819  
FXUS64 KJAN 230501 AAA  
AFDJAN  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE JACKSON MS  
1201 AM CDT WED AUG 23 2017  
   
UPDATE
 
 
UPDATED FOR 06Z AVIATION DISCUSSION  
 

 
   
AVIATION
 
 
06Z TAF DISCUSSION:  
ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS WILL CONTINUE  
OVERNIGHT BETWEEN GLH AND GWO AS A COLD FRONT TRIES TO MOVE INTO  
THE AREA. THE CONVECTION WILL BEGIN BREAKING OUT FURTHER SOUTH  
AFTER SUNRISE AS THE FRONT CONTINUES MOVING SOUTH. CEILINGS AND  
VISIBILITIES WILL BE LOWERED AT TAF SITES THAT RECEIVE A STORM,  
OTHERWISE VFR CONDITIONS WILL PREVAIL THROUGH THE PERIOD./26/  
 

 
   
DISCUSSION
 
 
THE OUTFLOW FROM THE STORMS WHICH SPARKED ALONG THE FRONT IN THE  
MID-MS VALLEY TODAY ARE NOW PUSHING SOUTHWARD THROUGH NORTHERN MS.  
WITH THE LOSS OF DAYTIME HEATING AND FURTHER WEAKENING OF  
INSTABILITY, THIS LINE OF STORMS IS NOT EXPECTED TO MAKE IT TOO  
MUCH FURTHER WITHOUT BREAKING UP. NONE OF THE HI-RES MODELS EVEN  
SHOW IT MAKING IT INTO OUR CWA TONIGHT. HOWEVER, THIS OUTFLOW DOES  
SEEM TO HAVE THE MOMENTUM TO REACH AT LEAST OUR NORTHERN  
COUNTIES WITHIN THE NEXT COUPLE HOURS. THEREFORE, THE POPS HAVE  
BEEN TWEAKED FOR THIS UPDATE. /10/  
 
PRIOR DISCUSSION BELOW:  
 
THROUGH WEDNESDAY:  
ISOLATED CONVECTION CONTINUES THIS AFTERNOON AS A  
WEAK SHORTWAVE PASSES THROUGH THE OHIO VALLEY AND A WEAK UPPER LOW  
SITS OVER THE WESTERN GULF. THE LOCAL MICROBURST CHECKLIST INDICATED  
LOW POTENTIAL FOR ROBUST STORMS TODAY, AND SO FAR THIS HAS BEEN THE  
CASE. MUCH OF THIS ACTIVITY WILL DIE OFF WITH THE LOSS OF DIURNAL  
HEATING. HOWEVER, SOME LIMITED POTENTIAL FOR PRECIP WILL PERSIST  
OVER NORTHERN PORTIONS OF THE FORECAST AREA OVERNIGHT AHEAD OF AN  
APPROACHING COLD FRONT. THIS FRONT CURRENTLY EXTENDS FROM THE  
CENTRAL PLAINS THROUGH THE MID-MS VALLEY AND IS SLIDING SOUTHWARD  
TOWARD THE REGION. IT SHOULD REACH NORTH MS DURING THE DAY TOMORROW,  
BRINGING A SHARPER FOCUSING MECHANISM FOR SCATTERED TO NUMEROUS  
SHOWERS AND THUNDERSTORMS, PARTICULARLY DURING THE AFTERNOON WHEN  
INSTABILITY WILL BE GREATEST. GIVEN FAIRLY TYPICAL (OR SOMEWHAT  
WEAKER DUE TO CLOUDS) INSTABILITY AND UNIMPRESSIVE DEEP LAYER SHEAR,  
NO NOTABLE SEVERE WEATHER THREAT IS ANTICIPATED. A FEW INSTANCES OF  
LOCALLY HEAVY RAINFALL CAN'T BE RULED OUT GIVEN SUFFICIENT DEEP  
LAYER MOISTURE AND POTENTIALLY SLOW STORM MOTIONS, BUT THIS THREAT  
REMAINS TOO LOW FOR MENTION IN THE HWO. /DL/  
 
WEDNESDAY NIGHT THROUGH TUESDAY...  
 
