Severe Thunderstorm Warning 499, NWS Jackson, MS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
240 PM CDT WED AUG 2 2000

LOOKING AT SATELLITE VAPOR IMAGERY...A STATIONARY UPPER TROF
/ASSOCIATED SHEAR AXIS...EXTENDED OVER THE MISSISSIPPI VALLEY.
IT ALSO SHOWED GOOD MOISTURE OVER THE SOUTHEAST HALF OF THE
REGION...WHERE SCATTERED CONVECTION WAS TAKING PLACE.  THE
STATIONARY UPPER LOW ASSOCIATED WITH THIS TROF WAS OVER THE GREAT
LAKES. A WEAK BOUNDARY WAS NOTED ACROSS THE NORTH HALF.

MOVING TO THE SHORTRANGE MODELS. THE MESO-ETA KEEPS THE STATIONARY
UPPER TROF OVER THE REGION THROUGH FRIDAY AFTERNOON. A SERIES OF
SHORTWAVES WILL ROTATE AROUND THE TROF...BUT THE TRACKING OF
SHORTWAVES AND FOCUS ON OUTFLOW BOUNDARIES WILL CONTINUE TO BE
DIFFICULT TO FORECAST. MEAN MOISTURE WILL BE CONFINED TO THE
SOUTHEAST THROUGH THURSDAY...BEFORE DEVELOPING ACROSS THE NORTH
THURSDAY NIGHT INTO FRIDAY. IT SPREAD ACROSS THE REST OF THE REGION
ON FRIDAY NIGHT. CROSS SECTIONS CONFIRMS THAT MEAN MOISTURE WILL
DEEPEN ACROSS THE REGION THURSDAY NIGHT INTO FRIDAY. LOOKING AT THIS
AFTERNOONS PRECIP COVERAGE IN THE SOUTHEAST...IT DID NOT FAIR VERY
WELL IN COVERAGE OR AMOUNTS. FOR THIS EVENING ITS PAINTS A FEW
SHOWERS OVER WEST MISSISSIPPI...WHICH IS UNREASONABLE. ONCE AGAIN
MODELS ARE HAVING TROUBLE TRACKING MESO LEVEL ELEMENTS. ON THURSDAY
IT KEEPS THE FORECAST AREA DRY...BEFORE DEVELOPING SOME PATCHY
ACTIVITY IN THE WEST AND NORTH THURSDAY NIGHT. ON FRIDAY IT DEVELOPS
SOME CONVECTIVE ACTIVITY IN THE NORTH. THE UPPER JET WILL MOVE
ACROSS THE REGION DURING THE PERIOD. ON THE VERTICAL VELOCITY FRONT
THE SIGNATURES WILL BE RATHER WEAK...EXCEPT FOR THE NORTH ON
FRIDAY... THROUGH THE PERIOD. COOLER MIDLEVEL TEMPS WILL STAY TO THE
NORTH THROUGH THE PERIOD. ON THE SURFACE A WEAK BOUNDARY WILL BE
OVER THE NORTH. THE NGM MODEL ALSO HAD THE STATIONARY UPPER TROF
THROUGH THE PERIOD...BUT WEAKENING ON FRIDAY...WITH A SERIES OF
SHORTWAVES ROTATING ACROSS THE REGION. THE NGM ALSO DID NOT
INTIALIZE THIS MORNINGS OR AFTERNOONS MESO LEVEL CONVECTIVE COVERAGE
VERY WELL EITHER WITH TOO MUCH EMPHASIS TO THE WEST. IT PAINTS LIGHT
TO MODERATE AMOUNTS TONIGHT THROUGH FRIDAY. IT SHOWS THE BEST MEAN
MOISTURE OVER THE CENTRAL AND EAST THIS EVENING...BEFORE IT RETREATS
TO THE SOUTHEAST ON THURSDAY. IT BUILDS BACK ACROSS THE REGION
THURSDAY NIGHT INTO FRIDAY. VERTICAL VELOCITIES WILL BE MARGINAL
THROUGH THE PERIOD. ON THE SURFACE A WEAK BOUNDARY WILL BE IN THE
NORTH. THE AVN MODEL KEEPS THE TROF OVER THE REGION UNTIL FRIDAY
NIGHT...WHEN IT MOVES OFF TO THE EAST. ON THE SURFACE IT BRINGS A
BOUNDARY DOWN TO JUST NORTH OF THE FORECAST AREA ON FRIDAY NIGHT. IT
INITIALIZED THE PRECIPITATION FAIRLY WELL...IT PAINTS LIGHT AMOUNTS
TO THE SOUTH...THIS EVENING AND LIGHT TO MODERATE AMOUNTS IN THE
SOUTH HALF ON THURSDAY. IT DRYS OUT FROM THE NORTHWEST ON THURSDAY
EVENING...BEFORE REDEVELOPING OVER THE SOUTH HALF ON FRIDAY AND
DRYING OUT FRIDAY NIGHT.

