005  
FXUS64 KJAN 220308  
AFDJAN  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE JACKSON MS  
1008 PM CDT SAT APR 21 2018  
   
UPDATE
 
 
UPDATED FOR EVENING DISCUSSION.  
 

 
   
DISCUSSION
 
 
SATELLITE IMAGERY CONTINUES TO SHOW A COMPACT AND SLOW MOVING  
UPPER-LEVEL LOW CENTERED OVER THE SOUTHERN PLAINS. REGIONAL RADAR  
MOSAICS REVEAL MULTIPLE AREAS OF ONGOING THUNDERSTORMS AND  
SHOWERS ACROSS THE ARKLATEX ALONG AND AHEAD OF AN ADVANCING COLD  
FRONT. MOISTURE CONTINUES TO INCREASE ACROSS THE ARKLAMISS WITH  
THE 00Z JAN SOUNDING ALREADY EXHIBITING INCREASED MOISTURE AT  
MULTIPLE LEVELS COMPARED TO THE 12Z SOUNDING FROM THIS MORNING.  
SHOWERS HAVE ALREADY OVERSPREAD PORTIONS OF THE DELTA AND WILL  
GRADUALLY PUSH EAST, HOWEVER MEASURABLE PRECIP COULD BE HARD TO  
COME BY WITH THIS EARLY ACTIVITY DUE TO EVAPORATION AS THE COLUMN  
CONTINUES TO SATURATE. EMBEDDED THUNDERSTORMS WILL ALSO BEGIN TO  
MOVE IN OVERNIGHT, BUT THE MAIN SEVERE THREAT WILL BE AFTER  
DAYBREAK TOMORROW. SEE PREVIOUS DISCUSSION BELOW FOR DETAILS  
REGARDING THE SEVERE/FLASH FLOODING POTENTIAL AS CURRENT THINKING  
HASN'T CHANGED. ONLY CHANGES MADE WITH THIS FORECAST UPDATE WAS TO  
SLIGHTLY ADJUST TIMING AND COVERAGE OF POPS AND TWEAK HOURLY  
TEMPS. OTHERWISE, THE ONGOING FORECAST IS ON TRACK AND NO OTHER  
CHANGES WERE NEEDED. /TW/  
 
PRIOR DISCUSSION BELOW:  
 
TONIGHT AND SUNDAY:  
 
A RELATIVELY COMPACT BUT POTENT CUTOFF UPPER LOW CURRENTLY  
SITUATED OVER KS/OK WILL BE THE PRIMARY FEATURE OF INTEREST FOR  
SENSIBLE WEATHER IMPACTS IN OUR REGION OVER THE NEXT 24 HOURS.  
WARM/MOIST SOUTHERLY FLOW IS ALREADY UNDERWAY AHEAD OF THIS SYSTEM  
THIS AFTERNOON, WITH CLOUDS BEGINNING TO INCREASE FROM THE WEST.  
RADAR HAS ALREADY PICKED UP ON HIGHER LEVEL ECHOES THROUGH THE  
DAY, BUT CONDITIONS HAVE REMAINED TOO DRY AT THE SURFACE FOR  
MEASURABLE RAIN THUS FAR. HOWEVER, THE LOW LEVELS WILL CONTINUE TO  
STEADILY MOISTEN OVERNIGHT AS ADVECTION INCREASES AHEAD OF THE  
SURFACE LOW TRACKING ACROSS THE ARKLATEX. A WEAK WARM FRONTAL  
FEATURE WILL LIFT NORTHWARD DURING THE OVERNIGHT HOURS INTO EARLY  
SUNDAY MORNING, WITH MEASURABLE RAIN BEGINNING TO SPREAD OVER THE  
WESTERN HALF OF THE AREA BEFORE DAYBREAK (LIGHTER SHOWERS POSSIBLE  
OVER THE EASTERN HALF AS WELL). ALONG WITH CONDITIONS BEING  
WARMER OVERNIGHT, IT WILL ALSO BE QUITE BREEZY AS THE SURFACE  
PRESSURE GRADIENT TIGHTENS BETWEEN THE APPROACHING SYSTEM AND A  
LINGERING RIDGE LINGERING ALONG THE ATLANTIC COAST.  
 