THE PERIOD WILL START OFF WITH SUBTROPICAL RIDGING ACROSS THE  
EASTERN GULF OF MEXICO, TROUGHING ACROSS THE GREAT LAKES AND A  
BUILDING RIDGE OVER THE DESERT SOUTHWEST. A SURFACE COLD FRONT  
WILL ALSO BE DROPPING SOUTH THROUGH THE ARKLAMISS IN ASSOCIATION  
WITH A DEPARTING LOW OVER SOUTHEAST CANADA. AREAS OF CONVECTION  
ARE EXPECTED TO BE ONGOING DURING THE EARLY EVENING HOURS ON  
WEDNESDAY AS THE FRONT DROPS THROUGH THE AREA. EXPECT A FEW  
ISOLATED TO POSSIBLY SCATTERED SHOWERS AND STORMS TO CONTINUE  
OVERNIGHT ALONG AND AHEAD OF THE FRONT. BY THURSDAY MORNING,  
LATEST GLOBAL MODELS ARE IN AGREEMENT ON THE FRONT DRAPED ALONG OR  
JUST TO THE SOUTH OF I- 20 WHICH WILL HELP TO FOCUS SHOWER AND  
STORM CHANCES MAINLY SOUTH OF I-20 DURING THE DAY ON THURSDAY. A  
FEW STRONG STORMS WITH ISOLATED GUSTY WINDS CANNOT BE RULED OUT  
BOTH EARLY WEDNESDAY EVENING AND DURING THE DAY THURSDAY BUT  
SEVERE WEATHER IS NOT EXPECTED WITH LAPSE RATES, VERTICAL TOTALS  
AND SHEAR REMAKING LESS THAN IDEAL FOR ROBUST CONVECTION.  
MOISTURE POOLING AHEAD OF THE FRONT WILL HELP TO RESULT IN 2 INCH  
PWATS AND WHEN COMBINED WITH WEAK FLOW COULD RESULT IN LOCALLY  
HIGHER RAINFALL TOTALS, HOWEVER ANY FLASH FLOODING LOOKS TO REMAIN  
ISOLATED SO WILL NOT MENTION IN THE HWO. MUCH DRIER AIR WILL  
FILTER IN BEHIND THE FRONT THURSDAY INTO FRIDAY WITH DEWPOINTS  
DROPPING INTO THE UPPER 50S ALONG THE HWY 82 CORRIDOR AND LOW 60S  
FURTHER SOUTH. THIS DRIER AIR SHOULD KEEP ANY AFTERNOON SHOWERS OR  
STORMS LIMITED TO THE EXTREME SOUTHERN PORTION OF THE AREA OR  
OUTSIDE OF OUR CWA COMPLETELY DEPENDING ON WHERE THE FRONT STALLS  
OUT AT.  
 
FORECAST UNCERTAINTY STARTS TO INCREASE BY THE WEEKEND AND  
ESPECIALLY INTO EARLY NEXT WEEK AS THE MODELS CONTINUE TO TRY AND  
RESOLVE THE EVOLUTION OF THE REMNANTS OF TROPICAL STORM HARVEY.  
THESE REMNANTS ARE CURRENTLY LOCATED OVER THE YUCATAN PENINSULA AND  
ARE PROGGED TO MOVE INTO THE BAY OF CAMPECHE AND THEN GULF OF MEXICO  
THURSDAY AND FRIDAY. THERE'S GOOD CONSENSUS IN THAT STRENGTHENING  
WILL OCCUR WITH A TROPICAL SYSTEM DEVELOPING OFF THE COAST OF  
SOUTHEAST TEXAS. THIS SYSTEM WILL BE MOVING AROUND THE WESTERN EDGE  
OF THE SUBTROPICAL RIDGING IN THE EASTERN GULF OF MEXICO WHILE THE  
DESERT SOUTHWEST RIDGE EXPANDS INTO PORTIONS OF WEST TEXAS AND  
STRENGTHENS OVER THE GREAT BASIN. THIS SYNOPTIC EVOLUTION WOULD  
SLOW DOWN THE SYSTEM MOVEMENT UNTIL A WEAKNESS IN THE RIDGING  
DEVELOPS AS A SHORTWAVE TROUGH DROPS INTO THE SOUTHERN PLAINS AND  
PICKS UP/PHASES WITH THE TROPICAL SYSTEM AFTER MAKING POTENTIAL  
LANDFALL IN TEXAS. GLOBAL MODELS OFFER A PLETHORA OF WIDELY  
VARYING SOLUTIONS, AS WOULD BE EXPECTED SINCE MODELS OFTEN  
STRUGGLE WITH SYSTEMS THAT HAVEN'T DEVELOPED YET, HOWEVER THERE IS  
SOME INCREASING CONCERN FOR FLASH FLOODING ACROSS AT LEAST SOME  
PORTION OF THE ARKLAMISS DURING THE LATE WEEKEND AND EARLY NEXT  
WEEK TIME FRAME AS DEEP TROPICAL MOISTURE GETS LIFTED THROUGH THE  
AREA ALONG THE RETREATING FRONTAL BOUNDARY/BAROCLINIC ZONE.  
EXPLICIT MODEL QPF PRODUCTS PAINT SWATHS OF 10-15 INCHES OF RAIN  
ANYWHERE FROM COASTAL TEXAS THROUGH THE ARKLAMISS AND INTO  
TENNESSEE BUT HAVE LACKED RUN- TO-RUN CONSISTENCY. EXACT PLACEMENT  
OF THE AXIS OF HEAVIEST RAINFALL TOTALS WILL BE HIGHLY DEPENDENT  
ON THE TIMING AND EVOLUTION OF THE KEY SYNOPTIC FEATURES AND GIVEN  
THE INCONSISTENCIES DISPLAYED IN THE LAST FEW RUNS OF MODEL  
GUIDANCE THE READER IS ENCOURAGED TO STAY ABREAST OF THE LATEST  
FORECAST AND NOT TO FOCUS ON ANY ONE MODEL SOLUTION. WITH THE  
TIMING FAVORING THE DAY 6-9 TIME FRAME WILL ALSO HOLD OFF ON  
MENTIONING IN THE HWO/GRAPHICS FOR NOW, BUT WILL CLOSELY MONITOR  
THE TRENDS FOR INCLUSION IN LATER FORECASTS. /TW/  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
JACKSON 74 91 71 87 / 10 52 28 30  
MERIDIAN 74 91 71 87 / 11 57 30 27  
VICKSBURG 74 91 71 87 / 9 46 29 31  
HATTIESBURG 73 92 73 89 / 8 51 32 50  
NATCHEZ 73 90 72 86 / 7 44 32 48  
GREENVILLE 74 88 68 86 / 21 53 14 9  
GREENWOOD 74 89 68 86 / 20 56 16 11  
 

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

 
 

 
 
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