600  
FXUS64 KJAN 201100 AAA  
AFDJAN  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE JACKSON MS  
600 AM CDT SUN MAY 20 2018  
   
UPDATE
 
 
UPDATED FOR 12Z AVIATION DISCUSSION  
 

 
   
AVIATION
 
 
12Z TAF DISCUSSION:  
 
TAF SITES ARE LOOKING MAINLY VFR THIS MORNING, BUT CONDITIONS WILL  
DETEORIORATE AROUND MANY SITES THIS AFTERNOON DUE TO A GOOD DEAL  
OF THUNDERSTORMS POPPING UP IN THE HEAT OF THE DAY. SOME VERY  
LOCALIZED IFR CONDITIONS AND BRIEF GUSTY WINDS WILL BE POSSIBLE IN  
THE AFTERNOON AT ALL SITES IN ASSOCIATION WITH ANY THUNDERSTORMS.  
OTHERWISE, WINDS AWAY FROM STORMS TODAY WILL BE RATHER LIGHT AND  
VARIABLE WITH SOME FLIGHT CAT RESTRICTIONS POSSIBLE EARLY MONDAY  
MORNING DUE TO A COMBINATION OF CEILING AND VISIBILITY  
RESTRICTIONS. /BB/  
 

 
   
DISCUSSION
 
 
TODAY AND TONIGHT:  
 
THERE WAS QUITE A BIT THUNDERSTORM ACTIVITY OVERNIGHT IN PORTIONS  
OF SOUTHEASTERN MS AS THE SLOW EVOLUTION TOWARD A WETTER PATTERN  
WAITED UNTIL SUNDOWN YESTERDAY TO BEGIN IN OUR REGION. ABOVE  
AVERAGE WARMTH AND HUMIDITY, COMBINED WITH RELATIVELY CHILLY  
TEMPERATURES ALOFT, CREATED A GOOD DEAL OF INSTABILITY THAT ONLY  
REQUIRED SUBTLE CONVERGENCE TO "BREAK THE LID" THAT HAS BEEN  
LARGELY KEEPING MOST OF THE CONVECTION AT BAY THE LAST FEW DAYS.  
 
TODAY THE "LID" HOLDING DOWN DEEP CONVECTION IS EXPECTED TO GIVE  
WAY ACROSS THE ENTIRE REGION (NOT JUST IN SOUTHEASTERN MS) DURING  
THE AFTERNOON AND EVENING HOURS. SINCE OUR EARLY TRANSITION INTO A  
SUMMER-LIKE PATTERN (DEVOID OF MAJOR SYNOPTIC FORCING MECHANISMS  
AND WIND SHEAR) HAS OCCURRED, WE ONLY EXPECT SUBTLE FACTORS TO  
HELP TIP THE SCALES TOWARD LOTS OF THUNDERSTORM ACTIVITY,  
ESPECIALLY SINCE MOISTURE CONTINUES TO GRADUALLY INCREASE. NOT TO  
GET INTO THE WEEDS OVER MUCH, BUT THE MAIN WEAK POSITIVE FACTORS  
FOR CONVECTIVE DEVELOPMENT (ASIDE FROM LOTS OF INSTABILITY) LOOK  
TO BE FAVORABLE DIVERGENCE IN JET-LEVEL WIND FIELDS AND MINOR  
LOWER LEVEL WIND AND MOISTURE CONVERGENCE AS EASTERLY FLOW  
IMPINGES FROM AL. HREF GUIDANCE SUGGESTS PEAK WORKING CAPE LEVELS  
BY EARLY AFTERNOON SHOULD RANGE FROM AT LEAST 2500 TO 3500 J/KG  
WITH SURFACE TEMPERATURES RANGING FROM 88 TO 92 DEGREES.  
RELATIVELY STEEP LAPSE RATES AND SOME DRY AIR AVAILABLE WELL ALOFT  
WILL INCREASE THE RISK FOR SOME MICROBURSTS AND LARGER SCALE  
DOWNBURSTS WITH SLIGHTLY ORGANIZED LINE SEGMENTS. GIVEN THE  
INGREDIENTS AVAILABLE IT WOULD BE SURPRISING IF THERE WERE NOT AT  
LEAST SEVERAL SEVERE STORMS THIS AFTERNOON SO WE HAVE GONE AHEAD  
AND INCLUDED A LOCAL MARGINAL SEVERE RISK IN OUR HWO AND GRAPHICS.  
THE MAIN RISK WILL BE DAMAGING WIND GUSTS, ALTHOUGH SOME HAIL  
CERTAINLY CANNOT BE RULED OUT.  
 
