Severe Thunderstorm Warning 489, NWS Jackson, MS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
215 PM CDT SUN JUL 30 2000

LOOKING AT SATELLITE VAPOR IMAGERY...A MIDLEVEL SHORTWAVE
TROF/ASSOCIATED VORT MAX...EXTENDED FROM THE OHIO VALLEY TO THE
LOWER MISSISSIPPI VALLEY. THE STATIONARY UPPER LOW ASSOCIATED WITH
THIS TROF WAS OVER THE OHIO VALLEY. SCATTERED SHOWERS AND
THUNDERSTORMS WERE NOTED ACROSS THE REGION. THE WEAK STATIONARY
FRONT WAS POSITIONED JUST WEST-NORTHWEST OF THE FORECAST AREA. THE
CLOUD COVER HAD HELPED TO DECREASE CONVECTIVE INSTABILITY AND
COVERAGE THIS AFTERNOON. SOME CONVECTION HAD FORMED OVER NORTH
LOUISIANA...WHICH SHOULD AFFECT OUR REGION THIS EVENING.

MOVING TO THE SHORTRANGE MODELS. THE MESO-ETA SHOWED THAT THE CLOUD
COVER HAD DECREASED THE CONVECTION ACROSS THE REGION. THE CONVECTION WILL PICK
UP AGAIN DURING MONDAY AND DECREASE DURING THE AFTERNOON WITH THE
CONTINUED CLOUD COVER. GOOD MEAN MOISTURE AND THE UPPER TROF AXIS
WILL CONTINUE THROUGH THE PERIOD. AS FAR AS UPPER JET DYNAMICS THE
RIGHT REAR QUAD WILL AFFECT THE NORTHERN SECTIONS TONIGHT THROUGH
TUESDAY. LOOKING AT VERTICAL VELOCITIES THE BEST ACTION WILL BE
SOUTH OF THE FORECAST AREA TONIGHT. ON MONDAY VERTICAL VELOCITIES
WILL DEVELOP IN THE DELTA REGION WITH THE CONVECTION...BUT WILL
DECREASE BY MID-AFTERNOON INTO THE EVENING. VERTICAL VELOCITIES
LOOKED TO BE GENERALLY WEAK ON TUESDAY. MEAN MOISTURE WILL BE
PLENTIFUL DURING THE SHORT RANGE PERIOD. ON THE SURFACE THE WEAK
STATIONARY FRONT WILL BE REDUCED TO A TROF THAT WILL STAY NORTHWEST
OF THE FORECAST AREA. THE ETA MODEL WAS GENERALLY SIMILAR WITH THE
SURFACE AND UPPER FEATURES. THE NGM MODEL SEEMED TO OVER ESTIMATE
THE INITIALIZATION ON THE PRECIP COVERAGE AND AMOUNTS...THEN IT
UNDERESTIMATED THE COVERAGE BY NOON...BEFORE HITTING THE EASTERN
SECTIONS BY EVENING. ON MONDAY THROUGH TUESDAY IT DOES NOT HAVE MUCH
COVERAGE WITH MOST OF THE EMPHASIS IN THE SOUTH. IT SHOWES GENERALLY
WEAK VERTICAL VELOCITIES THROUGH TUESDAY...MAINLY IN THE SOUTH. THE
AVN MODEL KEEPS THE UPPER TROF OVER THE REGION THROUGH TUESDAY
NIGHT...BEFORE MAKING IT A SHEAR AXIS BY WEDNESDAY MORNING. ON THE
SURFACE THE WEAK TROF WILL STAY GENERALLY NORTHWEST OF THE REGION.
IT DID NOT INTIALIZE THE CONVECTIVE COVERAGE OR AMOUNTS VERY WELL
AND KEEPS GENERALLY LIGHT TO MODERATE AMOUNTS FOR THE NEXT SEVERAL
DAYS. OTHERWISE COOLER MIDLEVEL TEMPERATURES WILL MOVE INTO THE
NORTHERN SECTIONS TONIGHT THROUGH MONDAY AFTERNOON. IT WILL
REDEVELOP OVER THE NORTH HALF MONDAY NIGHT INTO TUESDAY.

