182  
FXUS64 KJAN 181436  
AFDJAN  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE JACKSON MS  
936 AM CDT THU APR 18 2019  
   
UPDATE
 
 
UPDATED FOR MORNING DISCUSSION.  
 

 
   
DISCUSSION
 
 
A WIDESPREAD SEVERE WEATHER EPISODE IS STILL EXPECTED TODAY WITH  
ALL HAZARDS LIKELY. A STRONG SHORTWAVE TROUGH CURRENTLY OVER THE  
SOUTHERN PLAINS WILL CONTINUE TO LIFT NORTHEAST THROUGH THE LOWER  
MISSISSIPPI RIVER VALLEY TODAY. THE MAIN SURFACE LOW OVER NORTHERN  
MICHIGAN WILL CONTINUE TO LIFT THROUGH THE GREAT LAKES REGION WITH  
AN ATTENDANT COLD FRONT DRAPED THROUGH THE MISSISSIPPI VALLEY.  
SECONDARY CYCLOGENESIS IS ONGOING ALONG THE FRONTAL BOUNDARY OVER  
EAST TEXAS WITH A DEEPENING LOW PROGGED TO LIFT INTO NORTHERN  
MISSISSIPPI THROUGH THE DAY. WIDESPREAD SHOWERS AND THUNDERSTORMS  
ARE ALREADY ONGOING ACROSS PORTIONS OF THE DELTA INTO CENTRAL  
LOUISIANA. THE MAJORITY OF THIS ACTIVITY, ESPECIALLY ACROSS THE  
DELTA, REMAINS ELEVATED ABOVE A SLOWLY PROPAGATING COLD POOL.  
LITTLE ADDITIONAL FORWARD PROGRESS OF THE COLD POOL IS EXPECTED AS  
IT ENCOUNTERS STRENGTHENING LOW-LEVEL WIND FIELDS IN RESPONSE TO  
THE AFOREMENTIONED DEEPENING SURFACE LOW. WARM AND MOIST ADVECTION  
ACROSS THE CAPPED WARM SECTOR WILL HELP 1000-1500 J/KG OF MLCAPE  
TO BUILD THROUGH THE AFTERNOON BENEATH STRENGTHENING VERTICAL WIND  
SHEAR, ESPECIALLY IN THE 0-1KM LAYER.  
 
EARLY MORNING RUNS OF THE HI-RES CAM GUIDANCE CONTINUE TO DEPICT  
AN INTENSE QLCS MOVING THROUGH THE AREA LATE THIS MORNING THROUGH  
THE EARLY EVENING HOURS. ONGOING UPSTREAM CONVECTION IS EXPECTED  
TO CONGEAL INTO A SOLID LINE OF STORMS AS STRONG FORCING FOR  
ASCENT AND STOUT PRESSURE FALLS OVERSPREAD THE AREA. A SEMI-  
DISCRETE SUPERCELL OR TWO WILL ALSO BE POSSIBLE AHEAD OF THE LINE.  
FAVORABLE PARAMETER SPACE WILL BE SUPPORTIVE OF TORNADOES, BOTH  
LINE EMBEDDED AND IN ANY PRE-LINE SUPERCELLS, OF WHICH A FEW COULD  
BE STRONG, IN ADDITION TO DAMAGING WINDS OF 70-80MPH AND ISOLATED  
HAIL UP TO QUARTER SIZE. ANOMALOUS MOISTURE COMBINED WITH HEAVY  
RAINFALL RATES WILL ALSO LEAD TO FLASH FLOODING AS 2-4" OF RAIN  
WITH LOCALLY HIGHER AMOUNTS COULD FALL IN A SHORT AMOUNT OF TIME.  
THE ONGOING GRAPHICS REMAIN ON TRACK AND NO MAJOR CHANGES WERE  
NEEDED WITH THIS FORECAST UPDATE. /TW/  
 
PRIOR DISCUSSION BELOW:  
 
TODAY AND TONIGHT...CHANCES FOR SEVERE STORMS AND HEAVY RAINFALL  
RESULTING IN FLASH FLOODING, WILL BE POSSIBLE ACROSS THE ARKLAMISS  
FROM LATE THIS MORNING THROUGH EARLY THIS EVENING. THE MOST INTENSE  
STORMS WILL BE CAPABLE OF PRODUCING WINDS GUSTS OF 70-80 MPH, IN  
ADDITION TO TORNADOES, TO WHICH A STRONG TORNADO CANNOT BE RULED  
OUT, AND HAIL TO THE SIZE OF QUARTERS. ALSO, HIGH RAINFALL RATES IN  
A SHORT AMOUNT OF TIME AND THE POTENTIAL FOR TRAINING STORMS, COULD  
RESULT IN FLASH FLOODING ACROSS THE FORECAST AREA WHERE SOILS ARE  
ALREADY SATURATED FROM RECENT HEAVY RAINS. RAINFALL TOTALS ON THE  
ORDER OF 2-4 INCHES WILL BE POSSIBLE ACROSS THE FORECAST AREA, WITH  
LOCALIZED HIGHER AMOUNTS POSSIBLE. AS A RESULT, A FLASH FLOOD WATCH  
IS IN EFFECT UNTIL 10 PM TONIGHT FOR THE ENTIRE CWA.  
 
