Area Forecast Discussion
Issued by NWS Jackson, MS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS64 KJAN 181706 AAB
AFDJAN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON MS
1200 PM CDT SAT APR 18 2015

.UPDATE... IN THE PAST HOUR OR TWO IT IS BECOMING INCREASINGLY
APPARENT THAT DEEP CONVECTION STRETCHING FROM THE NORTH CENTRAL GULF
TO THE WESTERN GULF IS REALLY GOING TO HAMPER VIGOROUS THUNDERSTORM
DEVELOPMENT OVER THE LOWER MS VALLEY LATE TODAY INTO THIS EVENING.
STILL NOT CONVINCED THAT MOISTURE...LIFT AND INSTABILITY INGREDIENTS
WILL NOT BE ENOUGH AT LEAST ALONG AND SOUTHEAST OF THE NATCHEZ TRACE
CORRIDOR TO GET A FEW SEVERE STORMS GOING EVENTUALLY WITH A HEAVY
RAIN THREAT PERSISTING AS WELL. FOR THAT REASON WE HAVE DOWNPLAYED
SEVERE POTENTIAL IN ALL AREAS THROUGH THE REST OF TODAY AND INTO
TONIGHT IN ALL AREAS (ALTHOUGH KEEPING SOME RISK GOING IN THE
SOUTHEAST HALF OF THE CWA). WE WILL WATCH TRENDS CLOSELY TO ADJUST
WITH THE AFTERNOON UPDATE. /BB/

&&

.PREV DISCUSSION... /ISSUED 1025 AM CDT SAT APR 18 2015/

UPDATE... THINGS THIS MORNING ARE EVOLVING GENERALLY AS
ANTICIPATED...ALTHOUGH QUESTION MARKS GOING INTO LATE TODAY STILL
PERSIST IN SOME MEASURE OWING TO THUNDERSTORMS ANCHORED TO THE SE LA
COAST. THESE STORMS WERE PREVIOUSLY SPREADING A LIGHT RAIN SHIELD
INTO MY SOUTHERN ZONES...BUT THE NORTHWARD EXTENT OF THIS PRECIP HAS
SHRUNK IN THE LAST FEW HOURS. ALSO...VIGOROUS STORMS JUST SOUTH OF
THE COAST HAVE BEEN GRADUALLY LOSING COVERAGE SINCE DAYBREAK AND
THEY SHOULD EBB QUICKLY INTO MIDDAY AS UPPER JET PULLING BACK TO THE
WEST REMOVES MUCH OF THE UPPER LEVEL SUPPORT. HOWEVER...IF SAID
EVOLUTION DOES NOT COME TO PASS WITH HASTE THEN MOISTURE TRANSPORT
BLOCKING AND CLOUD COVER INTO SOME OF MY SOUTHERN ZONES WILL HINDER
POTENTIAL FOR VIGOROUS INLAND THUNDERSTORM FORMATION AS WE GO INTO
THIS AFTERNOON.

BUT ASSUMING THE LATTER CAVEAT IS NOT AN ISSUE...LATEST HRRR AND
DOWNSCALED NAM RUNS POINT TO WORRISOME STORMS MOVING INTO MY
SOUTHERN ZONES (ESPECIALLY SOUTH CENTRAL AND SE MS) ZONES FROM MID
AFTERNOON THROUGH MID EVENING. ATMOSPHERIC LAPSE RATES WILL MAINLY
BE AT OR LESS THAN 6 C/KM IN THE H700-H500 LAYER BUT MLCAPE PEAKING
OVER 1000 J/KG SHOULD BE SUFFICIENT GIVEN EXPECTED LOW LEVEL AND
DEEP LAYER SHEAR TO PRODUCE ORGANIZED STORMS. ONCE AGAIN...A FEW
TORNADOES CANNOT BE RULED OUT.

THERE IS NOT ENOUGH EVIDENCE YET TO GO CHANGING THE PREVIOUS
FORECAST AND SEVERE WEATHER EXPECTATIONS MUCH. HOWEVER...WE WILL BE
WATCHING TRENDS CLOSELY OVER THE NEXT FEW HOURS AND WILL SEE IF VERY
RECENT HRRR HINTS THAT SEVERE RISK WILL BE STRONGLY FOCUSING
SOUTHEAST OF THE NATCHEZ TRACE APPEAR SOLID. IF THAT IS THE CASE WE
WILL UPDATE ACCORDINGLY...BUT EVEN IF WE DO FOCUS THE SEVERE RISK
EVEN MORE CONSIDERABLY IN SOUTHERN ZONES THE RISK OF LOCALIZED
FLOODING PROBLEMS STILL LOOKS TO EXTEND ACROSS A MUCH LARGER PORTION
OF THE FORECAST AREA. /BB/

