182  
FXUS64 KJAN 212353 AAA  
AFDJAN  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE JACKSON MS  
653 PM CDT SAT OCT 21 2017  
   
UPDATE
 
 
UPDATED FOR 00Z AVIATION DISCUSSION  
 

 
   
AVIATION
 
 
00Z TAF DISCUSSION: ISOLD TSRA WERE NOTED IN VCTY OF GLH, HKS, AND  
JAN AT 23Z. THIS ACTIVITY WL DIMINISH BY 01Z BUT REMAIN POSSIBLE  
AT GLH OVERNIGHT. ELSEWHERE, VFR CONDS WL CONT THROUGH THE  
EVENING. MVFR CIGS WL BEGIN MOVING IN FROM THE WEST AFTER 11Z. IN  
VCTY OF HBG, MVFR VSBYS WL BE PSBL BY 09Z. SHRA/TSRA COVERAGE  
WL INCREASE FROM THE WEST SUNDAY MORNING ALONG AND AHEAD OF A COLD  
FRONT. MVFR CIGS AND VSBYS WL ACCOMPANY THE CONVECTIVE  
ACTIVITY.CONDS WL IMPROVE SUNDAY AFTN AND EVNG FROM THE WEST AS  
THE COLD FRONT SHIFTS ACROSS THE AREA. /22/  
 

 
   
DISCUSSION
 
 
TONIGHT AND SUNDAY: WARM ADVECTION SHOWERS AND A FEW  
THUNDERSTORMS CONTINUE TO BREAK OUT OVER SOUTH AND EAST CENTRAL  
LA AS DEEP MOISTURE (DEWPOINTS IN THE MID 70S) POOLS ALONG THE  
GULF COAST. ALL OF THIS OCCURRING AHEAD OF A STORM SYSTEM TAKING  
SHAPE OVER THE PLAINS WHICH LOOKS TO DEEPEN AS IT APPROACHES THE  
MS VALLEY. THE SCATTERED WARM ADVECTION SHOWERS WILL CONTINUE IN  
THE WEST OVERNIGHT AS A QLCS GETS GOING OVER OK/TX AND APPROACHES  
THE WESTERNMOST PARTS OF THE FORECAST AREA BY SUNRISE SUNDAY.  
 
BY SUNDAY MORNING DEEP MOISTURE WILL BE IN PLACE AS PWS APPROACH  
1.85 INCHES AND SURFACE DEWPOINTS RISE INTO THE LOWER 70S. WITH SUCH  
MOISTURE, VERY EFFICIENT RAINFALL WILL OCCUR LIKELY PRODUCING 2-3  
INCHES BEFORE ENDING LATE SUNDAY NIGHT.  
 
ALSO OF CONCERN WILL BE A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER  
SOUTHEAST PORTIONS SUNDAY AFTERNOON. CAPES OF 1500-2500J/KG WILL  
NUDGE NORTHWARD INTO SOUTHEAST MS WHILE THE DEEP SHEAR INCREASES TO  
30-40 KNOTS. THIS MAY ALLOW SOME OF THE MORE ROBUST STORMS TO  
PRODUCE SOME DAMAGING WINDS AND/OR HAIL. /26/  
 
SUNDAY NIGHT THROUGH FRIDAY:  
 
BY SUNDAY NIGHT, EXPECT THE DEEP LONGWAVE TROUGH TO BE AMPLIFYING  
& DIVING THROUGH THE ARKLATEX & QUICKLY TOWARDS & THROUGH THE  
ARKLAMISS. THIS WILL HELP COLD FRONT TO QUICKLY MOVE THROUGH THE  
AREA OVERNIGHT. THERE WILL LIKELY BE SOME ANAFRONTAL SHOWERS & A  
FEW THUNDERSTORMS, WITH BEST POPS & STORMS RESIDING ACROSS EASTERN  
MISSISSIPPI. THIS WILL BE DUE TO THE FACT OF BETTER LIFT & JET  
DYNAMICS/DIFFLUENCE OVER THAT AREA. PWS WILL BE JUST HIGH ENOUGH  
IN THE WAKE TO HELP SPARK SOME SHOWER & THUNDERSTORM DEVELOPMENT  
BEFORE MIDNIGHT OR SO BEFORE DRIER AIR QUICKLY FILTERS IN THE  
WAKE. DUE TO SOME LINGERING MOISTURE IN THE +1.5-1.75 INCH RANGE  
ACROSS EASTERN & SOUTHERN ZONES (90TH+ PERCENTILE), EXPECT SOME  
HEAVY DOWNPOURS TO STILL BE POSSIBLE. KEPT THE HWO GOING INTO THE  
NIGHT BUT LIKELY WILL BE EARLIER FOR ANY FLOODING THREAT ACROSS  
THE EAST.  
 