A POTENT AND STILL DEEPENING MID/UPPER LEVEL LOW PRESSURE SYSTEM,  
WILL DIG SOUTH AND PIVOT EAST INTO THE LOWER MISSISSIPPI RIVER  
VALLEY OVER THE NEXT 24 HOURS. THE RESULTING INCREASED FLOW  
THROUGHOUT THE ATMOSPHERE OVER THE REGION AHEAD OF IT, WILL CAUSE  
ANOMALOUS MOISTURE INCREASE ACROSS THE CWA, RESULTING IN INCREASED  
INSTABILITY ACROSS THE FORECAST AREA THROUGH THE LATE MORNING AND  
AFTERNOON HOURS TODAY. WIND SHEAR VALUES WILL INCREASE ACROSS THE  
FORECAST AREA DURING THIS TIME AS WELL.  
 
MEANWHILE AT THE SURFACE, THE SOUTHEAST DIGGING MID/UPPER LEVEL LOW  
WILL BE RESPONSIBLE FOR CAUSING A STRONG COLD FRONT TO DEVELOP  
ACROSS THE SOUTHERN PLAINS AND STRETCHING SOUTH INTO SOUTH TEXAS.  
THIS FRONT WILL BEGIN SHIFTING EAST TOWARDS THE ARKLAMISS THROUGH  
THE DAY. HOWEVER AHEAD OF THIS, A LARGE EAST ADVANCING OUTFLOW  
BOUNDARY STRETCHES SOUTHWEST FROM THE MISSOURI BOOTHEEL, THROUGH THE  
ARKLATEX, AND INTO SOUTH TEXAS.  
 
AS TODAY PROGRESSES, THIS COLD POOL(S) WILL CONTINUE ITS EAST  
ADVANCEMENT, BUT SHOULD WEAKEN AT BIT THROUGH THE EARLY MORNING  
HOURS DUE TO A DIURNAL HEATING MINIMUM. HOWEVER, AS HEATING ENSUES  
FROM THE LATE MORNING THROUGH THE AFTERNOON HOURS, INSTABILITY, WIND  
SHEAR, AND ASCENT INCREASE ACROSS THE FORECAST AREA AS A SURFACE LOW  
DEVELOPS AND LIFTS NORTHEAST THROUGH THE CWA. THIS WILL RESULT IN  
ROBUST THUNDERSTORMS DEVELOPING AND BECOMING ORGANIZED OUT AHEAD OF  
THE AFOREMENTIONED COLD FRONT. IT'LL AGAIN BE DURING THIS TIME,  
LATE MORNING THROUGH EARLY EVENING, WHEN THE CHANCES FOR SEVERE  
THUNDERSTORMS AND FLASH FLOODING INCREASE ACROSS THE ENTIRE  
ARKLAMISS.  
 
HIGH-RES MODELS ARE IN GOOD AGREEMENT AND CONTINUE TO INDICATE THE  
OVERALL MODE OF CONVECTION BEING IN THE FORM OF AN INTENSE QLCS  
SHIFTING EAST ACROSS THE FORECAST AREA. WITH BOWING SEGMENTS  
EXPECTED WITHIN THIS LINE, DAMAGING STRAIGHT-LINE WINDS ARE  
EXPECTED, IN ADDITION TO THE POTENTIAL FOR TORNADOES SPINNING UP  
ALONG BREAKS IN THE LINE. SOME MODELS ALSO CONTINUE TO INDICATE THE  
POTENTIAL FOR DISCRETE SUPERCELLS LIFTING NORTHEAST ACROSS MAINLY  
SOUTHERN MISSISSIPPI AHEAD OF THE QLCS.  
 
THE TIGHTENING PRESSURE GRADIENT OVER THE AREA BOTH PRE AND POST-  
FRONTAL, WILL RESULT IN GUSTY SOUTHERLY WINDS TODAY AND GUSTY  
NORTHERLY WINDS THIS EVENING AND OVERNIGHT. SURFACE WINDS COULD  
BECOME SUSTAINED BETWEEN 15-25 DURING THIS TIME, WITH GUSTS BETWEEN  
25-35 MPH POSSIBLE. AS A RESULT, I'VE INTRODUCED A "LIMITED" THREAT  
FOR STRONG GRADIENT WINDS ACROSS THE ENTIRE ARKLAMISS INTO THE HWO  
FOR TODAY INTO TONIGHT. /19/  
 
