504  
FXUS64 KHUN 181551  
AFDHUN  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE HUNTSVILLE AL  
1051 AM CDT THU OCT 18 2018  
   
NEAR TERM
 
(REST OF TODAY)  
ISSUED AT 1051 AM CDT THU OCT 18 2018  
 
MORNING SURFACE ANALYSIS SHOWS A BROAD AREA OF HIGH PRESSURE OVER THE  
MIDWEST AS THE MAIN INFLUENCE ON TN VALLEY WEATHER, BUT MODEL  
INITIALIZATIONS CONTINUE TO SHOW AN EXTENDED WEST-EAST ORIENTED SHEAR  
AXIS DRAPED ACROSS THE REGION AS WELL. GOES-EAST IMAGERY SHOWS A  
BAND OF PERSISTENT MID/HIGH-LEVEL CLOUDINESS ACCOMPANYING THIS  
FEATURE, OVER THE TN VALLEY AT LEAST. BETWEEN WEAK PERSISTENT COLD  
AIR ADVECTION AND THE CONTINUED CLOUD COVER, TEMPERATURES HAVE  
LARGELY REMAINED IN THE MID-UPPER 50S; ONLY A FEW SITES RECEIVING  
MORE SUNSHINE HAVE RISEN INTO THE THE 60S.  
 
MOISTURE WILL REMAIN CONFINED TO THE MID AND UPPER LEVELS THROUGH  
TODAY, SO A DRY FORECAST STILL LOOKS GOOD. THE FORECAST HAS BEEN  
UPDATED TO INCREASE CLOUD COVER FOR A LONGER PERIOD OF TIME, MORE IN  
LINE WITH THE GFS AND BLENDED GUIDANCE PROGS. THIS MAY INHIBIT  
TEMPERATURES A LITTLE MORE THAN THE CURRENT HIGH FORECAST (MID-UPPER  
60S) SUGGESTS, SO TEMPERATURES WILL BE NUDGED DOWN SLIGHTLY.  
   
SHORT TERM
 
(TONIGHT THROUGH SATURDAY NIGHT)  
ISSUED AT 307 AM CDT THU OCT 18 2018  
 
THE SURFACE HIGH WILL MOVE OFF OF THE MID ATLANTIC COAST LATER  
TONIGHT, WITH SURFACE FLOW BECOME MORE SOUTHERLY. MEANWHILE, THE AXIS  
OF THE UPPER RIDGE WILL BUILD AGAIN INTO THE AREA, KEEPING SOME FLOW  
OF MOISTURE ACROSS THE TN VALLEY. DESPITE THE RETURN FLOW SETTING UP  
OVERNIGHT, TEMPERATURES WILL STILL BE ABLE TO COOL QUITE A BIT, WITH  
LOWS BOTTOMING OUT IN THE UPPER 40S TO LOWER 50S. THE UPPER RIDGE  
AXIS WILL MOVE EAST OF THE AREA DURING THE DAY FRIDAY AS A  
PROGRESSIVE TROUGH EJECTS INTO THE PLAINS. AS FLOW BECOMES SOUTHERLY  
THROUGH THE VERTICAL COLUMN, PW VALUES WILL CLIMB ABOVE 1.5 INCHES  
BY FRIDAY AFTERNOON. THIS WILL RESULT IN AN INCREASE IN CLOUD COVER,  
BUT NOT BEFORE TEMPS REACH INTO THE MID 70S.  
 
A COLD FRONT, ASSOCIATED WITH THE AFOREMENTIONED UPPER TROUGH, WILL  
BE JUST ON THE DOORSTEP OF THE TN VALLEY BY SUNSET ON FRIDAY AND THEN  
QUICKLY MOVE TO THE EAST THROUGH THE OVERNIGHT HOURS. WITH AN  
ABUNDANCE OF MOISTURE AND PLENTY OF LIFT, NUMEROUS TO WIDESPREAD  
SHOWERS WILL SHIFT EASTWARD ACROSS THE AREA, WITH THE HIGHEST  
COVERAGE EXPECTED TO BE JUST BEHIND THE FRONT. THE FRONT WILL BE WELL  
SOUTH OF THE AREA BY DAYBREAK ON SATURDAY, WITH THE POST-FRONTAL  
RAINFALL SLOWLY EXITING THE AREA DURING THE MID MORNING HOURS. THE  
AIRMASS BEHIND THE FRONT WILL BE QUITE COLD AND DRY, WITH THE DRIER  
AIR QUICKLY FILTERING IN DURING THE AFTERNOON. THE COMBINATION OF  
COLD AIR ADVECTION AND LINGERING CLOUD COVER DURING THE DAYLIGHT  
HOURS WILL KEEP HIGHS IN THE LOWER TO MID 60S. CLOUDS WILL THEN  
DECREASE OVERNIGHT AS THE UPPER FLOW BECOMES NORTHWESTERLY. THE  
ASSOCIATED SURFACE HIGH WILL BE FAIRLY STRONG AS IT BUILDS  
SOUTHEASTWARD INTO THE AREA. THIS WILL KEEP THE PRESSURE GRADIENT  
FAIRLY TIGHT OVERNIGHT AND WINDS WILL NOT REALLY DROP OFF. WHILE THIS  
MEANS RADIATIONAL COOLING WILL NOT BE FAIRLY STRONG, THE COLD AIR  
ADVECTION WILL BE AND THUS OVERNIGHT LOWS WILL DROP INTO THE UPPER  
30S TO LOWER 40S. FROST DOES NOT APPEAR LIKELY SATURDAY NIGHT, GIVEN  
THE WINDS AND DEWPOINT DEPRESSIONS GREATER THAN 5 DEGREES.  
   
