807  
FXUS64 KHUN 240539  
AFDHUN  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE HUNTSVILLE AL  
1239 AM CDT FRI MAR 24 2017  
   
UPDATE
 
 
FOR 06Z TAFS.  
 

 
   
NEAR TERM
 
(REST OF TONIGHT)  
ISSUED AT 929 PM CDT THU MAR 23 2017  
 
SATELLITE IMAGERY AS OF 02Z SHOWS A DECK OF LOW/MID LEVEL CLOUDS OVER  
MOST OF GA AND IS BEGINNING TO SPREAD INTO NE AL. WINDS WILL REMAIN  
OUT OF THE SE AT THE SURFACE BUT, ALOFT WINDS ARE STARTING TO TURN  
BACK TO THE S/SW. THIS IS DUE TO A LLJ DEVELOPING TO OUR WEST AHEAD  
OF THE SYSTEM THAT WILL IMPACT THE AREA ON SATURDAY. SURFACE OBS ARE  
ALREADY SHOWING A SLOW BUT STEADY INCREASE IN MOISTURE WITH DEWPOINTS  
INCREASING BACK INTO THE UPPER 40S TO LOWER 50S JUST TO OUR SW. WE  
CAN EXPECT THESE VALUES TO SPREAD INTO THE AREA TONIGHT.  
 
THE LLJ WILL ALSO MAKE FOR A BREEZY NIGHT ACROSS THE TN VALLEY WITH  
GUSTS OF 15 TO 20 MPH POSSIBLE ALL NIGHT. THE INCREASING MOISTURE AND  
WINDS, COMBINED WITH ADDITIONAL CLOUD COVER TONIGHT WILL KEEP TEMPS  
MILD TONIGHT WITH VALUES REMAINING IN THE 50S. SOME SITES OUT WEST  
MAY NOT DROP BELOW 60 TONIGHT. SO, WITH THAT SAID, HAVE BUMPED TEMPS  
UP A BIT FROM THE PREVIOUS SHIFT. THE REST OF THE FORECAST IS ON  
TRACK.  
   
SHORT TERM
 
(FRIDAY THROUGH SATURDAY NIGHT)  
ISSUED AT 338 PM CDT THU MAR 23 2017  
 
FLOW ALOFT WILL BACK TO THE SOUTHWEST AND INCREASE DURING THE DAY  
TOMORROW AS THE SOUTHERN HIGH PLAINS SHORTWAVE TROUGH ADVANCES SLOWLY  
EASTWARD ACROSS WESTERN OK/KS. TEMPERATURES WILL BE DICTATED BY HOW  
QUICKLY THE MORNING STRATUS LAYER MIXES OUT -- IF IT DOES AT ALL.  
FORECAST SOUNDINGS SUGGEST THAT STRATUS MAY BE VERY SLOW TO  
LIFT...WITH BREAKS POSSIBLY NOT OCCURRING UNTIL MID-LATE AFTERNOON.  
THUS, IN SPITE OF A CONTINUATION OF STRONG SOUTHEASTERLY LOW-LEVEL  
FLOW WE HAVE FORECASTED HIGHS IN THE U60S EAST AND LOWER 70S WEST --  
A LITTLE BELOW MOS GUIDANCE IN A FEW SPOTS.  
 
MODELS INDICATE THAT THE TROUGH WILL TRACK EASTWARD INTO THE WESTERN  
OZARKS FRIDAY NIGHT...WITH DEEP-LAYER FORCING FOR ASCENT INCREASING  
MOST SUBSTANTIALLY DURING THIS PERIOD...BASED ON MAGNITUDE OF 12-HR  
HEIGHT FALLS ALOFT. LIFT VIA LOW-LEVEL WARM ADVECTION WILL ALSO  
INCREASE DURING THIS PERIOD AS THE SOUTHWESTERLY LOW-LEVEL JET  
INCREASES TO 40-50 KNOTS...AND THIS SHOULD SUPPORT AN INCREASE IN  
SHOWERS/THUNDERSTORMS BEFORE SUNRISE ACROSS MAINLY NORTHWEST AL -- AS  
DEWPOINTS BEGIN TO INCREASE INTO THE U50S/L60S.  
 
