Special Weather Statement, NWS Nashville, TN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE NASHVILLE TN
715 PM CDT WED OCT 17 2012

.UPDATE...FOR 00Z AVIATION DISCUSSION.
&&

.AVIATION...00Z AVIATION DISCUSSION.
CONCERNS CENTER AROUND LLWS/WIND GUSTS MIXING DOWN TO SFC AS SFC FRONT
APPROACHES/MOVES THRU MID STATE 08/03Z-08/13Z...ALONG WITH SFC GUSTS FROM
SHWRS/TSTMS. SHORT RANGE MODELS SUGGESTING STRONG LOW LEVEL JET DYNAMICS IN
PLACE DURING THIS PERIOD...TEMPO SFC GUSTS TO 35KT-40KT NOT OUT OF QUESTION
WITH LLWS OF 60KTS WITHIN 2KFT OF SFC. EXPECT LINE OF SHWRS/TSTMS TO MOVE
INTO/ACROSS TAF LOCATIONS WITH TEMPO GROUPS SHOWING OVERALL BEST TIMING
POTENTIAL FOR IMPACTS AT TAF SITES. EXPECT CLRING W TO E 18/09Z-18/15Z TIME
FRAME...WITH STRONG PRESSURE GRADIENT BEHIND FRONTAL PASSAGE RESULTING IN
20KT-25 KT GUST 18/17Z-18/23Z.
&&

.PREV DISCUSSION.../ISSUED 501 PM CDT WED OCT 17 2012/

UPDATE...
DEVELOPING LINE OF STORMS EXTENDS FROM CENTRAL MO SOUTHWARD
THROUGH NW AR. CONVECTION ALSO ATTEMPTING TO FLARE UP ACROSS
EASTERN AR. MODELS CONTINUE TO KEEP THE CONVECTION WEST OF THE MID
STATE UNTIL 8PM OR 9PM. WILL GO AHEAD AND UPDATE GRIDS TO REFLECT
THE TIMING OF WHEN THE ORGANIZED CONVECTION WILL ARRIVE. ZONES
HAVE ALREADY BEEN SENT WITH A LITTLE EXTRA EMPHASIS ON TIMING.
ADDITIONALLY...I WILL ADD THE POTENTIAL FOR GUSTY WINDS TO
ACCOMPANY THE STORMS. THOUGH INSTABILITY LEVELS ARE
MARGINAL AND THE SLIGHT RISK IS JUST TO THE WEST...THERE IS A LOT
OF WIND ENERGY WITH THIS APPROACHING SYSTEM. ZONE UPDATE HAS BEEN
SENT AS OF A FEW MINUTES AGO.

PREV DISCUSSION.../ISSUED 213 PM CDT WED OCT 17 2012/

DISCUSSION...
BREEZY SOUTHERLY FLOW ACROSS THE TENNESSEE AND OHIO VALLEYS THIS
AFTERNOON WITH VWP SHOWING 25KT AT THE TOP OF THE BOUNDARY LAYER
AND 25KTS TO 30 KTS FROM 925MB TO 850 MB. WINDS WILL INCREASE IN
MIDDLE TENNESSEE AS WE THROUGH THE AFTERNOON AND INTO THE EVENING
AS A POTENT STORM SYSTEM APPROACHES FROM THE WEST WITH A TIGHTENING
SURFACE PRESSURE GRADIENT.

CONVECTION HAS BEEN A LITTLE SLOW DEVELOPING OVER THE MIDDLE AND
LOWER MISSISSIPPI VALLEYS TODAY AS STRONG CAP (SEE 18Z LITTLE ROCK
SOUNDING FOR EXAMPLE) HAS CONTINUED TO HOLD BUT I BELIVE IT WILL WEAKEN
SHORTLY OVER SOUTHWEST MISSOURI AND NORTHWEST ARKANSAS ALLOWING
THUNDERSTORMS TO QUICKLY DEVELOP IN THOSE AREAS. ONCE THIS HAPPENS
EXPECT TO SEE A LINE (OLD FASHION SQUALL LINE) DEVELOP DURING THE
AFTERNOON FROM WESTERN MISSOURI DOWN INTO EASTERN OKLAHOMA. THE
SQUALL LINE WILL WORK EAST AND INTO ARKANSAS DURING THE LATE
AFTERNOON. THE LEADING EDGE WILL APPROACH THE MISSISSIPPI RIVER IN
WEST TENNESSEE AROUND 00Z TODAY WITH THE LEADING EDGE NEAR THE
TENNESSEE RIVER BY 03Z AND ALONG INTERSTATE 65 AROUND 06Z AND THEN
NEARING THE PLATEAU BY 09Z. MY TIMING MAY BE A LITTLE OFF AS
SQUALL HAS YET TO DEVELOP BUT THIS IS MY BEST ESTIMATE AT THIS
TIME. THE SQUALL LINE WILL EXIT THE PLATEAU SHORTLY AROUND
DAYBREAK FOLLOWED BY A COUPLE OF HOURS OF SHOWERS THURSDAY MORNING
OVER EASTERN MIDDLE TN/PLATEAU. LOOK FOR CLEARING SKIES FROM THE
WEST LATE TONIGHT AND THURSDAY MORNING. PACIFIC AIR WILL FOLLOW SO
NO MAJOR CHANGES IN TEMPERATURES FOR THE NEXT SEVERAL DAYS.