SO WITH THIS IN MIND WILL PUT IN BEST SCATTERED POPS IN THE
SOUTHEAST FOR TONIGHT THROUGH THURSDAY. WILL KEEP LOW TO SCATTERED
POPS THROUGH THE FORECAST PERIOD...WITH UPPER TROF OVER THE REGION.
MOS HIGH/LOW TEMPS LOOK GENERALLY OK. THE AVN INITIALIZED THE
CONVECTIVE COVERAGE THE BEST. SO WILL FOLLOW THE AVN MODEL. ALL
MODELS DID FAIRLY WELL IN INITIALIZING SURFACE AND UPPER FEATURES.
LOCATIONS OF OUTFLOW BOUNDARIES/TRACKING OF SHORTWAVES WILL BE
DIFFICULT TO FOCUS ON...IN THIS PACKAGE. CONFIDENCE IS LOW ON
TRACKING LIFTING MECHANISMS...SINCE THE MODELS DONT WORK TO WELL ON
THE MESO-SCALE THIS TIME OF YEAR.

QPF DISCUSSION: DRIER AIR NOTED ON WATER VAPOR SLIDING ACROSS WESTERN
PORTIONS OF THE FORECAST TODAY RELATED TO WEAKENING MID LEVEL SHEAR
AXIS. THIS IS NOTED WELL ON THE 12Z PRECIP WATER PLOT WITH GENERALLY
LESS THAN 1.5 IN NW HALF AND 1.7-1.9 SE HALF-THIRD IN DEEPER MOISTURE
PLUME. NGM TOO WET...ETA TOO DRY. A COMPROMISE BETWEEN THE AVN/HPC
VALUES LOOKS REASONABLE PER CURRENT RADAR/SATELLITE/MOISTURE
CONVERGENCE TRENDS. PAINTING 0.1-0.2 BASIN AVERAGES SE TO ZERO NW
CWFA WITH MOISTURE BEING TOO SHALLOW FOR BROADSCALE QPF.

EXTENDED DISCUSSION:LOOKING AT THE MRF MODEL...IT SHOWS THE TROF
AXIS EAST OF THE REGION...ALONG WITH THE MEAN MOISTURE ON SATURDAY.
ON THE SURFACE HIGH PRESSURE AND SOUTHERLY FLOW WILL BE PREVALENT.
ON SUNDAY A BROAD FLAT RIDGE WILL HAVE DEVELOPED ACROSS THE LOWER
MISSISSIPPI VALLEY. ON MONDAY SOME MEAN MOISTURE WILL DEVELOP
ACROSS THE REGION FROM THE SOUTHEAST QUARTER. A BOUNDARY WILL
REMAIN WELL NORTH OF THE FORECAST AREA DURING THE PERIOD.  LOOKING
AT THE CANADIAN MODEL...A BROAD FLAT RIDGE WILL REDEVELOPS OVER THE
REGION DURING BY SATURDAY AND WILL CONTINUE THROUGH MONDAY. MEAN
MOISTURE WILL BE EAST OF THE REGION...AS OUR SUMMER PATTERN RETURNS.
THE EUROPEAN MODELS WERE ALSO SIMILAR THE THE SUMMER LIKE LOW LEVEL
SOUTHERLY FLOW PATTERN. NO SIGNIFICANT MEAN MOISTURE AROUND. THE NOGAPS HAD
A SIMILAR SURFACE/UPPER PATTERN...BUT SHOWED SOME CONVECTIVE COVERAGE
FOR SUNDAY AND MONDAY. MANUAL PROGS ON THE SURFACE SHOWS A FRONT
APPROACHING FROM THE NORTHEAST AND PUSHES BACK TO THE NORTH AS A FRONTAL
SYSTEM PUSHS THROUGH THE PLAINS ON SUNDAY.  WILL FOLLOW A COMBO OF
THE CANADIAN/MRF/EUROPEAN MODELS. THE NOGAPS LOOKED TO BE TOO WET ON
SUNDAY/MONDAY. SO WITH THIS IN MIND WILL GO FOR A CHANCE OF
AFTERNOON AND EVENING THUNDERSTORMS EACH DAY.

PRELIM NUMBERS...
JAN 071/091 071/091 343
MEI 070/091 071/091 454

.JAN...
AR...NONE
LA...NONE
MS...NONE.
17