LONG TERM
 
(SUNDAY THROUGH WEDNESDAY)  
ISSUED AT 307 AM CDT THU OCT 18 2018  
 
THE RIDGE BUILDING IN THE SOUTHERN PLAINS UP INTO THE INTERMOUNTAIN  
WEST WILL PUSH A TROUGH ACROSS NEW ENGLAND THIS WEEKEND. THIS WILL  
ALLOW FOR A SFC HIGH IN THE MIDWEST TO BUILD INTO THE REGION SUNDAY  
AND MONDAY. THE DECREASING CLOUD COVER AND LIGHT WINDS WILL ALLOW FOR  
GOOD RADIATIONAL COOLING GETTING TEMPS DOWN INTO THE UPPER 30S! THIS  
WILL ALSO GIVE WAY TO THE POTENTIAL FOR PATCHY FROST ACROSS SOUTHERN  
MIDDLE TN AND HIGHER ELEVATIONS IN NE AL EARLY MONDAY MORNING.  
DAYTIME HIGHS ON SUNDAY WILL BE IN THE UPPER 50S, WARMING UP INTO THE  
LOWER 60S ON MONDAY DUE TO SOUTHEASTERLY WINDS. THIS WILL MOVE IN  
SOME CLOUD COVER MONDAY NIGHT, AND KEEP OVERNIGHT LOWS IN THE UPPER  
40S.  
 
A TROUGH WILL SLIDE INTO THE GREAT LAKES ON TUESDAY, SLOWING DOWN THE  
EASTWARD PROGRESSION OF THE RIDGE. THE SFC HIGH WILL BE PUSHED INTO  
THE MID ATLANTIC BY TUESDAY AFTERNOON, KEEPING CONDITIONS DRY FOR ONE  
MORE DAY. DAYTIME HIGHS WILL BE A TAD WARMER IN THE UPPER 60S. MODELS  
DIVERGE FOR THE REST OF THE EXTENDED FORECAST. A SERIES OF WEAK  
DISTURBANCES WILL GLIDE UP THE SOUTHWESTERLY FLOW INTO THE REGION  
AND GIVE WAY TO A ISO/SCT SHOWERS WEDNESDAY AFTERNOON AND EVENING.  
THE ECMWF KEEPS THE TROUGH LINGERING OVER THE GREAT LAKES ON  
WEDNESDAY, FURTHER SLOWING DOWN THE RIDGE WHICH WILL IN TURN WEAKEN A  
SFC LOW COMING UP OUT OF TX AND QUICKLY SLIDE IT RIGHT OVER AL IN  
SEMI- ZONAL FLOW. THE GFS ON THE OTHER HAND LETS THE TROUGH EXIT  
QUICKLY, PROGRESSES THE RIDGE AND HAS A STRONGER, SLOWER SFC LOW LIFT  
JUST NW OF THE TN VALLEY. BOTH SOLUTIONS WILL BRING RAINFALL FOR THE  
TN VALLEY WEDNESDAY NIGHT AND THURSDAY, HOWEVER THE RAINFALL  
COVERAGE AND AMOUNTS WILL VARY DEPENDING ON THE SOLUTION YOU FAVOR.  
WITH THIS IN MIND, STAYED CLOSE TO THE BLEND.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)  
ISSUED AT 600 AM CDT THU OCT 18 2018  
 
VFR CONDITIONS WILL PREVAIL AT THE KMSL AND KHSV TERMINALS THROUGH  
THE PERIOD. OTHER THAN PASSING HIGH CLOUDS, SKIES WILL REMAIN MOSTLY  
CLEAR. WINDS WILL GENERALLY BE FROM THE NORTHEAST, BETWEEN 7 AND  
10KTS DURING THE DAY AND BECOME LIGHT OVERNIGHT.  
 

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

 
 

 
 
NEAR TERM...BCC  
SHORT TERM...73  
LONG TERM...JMS  
AVIATION...73  
 
FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE  
AT WEATHER.GOV/HUNTSVILLE.  
 
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