SOME CONVECTION WILL ALMOST CERTAINLY LINGER WELL INTO THE  
EVENING, WITH CAMS GUIDANCE SUGGESTING THIS IS MORE LIKELY ACROSS  
PORTIONS OF EASTERN MS. BUT BY LATE TONIGHT WE ANTICIPATE  
CONDITIONS WILL BE MAINLY DRY WITH MAYBE A BIT OF PATCHY FOG IN  
AREAS WHERE DOWNPOURS ARE RECEIVED TODAY. LOWS BY DAYBREAK MONDAY  
MAY BE A TOUCH COOLER THAN THIS MORNING, CONSIDER THE INFLUENCE OF  
LATTER DAY COOLING PRECIPITATION. /BB/  
 
MONDAY THROUGH NEXT SATURDAY:  
 
THE SUMMER-TYPE PATTERN WILL BE THE NORM ACROSS THE FORECAST AREA  
THROUGHOUT THIS PORTION OF THE FORECAST. OFF AND ON PERIODS OF  
WEAK TROUGHING AND RIDGING ALOFT, WEAK FLOW ALOFT, WARM  
TEMPERATURES, AND PLENTY OF MOISTURE, WILL RESULT IN MAINLY  
DIURNAL CHANCES FOR SHOWERS AND STORMS IN THE 30- 50% RANGE EACH  
AFTERNOON. CONVECTION EACH DAY LOOKS SCATTERED IN NATURE. WHERE  
THE BEST CHANCES FOR CONVECTION EACH DAY CONTINUES TO LOOK TO  
LARGELY DEPEND UPON WHERE ANY LINGERING OUTFLOW BOUNDARIES FROM  
THE PREVIOUS DAY'S CONVECTION RESIDES. ALTHOUGH THESE BETTER RAIN  
CHANCES WILL AGAIN FALL DURING THE HEAT OF THE DAY, SOME  
CONVECTION WILL LIKELY LINGER A FEW HOURS INTO THE EVENING  
PERIODS. WHILE CONFIDENCE IS CURRENTLY QUITE LOW IN ANY ORGANIZED  
SEVERE STORMS, AN ISOLATED STRONG TO POTENTIALLY SEVERE STORM  
CANNOT BE RULED OUT EACH AFTERNOON. GUSTY WINDS WILL BE THE  
PRIMARY CONCERN WITH SUCH STORMS. LOCALLY HEAVY DOWNPOURS AND  
FREQUENT LIGHTNING CAN ALSO BE EXPECTED.  
 
AS ELUDED TO ABOVE, WARM CONDITIONS WILL PERSIST AREAWIDE THROUGH  
THE PERIOD. HIGHS EACH DAY LOOK TO PEAK TO AROUND THE 90 DEGREE  
MARK, BUT SCATTERED CONVECTION EACH AFTERNOON COULD HAVE A LARGE  
BEARING ON WHETHER TEMPERATURES WARM THAT MUCH. AGAIN, WHILE MOST  
OF THE CONVECTION EACH DAY WILL DISSIPATE DURING THE EVENING HOURS  
AS DAYTIME HEATING IS LOST, SOME LINGERING CLOUDS WILL BE PRESENT  
ACROSS THE REGION DURING THE OVERNIGHT HOURS. LOWS WILL REMAIN  
MILD AS THEY RANGE FROM THE MID 60S TO LOWER 70S. /19/  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
JACKSON 88 67 89 68 / 57 29 51 22  
MERIDIAN 90 67 88 65 / 43 50 47 23  
VICKSBURG 90 68 90 68 / 44 25 51 23  
HATTIESBURG 89 66 89 67 / 49 39 52 26  
NATCHEZ 90 67 89 69 / 45 31 51 24  
GREENVILLE 90 71 89 70 / 54 34 50 22  
GREENWOOD 90 69 90 68 / 39 34 52 19  
 

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

 
 

 
 
19/BB  
 
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