Severe Thunderstorm Warning 70, NWS New Orleans, LA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS/BATON ROUGE LA
300 PM CDT SUN JUL 21 2002

SIL 12Z SOUNDING REVEALED A CAPE VALUE NEAR 4500 J/KG...LIFTED INDEX
AROUND -9 AND PRECIPITABLE WATER VALUE AROUND 2 INCHES. AREAL
PRECIPITABLE WATER PLOTS SHOWED A SWATH OF 2 INCHES AND GREATER FROM
WEST CENTRAL ARKANSAS TO SOUTHEAST MISSISSIPPI TO SOUTH OF THE
FLORIDA PANHANDLE. UPPER AIR ANALYSIS REVEALED A TROUGH ALONG THE
EASTERN SEABOARD WITH AN ASSOCIATED VORT LOBE FROM THE CAROLINAS TO
NORTH ALABAMA TO NORTH MISSISSIPPI. MOSAIC RADAR IMAGERY REVEALED
SCATTERED SHOWERS AND THUNDERSTORMS AT THE BASE OF THE TROUGH AND
OVER THE SWATH OF MOISTURE. IN ADDITION...UPPER AIR HAND ANALYSIS
REVEALED A VORT MAX AT 400MB OVER THE SWATH OF MOISTURE AHEAD OF THE
MAIN TROUGH OVER SOUTH MISSISSIPPI. THE VORT MAX PRODUCED CONVECTION
FROM FLORIDA PANHANDLE TO THE MISSISSIPPI COAST THIS MORNING. A
SURFACE RIDGE AXIS WAS NOTED FROM CENTRAL FLORIDA TO NORTH GULF TO
SOUTHEAST TEXAS. IN ADDITION...ANTICYCLONIC CIRCULATION WAS NOTED AT
850MB AND 700MB OVER SOUTHEAST LOUISIANA.

SHORT RANGE MODELS ARE IN AGREEMENT WITH A VIGOROUS SHORT WAVE IN
THE NORTHERN STREAM OVER JUST NORTH OF MONTANA DIVING SOUTHEAST AND
DAMPENING THE WEAK UPPER LEVEL HIGH OVER THE MID MISSISSIPPI VALLEY
LATE TODAY INTO MONDAY. THE UPPER LEVEL HIGH REDEVELOPS OVER THE
INTERIOR ROCKIES AND AMPLIFIES LATE MONDAY. AT THE SAME TIME...THE
UPPER LEVEL TROUGH OVER THE CAROLINAS DROPS SOUTH OVER GEORGIA. THE
MODELS DISAGREE WITH THE MOISTURE AXIS. ETA BRINGS THE SWATH OF
MOISTURE ACROSS THE FORECAST AREA MONDAY AND MONDAY NIGHT WITH PW
VALUES OF 2 INCHES AND GREATER ACROSS THE SOUTH HALF OF FORECAST
AREA...WHILE NGM AND AVN HAVE THE SWATH OF MOISTURE FROM NORTH
FLORIDA TO THE MISSISSIPPI COAST. WILL NOT WAVER OVER THESE LITTLE
DIFFERENCES. HIGH AT 850 AND 700MB BREAK DOWN AND ALLOW THE TROUGH
TO DROP SOUTHWEST OVER GEORGIA AND ALABAMA AT 850 AND 700MB. THE
NORTH TO NORTHEAST FLOW WILL ADVECT MOISTURE THROUGHOUT THE COLUMN
OVER THE FORECAST AREA. WILL CONTINUE CHANCE POPS EAST AND SOUTH
ZONES TONIGHT AND MONDAY...NORTHWEST FORECAST AREA WILL CONTINUE
WITH A SLIGHT CHANCE TONIGHT AND MONDAY. WITH THE TROUGH OVER THE
CAROLINAS DROPPING SOUTHWEST OVER GEORGIA AND ALABAMA...THICKNESS
VALUES ARE EXPECTED TO FALL SLIGHTLY. IN ADDITION...CHANCE POPS IN
THE FORECAST....AND THE ABUNDANCE OF MOISTURE FROM THE EAST...DAY
AND NIGHT TIME TEMPERATURES ARE EXPECTED TO DROP 1 OR 2
DEGREES...BELOW HEAT ADVISORY CRITERIA FOR NIGHT TIME TEMPS. WILL
ALLOW THE HEAT ADVISORY TO DIE. WILL CONTINUE TO HIGHLIGHT HEAT
INDICES IN THE ZONES.

