADDITIONAL CAA ON WEDNESDAY TO REINFORCE THE COOLER CONDITIONS  
ALREADY IN PLACE. DAYTIME HIGHS IN THE UPPER 50S DEGREES AND LOWS IN  
THE UPPER 30S/LOWER 40S ACROSS THE TN VALLEY WILL BE AROUND 10  
DEGREES BELOW NORMAL! WEDNESDAY NIGHT, DEPENDING ON HOW QUICKLY  
CLOUDS MOVE OUT, RADIATIONAL COOLING WOULD ALLOW FOR TEMPS TO FALL A  
FEW MORE DEGREES. WITH THIS IN MIND, FROST COULD BE POSSIBLE IN A FEW  
LOCATIONS BUT WILL WATCH ADDITIONAL TRENDS AS WE GET CLOSER IN THE  
FORECAST.  
 
IF YOU ARE LOOKING FOR A BREAK IN THE COLD WEATHER, THE TROUGH  
QUICKLY LIFTS NORTHEAST AND IS REPLACED BY A WEAK RIDGE ON THURSDAY  
AND FRIDAY. THIS WILL ALLOW TEMPERATURES TO WARM UP INTO THE UPPER  
60S WITH OVERNIGHT LOWS RANGING FROM THE LOW TO UPPER 40S. HOWEVER,  
EVEN THE RIDGE IS SHORT LIVED, AS IT IS PUSHED EASTWARD BY THE NEXT  
SYSTEM MOVING ACROSS THE MIDWEST. THIS SYSTEM WILL BRING ANOTHER  
COLD FRONT WITH OUR NEXT ROUND OF SHOWERS OVER THE WEEKEND. MODELS  
ARE STILL IN DISAGREEMENT AND EVEN HAVE RUN TO RUN INCONSISTENCY.  
FOR EXAMPLE, THERE IS A 24 HOUR TIMING DIFFERENCE BETWEEN THE GFS  
AND THE ECMWF. THE GFS IS STILL RUNNING FASTER BRINGING THE PRECIP  
THROUGH ON SATURDAY COMPARED TO THE ECMWF THAT MOVES IT THROUGH THE  
TN VALLEY ON SUNDAY. WITH THE CONSISTENT MODEL DISAGREEMENT, WENT  
WITH A BLEND OF THE GFS/ECMWF FOR THIS FORECAST PACKAGE. SO IF  
PLANNING ANY OUTDOOR EVENTS FOR THE WEEKEND, STAY TUNED TO THE  
FORECAST FOR ADDITIONAL UPDATES.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)  
ISSUED AT 1144 PM CDT SAT OCT 21 2017  
 
VFR CONDITIONS WILL PREVAIL AT THE HSV/MSL TERMINALS OVERNIGHT WITH A  
SE FLOW AROUND 8 KTS AND FEW STRATOCU BENEATH SCT-BKN LAYERS OF  
ALTOSTRATUS/CIRROSTRATUS CLOUDS. WINDS WILL BEGIN TO GRADUALLY VEER  
AND INCREASE BY 22/15Z AS A COLD FRONT APPROACHES THE REGION FROM  
THE WEST, WITH SUSTAINED SPEEDS ARND 12 KTS AND GUSTS UP TO 20 KTS  
EXPECTED FOR REMAINDER OF THE MORNING AND AFTERNOON. ALTHOUGH CLOUD  
COVERAGE WILL INCREASE DURING THIS PERIOD, BKN-OVC CIGS SHOULD ONLY  
DESCEND TO ARND 8 KFT THRU LATE AFTERNOON/EARLY EVENING. THREAT FOR  
SCT SHRA/TSRA WILL BEGIN TO INCREASE AT MSL/20Z AND HSV/22Z. HOWEVER,  
MORE WIDESPREAD SHRA AND EMBEDDED TSRA WILL LIKELY OCCUR BTWN  
23/00-06Z AS A WAVE OF LOW PRESSURE FORMS ALONG THE FRONT, FORCING IT  
TO DECELERATE AS IT MOVES ACROSS THE TN VALLEY. ALTHOUGH NOT  
EXPLICITLY NOTED IN TAFS, CIGS MAY FALL TO ARND 1500 FT AT BOTH  
AIRPORTS BTWN 04-06Z, AND A WIND SHIFT TO NNW MAY ALSO OCCUR AT MSL  
CLOSE TO 06Z.  
 

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

 
 

 
 
NEAR TERM...AMP.24  
SHORT TERM...AMP.24  
LONG TERM...JMS  
AVIATION...70/DD  
 
FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE  
AT WEATHER.GOV/HUNTSVILLE.  
 
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