AS THE TROUGH EJECTS THROUGH & STRONG HIGH PRESSURE BUILDS DOWN  
INTO WESTERN TO SOUTHERN PLAINS, THIS WILL HELP DRIVE MUCH DRIER &  
COOLER AIR INTO THE REGION. THIS WILL HELP DRIVE DOWN PWS AROUND  
TO HALF TO THREE QUARTERS OF AN INCH. HOWEVER, ANOTHER DEEP &  
ANOMALOUS TROUGH WILL DIG DOWN EVEN DRIER & COLDER ENVIRONMENT IN  
THE WAKE BY MID-WEEK. THIS TROUGH IS EXTREMELY ANOMALOUS, WITH  
850MB TEMPERATURES & 500MB HEIGHTS APPROACHING ONLY AROUND THE 1ST  
PERCENTILE OR SO. WITH ONLY 1-4+ DEG C AT 850MB, THIS WILL BRING  
HIGHS POSSIBLY SOME 8-10 DEGREES BELOW NORMAL BY WEDNESDAY  
AFTERNOON IN THE LOW-MID 60S. WENT COOLER FOR HIGHS ON WEDNESDAY  
DUE TO THAT SETUP. WET SOILS SHOULD LIMIT SOME MIXING BUT WE WILL  
BE VERY DRY WITH DEWPOINTS FALLING INTO THE MID 40S BY TUESDAY  
WITH THEM FALLING INTO THE MID-UPPER 30S BY THURSDAY. FIRE WEATHER  
CONCERNS SHOULD BE LOWER DUE TO RECENT HEAVY RAINFALL BUT DUE TO  
HUMIDITY LEVELS BEING BELOW CRITICAL LEVELS & STRONG PRESSURE  
GRADIENT, THIS WILL HAVE TO BE MONITORED AROUND EARLY-MID WEEK.  
DUE TO ~1025MB SURFACE HIGH OVER TEXAS & STRONG GRADIENT ON  
WEDNESDAY & DEVELOPING LOW OVER THE NORTHERN PLAINS THURSDAY  
MORNING, WINDS WILL STAY UP ENOUGH IN THIS ENVIRONMENT TO KEEP  
LOWS FROM FALLING OFF TOO MUCH. WENT SLIGHTLY COOLER ON LOWS  
(STILL 5+ DEGREES BELOW NORMALS) BUT NOT TOO MUCH DUE TO FACTORS  
PREVIOUSLY MENTIONED.  
 
ANOTHER ANOMALOUS TROUGH WILL DIG DOWN BY MID-LATE WEEK OVER THE  
WESTERN HALF OF THE NATION, WITH THE GFS & CANADIAN BEING SLIGHTLY  
FASTER & MORE PROGRESSIVE TO MOVE EAST. THIS IS LIKELY DUE TO THE  
INJECTION OF A STRONG TYPHOON OVER THE WEST PACIFIC, HELPING  
BUCKLE THE PATTERN DOWNSTREAM. SIMILAR TO THE UPCOMING COLD FRONT,  
THIS HAS POTENTIAL TO BE PRETTY CHILLY IN THE WAKE BUT LIKELY IN  
STORE SOMETIME NEXT WEEK. THE EURO IS SLOWER WITH THIS COLD  
FRONTAL PASSAGE & SIDED TOWARDS THIS SLOWER SOLUTION DUE TO  
STRONG LONGWAVE AMPLIFICATION & STRENGTHENING HIGH-LATITUDE  
BLOCKING. DUE TO THIS SLOWED DOWN POPS MOVING IN ON FRIDAY,  
ESPECIALLY EASTERN HALF OF THE AREA UNTIL AFTER THE PERIOD. BUT IT  
COULD BE EVEN LATER INTO THE WEEKEND MORE RAIN & STORMS WOULD BE  
POSSIBLE IF THE NEW SLOWER 12Z EURO SOLUTION PANS OUT. /DC/  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
JACKSON 69 78 54 72 / 36 99 76 12  
MERIDIAN 65 79 59 73 / 7 84 92 19  
VICKSBURG 69 78 52 74 / 31 99 60 7  
HATTIESBURG 68 80 59 74 / 7 94 84 11  
NATCHEZ 70 78 52 72 / 45 99 54 6  
GREENVILLE 68 75 52 73 / 32 100 56 10  
GREENWOOD 69 76 53 72 / 27 99 66 16  
 

 
   
JAN WATCHES/WARNINGS/ADVISORIES
 
 
MS...NONE.  
LA...NONE.  
AR...NONE.  
 

 
 

 
 
22/DC/26  
 
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