033  
FXUS64 KHUN 270039  
AFDHUN  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE HUNTSVILLE AL  
739 PM CDT THU APR 26 2018  
   
UPDATE
 
 
FOR 00Z TAFS.  
 

 
   
NEAR TERM
 
(TONIGHT)  
ISSUED AT 200 PM CDT THU APR 26 2018  
 
EARLY AFTERNOON SURFACE ANALYSIS SHOWED A BROAD AREA OF LOW PRESSURE  
EXTENDING FROM NORTHEAST MISSISSIPPI TO NORTHERN GEORGIA. WATER VAPOR  
IMAGERY AND REGIONAL RADAR IMAGERY SHOW THE CENTER OF THE UPPER LOW  
ACROSS NORTHEAST MISSISSIPPI.  
 
THE INITIAL BAND OF PRECIPITATION/CONVECTION ASSOCIATED WITH THE WARM  
CONVEYOR BELT HAS MOVED EAST OF THE AREA TODAY NOW EXTENDING FROM  
NORTHEAST GA INTO SOUTHERN ALABAMA. GOES-16 GLM DATA SHOWS THE BULK  
OF THE LIGHTNING WITH THIS LINE CONFINED TO SOUTHEAST ALABAMA.  
CONVECTION ASSOCIATED WITH THE UPPER LOW WAS NOTED ACROSS MIDDLE  
TN INTO NORTHERN AL.  
 
EXPECT SCATTERED CONVECTION TO CONTINUE THROUGH EARLY EVENING DUE TO  
STEEP MID LEVEL LAPSE RATES AND AT LEAST MARGINAL LOW LEVEL  
MOISTURE. VERY LITTLE IN THE WAY OF INSTABILITY NOTED PER SPC  
MESOANALYSIS AND HIGH RESOLUTION SOUNDINGS, BUT WE COULD SEE SOME  
THUNDER ACROSS NORTHEAST COUNTIES THROUGH SUNSET.  
 
HAVE HELD ON TO LOW POPS THIS EVENING. GIVEN THE WET/SOMEWHAT  
SATURATED GROUNDS AND COOLER AIRMASS BUILDING IN WILL MAINTAIN  
MENTION OF PATCHY FOG OVERNIGHT INTO EARLY FRIDAY. DESPITE CLOUDY  
CONDITIONS TEMPERATURES WILL STILL DROP INTO THE 40S AREAWIDE  
OVERNIGHT.  
   
SHORT TERM
 
(FRIDAY THROUGH SATURDAY)  
ISSUED AT 200 PM CDT THU APR 26 2018  
 
AFOREMENTIONED UPPER LOW WILL EXIT QUICKLY EAST EARLY ON FRIDAY.  
HOWEVER, THE NORTHWESTERLY UPPER FLOW WILL REMAIN ESTABLISHED ACROSS  
THE AREA IN PART DUE TO A SHEAR AXIS/VORTICITY AXIS DIVING TO OUR  
SOUTHEAST ACROSS THE DEEP SOUTH/NORTHERN GULF COAST. THE PASSAGE OF  
THIS SYSTEM SHOULD BE FAR ENOUGH SOUTH TO LIMIT ANY NOTABLE IMPACT  
AND KEEP FRIDAY DRY. WITH CLEARING SKIES BY AFTERNOON EXPECT  
TEMPERATURES TO REBOUND TO NEAR NORMAL LEVELS.  
 
AN UPPER LOW WILL PERSIST ACROSS THE GREAT LAKES THROUGH THE FIRST  
PART OF THE WEEKEND WITH GENERALLY CYCLONIC FLOW ACROSS THE EASTERN  
1/3 OF THE CONUS. THIS MAY RESULT IN VERY WEAK VORTICITY ADVECTION  
AND AN INCREASE IN CLOUD COVER ON SATURDAY. HOWEVER, THE LOWER  
TROPOSPHERE SHOULD REMAIN DRY ENOUGH TO KEEP THE FORECAST DRY AND  
RELATIVELY PLEASANT FOR NOW.  
   
LONG TERM
 
(SATURDAY NIGHT THROUGH WEDNESDAY)  
ISSUED AT 200 PM CDT THU APR 26 2018  
 
BY SUNDAY, THE EXITING TROUGH OVER THE APPALACHIANS TO THE EAST COAST  
WILL LEAVE MUCH OF THE OH/TN VALLEY/SOUTHERN PLAINS WITHIN THE  
EASTERN FLANK OF A SHORTWAVE RIDGE. MEANWHILE, THE SURFACE HIGH  
PRESSURE SYSTEM WILL SLOWLY EDGE SOUTH FROM THE OH RIVER VALLEY  
EARLY ON SUNDAY MORNING WHICH WILL RESULT IN COOLER AIR ADVECTING  
SOUTHWARD. BECAUSE OF THIS COOL AIR, DAYTIME HIGHS WILL BE LOWER THAN  
SATURDAY WITH HIGHS IN THE MID TO UPPER 60S.  
 