SO WITH THIS IN MIND WILL PUT IN BEST POPS IN THE SOUTHEAST HALF FOR
TONIGHT. WILL KEEP SCATTERED POPS THROUGH THE FORECAST PERIOD WITH
UPPER TROF OVER THE REGION. MOS HIGH/LOW TEMPS LOOK GENERALLY
OK...CONSIDERING THE CLOUD COVER AND CHANCES OF RAIN. THE MESO-ETA
INITIALIZED THE CONVECTIVE COVERAGE...SURFACE AND UPPER FEATURES THE
BEST.

QPF DISCUSSION:WILL FOLLOW THE MESO ETA...SINCE IT INITIALIZED THE QPF
FIELDS THE BEST. THE BEST AMOUNTS WILL BE IN THE SOUTH HALF THIS
EVENING. PRECIPITABLE WATER WILL BE 1.5 TO 1.8 INCHES. ON MONDAY
WILL PUT THE HIGHEST AMOUNTS AROUND THE WEAK BOUNDARY TO OUR
NORTHWEST. WILL GO WITH BASIN AMOUNTS OF .10 TO AROUND .40 INCH.
NCEP AMOUNTS LOOKED TO BE A LITTLE HIGH IN THE SOUTHEAST SECTIONS OF
AROUND .50 INCH.

EXTENDED DISCUSSION:LOOKING AT THE MRF MODEL...IT SHOWS A BROAD
CLOSED UPPER LOW OVER THE LOWER MISSISSIPPI VALLEY ON WEDNESDAY WITH
GOOD MEAN MOISTURE. A SURFACE TROF WILL EDGE THE NORTHWEST CORNER OF
THE REGION...WHILE A SURFACE LOW HOLDS OVER THE NORTHEAST GULF. ON THURSDAY
THE CLOSED LOW WILL MOVE TO SOUTHEAST TEXAS AS THE GULF SURFACE LOW
MOVES TO THE SOUTHEAST LOUISIANA COAST...THEN TO SOUTHWEST
MISSISSIPPI WITH RICH MEAN MOISTURE ACROSS THE REGION. ON FRIDAY THE
REGION WILL BE CAUGHT IN AN UPPER SHEAR AXIS BETWEEN THE TWO UPPER
RIDGES AND THE SURFACE LOW WILL BE OVER NORTHERN LOUISIANA. MEAN
MOISTURE WILL DRY OUT SOME OVER THE SOUTHEAST HALF. LOOKING AT THE
CANADIAN MODEL...IT SHOWS ONLY MARGINAL MEAN MOISTURE OVER THE REGION
WITH THE WEAK TROF CAUGHT BETWEEN THE UPPER RIDGES. ON THE SURFACE
GENERAL HIGH PRESSURE. ON THURSDAY IT SHOWS ALL THE MEAN MOISTURE
IN THE GULF. ON FRIDAY UPPER TROF CONTINUES OVER THE REGION WITH AN
UPPER LOW OVER SOUTHWEST LOUISIANA. THE EUROPEAN MODELS WERE SIMILAR
TO THE CANADIAN IN MARGINAL MEAN MOISTURE WITH THE WEAK TROF CAUGHT
BETWEEN THE TWO UPPER RIDGES. THE NOGAPS MODEL SHOWED SOME MEAN MOISTURE
ACROSS THE REGION WEDNESDAY THROUGH FRIDAY. MANUAL PROGS ON THE SURFACE
SHOW A WEAK TROF OVER NORTHWEST MISSISSIPPI THROUGH LOUISIANA ON
FRIDAY. SO WITH THIS IN MIND WILL GO FOR A CHANCE OF THUNDERSTORMS
EACH DAY.

PRELIM NUMBERS...
JAN 072/088 071/090 443
MEI 071/090 070/090 543

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