FRIDAY THROUGH SATURDAY NIGHT...A DEEPENING UPPER TROUGH WILL DIG  
SOUTHWARD THROUGH THE MS VALLEY AND EVENTUALLY CLOSE OFF TO FORM  
AN IMPRESSIVE LOW OVER THE TN VALLEY. RESULTING COLD CYCLONIC  
FLOW ABOVE THE ARKLAMISS REGION WILL SUPPORT SCATTERED TO NUMEROUS  
SHOWERS FRIDAY AS SUBSTANTIAL INSTABILITY DEVELOPS EVEN WITH  
AFTERNOON SURFACE TEMPERATURES ONLY IN THE MID/UPPER 50S. SOME  
THUNDERSHOWERS AND PERHAPS EVEN SMALL HAIL COULD DEVELOP DURING  
THE AFTERNOON GIVEN THE STEEP LAPSE RATES AND LOW FREEZING LEVELS.  
IN ANY CASE, EXPECT MUCH BELOW NORMAL TEMPERATURES FOR THIS TIME  
OF THE YEAR WITH BREEZY NORTHWESTERLY SURFACE WIND AND  
CLOUDS/PRECIP MAKING FOR UNCOMFORTABLE MID APRIL CONDITIONS. AS  
WE GO INTO THE WEEKEND, PRECIP CHANCES WILL END AND CONDITIONS  
WILL IMPROVE SIGNIFICANTLY WITH MUCH MILDER DAYTIME TEMPERATURES,  
BUT NIGHTS WILL REMAIN CHILLY AS CLEARING SKIES/LIGHT WIND  
COMBINE TO BRING IDEAL COOLING WITH LOWS DROPPING WELL INTO THE  
40S.  
 
SUNDAY THROUGH NEXT WEDNESDAY NIGHT...MID/UPPER LEVEL RIDGING WILL  
INCREASE OVER THE ARKLAMISS REGION SUPPORTING WARMER TEMPERATURES  
AND CONTINUED MOSTLY DRY WEATHER THROUGH EARLY WEEK, BUT THERE ARE  
INDICATIONS THAT A SLOW-MOVING SHORTWAVE TROUGH CROSSING THE  
SOUTHERN PLAINS MAY EVENTUALLY INCREASE RAIN CHANCES OVER THE  
ARKLAMISS BY THE TIME WE GET TO WEDNESDAY AND WED NIGHT. /EC/  
 

 
   
AVIATION
 
 
12Z TAF DISCUSSION:  
A MIX OF MVFR/VFR CEILINGS ARE BEING OBSERVED AT TAF SITES THIS  
MORNING, AS A RESULT OF PATCHY LOW STRATUS ACROSS THE AREA.  
INCREASING SOUTHERLY WINDS WILL CONTINUE TO PROMOTE LOW-LEVEL  
MOISTURE INCREASE ACROSS THE REGION TODAY, WITH MVFR CEILINGS  
STEADILY BECOMING MORE PREVALENT THROUGH THE MORNING. FOR TODAY, A  
STRONG STORM SYSTEM WILL BRING ANOTHER BOUT OF SEVERE STORMS TO THE  
ARKLAMISS FROM AS EARLY AS 16Z THIS MORNING ACROSS THE DELTA REGION,  
AND ENDING BY 02Z THIS EVENING ACROSS EAST AND SOUTHEAST  
MISSISSIPPI. DAMAGING WIND GUSTS, LARGE HAIL, AND TORNADOES WILL ALL  
BE POSSIBLE AS STORMS RACE EAST ACROSS THE REGION THROUGH MUCH OF  
THE AFTERNOON HOURS, IN ADDITION TO TORRENTIAL DOWNPOURS. AHEAD OF  
THIS LINE THROUGH THE FORECAST PERIOD, WINDS WILL BE GUSTY FROM THE  
SOUTH, ESPECIALLY ACROSS THE DELTA WHERE WINDS COULD BECOME  
SUSTAINED AROUND 22 KNOTS AND GUSTING TO AROUND 30 KNOTS AT TIMES.  
BEHIND THE FRONT, WINDS WILL BECOME NORTHWESTERLY WHILE REMAINING  
BREEZY INTO THURSDAY NIGHT. /19/  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
JACKSON 75 49 59 41 / 100 57 57 8  
MERIDIAN 79 50 60 40 / 100 97 53 20  
VICKSBURG 73 50 62 42 / 100 47 42 4  
HATTIESBURG 78 51 63 41 / 100 97 36 7  
NATCHEZ 74 49 62 42 / 100 47 28 2  
GREENVILLE 70 50 59 44 / 100 51 36 4  
GREENWOOD 73 50 57 40 / 100 60 62 9  
 

 
   
JAN WATCHES/WARNINGS/ADVISORIES
 
 
MS...FLASH FLOOD WATCH THROUGH THIS EVENING FOR MSZ018-019-025>066-  
072>074.  
 
LA...FLASH FLOOD WATCH THROUGH THIS EVENING FOR LAZ007>009-015-016-  
023>026.  
 
AR...FLASH FLOOD WATCH THROUGH THIS EVENING FOR ARZ074-075.  
 

 
 

 
 
TW/19/EC  
 
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