ESPECIALLY WITH THE FAST LINE MOVEMENT THERE IS THE CHANCE THAT A
FEW STORMS COULD CONTAIN DAMAGING STRAIGHT LINE WINDS AND HAIL AS
THEY MOVE THROUGH MIDDLE TENNESSEE TONIGHT. THE BEST CHANCE WOULD
BE OVER WESTERN AREAS OF THE MID STATE. ONCE THE SQUALL NEARS THE
TENNESSEE RIVER THE THERMODYNAMICS WEAKEN WHILE THE WIND FIELDS
REMAIN STRONG WITH BULK SHEAR ON THE ORDER OF 40 KT TO 45 KTS 0-3
KM. I THINK THE TORNADO THREAT IS MINIMAL SINCE THE BEST JET
CONFIGURATION IS ACROSS SOUTHERN ARKANSAS/WESTERN MISSISSIPPI AND
NORTHEAST LOUISIANA WHERE THE LOW AND MID LEVEL JETS INTERSECT.

AFTER THIS SYSTEM BLOWS THROUGH TONIGHT I HAVE NO RAIN IN THE
FORECAST THROUGH MUCH OF NEXT WEEK WITH THE NEXT SYSTEM MOVING IN
ON SATURDAY THE 27TH OF OCTOBER.

BOYD

&&

.OHX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

31

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE NASHVILLE TN
825 PM CDT WED OCT 17 2012

TNZ005>011-022>034-056>066-075-077>080-093>095-181545-
STEWART-MONTGOMERY-ROBERTSON-SUMNER-MACON-CLAY-PICKETT-BENTON-
HOUSTON-HUMPHREYS-DICKSON-CHEATHAM-DAVIDSON-WILSON-TROUSDALE-
SMITH-JACKSON-PUTNAM-OVERTON-FENTRESS-PERRY-HICKMAN-LEWIS-
WILLIAMSON-MAURY-MARSHALL-RUTHERFORD-CANNON-DE KALB-WHITE-
CUMBERLAND-BEDFORD-COFFEE-WARREN-GRUNDY-VAN BUREN-WAYNE-LAWRENCE-
GILES-
825 PM CDT WED OCT 17 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR MIDDLE TENNESSEE.

.DAY ONE...TONIGHT

A COLD FRONT IS EXPECTED TO SWEEP ACROSS THE MID STATE TONIGHT AND
PRODUCE THE POSSIBILITY FOR SEVERE THUNDERSTORMS...ESPECIALLY WEST
OF INTERSTATE 65. THE MAIN THREAT IS EXPECTED TO BE DAMAGING
STRAIGHT LINE WINDS AND HAIL. A LINE OF THUNDERSTORMS IS EXPECTED TO
REACH THE TENNESSEE RIVER AROUND 10 PM THIS EVENING...THE NASHVILLE
AREA AROUND MIDNIGHT...AND THEN REACH THE CUMBERLAND PLATEAU AROUND
2 AM.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY...

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER CALL TO ACTION STATEMENT...

REPORTS FROM TRAINED WEATHER SPOTTERS MAY BE NEEDED TONIGHT.

SPOTTER THUNDERSTORM REPORTING CRITERIA...
TORNADO
FUNNEL CLOUD
FLOODING
HAIL >= 1/2 INCH
WINDS > 50 MPH (MEASURED)
STRUCTURAL DAMAGE
TREES OR POWER LINES DOWN

21

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE NASHVILLE TN
1014 PM CDT WED OCT 17 2012

TNZ005-006-022>025-056-057-180415-
BENTON-DICKSON-HICKMAN-HOUSTON-HUMPHREYS-MONTGOMERY-PERRY-STEWART-
1014 PM CDT WED OCT 17 2012

...SIGNIFICANT WEATHER ADVISORY FOR BENTON...DICKSON...HICKMAN...
HOUSTON...HUMPHREYS...MONTGOMERY...PERRY AND STEWART COUNTIES...

AT 1009 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING
STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM NEAR MURRAY TO
SOUTHWEST OF BUENA VISTA...OR JUST WEST OF THE TENNESSEE
RIVER...MOVING EAST AT 50 MPH.

THESE STORMS WILL BE NEAR...
  DOVER BY 1035 PM CDT.
  TENNESSEE RIDGE BY 1045 PM CDT.
  ERIN BY 1050 PM CDT.
  WAVERLY BY 1055 PM CDT.
  LINDEN BY 1105 PM CDT.
  DICKSON BY 1115 PM CDT.

WIND GUSTS OF AROUND 50 MPH ARE EXPECTED WITH THESE STORMS...AS WELL
AS HEAVY RAINFALL AND DANGEROUS CLOUD-TO-GROUND LIGHTNING.

PEOPLE IN THE CITIES OF CAMDEN...DOVER...NEW JOHNSONVILLE...
TENNESSEE RIDGE...ERIN...WAVERLY...MCEWEN...LINDEN AND DICKSON
SHOULD MONITOR THE WEATHER SITUATION CLOSELY. LISTEN FOR POSSIBLE
WARNINGS AND BE PREPARED TO TAKE APPROPRIATE ACTION SHOULD SEVERE
WEATHER THREATEN.

LAT...LON 3667 8786 3664 8784 3665 8721 3638 8724
      3633 8729 3632 8725 3595 8729 3561 8766
      3549 8773 3559 8803 3572 8804 3581 8798
      3585 8822 3612 8822 3626 8809 3636 8810
      3637 8801 3644 8807 3657 8804 3667 8808

AL