Severe Thunderstorm Warning 280, NWS Little Rock, AR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LITTLE ROCK AR
128 PM CDT SAT AUG 24 2002

SO MUCH FOR MODEL CONSENSUS ON THE FORECAST MESOSCALE CONVECTIVE
SYSTEM TONIGHT/SUNDAY MORNING. THE CANADIAN IS THE ONLY 12Z MODEL
WHICH LOOKS SUBSTANTIALLY LIKE IT DID YESTERDAY. THE AVN SHOWS SOME
SIMILARITIES TO ITS RUN FROM 24 HOURS AGO...WHILE THE ETA IS
SIGNIFICANTLY DIFFERENT FROM ITS RUN YESTERDAY MORNING. THE NEW RUC
AND MESOETA DO NOT CORRECTLY INITIALIZE THE ONGOING CONVECTION OVER
NORTHEAST OKLAHOMA/SOUTHWEST MISSOURI OR NEBRASKA...SO THEY ARE OF
LITTLE HELP. FORECAST PROCESS WILL FOCUS ON EXTRAPOLATION OF CURRENT
TRENDS FOR THE SHORT TERM FORECAST...A PROCESS OF ELIMINATION FOR
THE SECOND THROUGH FOURTH PERIODS...AND MODEL CONSENSUS FOR THE
LATER PERIODS. MODEL CONSENSUS IS QUITE BETTER IN THE LATER PERIODS
OF THIS FORECAST /WHEN SYNOPTIC FEATURES ARE EXPECTED TO BECOME THE
MAIN PLAYERS/ THAN IN THE EARLY PERIODS /WHEN MESOSCALE FEATURES ARE
EXPECTED TO DOMINATE/.

IN THE SHORT TERM...CONVECTION APPROACHING NORTHWEST ZONES AT 18Z
WILL CONTINUE MOVING SOUTHEAST. WILL PUT HIGHER POPS FOR THE FIRST
SIX HOURS IN THE NORTHERN ZONES...AND MAY EXTEND THESE FARTHER SOUTH
DEPENDING ON HOW MUCH CONVECTION GETS GOING BY RELEASE TIME.

OVERNIGHT...CONFIDENCE IN THE MCS TIMING/PLACEMENT/MOVEMENT IS
DECREASING. WILL LOWER THE HIGHEST POPS A LITTLE BIT AND EXPAND THE
AREA OF CONCERN.

SUNDAY...LOTS WILL DEPEND ON THE EVOLUTION OF THE PRESUMED MCS
OVERNIGHT. ETA IS THE ONLY MODEL ADVERTISING DEVELOPMENT ALONG THE
AR/OK BORDER DURING THE EARLY MORNING. ETA IS ALSO THE ONLY MODEL
WHICH SHOWS DIVERGENCE IN THE RIGHT EXIT REGION /TYPICALLY A
CONVERGENT AREA/ OF THE 250 MB JET STREAK. ETA IS ALSO ALONE IN
SHOWING DEEPER SOUTHWARD DIGGING OF THE JET STREAK VERSUS ROTATING
IT EASTWARD ACROSS THE MS RIVER VALLEY. WITH ALL THAT SAID...WILL
DISCARD THE ETA AND FOLLOW THE CANADIAN/AVN SOLUTION. THESE MODELS
CONTINUE THE TREND FROM YESTERDAY OF TRACKING THE MCS ACROSS
NORTHERN ZONES OVERNIGHT...EXCEPT PERHAPS A BIT FARTHER NORTH THAN
THEIR PREVIOUS RUNS. BEHIND THE MCS...LIKELY WILL SEE ENOUGH
RESIDUAL MOISTURE TO KEEP CLOUDS IN FOR A WHILE AND RETARD
TEMPERATURES...WHICH IS ALREADY ACCOUNTED FOR. HIGHER POPS FOR THE
AFTERNOON WILL REMAIN IN THE SOUTH WHERE THE OUTFLOW
BOUNDARIES/EFFECTIVE FRONT WILL HELP FOCUS CONVECTION.

MONDAY...SLIGHT CHANCE POPS WILL REMAIN INTACT AS THERE IS NOT YET
QUITE ENOUGH MODEL CONSENSUS TO REMOVE THEM. AVN STILL INDICATES A
WEAK WAVE APPROACHING FROM THE NORTH WITH JUST ENOUGH MOISTURE
AVAILABLE.

EXTENDED...MINIMAL CHANGES ANTICIPATED.

PRELIMINARY NUMBERS...SUBJECT TO CHANGE...ESPECIALLY FIRST PERIOD...

LIT 73 89 71 91 69 / 30 40 10 20
HOT 73 92 71 93 69 / 30 40 10 20
HRO 68 86 66 87 65 / 60 20 10 20
PBF 74 92 72 91 70 / 30 50 20 20

.LZK...NONE.

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