ALTHOUGH GUIDANCE DOES NOT INDICATE THAT THE UPSTREAM TROUGH WILL  
DEEPEN SIGNIFICANTLY ON SATURDAY, IT DOES APPEAR TO ASSUME A  
NEGATIVE-TILT AS IT PIVOTS NORTHEASTWARD ACROSS MO -- AND THIS SHOULD  
ACT TO FURTHER STRENGTHEN UPWARD VERTICAL MOTIONS ACROSS OUR  
FORECAST AREA IN LIGHT OF ADDITIONAL FACTORS MENTIONED ABOVE. THUS...  
AS THE PLUME OF GREATER LOW-LEVEL MOISTURE SPREADS NORTHEASTWARD  
THROUGH THE DAY...WIDESPREAD SHOWERS/THUNDERSTORMS SHOULD GRADUALLY  
SHIFT EASTWARD TO ENCOMPASS NEARLY THE ENTIRE CWFA BY LATE AFTERNOON.  
THIS ACTIVITY WILL BE DEVELOPING IN A ZONE OF STRONG LOW- LEVEL WAA  
AND SHOULD NOT BE RELATED TO A DISCERNIBLE LOW-LEVEL BOUNDARY...BUT  
IT WILL POSE A RISK OF SEVERE WEATHER BASED ON MLCAPE IN THE 500-1000  
J/KG RANGE AND DEEP-LAYER SHEAR OF 30-40 KNOTS. ALTHOUGH THE  
DISTRIBUTION OF CAPE SUGGESTS A THREAT FOR BOTH MARGINALLY DAMAGING  
WINDS AND LARGE HAIL...0-3 KM SHEAR OF 30-35 KNOTS PRESENTS CONCERN  
FOR THE DEVELOPMENT OF LOW-LEVEL MESOCYCLONES AND BRIEF TORNADOES  
WITH THE DEEPEST UPDRAFTS. THIS ACTIVITY WILL LIKELY PROGRESS  
EASTWARD DURING THE AFTERNOON HOURS...WITH ANOTHER SEPARATE EPISODE  
OF CONVECTION ANTICIPATED AS A REMNANT DRYLINE SHIFTS EASTWARD INTO  
THE REGION LATE SATURDAY AFTERNOON. SUBTLE LOW- LEVEL STREAMLINE  
CONFLUENCE WILL EXIST IN THE VICINITY OF THIS BOUNDARY...SUPPORTING A  
MORE LINEAR CONVECTIVE FEATURE AS IT SPREADS SLOWLY EASTWARD  
SATURDAY NIGHT AND EARLY SUNDAY MORNING. ALTHOUGH BOTH LOW-LEVEL AND  
DEEP-LAYER SHEAR ARE FORECAST TO WEAKEN WITH TIME SATURDAY EVENING, A  
RISK OF SEVERE STORMS WILL EXIST WITH THIS FEATURE AS WELL.  
   
LONG TERM
 
(SUNDAY THROUGH WEDNESDAY)  
ISSUED AT 338 PM CDT THU MAR 23 2017  
 
THE STRONG NATURE OF THE SURFACE HIGH LOOKS TO KEEP THE MAIN FRONT  
ASSOCIATED WITH THE SURFACE LOW MOVING INTO THE GREAT LAKES REGION TO  
OUR NORTHWEST THROUGH SUNDAY. HOWEVER, THE WEAKENING/DEPARTING  
CONVERGENCE BOUNDARY RESPONSIBLE FOR THE ACTIVITY OVERNIGHT WILL  
CONTINUE TO PUSH SOUTHEAST AND INTO GEORGIA ON SUNDAY. THIS SHOULD  
PRODUCE A TRAILING LINE OF ISOLATED TO SCATTERED SHOWERS AND  
THUNDERSTORMS IN NORTHEASTERN ALABAMA INTO CULLMAN COUNTY. THIS  
ACTIVITY WILL BE SLOW TO MOVE OUT OF THE AREA INTO GEORGIA AND  
CENTRAL ALABAMA ON SUNDAY. BASED ON MOST MODEL GUIDANCE INCLUDING THE  
GFS, THIS COULD LAST INTO THE EARLY AFTERNOON HOURS. SO MOSTLY  
CLOUDY CONDITIONS WILL LIKELY HOLD ON AS WELL IN THESE AREAS AND INTO  
CULLMAN COUNTY. DUE TO THE EXPECTED MORE STABLE NATURE OF THE  
ATMOSPHERE DUE TO PREVIOUS CONVECTION, NOT EXPECTING ANY STRONG  
STORMS AS INSTABILITY WILL BE ELEVATED AND MINIMAL. SOME CLEARING MAY  
OCCUR WEST OF I-65 AND WITH VERY WARM 925 TEMPERATURES NEAR AND JUST  
AHEAD OF THE BOUNDARY, MIXING SHOULD ALLOW HIGHS TO CLIMB INTO THE  
LOWER TO MID 70S IN MOST LOCATIONS. SOME 75 TO 80 DEGREE TEMPERATURES  
LOOK REASONABLE GIVEN 925 MB TEMPERATURES AND POSSIBLY MORE SUNSHINE  
WEST OF I-65. HOWEVER, MODELS DO WEAKEN THE CENTER OF THE RIDGE  
ALOFT OVER THE SOUTHEAST AND SHIFT IT FURTHER EAST INTO THE ATLANTIC,  
AFTER THIS BOUNDARY PUSHES INTO GEORGIA.  
 
