Severe Thunderstorm Warning 445, NWS Jackson, MS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
230 PM CDT THU JUL 20 2000

HEAT WAVE OF RECENT DAYS WILL WANE AS PROGRESSIVE MESOSCALE
CONVECTIVE WEATHER COMPLEX PUSHES SOUTHEAST INTO OUR CWFA THIS
AFTERNOON/EVENING. WEAK FRONTAL BOUNDARY STRETCHING FROM NEAR
KLIT-KGWO-NORTH OF KMEI AROUND 15Z WILL SERVE TO HELP FOCUS
THUNDERSTORM DEVELOPMENT ACROSS CWFA THROUGH 00Z SUN.

UPPER LEVEL (500 MB) PATTERN CONSISTENT IN MODELS WITH LARGE RIDGE
WELL-ESTABLISHED OVER WESTERN STATES AND CENTERED OVER THE GREAT
BASIN REGION. SEVERAL SHORTWAVES WILL MOVE OVER TOP OF RIDGE AND
PLUNGE INTO BASE OF TROUGH THAT EXTENDS FROM GRTLAKES INTO SOUTHERN
STATES THROUGH NEXT 48 HRS. 300 MB JET DYNAMICS WILL PROVIDE
SUBSTANTIAL PUNCH FOR STORM DEVELOPMENT...MAINLY N OF OUR CWFA. BEST
TIME-FRAME FOR THUNDERSTORMS OVER MOST OF CWFA APPEARS TO BE IN 06Z-
12Z ARENA...WHEN BEST UVV OCCURS IN MODELS FROM KMEM-KJAN AND
SPREADING EAST WITH TIME.

SOME RISK FOR SEVERE THUNDERSTORMS APPEARS EVIDENT FROM SIGNIFICANT
INSTABILITY PARAMETERS IN MODELS AND FROM OBSERVED WEATHER. FROM
LAPS...LI'S OVER CWFA RUNNING -4 TO -8 AT 18Z. ALSO IN LAPS...CAPE
VALUES ARE GREATER THAN 4000 J/KG...MAINLY OVER NRN MS...WITH NO
CONVECTIVE INHIBITION. REVIEW OF OMEGA PROGS CONFIRMS GREATEST RISK
IN CLOSE PROXIMITY TO FRONT. AFTER 12Z SAT...ETA 300 MB WINDS PLACE
EASTERN MS ZONES IN MOST FAVORABLE AREA FOR THUNDERSTORMS...SOUTHERN
PORTION OF CWFA EXPECTED TO GET CONVECTION AIDED BY ANY OUTFLOW
BOUNDARIES FROM THIS AFTERNOON/TONIGHT'S ACTIVITY.

IMPULSES RIPPLING THROUGH OUR CWFA WILL ENCOUNTER MOISTURE-RICH
AIR. LAYER PRECIP WATER VALUES FORECAST TO REMAIN IN 1.75" TO >2"
RANGE THROUGH SAT. SURFACE DEWPOINTS WILL GENERALLY REMAIN ABOVE 70
DEGREES AS WELL. BY 06Z SAT...AIRMASS WILL BEGIN TO DRY OUT FROM
WEST BEFORE REBOUNDING INTO 70S MOST AREAS BY SUN.

MAIN QUESTION REMAINS EXTENT OF CLOUD COVER ON FRI AND AMOUNT OF
SOLAR INHIBITION TO EXPECT. COOLER AIR ADVECTS INTO CWFA FROM THE
NORTH BEHIND SURFACE FRONT. WILL GO WITH CURRENT TREND AS GUID TEMPS
TRENDING TO CLIMATOLOGY AFTER FRI NIGHT AND REMAINING SO THROUGH
EARLY NEXT WEEK. EXPECT DAYTIME HIGHS INTO LOWER/MIDDLE 90S AND LOWS
DROPPING INTO UPPER 60S/LOWER 70S BY SAT NIGHT. SHORTWAVE WILL DROP
INTO SRN ZONES OF MS/LA BY SUN...WITH A NEAR-STATIONARY BOUNDARY
PROVIDING PRIMARY FOCUS FOR ADDITIONAL SHOWERS/THUNDERSTORMS THROUGH
EARLY NEXT WEEK.

QPF DISCUSSION:  AS BOUNDARY DROPS FURTHER SOUTH TONIGHT AND NEXT
SHORTWAVE MOVES ACROSS THE FORECAST AREA...EXPECT TO SEE PRECIP
THROUGH EARLY EVENING HOURS AND AGAIN DURING PRE-DAWN HOURS OVER
NORTHERN ZONES.

FOR PERIOD TO 12Z FRI...WILL GO WITH AREAL AVERAGE AMOUNTS OF ONE
QUARTER TO ONE HALF INCH IN NORTHWEST AND LESS THAN ONE TENTH IN
SOUTHEAST. AMOUNTS WILL BE A COMPROMISE BETWEEN ETA AND AVN. IN
STRONGER STORMS...HOURLY AMOUNTS OVER ONE INCH ARE POSSIBLE.

JAN 074/097/072/093 3443
MEI 073/098/072/094 3544

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