AS THIS RIDGE SHIFTS EAST BEHIND THE EXITING TROUGH, IT WILL AMPLIFY  
OVER THE EASTERN HALF OF THE CONUS AND REMAIN IN PLACE OVER THROUGH  
AT LEAST TUESDAY BRINGING DRY AND WARM WEATHER. MEANWHILE, A MEAN  
TROUGH WILL BE IN PLACE OVER THE INTERMOUNTAIN WEST WITH SEVERAL  
EMBEDDED SHORTWAVE TROUGHS MOVING WITHIN THE TROUGH AND GRADUALLY  
WEAKENING THE DOWNSTREAM RIDGE. THE TIMING OF THE RIDGE BREAKDOWN  
WILL CONTINUE TO BE A CHALLENGE WITH MODELS AND ALREADY SEEING  
DIFFERENCES WITH AREAL EXTENT OF POPS BEGINNING ON WEDNESDAY INTO  
WEDNESDAY NIGHT AS A SERIES OF SHORTWAVES MOVING WITHIN THE LONGWAVE  
TROUGH SLOWLY MOVE EAST. IF THE LIFT ASSOCIATED WITH ONE OF THE  
EMBEDDED TROUGHS DOES EDGE CLOSE ENOUGH TO THE TN VALLEY, THERE IS  
ENOUGH INSTABILITY ON WEDNESDAY AND WEDNESDAY NIGHT TO SUPPORT  
THUNDERSTORMS MAINLY OVER NW AL, BUT HAVE LEFT LOW CHANCES IN THE  
FORECAST AT THIS POINT.  
 
SO, WITH THIS SUBTROPICAL JET PATTERN IN PLACE, DAYTIME HIGH  
TEMPERATURES WILL ACTUALLY BE NEAR TO SLIGHTLY WARMER THAN AVERAGE IN  
THE UPPER 70S TO LOW 80S ON MONDAY THROUGH WEDNESDAY AFTER THE COOL  
DAY ON SUNDAY. OVERNIGHT LOWS WILL ALSO WARM UP FROM THE 40S/50S ON  
SUNDAY NIGHT/MONDAY NIGHT INTO THE 60S BY TUESDAY/WEDNESDAY NIGHTS.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)  
ISSUED AT 739 PM CDT THU APR 26 2018  
 
A WEAKENING UPPER LOW CURRENTLY ACROSS SOUTHEASTERN TN/NORTHWESTERN  
GA WILL CONTINUE TO LIFT NORTHEASTWARD THIS EVENING, WITH ASSOCIATED  
PCPN NOW SHIFTING EWD AND AWAY FROM THE TERMINALS. LOWER CLOUDS  
COMPRISED OF SCT-BKN STRATOCU ARND 1500 FT BENEATH BKN STRATUS ARND  
5000 FT WILL LIKELY PERSIST THRU LATE EVENING, BEFORE A WEAK SURGE OF  
DRIER AIR BEGINS TO ERODE THIS CLOUD COVER. ABUNDANT BOUNDARY LAYER  
MOISTURE, COUPLED WITH DIMINISHING NORTHWEST FLOW AND CLEARING SKIES  
WILL BE FAVORABLE FOR THE DEVELOPMENT OF FOG BY 04Z, WITH IFR  
CIG/VSBY REDUCTIONS PSBL AT TIMES, AND ESPECIALLY BTWN 06-10Z.  
ALTHOUGH A BIT OF UNCERTAINTY DOES REMAIN REGARDING THE IMPACT OF  
INCREASING HIGH CLOUDINESS AND SLIGHTLY ELEVATED SFC WINDS ON THE  
COVERAGE/DENSITY OF FOG, MODELS DO AGREE THAT VSBY REDUCTIONS SHOULD  
IMPROVE BY 13-14Z. WINDS WILL BACK TO WEST-NORTHWEST BY 17Z AHEAD OF  
AN APPROACHING COLD FRONT, AND INCREASE TO 08G18 KTS WITH THE ONSET  
OF DEEPER MIXING. SCT-BKN CU IS EXPECTED DURING THE AFTN, WITH CLOUD  
BASES ARND 5 KFT.  
 

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

 
 

 
 
NEAR TERM...15  
SHORT TERM...15  
LONG TERM...SL.77  
AVIATION...70/DD  
 
FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE  
AT WEATHER.GOV/HUNTSVILLE.  
 
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