SINCE THE MAIN FRONT WILL STILL REMAIN NORTHWEST OF THE AREA, NOT  
MUCH MODIFICATION OF THE AIR MASS IS EXPECTED BEHIND THE DEPARTED  
BOUNDARY. MODELS CONTINUE TO QUICKLY DEVELOP ANOTHER UPPER LEVEL  
DISTURBANCE MOVING EAST OUT OF SOUTHWESTERN ARKANSAS TOWARDS THE  
TENNESSEE VALLEY AND DEVELOP A NEW FRONTAL BOUNDARY TO THE NORTHWEST  
OF THE TENNESSEE VALLEY ON MONDAY MORNING. WITH DECENT LOWER LEVEL  
WINDS REDEVELOPING AHEAD OF THE APPROACHING SYSTEM (925 MB WINDS ~ 30  
KNOTS), THIS SHOULD ADVECT LOWER 60S DEGREE DEWPOINTS AT LEAST INTO  
LOCATIONS WEST OF I-65. THIS ALONG WITH HIGHS IN THE MID 70S SHOULD  
COMBINE TO PRODUCE STRONG SURFACE BASED INSTABILITY (CAPE VALUES  
1000-1500 J/KG) AND ELEVATED INSTABILITY (MUCAPE VALUES ~ 2000 J/KG).  
MOST OF THIS LOOKS RIGHT NOW TO BE IN THE HAIL GROWTH AREA OF THE  
ATMOSPHERIC COLUMN. WET-BULBS ARE ALSO ARE FORECAST BY MODELS TO BE  
BETWEEN 7000 AND 9000 FEET MUCH OF THE DAY. SO GIVEN FAIRLY STRONG  
LIFT, AS THE SURFACE AND ASSOCIATED STRONG DYNAMICS MOVE ACROSS THE  
TENNESSEE VALLEY, EXPECT A POTENTIAL FOR STRONG TO SEVERE STORMS ON  
MONDAY. MAIN THREAT AT THIS TIME LOOKS TO BE LARGE HAIL AND DAMAGING  
WINDS, BUT THIS COULD CHANGE AS WE GET CLOSER TO THE EVENT. ISOLATED  
TO SCATTERED SHOWERS AND STORMS COULD LINGER INTO TUESDAY, AS THE  
FRONT IS SLOW TO PUSH ALABAMA. THESE STORMS SHOULD JUST PRODUCE SOME  
LIGHTING AND GUSTY WINDS THOUGH.  
 
SOMEWHAT COOLER AND DRIER AIR WILL MOVE INTO NORTHERN ALABAMA  
TUESDAY NIGHT INTO WEDNESDAY, AS UPPER LEVEL RIDGING SLOWLY BUILDS  
OVER MUCH OF THE SOUTHEAST. A FEW SHOWERS AND THE SLIGHTLY COOLER  
TEMPERATURES COULD LINGER INTO WEDNESDAY. HIGHS WILL RETURN TO THE  
UPPER 60S OR LOWER 70S MUCH OF THAT PERIOD, WITH LOWS PRIMARILY IN  
THE 50S.  
 
A MORE UNSETTLED PERIOD IS EXPECTED BY LATER IN THE WEEK AS ANOTHER  
STRONG SYSTEM PUSHES FROM TEXAS TOWARDS THE TENNESSEE VALLEY. GIVEN  
THE STRONG RIDGE SETTING UP ALOFT IN MOST MODELS TUESDAY THROUGH THE  
END OF THE WEEK, DELAYED POP FROM QUICKER ECMWF SOLUTION.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)  
ISSUED AT 1239 AM CDT FRI MAR 24 2017  
 
VFR CIGS SHOULD CONTINUE FOR A FEW HOURS; HOWEVER MVFR CLOUDS SHOULD  
OVERSPREAD THE AREA FROM THE SE AROUND 09Z. THESE LOWER CIG VALUES,  
ALONG WITH SOMEWHAT HIGHER WINDS ALOFT WILL PRODUCE LOW LEVEL WIND  
SHEAR AROUND DAYBREAK FRIDAY. SE-S WINDS AT THE SURFACE SHOULD  
INCREASE INTO THE 10-20KT RANGE DURING MID/LATE MORNING, ALLEVIATING  
THE LLWS ISSUE. VFR WEATHER SHOULD ALSO RETURN IN THE MORNING, AND  
CONTINUING FOR THE REMAINDER OF THE TAF.  
 

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

 
 

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