Special Weather Statement, NWS Jackson, MS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
1105 AM CDT SAT JUL 7 2012

.UPDATE...

MINOR ADJUSTMENTS WERE MADE TO THE RAIN CHANCES FOR THIS
AFTERNOON...BUT THE OVERALL FORECAST IS GENERALLY ON TRACK THROUGH
TONIGHT. THE THUNDERSTORM FORECAST FOR THIS AFTERNOON CONTINUES TO BE
RATHER UNCERTAIN WITH LOWER LEVEL ANTICYCLONIC FLOW OVER THE
ARKLAMISS INHIBITING CONVECTIVE DEVELOPMENT FOR THE VERY NEAR TERM.
THE WESTWARD MOVING WEAK MID LEVEL CONVECTIVE VORTEX OVER AL IS
STRUGGLING TO INITIATE NEW SHOWERS/TSTM DOWNSTREAM IN EASTERN MS FOR
NOW AS IT ENCOUNTERS THE SUBSIDENT AIRMASS...BUT STILL EXPECT STRONG
INSOLATION WILL LEAD TO A VERY UNSTABLE AIRMASS WITH SFC-BASED CAPE
EXPECTED TO EXCEED 3500 J/KG FOR MUCH OF THE AREA. IN ADDITION...15
TO 20KTS OF MID LEVEL FLOW WILL SUPPORT MULTICELL STORM GROWTH AND
MOVEMENT MAKING FOR GREATER STORM COVERAGE. WILL CONTINUE TO MONITOR
CLOSELY FOR SIGNS OF BETTER CONVECTIVE DEVELOPMENT AND RELAY UPDATES
IN TSTM TIMING FORECAST. /EC/

&&

.PREV DISCUSSION... /ISSUED 327 AM CDT SAT JUL 7 2012/

SHORT TERM...LOW LEVEL CONVERGENCE/850 MB TROUGHING THAT EXTENDS
FROM AL INTO SERN ZONES WILL MAINTAIN GOOD LOW LEVEL FORCING OVER
SRN ZONES TODAY. THIS..ALONG WITH SEA BREEZE INFLUENCES...WILL
SUPPORT CONVECTION IN THE MOIST AIR MASS PARKED OVER THE AREA. HIGH
RES MODELS CONTINUE THE TREND OF TRACKING HEALTHY CONVECTION INTO
THE AREA FROM THE EAST DURING THE DAY...INITIATING STORMS EAST OF US
IN A REGION OF BETTER LOW LEVEL CONVERGENCE AND A MORE UNSTABLE AIR
MASS. AS UPPER RIDGING CONTINUES TO WEAKEN...THE AIR MASS TO THE N
AND E WILL BECOME A BIT MORE STABLE AND SHOULD ULTIMATELY STOP THE
PATTERN OF THE PAST FEW DAYS OF CONVECTION DEVELOPING TO OUR N AND E
AND PUSHING WWD INTO THE ARKLAMISS. HOWEVER...THE AIR MASS UPSTREAM
WILL REMAIN SOMEWHAT UNSTABLE TODAY SO WILL FOLLOW THE HIGH RES
SOLUTIONS FOR THIS AFTERNOON AND PAINT STORM CHANCES OVER CENTRAL
AND NRN AREAS AGAIN THIS AFTERNOON AND EVENING...ESPECIALLY FARTHER
EAST. AS A RESULT HAVE INCREASED MAV MOS POPS FOR NE/ECNTRL ZONES
FOR TODAY. PERSISTENT CONVECTION OCCURRING OVER ERN THIS MORNING
SUGGESTS THAT UPSTREAM AREAS REMAIN SUFFICIENTLY UNSTABLE ENOUGH TO
PRODUCE CONVECTION OR ASSOCIATED OUTFLOWS INTO ERN MS TODAY.

