Severe Thunderstorm Warning 209, NWS Nashville, TN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NASHVILLE TN
255 PM CDT SUN JUN 25 2000

FORECAST QUANDARIES...PCPN CHANCES...TEMPS.

CURRENT ASOS/AWOS OBSERVATIONS...RADAR MOSAICS...REGIONAL SATELLITE
IMAGERY...AND MSAS/SURFACE ANALYSES SHOWING SURFACE TROUGH
OVER NORTHERN CWA WITH WIDELY SCATTERED CONVECTION INITIATING ALONG
IT. DEWPOINT DEPRESSIONS ARE AVERAGING 15 TO 20 DEGREES WITH SURFACE
WIND FIELDS MAINLY SWLY. REGION EXPERIENCING PARTLY CLOUDY SKY
CONDITIONS DUE TO WEAK SURFACE RIDGING AT THIS TIME...BUT WITH
SURFACE LI/S APPROACHING -5 AND K INDICES IN THE LOW 30S...ATMOSPHERE
INSTABILITY DEVELOPING. PCPN WATER VALUES IN THE 1.5 INCH RANGE ALSO.
RUC/UPPER AIR CHART DEPICTIONS SHOWING UPPER LEVEL TROUGHING SUPPORT
WITH VORT MAX CENTERED IN S IN. MOISTURE DEPTH EXTENDING INTO
THE MID LEVELS...ESPECIALLY NORTHERN PORTIONS...WITH DEVELOPING
WESTERLY FLOW ALOFT.

NGM/S 12Z SUN REGIONAL MODEL RUNS INITIALIZATION MOST ACCURATE...
WITH ETA/AVN SLIGHTLY LESS AMPLIFIED BUT ALSO "IN THE BALL PARK".
AVN HAS BEEN MOST CONSISTENT WITH POPS OVER THE LAST FEW MODEL RUNS.
NGM SOLUTION SEEMS TO BE COMING "MORE IN LINE" WITH AVN SOLUTION ON
POPS. AS A RESULT...WILL LEAN TOWARD A COMPROMISE NGM/AVN SOLUTION
THROUGH 00Z WED.

LOOK FOR SURFACE TROUGH TO MOVE EAST OF REGION THIS AFTERNOON WITH
SOUTHERLY FLOW CONTINUING UNDER WEAK RIDGING INFLUENCES TONIGHT.
MID LEVELS DRY AIR ADVECTION SHOULD DEVELOP WITH UPPER LEVEL FLOW
BECOMING MORE ZONAL. HOWEVER...PREVALENT LOW LEVEL MOISTURE SHOULD
SUPPORT PARTLY CLOUDY SKY CONDITIONS TONIGHT. WILL CONTINUE
MENTIONING OF ISOLATED MAINLY EVENING THUNDERSTORMS TONIGHT.
OF PARTICULAR NOTE...LOW PRESSURE SYSTEM DEVELOPMENT  ACROSS
UPPER MICHIGAN WITH TRAILING COLD FRONT INTO THE THE TX PANHANDLE
REGION BY 12Z MON.

SURFACE LOW PRESSURE SYSTEM WILL MOVE INTO WESTERN TN BY 00Z TUE
WITH WEAK RIDGING AND SWLY FLOW TO CONTINUE INFLUENCING REGIONAL
WEATHER. VARIABLE CLOUDINESS AND SCATTERED POPS THROUGH 00Z TUE
SHOULD PREVAIL. AS THE FRONT MOVES INTO W CWA BY 12Z TUE...ALONG
WITH SHORTWAVE PASSAGES...LOOK FOR SKIES TO BECOME CLOUDY MONDAY
NIGHT WITH THE BEST CHANCE FOR SCATTERED CONVECTION AFTER 06Z TUE
TO 18Z TUE. MODEL INSTABILITY PARAMETERS SUPPORT CONVECTIVE
DEVELOPMENT...BUT ATMOSPHERE SHOULD NOT DESTABILIZE ENOUGH
TO SUPPORT SVR CONVECTION. SKIES WITH REMAIN MOSTLY CLOUDY ON
TUESDAY WITH GRADUAL DECREASE IN CLOUDINESS DURING THE AFTERNOON
WEST. EVEN WITH FRONTAL PASSAGE...CAN NOT RULE OUT SCATTERED
CONVECTION AGAIN DURING THE DAY ON TUESDAY WITH NW FLOW...PER
MODEL SOUNDINGS.

EXTENDED...CHANCE OF SHOWERS AND THUNDERSTORMS WILL CONTINUE THROUGH
12Z FRI...WITH DECREASING CLOUDINESS REGION WIDE ON FRIDAY AS
UPPER LEVEL TROUGH MOVES EAST OF REGION.

TEMPS...WITH LOWS TEMPS AT BNA THIS MORNING IN THE UPPER 70S
UNDER SWLY FLOW...AND THIS FLOW EXPECTED TO CONTINUE THROUGH
12Z TUE...WILL RAISE AVN/NGM LOWS A FEW DEGREES...ESPECIALLY
MONDAY NIGHT WITH INCREASED CLOUD COVER. NGM MOS HAS VERIFIED
WELL WITH HIGH TEMPERATURE VALUES AS OF LATE...AND WILL LEAN
TOWARD ACCORDINGLY.

PRELIMINARY NUMBERS FOR COORDINATION PURPOSES ONLY...

BNA 07z3/093/075/088 1344
CSV 067/088/069/082 1334

.BNA...NONE.
14
JBW