BEYOND 48 HOURS...SHORT WAVE IN THE NORTHERN STREAM WILL BECOME
SHEARED ROTATING AROUND THE MAIN LOW OVER THE HUDSON BAY. THE
ASSOCIATED SURFACE LOW/TROUGH WILL PULL EAST ALLOWING A FRONT/TROUGH
TO PUSH SOUTHEAST INTO THE MID SOUTH BY WEDNESDAY MORNING AND BECOME
STATIONARY MAINLY ALONG INTERSTATE 20 THU. THE FRONTAL BOUNDARY MAY
BECOME DIFFUSE BEFORE PUSHING INTO THE FORECAST AREA SAT AND SUN. NO
CHANGE TO THE EXTENDED FOR NOW.

PRELIM NUMBERS...

MCB 73/93/72/92 3423  BTR 74/93/74/93 2323 MSY 77/92/76/93 3424
GPT 74/93/75/92 3424

.NEW...NONE
LA...NONE.
MS...NONE.

18

LAZ034>040-046>050-056>070-MSZ068>071-077-080>082-221200-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE NEW ORLEANS LA
1100 AM CDT SUN JUL 21 2002

...HEAT ADVISORY IS IN EFFECT FOR LOWER SOUTHEAST LOUISIANA...
...HEAT INDEX VALUES RANGING FROM 102 TO 110 THIS AFTERNOON...

.SYNOPSIS...STRONG HIGH PRESSURE AFFECTING THE CENTRAL GULF COAST
REGION WILL AGAIN LEAD TO DANGEROUS HEAT STRESS CONDITIONS ACROSS
THE FORECAST AREA THIS AFTERNOON. A SERIES OF WEAK UPPER LEVEL
DISTURBANCES WILL ALSO MOVE SOUTHWARD ACROSS THE LOWER MISSISSIPPI
VALLEY THIS AFTERNOON AND TONIGHT. WITH AN UNSTABLE AIRMASS ALREADY
IN PLACE...SCATTERED SHOWERS AND THUNDERSTORMS WILL ALSO BE POSSIBLE
ACROSS SOUTHEAST LOUISIANA AND SOUTH MISSISSIPPI THROUGH TONIGHT.

.THUNDERSTORMS...
SCATTERED THUNDERSTORMS ARE EXPECTED TO DEVELOP AS THESE UPPER LEVEL
DISTURBANCES INTERACT WITH OLD OUTFLOW BOUNDARIES AND DEVELOPING
LAKE AND SEA BREEZE BOUNDARIES. THUNDERSTORM WIND GUSTS TO 50
MPH...FREQUENT LIGHTNING AND LOCALLY HEAVY RAINFALL ARE LIKELY WITH
THE STRONGER STORMS. IN ADDITION...A FEW STORMS COULD APPROACH
SEVERE THRESHOLDS WITH THE POTENTIAL FOR DAMAGING WINDS.

.EXCESSIVE HEAT...
TEMPERATURES THIS AFTERNOON WILL BE IN THE MID 90S WITH HEAT INDEX
VALUES AROUND 105 TO 110 DEGREES IN THE ADVISORY AREA SOUTH OF LAKE
PONTCHARTRAIN...AND 102 TO 105 DEGREES ELSEWHERE.

.ACTIONS...HEAT PRECAUTIONS SHOULD BE TAKEN THIS AFTERNOON.

FOR MORE INFORMATION...VISIT OUR WEB SITE AT WWW.SRH.NOAA.GOV/LIX
(ALL LOWER CASE).