THE GFS IS THE OUTLIER AS FAR AS POPS ARE CONCERNED FOR TONIGHT WITH
LIKELY POPS IN THE NE. ITS HARD TO CUT THESE IN THE FACE OF
PERSISTENCE AND THE FACT THAT CONVECTION IS EXPECTED TO LINGER INTO
THE EVENING HOURS. HOWEVER CONSIDERING SLIGHTLY LOWER POPS/COVERAGE
PAINTED BY OTHER GLOBAL AND HI RES MODELS THESE POPS WILL BE TRIMMED
TO A MORE SCATTERED COVERAGE FOR THE EVENING AND FOLLOW THE AVG GFS
ENSEMBLE VALUES.

UPPER TROUGHING BEGINS TO AMPLIFY OVER THE AREA SUNDAY AND DIFFUSE
850 MB CYCLONIC FLOW EXPANDS NWD INTO THE FORECAST AREA...
PARTICULARLY WRN ZONES. ONCE AGAIN THE GFS PAINTS POPS FOR THE
SUNDAY NIGHT PERIOD MUCH HIGHER THAN THE OTHER MODELS. MORE
WIDESPREAD COVERAGE ADVERTISED BY THE GFS IS POSSIBLE CONSIDERING
THE AMPLIFYING UPPER TROUGH AND DEVELOPING SURFACE TROUGH FROM TX
INTO NRN AR BUT WITHOUT MORE FOCUSED FORCING INDICATED IN THE
FORECAST AREA AVG GFS ENSEMBLE POPS WERE USED FOR NOW.

HIGHS WILL CONTINUE TO COOL A LITTLE EACH DAY DUE TO GRADUALLY
DECREASING HEIGHTS...CLOUD COVER AND INCREASING RAIN CHANCES.

LAPSE RATES/VERTICAL TOTALS WILL BE HIGHEST OVER NRN ZONES THIS
AFTERNOON BUT FORCING WILL BE MOST ORGANIZED IN THE SOUTH. WITH
STILL RELATIVELY WARM TEMPERATURES AND PLENTY OF MOISTURE IN PLACE
WILL MENTION THE POSSIBILITY OF STRONG POSSIBLY SEVERE STORMS ACROSS
THE AREA FOR THIS AFTERNOON.

LONG TERM...SOME HEAT/DROUGHT RELIEF APPARENT IN THE LONG TERM WITH
INCREASED RAIN CHANCES AND MORE CLOUD COVER...RESULTING IN COOLER
TEMPERATURES.

INCREASED RAIN/CLOUD PATTERN WILL BE ONGOING MONDAY AS AN INVERTED
SUB-TROPICAL TROUGH PHASES WITH A L/WV TROUGH ACROSS THE GREAT
LAKES/OHIO VALLEY AND WEAKENS THE ONCE DEEP RIDGE OVER THE MID MS
VALLEY THIS WEEKEND. THIS WEAKNESS IS DEPICTED WELL ACROSS THE NWP
SUITE WITH NOTABLE H5 TROUGHING STRENGTH DIFFERENCES BETWEEN GFS/EC
AND THEIR HANDLING OF AN BNDRY NORTH OF THE REGION IN THE TUE-FRI
TIMEFRAME. WHILE AIRMASS SHOWERS/TSTORMS WILL OCCUR WELL AHEAD OF
THE BNDRY...A MAJORITY OF THE PRECIPITATION SHOULD BE FOCUSED ALONG
AND JUST SOUTH OF A BNDRY WHERE CONVERGENCE WILL BE GREATEST AS IT
SLOWLY APPROACHES THE REGION TUES/WED. SHOWER/TSTORM PROBABILITIES
WILL BE ON THE CHANCE TO LIKELY SIDE /40-70%/ DURING THE AFTNS WITH
AT LEAST SLIGHT CHANCE DURING THE OVERNIGHT PERIODS. WITH MLCAPE
/1500-2500 J/KG/...PWATS /1.8-2 IN/...AND SLOW STORM MOTIONS...
LOCALIZED FLASH FLOODING APPEARS TO BE THE GREATEST RISK DURING
AFTNS. A FEW STRONG TO SEVERE TSTORMS CAN NOT BE ENTIRELY RULED OUT
ALSO BUT LAPSE RATES/VERTICAL TOTALS LOOK MARGINAL.

