Severe Thunderstorm Warning 212, NWS Nashville, TN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NASHVILLE TN
246 PM CDT SAT JUL 28 2001

ETA/NGM/AVN MODELS ALL UNDERFORECAST SOMEWHAT STRENGTH OF SURFACE
HIGH LOCATED OVER THE SOUTHEAST THIS MORNING. PREVIOUS ETA AND AVN
MODEL RUNS HAD BEST FORECAST LOCATION OF WARM FRONT LOCATED TO OUR N.

ALSO...850...700 AND 500 MB HEIGHTS WERE SLIGHTLY HIGHER THAN ALL
THREE MODELS PREDICTED IN OUR AREA.

ALL THREE MODELS INDICATE A SMALL VORTICITY MAXIMUM MOVING SLOWLY E
ACROSS OUR AREA THIS AFTERNOON...APPARENTLY ASSOCIATED WITH A WEAK
700/500 MB TROUGH. MODELS ALL SHOW AN UPPER LEVEL TROUGH WITH A
STRONGER AREA OF VORTICITY MOVING SE INTO OH VALLEY AREA BY 12Z
SUN...WITH POSITIVE ADVECTION ON OUR DOOR STEP

ALSO BY 12Z SUN...NEW AVN MOVES A SURFACE LOW E TO NEAR THE IN/OH
BORDER AREA...WITH ITS PRESSURE PATTERN SHOWING LITTLE CHANGE
BETWEEN THE TWO RUNS. ETA SOLUTION IS COMING IN LINE MORE WITH AVN
SOLUTION IN LOWERING SURFACE PRESSURES MORE OVER OUR AREA OVERNIGHT
THAN PREVIOUS ETA RUN. IT HOWEVER FORECASTS LOW TO BE OVER W OH. NGM
WAS SIMILAR TO ITS PREVIOUS FORECAST. I SUSPECT THINGS WILL BE A
LITTLE SLOWER TO EVOLVE...AT LEAST IN THE SHORT TERM...DUE TO
STRENGTH OF SOUTHEAST HIGH.

APPEARS BEST SURFACE CONVERGENCE WILL REMAIN N OF OUR AREA
OVERNIGHT. AXIS OF HIGHER THETA-E VALUES...BOTH SURFACE AND AT 850
MB...WILL HOWEVER BE NEAR THE KY/TN BORDER OVERNIGHT. I STILL EXPECT
THE MOST RAINFALL AND HIGHEST POPS WILL BE JUST N OF US. THERE
SHOULD BE A GRADUAL LESSENING OF PRECIP COVERAGE OVER OUR AREA LATER
THIS EVENING AS HEATING ENDS.

LOOKING AT FORECAST PATTERNS OF 500 VORTICITY...700/500
VORTICITY...AND CHANGE OF VORTICITY FROM 700 TO 500 MB...BEST CHANCE
OF RAIN IN THE MID STATE APPEARS TO BE ON SUNDAY...AND MAINLY DURING
THE MORNING INTO THE EARLY AFTERNOON HOURS ESPECIALLY IN THE N.

BEYOND THAT...TROUGH IN THE PACIFIC NW IS FORECAST TO INCREASE SOME
IN AMPLITUDE...WITH A CORRESPONDING DEVELOPMENT OF SOME TROUGHINESS
DOWN TO THE MID ATLANTIC STATES AND SE BY SUNDAY EVE. OUR UPPER LEVEL
FLOW WILL BECOME NORTHWEST LATER IN THE DAY ON SUNDAY AND USHER IN
MUCH DRIER AIR IN THE MID AND UPPER LEVELS...AS WELL AS DOWNWARD
MOTION SUNDAY NIGHT AND MONDAY.

ETA AND NGM BOTH FORECAST A WEAK SURFACE TROUGH TO MOVE S INTO OUR N
COUNTIES SUNDAY NIGHT AND REMAIN OVER THE AREA ON MONDAY. BECAUSE OF
NO UPPER LEVEL SUPPORT FOR THE MOST PART...WILL KEEP FORECAST DRY ON
MONDAY.

HIGH TEMPS ON SUN WILL BE TRICKY. LOOKS LIKE MEAN RELATIVE HUMIDITY
COULD EVEN BEGIN LOWERING LATER IN THE AFTERNOON. WITH NGM/AVN BOTH
SHOWING SOME WARMER AIR ADVECTING INTO PARTICULARLY THE N PART OF
OUR AREA AT 850 MB ON SUN...COULD MEAN MOS MAY BE TOO LOW WITH
HIGHS. WILL RAISE SLIGHTLY IN NW AND N BUT ONLY DEGREE OR
TWO...ANTICIPATING SOME SUNSHINE LATER IN THE AFTERNOON AND
LESSENING OF PRECIP COVERAGE. OTHERWISE WILL NOT STRAY FAR FROM MOS
FOR NEXT FEW PERIODS.

REGARDING POPS...THERE IS NOT THAT MUCH ACTIVITY AROUND THIS
AFTERNOON. SOME DEVELOPMENT NOW NOTED ON SATELLITE IR IMAGERY OVER
MO BOOTHEEL AND MAINLY OVER S CENTRAL KY AND E PART OF TN. WILL MOST
LIKELY LOWER THE HIGH POPS MOS FORECASTS FOR TONIGHT...ESPECIALLY IN
THE S. IN THE N WILL WAIT UNTIL LAST MINUTE TO DECIDE. HIGH POPS
LOOK REASONABLE ON SUN PER THE INFO. MENTIONED PREVIOUSLY. MAY
MENTION HEAVY RAIN POSSIBLE ON SUN AS PRECIPITABLE WATER STAYS HIGH
AT LEAST FOR THE FIRST PART OF SUN PER THE ETA MODEL.

PRELIMINARY NUMBERS

BNA 75/88/72/92 5821
CSV 70/82/67/87 7931

.BNA...NONE.

STEIGERWALDT