641  
FXUS64 KHUN 171936  
AFDHUN  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE HUNTSVILLE AL  
236 PM CDT SUN JUN 17 2018  
   
NEAR TERM
 
(TONIGHT)  
ISSUED AT 235 PM CDT SUN JUN 17 2018  
 
SHOWERS ARE GETTING AN EARLIER START TODAY WITH SCATTERED  
THUNDERSTORMS NOW IMPACTING MANY AREAS SOUTH OF THE TN RIVER (OUTSIDE  
OF A ROGUE CELL IN NE JACKSON COUNTY). THIS AREA IS ENHANCED PARTLY  
DUE TO ITS PROXIMITY TO A LOW TO MID LEVEL LOW PRESSURE AREA.  
CONTINUOUS SHOWERS AND THUNDERSTORMS ARE ONGOING IN CENTRAL AL DUE TO  
THIS LOW. PER RECENT LAPS SOUNDINGS, WE MAY HAVE JUST RECENTLY  
REACHED THE CONVECTIVE TEMP. IT ALSO LOOKS LIKE ANY LOW AND MID LEVEL  
CAP WE HAD HAS ERODED. THIS HAS CAUSED PRETTY QUICK DEVELOPMENT OVER  
THE LAST HOUR. MUCAPE AND SURFACE CAPE ARE NOW WELL OVER 3000 J/KG,  
DCAPE NEARING 1000 J/KG AND ACTUALLY AROUND 15KTS OF BULK SHEAR.  
GIVEN THE CAPE PROFILE, IF WE CAN GET SOME LIFT, THESE STORMS COULD  
BECOME STRONG QUICKLY, WHICH IS SORT OF EVIDENCED BY THE VERY QUICK  
LIGHTNING PRODUCTION WITH A FEW STORMS. THE DRY AIR ALOFT SHOULD  
INHIBIT SOME GROWTH BUT A STRONG ENOUGH UPDRAFT COULD PUSH THROUGH  
THAT. GUSTY WINDS AND SMALL HAIL WOULD BE POSSIBLE.  
 
THE GFS AND SOMEWHAT THE NAM HAS A WEAK 850MB BOUNDARY LIFTING NORTH  
THROUGH OUR AREA THROUGH AND AFTER 00Z. THERE IS A VERY WEAK SURFACE  
FEATURE ASSOCIATED WITH IT BUT IT'S ALSO LOCATED UNDER THE WEAKENING  
UPPER LOW THAT HAS BEEN HOVERING OVER N. AL. THIS COMBO COULD CAUSE  
REGENERATION OR CONTINUATION OF SHOWERS/STORMS THROUGH AT LEAST  
MIDNIGHT. AFTER THAT, THERE SHOULDN'T BE ENOUGH INSTABILITY TO SEE  
MANY SHOWERS.  
 
FOG HASN'T BEEN MATERIALIZING THE LAST FEW NIGHTS OTHER  
THAN VERY PATCHY SPOTS. HOWEVER, PLACES THAT GET RAIN TODAY COULD SEE  
FOG IN THE MORNING BUT WILL LEAVE IT OUT OF THE FORECAST AT THIS  
TIME. LOWS WILL BE IN THE LOWER 70S.  
   
SHORT TERM
 
(MONDAY THROUGH TUESDAY NIGHT)  
ISSUED AT 235 PM CDT SUN JUN 17 2018  
 
WHATEVER IS LEFT OF THE UPPER LOW WILL MOVE OFF TO THE WEST ON MONDAY  
WHILE THE LOW LEVEL SYSTEM THAT IMPACTED CENTRAL AL WILL MOVE EAST  
INTO SOUTH CENTRAL GEORGIA. THE LINGERING BOUNDARY BETWEEN THE TWO  
WILL KEEP HIGHER POPS IN THE EAST THAN IN THE WEST. LOWER INSTABILITY  
AND LESS LIFT WILL KEEP THE COVER TO 30% OR LESS BUT PW VALUES MAY  
REACH NEAR 2 INCHES, MEANING ANYTHING THAT DOES FORM WILL PRODUCE  
VERY HEAVY RAINFALL. HIGHS ON MONDAY LOOK TO BE A DEG OR TWO COOLER  
THAN PREVIOUS FORECASTS, IN THE UPPER 80S TO LOWER 80S. SHOWERS AND  
STORMS SHOULD DIMINISH SHORTLY AFTER SUNSET WITH LOWS REMAINING IN  
THE LOWER 70S.  
 