BY THURS...OPS GFS DEPICTS DEEPER H5 TROUGHING OVER MID MS VALLEY
AND BRINGS THE NOW ELEVATED BNDRY THROUGH REGION BY FRI MRNG WHILE
EC IS WEAKER AND HANGS/WASHES IT OUT NORTH OF THE REGION. GFS MEAN
AND INDIVIDUAL ENSEMBLES SUPPORT OP GFS DURING THIS TIME-FRAME (WITH
GFSMEN ACTUALLY DEEPER THAN THE OPS GFS). LITTLE SFC DEWPOINT
REFLECTION LOOKS TO OCCUR WITH THIS BNDRY PASSAGE BUT DRIER AIR
LOOKS TO FILTER IN H85 AND HIGHER. THIS SHOULD REDUCE (BUT NOT
ELIMINATE) RAIN CHANCES THROUGH THE LATER PART OF THE WEEK FOR AT
LEAST NRN/CNTRL AREAS. MID/UPPER CLOUDINESS...IN ADDITION TO
INSTABILITY-DRIVEN CU/TCU DURING THE AFTNS...SHOULD KEEP INSOLATION
DOWN. THIS COUPLED WITH 16-19C H85 TEMPS...WILL PROVIDE RELIEF FROM
THE HEAT WITH HIGHS RANGING IN THE UPPER 80S-LOW 90S. IT COULD BE
FORESEEABLE THAT SOME HIGH TEMPS MAY BE SLIGHTLY BELOW AVG TOWARDS
THE END OF THE WEEK...ESPECIALLY IF RAIN/STORMS OCCUR BEFORE BEST
HEATING.

FOR FORECAST ELEMENTS...HIGHS WERE DROPPED BELOW GUIDANCE MOST AFTNS
BY 2-4 DEGREES WITH LOWS RAISED /70F OR GREATER/ UNDER THE CLOUDY
AND MOIST CONDS. POPS CAME IN HIGHER AND ACCEPTED IN MOST CASES WITH
SOME ADDITIONAL INCREASES PRIOR TO WED. /ALLEN/

&&

.AVIATION...VFR CONDS TO PREVAIL THRU THE DAY TODAY UNDER INCREASING
CU 4-6K FT. TSRA COVERAGE IS XPCTD TO INCREASE AFTER 18-20Z FROM E TO
W IMPACTING MOST OF THE AIRFIELDS THRU THE AFTN/INTO THE EVENING.
TIMING SPECIFICS ARE DIFFICULT TO PINPOINT SO STAY TUNED FOR UPDATES.
STRONG GUSTY WINDS/HAIL XPCTD INVOF CONVECTIVE ACTIVITY. A GENERAL
DECREASE IN STORMS WILL UNFOLD LATER THIS EVENING/OVRNGT HOWEVER
ISOLD/SCT SHWRS NOT OUT OF THE QUESTION HEADED INTO TOMORROW MORNING.
SFC WINDS TO REMAIN LGT AND GENERALLY SOUTHERLY TODAY. /BK/

&&

.FIRE WEATHER...
MANY COUNTIES/PARISHES AROUND THE ARKLAMISS REMAIN UNDER BURN BANS
AS MOST LOCATIONS ARE WELL BELOW NORMAL IN RAINFALL FOR THE PAST
MONTH. HOWEVER...AREAS OF RAINFALL HAVE OCCURRED OVER THE PAST FEW
DAYS IN MANY AREAS...AND THE NUMBER OF LOCATIONS RECEIVING DECENT
RAINFALL SHOULD CONTINUE TO INCREASE OVER THE NEXT FEW DAYS. THE
LONGER RANGE FORECAST HOLDS GOOD POTENTIAL FOR A PERIOD OF ABOVE
NORMAL RAINFALL AND COOLER TEMPERATURES NEXT WEEK. IF WEATHER
CONDITIONS UNFOLD AS EXPECTED THROUGH THE WEEKEND AND INTO NEXT
WEEK...IT IS POSSIBLE THAT FIRE DANGER WILL BE SIGNIFICANTLY REDUCED.

&&

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

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