Severe Thunderstorm Warning 45, NWS Jackson, MS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
325 AM CST THU FEB 17 2000

SOME DENSE FOG NOTED EARLY THIS MORNING IN SURFACE OBS AND FOG
IMAGERY MOVING NORTH OVER SE MS. WILL ISSUE DENSE FOG ADVISORY FOR
SE PORTIONS.

NEAR STATIONARY BOUNDARY FROM JUST SOUTH OF KSHV-KHEZ TO NEAR KPIB
AS OF 08Z. THIS FEATURE TO BE THE MAIN PLAYER IN THE FORECAST TODAY.

DEVELOPING SYSTEM MOVING OUT THE ROCKIES WILL ALLOW LOW LEVEL WARM
AIR ADVECTION TO GET GOING TODAY OVER THE ARK-LA-MISS. ETA INDICATES
THAT BOUNDARY WILL BE A LITTLE DIFFICULT TO DISPLACE WITH INCREASING
LOWER LEVEL WARM ADVECTION...BUT SHOULD FINALLY MOVE INTO NORTH MS
BY LATE IN THE DAY. DECENT UPWARD VERTICAL MOTION...INITIALLY TODAY
IN THE 295-305K THETA LAYER...WILL INCREASE IN DEPTH BY THIS
AFTERNOON AS LEFT EXIT REGION OF 70-75 KNOT H25 JET STREAK PASSES
OVER THE CWFA NEAR THE WARM FRONTAL BOUNDARY. EXPECT NUMEROUS...
MOSTLY ELEVATED SHOWERS AND THUNDERSTORMS TO DEVELOP BY THE
AFTERNOON MAINLY NORTH OF THE BOUNDARY. DUE TO ELEVATED NATURE OF
CONVECTION AND WET-BULB ZERO HEIGHTS GENERALLY BELOW 10K
FEET...AGREE WITH SPC WITH POSSIBILITY OF LARGE HAIL BEING THE MAIN
SEVERE WEATHER THREAT TODAY.

WARM FRONT MOVES OUT OF THE AREA THIS EVENING WITH SHALLOW
DECOUPLING GETTING UNDERWAY BY 03Z. ALTHOUGH DECOUPLING WILL BE
SHALLOW...STILL ENOUGH TO CONTRIBUTE TO THE MESO SCALE LOW LEVEL JET
THAT WILL INTENSIFY DURING THE NIGHT AS 100+ KNOT H25 JET NOSES INTO
S MO BY 12Z FRIDAY. ALTHOUGH NO FOCUSING MECHANISMS WILL BE PRESENT
OVER THE CWFA TONIGHT...BELIEVE SCATTERED CONVECTION MAY STILL
RESULT WITH INCREASING ISENTROPIC UPGLIDE WITH INCREASING LOW LEVEL
JET BY MORNING.

ONGOING CONVECTION FRIDAY MORNING SHOULD TEMPORARILY DIMINISH AS LOW
LEVEL JET DECREASES AND PULLS AWAY TO THE NE. SURFACE COLD FRONT
WILL APPROACH THE CWFA FROM THE NW BY AFTERNOON FRIDAY. ALTHOUGH
RIGHT ENTRANCE REGION OF H25 JET PASSES NEAR THE AREA...LOW LEVEL
FORCING WITH THE FRONT APPEARS TO DOMINATE. STILL...EXPECT NUMEROUS
THUNDERSTORMS TO MOVE INTO THE AREA WITH THE FRONT. INSTABILITY...
WITH CAPES FROM 1000-1500 J/KG...AND DECENT SHEAR PROFILES...HELICITIES
FROM 200-300M2/S2...SHOULD SUPPORT SOME SUPERCELLULAR DEVELOPMENT.

CONVECTION CONTINUES TO DROP SE WITH THE FRONT FRIDAY EVENING WITH
CLEARING SKIES AND COOLER TEMPS IN ITS WAKE FOR SATURDAY. DRY
WEATHER SHOULD PREVAIL THROUGH MONDAY AS SURFACE HIGH PRESSURE
REMAINS IN CONTROL.

QPF DISCUSSION: WITH DECENT AREAL COVERAGE OF THUNDERSTORMS EXPECTED
THIS 24 HOUR PERIOD...BASIN AVERAGE AMOUNTS OF ONE QUARTER TO OVER
ONE HALF INCH ARE IN ORDER AS PER NCEP PROGS. ONLY ADJUSTMENT TO
NCEP PROG WILL BE TO SHIFT AXIS OF PRECIP SLIGHTLY TO THE NORTH DUE
TO MOST STORMS BEING ELEVATED IN NATURE AND OCCURRING WELL NORTH OF
THE SURFACE FRONT.

JAN 70/62/75/49 7463
MEI 67/61/77/50 7455

.JAN...
MS.}..DENSE FOG ADVISORY UNTIL 17/1600Z ZONES 063>066-072>074.
AR...NONE.
LA...NONE.
26

ARZ074-075-LAZ007>009-015-016-023>026-MSZ018-019-025>066-072>074-
180400-

AREA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE JACKSON MS
425 AM CST THU FEB 17 2000

A NEARLY STATIONARY FRONT WAS OVER CENTRAL MISSISSIPPI AND NORTHEAST
LOUISIANA EARLY THIS MORNING. STRONG SOUTH WINDS ABOVE THE FRONTAL
ZONE WILL PULL WARM MOIST AIR NORTHWARD FROM THE GULF...HELPING TO
DESTABILIZE THE AIRMASS ALOFT. AS AN UPPER LEVEL DISTURBANCE PASSES
THROUGH TODAY AND STRONG JET STREAM WINDS APPROACH FROM THE WEST...A
FEW SEVERE THUNDERSTORMS WILL BE POSSIBLE ROUGHLY ALONG AND NORTH OF
INTERSTATE 20.

THESE STORMS WILL BE ELEVATED. IN OTHER WORDS...THE WARM MOIST AIR
WHICH FUELS THE STORMS WILL NOT BE AT THE GROUND...IT WILL BE ABOVE
A SHALLOW LAYER OF COOL...STABLE AIR. STRONG THUNDERSTORM WINDS ARE
RARELY ABLE TO PENETRATE THIS COOL STABLE LAYER NEAR THE GROUND...SO
THE MAIN THREAT WITH THESE ELEVATED STORMS IS LARGE HAIL.

ACTIVATION OF STORM SPOTTERS...EMERGENCY MANAGEMENT PERSONNEL AND
HAM RADIO OPERATORS MAY BE REQUIRED THIS AFTERNOON OR TONIGHT.

FOR MORE INFORMATION...PLEASE VISIT OUR INTERNET WEB SITE AT
HTTP://WWW.JANNWS.STATE.MS.US        /IN LOWER-CASE LETTERS/