AVIATION...IFR CATEGORY STRATUS PREVAILS ACROSS THE TAF SITES THIS
MORNING WITH SHOWERS MOVING ACROSS HBG. EXPECT THESE CONDITIONS TO
PERSIST UNTIL LATE MORNING/EARLY AFTERNOON BEFORE FINALLY MIXING
OUT. SHRA WILL MOSTLY CONFINED TO LOCATIONS SOUTH OF THE HEZ-HBG
CORRIDOR THIS MORNING AS A CONVECTIVE COMPLEX SLIDES EASTWARD ALONG
THE COAST...BUT A NEW ROUND OF SHRA/TSRA IS EXPECTED BY MID/LATE
AFTERNOON LASTING INTO THE EVENING WITH AN APPROACHING DISTURBANCE.
THERE MAY BE A WINDOW OF OPPORTUNITY FOR BETTER FLYING CONDITIONS
DURING THE EARLY AFTERNOON...FOLLOWED BY POOR FLYING CONDITIONS
PERSISTING FROM MID/LATE AFTERNOON THROUGH THE EVENING.
/EC/15/

PREV DISCUSSION... /ISSUED 454 AM CDT SAT APR 18 2015/

SHORT TERM...TODAY THROUGH TONIGHT...AN ACTIVE WEATHER WEEKEND IS
IN STORE AS TWO ROUNDS OF SEVERE WEATHER ARE EXPECTED TO IMPACT THE
ARKLAMISS. THE FIRST ROUND WILL BE INITIATED BY INCREASINGLY
FAVORABLE CYCLONIC AND SHEARED FLOW DEVELOPING OVER THE LOWER MS
VALLEY REGION LATER THIS AFTERNOON AND EVENING. THE CONVECTIVE SYSTEM
CURRENTLY MOVING EAST ALONG THE THE LA COAST WILL DELAY TIMING OF THE
MORE SIGNIFICANT THUNDERSTORM ACTIVITY UNTIL MID/LATE AFTERNOON...BUT
VERY MOIST AND UNSTABLE AIR WITH PRECIPITABLE WATER VALUES > 1.75
INCHES AND ML CAPE NEAR 1000 J/KG SHOULD BE AVAILABLE FOR VIGOROUS
CONVECTIVE DEVELOPMENT AT THAT TIME. WITH DEEP LAYER AND LOW LEVEL
SHEAR ON THE INCREASE...STILL EXPECT ORGANIZED STORMS TO DEVELOP WITH
THE MOST FAVORABLE SET-UP FOR SEVERE WEATHER AND HEAVY RAINFALL
ALONG/SOUTH OF THE I-20 CORRIDOR...BUT WILL SAY THAT CONFIDENCE IS A
LITTLE SHAKIER NOW ON THIS SCENARIO BASED ON RECENT HIGH RES GUIDANCE
TRENDS. IF THE NEXT ROUND OF CONVECTIVE DOES NOT MATERIALIZE AS
ANTICIPATED DUE TO THE MORNING CONVECTION...OR IF IT DEVELOPS FARTHER
EAST...THEN IT IS POSSIBLE THAT MORE ROBUST CONVECTION WOULD IMPACT
NORTHERN PORTIONS OF THE ARKLAMISS AND THIS COULD ALLOW THE SEVERE
WEATHER/HEAVY RAINFALL THREAT TO SHIFT FARTHER NORTH AS WELL. STAY
TUNED FOR UPDATES TO THIS FORECAST LATER THIS MORNING AS CONVECTIVE
EVOLUTION HOPEFULLY BECOMES A LITTLE MORE CLEAR. /EC/

SUNDAY THROUGH SUNDAY NIGHT...MODELS FOR SUNDAY CONTINUE TO SUPPORT
THE RISK FOR SEVERE STORMS ALONG WITH SOME POTENTIAL FOR A HIGHER END
EVENT. WHAT IS STARTING TO BECOME MORE CLEAR IS MUCH OF THE DAY LOOKS
TO BE IN A LULL FROM CONVECTION AFTER MORNING ACTIVITY DEPARTS TO THE
EAST AND THE ROUND OF STORMS WILL BE MORE FOCUSED LATER BETWEEN A 5PM
TO 3AM WINDOW. IN THE WAKE OF THE SAT SYSTEM...MUCH STEEPER LAPSE
RATES WILL SPREAD OVER THE AREA (7.0 TO 7.5 C/KM)(29-31C VERTICAL
TOTALS). ALOFT MUCH COLDER TEMPS WILL MOVE IN WITH H5 READINGS OF -15
TO - 16C. THIS WILL ALL SUPPORT SBCAPE OF 2000-3000 J/KG AS SFC
HEATING REACHES AROUND 80 DEGREES. THIS WILL ALL SUPPORT VIGOROUS
STORMS WITH ROBUST UPDRAFTS. CONCURRENT WITH THIS WILL BE AN OVERALL
DRIER ATMOSPHERE COLUMN AS WELL WITH PWS AROUND 1.2 INCHES. THIS WILL
LEND TO KEEPING STORMS MORE DISCRETE ALONG WITH AN EASTWARD DEEP
LAYER (0-6KM) SHEAR VECTOR OF 40-50KTS. EXPECTATIONS ARE FOR NOT MANY
(ISO/SCT) SUPERCELLS THAT WILL PACK QUITE THE PUNCH. LARGE HAIL >
GOLF BALL SIZE APPEARS VERY POSSIBLE ALONG WITH DAMAGING WINDS WHICH
ALSO COULD BE HIGHER END. DUE TO THIS POSSIBILITY OF SEEING
SIGNIFICANT TYPE WEATHER (>2 IN HAIL)...WILL UP OUR OUTLOOK TO SIG
OVER A DECENT PORTION OF THE NW. ELSEWHERE THE OUTLOOK WILL REMAIN
SIMILAR AS STORMS MAY LOSE SOME POTENCY AS THEY PUSH FURTHER EAST AND
GET LATER INTO THE OVERNIGHT. /CME/

