Severe Thunderstorm Warning 63, NWS Nashville, TN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NASHVILLE TN
230 AM CDT MON MAY 21 2001

SURFACE LOW IS CENTERED OVER SOUTHEAST IOWA WITH THE ASSOCIATED COLD
FRONT STRETCHING SOUTHWESTWARD THROUGH SOUTHEAST OKLAHOMA AND THENCE
WESTWARD THROUGH NORTH TEXAS INTO NEW MEXICO. A PACIFIC NORTHWEST
SURFACE RIDGE HAS BEEN PUSHING INTO THE PLAINS WITH THE FRONT BEING PUSHED
SOUTHEASTWARD AT ALMOST 30 KT.

IN THE UPPER LEVELS...H5 LOW AND ASSOCIATED TROUGH CONTINUES TO PUSH
SOUTHEASTWARD INTO THE GREAT PLAINS. UPPER JET DIVES SOUTHEASTWARD
THROUGH ALBERTA INTO COLORADO AND THEN TURNS NORTHWARD THROUGH
MINNESOTA. A SECOND SOUTHERLY JET IS NOTED ACROSS LOWER BAJA
NORTHEASTWARD THROUGH CENTRAL TEXAS INTO CENTRAL ALABAMA. THE TROUGH
AND ASSOCIATED MASS DIVERGENCE WITH THE 2 JET STRUCTURE HAS BEEN GENERATING
STRONG THUNDERSTORM ACTIVITY OVER THE LOWER PLAINS FOR THE LAST
SEVERAL HOURS.

MODELS BRING THE CANADIAN TROUGH SOUTHEASTWARD FORMING A CLOSED H5 LOW
OVER THE OHIO VALLEY AND GREAT LAKES BY WEDNESDAY. THEY FIDDLE WITH
FOR 48 HRS BEFORE PUSHING IT NORTHEASTWARD THROUGH NEW ENGLAND BY
THE END OF THE WEEK. MODELS SEEM TO BE IN A LITTLE BIT BETTER
AGREEMENT ON FRONTAL TIMING...WITH THE CONSENSUS BEING MONDAY
EVENING FOR BNA AND MONDAY NIGHT AFTER MIDNIGHT FOR CROSSVILLE.
SELS OUTLOOK FOR THE ASSOCIATED CONVECTION IS IN THE SLIGHT RISK
AREA. THE DUAL JET STRUCTURE NOTED ABOVE SEEMS TO MELD INTO A SINGLE
JET WITH A 130KT SPEED MAX OVER NORTH MISSISSIPPI BY TUESDAY AM.
IT SEEMS TO TRY AND RESUME ITS DUAL JET STRUCTURE BY THU AM WITH ONE
JET FROM WESTERN KANSAS LOOPING AROUND THE BASE OF THE TROUGH
THROUGH EAST TENNESSEE AND A SECOND JET FROM SOUTHWEST TO NORTHEAST
OVER NORTHERN FLORIDA. WHILE POSSIBLE SEVERE ACTIVITY IS A
CONCERN...THE MORE OMINOUS POSSIBILITY IS HEAVY RAINFALL RESULTING
FROM THE DUAL JET STRUCTURE AND ITS ASSOCIATED DYNAMICS. THE MODELS
SKILL AT PREDICTING 24 HR TWO INCH OR BETTER RAINFALL AMOUNTS IS
HISTORICALLY BAD. HOWEVER...IM NOT JUMPING ON THE HEAVY RAIN BANDWAGON
JUST YET.

AVN SEEMS TO HAVE BACKED OFF SLIGHTLY ON THE 850 TEMP FORECAST. YSTDA
IT SAW A -2C TEMP OVER BNA BY TUE EVENING AND THE CURRENT RUN TAKES ITS
NO LOWER THAN 0C.

POPS AND TEMPS SEEMS TO BE IN THE BALL PARK WITH A FEW MOSTLY MINOR
ADJUSTMENTS.

BNA TE 079/059 065/045 066 18873
CSV TW 076/058 060/041 061 18795

.BNA...NONE.

JLM

TNZ005>011-022>034-056>066-075>080-093>097-221030-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE NASHVILLE TN
530 AM CDT MON MAY 21 2001

A COLD FRONT WILL APPROACH MIDDLE TENNESSEE LATE TODAY AND PASS TO
THE EAST BY EARLY TUESDAY MORNING. EXPECT NUMEROUS SHOWERS AND
THUNDERSTORMS TODAY AND TONIGHT. ISOLATED SEVERE THUNDERSTORMS
ARE EXPECTED. THE MAIN THREAT FROM THESE STORMS WILL BE DAMAGING
WINDS AND HAIL.

ACTIVATION OF EMERGxENCY MANAGERS AND STORM SPOTTER GROUPS IS
POSSIBLE THROUGH SUNRISE TUESDAY. STAY TUNED TO NOAA WEATHER
RADIO AND LOCAL MEDIA FOR ANY CHANGES.

JLM