MOST CAM GUIDANCE IS PICKING UP ON CONSIDERABLE CONVECTION SPREADING  
THROUGH THE EASTERN HALF OF THE AREA FROM AROUND DAYBREAK SUNDAY  
THROUGH THE MORNING HOURS WELL AHEAD OF THE COLD FRONT AT A TIME  
WHEN INSTABILITY REMAINS FAIRLY MARGINAL (IN SPITE OF INCREASING  
DEEP LAYER SHEAR). SYNOPTIC MODELS SHOW VARYING LEVELS OF AGREEMENT  
WITH THIS EVOLUTION. THE STRONGEST LOW LEVEL HELICITY IS FORECAST TO  
ACCOMPANY THIS MORNING ACTIVITY, THOUGH AGAIN AT A TIME WHEN  
INSTABILITY IS MORE QUESTIONABLE AND THE HREF SUGGESTS THE  
LIKELIHOOD OF DEEPER UPDRAFTS TO BE LOW. WHILE WE COULDN'T ENTIRELY  
RULE OUT SOME WIND DAMAGE THREAT IN THIS TIME FRAME, IT APPEARS  
GREATER POTENTIAL WILL HOLD OFF UNTIL LATER IN THE DAY.  
 
IT SEEMS PLAUSIBLE THAT IN AT LEAST SOME PORTION OF THE AREA THE  
ATMOSPHERE WILL STRUGGLE TO SUFFICIENTLY RECOVER FROM MORNING  
CONVECTION FOR REDEVELOPMENT TO OCCUR INTO THE AFTERNOON. HOWEVER,  
SOME OF THE AVAILABLE CAM MODELS (ALONG THE 12Z EURO AND NAM) DO  
SHOW REDEVELOPMENT AROUND MIDDAY NEAR THE US 49 TO I-55 CORRIDOR,  
SPREADING NORTH AND EASTWARD THROUGH THE EARLY EVENING. WITH AROUND  
50 KT OF 0-6 KM BULK SHEAR AND THE RESPECTABLE INSTABILITY AND LAPSE  
RATE, DAMAGING WINDS AND MARGINALLY SEVERE HAIL WOULD BE POSSIBLE  
WITH THESE STORMS. WITH THE STRONGER LOW LEVEL HELICITY PULLING OUT  
OF THE AREA AND MOST GUIDANCE SHOWING 0-3 KM BULK SHEAR MAGNITUDES  
<30 KT, THE TORNADO THREAT DOESN'T LOOK AS HIGH, BUT A TORNADO OR  
TWO WOULD STILL BE POSSIBLE. IN ADDITIONAL, HIGH RES GUIDANCE IS  
DEPICTING A FEW QPF STREAKS OF UP TO AROUND 4", SO WE CANNOT RULE  
OUT FLASH FLOODING. I'M NOT PARTICULARLY CONCERNED ABOUT THE  
FLOODING THREAT, BUT AS THERE IS LIMITED POTENTIAL AND WE ARE  
ALREADY ADVERTISING THIS IN THE HWO/GRAPHICS, I CERTAINLY DON'T HAVE  
ENOUGH CONFIDENCE TO PULL IT OUT. /DL/  
 
SUNDAY NIGHT INTO NEXT WEEKEND:  
 
THE FORECAST PATTERN LOOKS RATHER UNSETTLED OVER THE LOWER MS  
VALLEY THROUGH THE LONG TERM PERIOD, ALTHOUGH THE LACK OF  
CONSIDERABLE MOISTURE, WARMTH, AND INSTABILITY SHOULD KEEP THE  
RISK OF SEVERE WEATHER AND FLOODING QUITE LOW. THE MAIN ISSUE IS  
TRYING TO TIME IMPACT OF DISTURBANCES ON THE REGION AND MODEL  
CONSENSUS IS NOT VERY GOOD IN THAT REGARD, ESPECIALLY TOWARD THE  
END OF THE COMING WORK WEEK. WITH AT LEAST A FEW FRONTAL PASSAGES  
LIKELY AND A SUPPRESSED SOUTHERN BRANCH OF JET STREAM (AT LEAST  
EAST OF THE ROCKIES) TEMPERATURES SHOULD CONTINUE TO BE HELD AT  
LEAST A BIT BELOW NORMAL, IN GENERAL.  
 