LONG TERM...MONDAY THROUGH SATURDAY....MONDAY MORNING THE LARGE
CLOSED LOW IS EXPECTED TO BE CENTERED OVER THE UPPER MISSISSIPPI
VALLEY WITH ASSOCIATED LARGE AMPLITUDE UPPER LEVEL TROUGHING OVER
THE EASTERN TWO THIRDS OF THE CONUS. MODELS AGREE THAT THE
ASSOCIATED SURFACE LOW WILL BE OVER THE WESTERN GREAT LAKES REGION
MONDAY MORNING BUT THERE ARE TIMING DIFFERENCES WITH THE TRAILING
COLD FRONT THAT IS EXPECTED TO BE OVER SOUTHEAST MISSISSIPPI.
CONSENSUS PLACES THIS COLD FRONT AND THE BULK OF THE PRECIPITATION
JUST SOUTHEAST OF OUR CWA AT DAYBREAK BUT WL MAINTAIN LOW CHANCES OF
LIGHT RAIN IN OUR NORTHEAST THROUGH MID MORNING AS A WEAK SHORTWAVE
PASSES OVER OVERHEAD. DRY WEATHER IS EXPECTED AREAWIDE BY NOON.
SLIGHTLY COOLER AND MUCH DRIER AIR WILL FILTER INTO OUR CWA MONDAY
KNOCKING DEW POINTS INTO THE 40S DURING THE AFTERNOON. DRY WEATHER
IS EXPECTED TO LAST OVER OUR CWA THROUGH TUESDAY AS A SURFACE HIGH
MOVES EAST ACROSS OUR AREA. THIS SURFACE HIGH WILL SHIFT EAST
WEDNESDAY AND THE RESULTING RETURN FLOW WILL INCREASE MOISTURE TO
SUPPORT RAIN CHANCES AGAIN FROM THE WEST BY WEDNESDAY AFTERNOON.
WARMER THAN NORMAL TEMPERATURES AND GREATER RAIN CHANCES ARE
EXPECTED FOR THE END OF THE WEEK BUT THERE ARE SIGNIFICANT
DIFFERENCES IN THE MODELS WITH SOME MAIN FEATURES. THE NORTHERN
CLOSED LOW WILL MOVE SLOWLY EAST ACROSS THE GREAT LAKES REGION
TUESDAY AND WEDNESDAY AND BE OVER THE NEW ENGLAND STATES BY FRIDAY.
THIS LOW WILL TRY TO HELP SUPPORT ANOTHER COLD FRONT DROPPING INTO
OUR CWA THURSDAY INTO FRIDAY BUT INDUCED SHORTWAVE RIDGING
DOWNSTREAM OF A SECOND CLOSED LOW MOVING OVER THE DESERT SOUTHWEST
THURSDAY LOOKS TO IMPEDE THE COLD FRONT INTO OUR AREA. SHORTWAVES
ROUNDING THE BASE OF THE SOUTHERN CLOSED LOW LOOK TO COMBINE WITH
INCREASING MOISTURE AND DAYTIME HEATING FOR A ROUND OF CONVECTION
THURSDAY AND FRIDAY. BOTH GFS AND ECMWF OPEN THE CLOSED LOW AND
BRING THE REMAINING SHORTWAVE TROUGH ACROSS OUR REGION SATURDAY BUT
DIFFER ON THE SURFACE FEATURES WITH THE GFS DEPICTING A MUCH DEEPER
LOW AND STRONGER COLD FRONT ACROSS OUR AREA. FOR NOW...GREATEST POPS
THROUGH THE LONG TERM WILL BE CARRIED FRIDAY AND FRIDAY NIGHT. /22/

&&

.PRELIMINARY POINT TEMPS/POPS...
JACKSON       75  64  81  61 /  84  66  31  39
MERIDIAN      76  65  82  64 /  71  83  37  34
VICKSBURG     73  64  81  59 /  86  49  34  46
HATTIESBURG   77  66  84  65 /  86  78  33  28
NATCHEZ       75  64  82  60 /  91  54  28  42
GREENVILLE    73  63  81  57 /  58  47  49  57
GREENWOOD     74  63  79  59 /  56  55  44  56

&&

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

$$

JAN


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.