TUESDAY LOOKS TO BE THE DRIEST DAY IN THE SHORT TERM WITH THE RIDGE  
BUILDING DIRECTLY OVER THE AREA AND ENCOMPASSING MUCH OF THE SOUTHERN  
STATES, AS WELL AS SURFACE HIGH PRESSURE FINALLY TAKING OVER. WEAK  
SUBSIDENCE INVERSIONS IN THE SOUNDINGS WILL KEEP INSTABILITY FROM  
BEING AS HIGH AS PREVIOUS DAYS. THAT COMBINED WITH LITTLE TO NO  
NOTICEABLE LIFT WILL KEEP POPS IN THE ISOLATED RANGE, ALTHOUGH THAT  
MAY BE LOWERED THE CLOSER WE GET TO THE DAY. WITH LESS CLOUDS/RAIN,  
HIGHS WILL BE BACK INTO THE LOWER 90S AND HONESTLY, WE MAY NEED TO UP  
THESE A DEG OR TWO IN FUTURE UPDATES. RIGHT NOW THAT PUTS HEAT INDEX  
VALUES IN THE MID 90S TO AROUND 101. TUESDAY NIGHT REMAINS DRY WITH  
LOWS IN THE UPPER 70S.  
   
LONG TERM
 
(WEDNESDAY THROUGH SATURDAY)  
ISSUED AT 235 PM CDT SUN JUN 17 2018  
 
MEDIUM RANGE MODELS ARE IN FAR BETTER AGREEMENT REGARDING THE  
PATTERN THROUGHOUT THE EXTENDED RANGE (LESS SO FOR THE ENSEMBLES).  
THE TROUGH MOVING INTO THE GREAT BASIN OUT WEST WILL TRAVERSE THE  
CENTRAL PLAINS BY MID-WEEK, DIGGING INTO THE MISSOURI VALLEY BY 12Z  
FRIDAY. 12Z/17 ECMWF, GFS, AND CMC HAVE COME INTO BETTER AGREEMENT  
ON THE TROUGH ERODING THE SUBTROPICAL RIDGE, WHICH PRODUCES MORE OF  
A ZONAL FLOW FRIDAY INTO SATURDAY. HOWEVER, THERE IS NO REAL FRONTAL  
PASSAGE WITH THIS TROUGH, SO THE ONLY IMPACT OF NOTE WILL BE AN  
INCREASE IN POPS--AND JUST HOW MUCH THAT INCREASES IS STILL  
UNCERTAIN. IT WOULD NOT BE SHOCKING TO SEE AN MCS COME CLOSE TO THE  
AREA ESPECIALLY LATE FRIDAY OR SATURDAY WHEN THE MAIN TROUGH AXIS  
MOVES ACROSS THE AREA. HEAVY RAIN MAY ALSO BE A RISK GIVEN HIGHER-  
THAN-USUAL PRECIPITABLE WATER VALUES. FOR NOW, THE FORECAST WILL  
CONTINUE TO SHOW 50% RAIN CHANCES ESPECIALLY NORTH OF THE TENNESSEE  
RIVER AND INTO SOUTHERN TENNESSEE. THE TEMPERATURE FORECAST WILL  
REMAIN SEASONABLE, ALTHOUGH SOME SLIGHTLY- COOLER DAYS ARE POSSIBLE  
WHERE CLOUDS AND RAIN BECOME A LITTLE MORE WIDESPREAD.  
 
THIS BRIEF FLIRTATION WITH A TROUGH PATTERN WILL QUICKLY COME TO AN  
END LATE SATURDAY INTO SUNDAY AS THE TROUGH LIFTS NE AND THE  
SUBTROPICAL RIDGE BUILDS RIGHT BACK OVER THE AREA. WHILE POPS FOR  
SUNDAY WILL BE MAINTAINED, INCREASING SUBSIDENCE MAY LIMIT RAIN  
CHANCES BEYOND CURRENT EXPECTATIONS. TEMPERATURES WILL ALSO INCREASE  
BACK TO AT LEAST SLIGHTLY ABOVE-NORMAL VALUES.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)  
ISSUED AT 1221 CDT SUN JUN 17 2018  
 
VFR CONDITIONS EXPECTED THROUGH THE TAF PERIOD OUTSIDE OF A FEW  
BKN040 CIGS LATER THIS AFTERNOON. A FEW SHOWERS AND STORMS MAY  
DEVELOP TODAY BUT THE COVERAGE AT THIS POINT IS TOO LOW TO INCLUDE  
IN THE TAFS. WINDS WILL GENERALLY BE LIGHT AND LESS THAN 5KTS THROUGH  
THE TAF PERIOD.  
 

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

 
 

 
 
NEAR TERM...LN  
SHORT TERM...LN  
LONG TERM...BCC  
AVIATION...LN  
 
FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE  
AT WEATHER.GOV/HUNTSVILLE.  
 
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