THE FIRST DISTURBANCE TO DEAL WITH WILL BE BRINGING SHOWERS AND  
STORMS TO THE REGION IN THE SHORT TERM, BUT THE SIGNIFICANT  
ACTIVITY SHOULD BE ADVANCING EAST OF THE REGION DURING THE EARLY  
TO MID EVENING HOURS SUNDAY, OF COURSE TAKING LONGEST TO EXIT IN  
EASTERN MS. A WEAK COLD FRONT WILL PUSH THROUGH AND TRY TO CLEAR  
OUT CONDITIONS A BIT, BUT EXPECT LIGHTER SHOWERS WRAPPING AROUND  
THE BACKSIDE OF THE SLOWLY-DEPARTING UPPER LEVEL LOW TO AFFECT AT  
LEAST NORTHERN ZONES LATE IN THE NIGHT. THESE SHOWERS SHOULD  
CONTINUE IN AT LEAST ISOLATED TO SCATTERED FASHION ALONG AND NORTH  
OF THE I-20 CORRIDOR ON MONDAY WITH CLOUDS AND PRECIP HOLDING  
HIGHS DOWN BELOW 70 DEGREES IN MANY LOCATIONS. THE DISTURBANCE AND  
THE MOISTURE WRAPPING AROUND IT MAY ACTUALLY BE SO SLOW TO DEPART  
THAT ISOLATED SHOWERS AND ABUNDANT CLOUDS COULD CONTINUE THROUGH  
TUESDAY, ESPECIALLY IN EASTERN ZONES, WITH DAYTIME TEMPERATURES  
STRUGGLING TO REACH 70 DEGREES IN SOME CASES.  
 
BY TUESDAY NIGHT AND INTO WEDNESDAY THE UPPER LOW TO THE EAST WILL  
BE MOVING AWAY QUICKLY, FINALLY, BUT ANOTHER CLIPPER-TYPE  
DISTURBANCE SHOULD BE QUICKLY DROPPING OUR WAY AND SPREADING  
CLOUDS BACK IN FROM THE WEST. MODEL CONSENSUS IS NOT GREAT WITH  
TIMING OR INTENSITY OF PRECIPITATION ASSOCIATED WITH THIS  
DISTURBANCE SO LOWER-END RAIN CHANCES (WITH RELATIVELY MINIMAL  
CHANCES FOR STORMS) SPREAD FROM WEDNESDAY THROUGH THURSDAY. ONCE  
TIMING CONSENSUS IMPROVES CHANCES OF RAIN IN OUR FORECAST WILL  
PROBABLY INCREASE, BUT WILL BE MORE CONFINED TO A 12 HOUR PERIOD.  
 
THE FINAL EXPECTED DISTURBANCE AND ASSOCIATED FRONT SHOULD COME  
IN TOWARD FRIDAY OR SATURDAY, BUT TIMING CONSENSUS ON THIS IS EVEN  
WORSE THAN THE MIDWEEK SYSTEM. FORTUNATELY, AT THIS TIME THIS  
SYSTEM DOES NOT LOOK EXTREMELY POTENT SO HOPEFULLY ANOTHER  
WEEKEND'S OUTDOOR ACTIVITIES WILL NOT BE PUT IN JEOPARDY BY  
PERSISTENT BAD WEATHER. /BB/  
 

 
   
AVIATION
 
 
00Z TAF DISCUSSION:  
AS THE STORM SYSTEM APPROACHES THE AREA TONIGHT, CONDITIONS WILL  
BEGIN TO DETERIORATE WITH CEILINGS LOWERING TO MVFR AND IN SOME  
AREAS IFR RANGE THROUGH THE REMAINDER OF THE TAF PERIOD. SHOWERS  
AND THUNDERSTORMS WILL INCREASE AFTER MIDNIGHT GOING THROUGH THE  
MORNING HOURS, LEADING TO OCCASIONAL VISIBILITY REDUCTIONS AS  
WELL. SOUTHERLY WINDS WILL BE GUSTY AT TIMES ESPECIALLY ACROSS  
EAST MS, WITH SOME GUSTS OVER 25 KT POSSIBLE BEGINNING OVERNIGHT.  
SHRA/TSRA COULD RE-INTENSIFY SOME BEFORE ENDING FROM WEST TO EAST  
DURING THE MID/LATE AFTERNOON. /DL/EC/  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
JACKSON 62 72 54 68 / 78 99 22 17  
MERIDIAN 62 71 54 70 / 50 100 53 17  
VICKSBURG 64 73 53 68 / 100 81 11 19  
HATTIESBURG 64 73 55 72 / 48 100 31 7  
NATCHEZ 63 73 52 69 / 100 86 8 12  
GREENVILLE 62 70 55 66 / 100 75 25 29  
GREENWOOD 62 70 56 65 / 84 88 40 32  
 

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

 
 

 
 
TW/DL/EC/BB  
 
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