Flash Flood Warning 22, NWS Nashville, TN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NASHVILLE TN
1253 PM CDT THU MAY 20 2010

.UPDATE...FOR 18Z TAFS.

&&

.AVIATION...
ONGOING SCT-NUMEROUS SHWRS/STMS EXPECTED TO CONTINUE THROUGH THE
FORECAST PERIOD AS LL BOUNDARY AND UL TROUGH MOVE INTO/ACROSS THE
REGION. MVFR/IFR CONDITIONS LIKELY WITH PASSING STORMS BUT
VSBYS/CEILINGS OTHERWISE LIKELY TO REMAIN VFR AS AREA MOVES INTO
WARM SECTOR THROUGH 09-12Z OR SO. LOWER CEILINGS TOWARD 12Z
EXPECTED TO REMAIN THROUGH MUCH OF THE MORNING ON FRI.

&&

.PREV DISCUSSION... /ISSUED 942 AM CDT THU MAY 20 2010/

MESOSCALE UPDATE...
LEADING AREA OF STORMS MOVG NE IN NW MID TN. NO SVR BUT A FEW
STRONG CELLS BASED ON 30-40 VILS. LOCAL RAINFALL UP TO 1.5
INCHES.

WARM FRONT REMAINS SOUTH OF MID TN TDAY. DESTAB TO MARGINAL THIS
AFTERNOON W/MID-UPR 70S. LOCAL WRF MOVES BROKEN LINE OF STORMS INTO
MID TN THIS AFTERNOON...W/ISO STRONG TO SVR POSSIBLE.

PREV DISCUSSION... /ISSUED 643 AM CDT THU MAY 20 2010/

DISCUSSION...
FORECAST REASONING WILL BE BASED ON A LEAN TOWARD A MODEL
CONSENSUS SOLUTION FOR THE FORECAST PERIOD UNLESS OTHERWISE NOTED.

FORECAST QUANDARIES...AS A LOW PRESSURE SYSTEM CONTINUES TO TAKE
SHAPE OVER THE SRN AND CNTRL PLAINS THIS MORNING...AND A WIDE
AREA OF SHWRS/TSTMS APPROACHES THE MS RIVER VALLEY REGION...THE
AIRMASS ACROSS THE MID STATE WILL CONTINUE TO DESTABILIZE...AIDED BY
A WARM FRONT LIFTING NWD ACROSS THE AREA. AS ATMOSPHERIC MOISTURE
DEEPENS W TO E ACROSS THE MID STATE...EXPECT A SLIGHT CHANCE OF
SHWRS AND TSTMS THIS MORNING...GENERALLY W OF INTERSTATE 65...WITH A
PROGRESSION TO LIKELY SHWRS/TSTMS ACROSS AREAS ALONG AND W OF
INTERSTATE 65 THIS AFTERNOON...WITH ENOUGH INSTABILITY TO SUPPORT A
CHANCE TO SLIGHT CHANCE OF SHWRS AND TSTMS THIS AFTERNOON ACROSS
LOCATION GENERALLY E OF INTERSTATE 65. SPC HAS PLACED PORTIONS OF S
PERRY...SW LEWIS...W LAWRENCE...AND WAYNE COUNTIES IN A SLIGHT RISK
FOR SVR TSTMS THRU 12Z FRI...WITH THE MAIN CONCERNS BEING LARGE HAIL
AND DAMAGING WINDS. DID NOT ADDRESS THIS DIRECTLY IN THE ZONES...AND
THESE LOCATIONS WILL NEED TO BE MONITORED CAREFULLY TODAY AND INTO
THIS EVENING. EVEN IF SVR TSTMS DUE NOT DEVELOP...WOULD NOT BE
SURPRISED AT ALL TO SEE STRONG TSTMS AT LEAST ACROSS THESE
LOCATIONS...AS BEST INFLUX OF MOISTURE...INSTABILITY...AND LIFT
ACROSS THE MID STATE ARE EXPECTED IN THIS AREA. DUE ALSO EXPECT THE
BEST CHANCE OF SHWRS/TSTMS ACROSS THE ENTIRE MID STATE TONIGHT...AS
SFC/UPPER LEVEL LOWS ACROSS THE MID MS VALLEY...USHER IN ADDITIONAL
MOISTURE...INSTABILITY...AND LIFT...AIDED BY A THE WARM FRONT THAT
WILL MOVE INTO THE S OHIO RIVER VALLEY REGION BY LATE TONIGHT. AS
FOR TEMPS...WILL GO CLOSER TO THE NAM MOS FOR HIGHS/LOWS TODAY AND
TONIGHT.

BY FRI...CONSENSUS OF 12Z WED MODELS WAS SHOWING THAT MOST AREAS
WOULD GET MEASURABLE PRECIPITATION ON FRI...AS A WIDE AREA OF
DEEP MOISTURE WAS EXPECTED TO SWEEP EWD ACROSS THE AREA. THE 00Z
THU MODEL RUN SHOWING A MORE REALISTIC SCENARIO WITH BEST DYNAMICS
MOVING TO THE N OF THE MID STATE. AS A RESULT...STILL BELIEVE
SHWRS AND TSTMS WILL DEVELOP...BUT MAY NOT BE AS WIDESPREAD AS
PREVIOUSLY THOUGHT...AND THUS ADDRESSED FRI WITH LIKELY SHWRS AND
TSTMS...WITH A CHANCE OF TSTMS DURING THE AFTERNOON ACROSS THE TN
RIVER VALLEY REGION...WHERE ADVECTION OF A DRIER AIRMASS LOOKS TO
BEGIN DEVELOPING. FOR FRI NIGHT...WILL GO WITH A GENERAL DECREASE IN
SHWR/TSTM ACTIVITY W TO E...WITH MAIN AREAS EXPERIENCING RAINFALL
AFTER MIDNIGHT ALONG AND E OF INTERSTATE 65.

HIGH PRESSURE WILL GENERALLY BE IN CONTROL OF THE WEATHER PATTERN
FOR THE UPCOMING WEEKEND. EVEN WITH THIS RIDGING...ENOUGH MOISTURE
AND INSTABILITY WILL BE AROUND AT LEAST ON SAT TO RESULT IN
MAINLY DIURNAL BASED ISOLATED SHWRS AND TSTMS ACROSS THE
CUMBERLAND PLATEAU REGION. AS OF THIS POINT...WILL CONTINUE TO
KEEP SUN DRY...BUT LATEST MODEL RUNS SHOWING INCREASING MOISTURE
AND INSTABILITY ON SUN ALSO...AND WILL WAIT FOR ADDITIONAL MODEL
RUNS FOR FURTHER CLARIFICATION BEFORE MENTIONING IN FORECAST.

BY THE FIRST PART OF NEXT WEEK...CONTINUE TO EXPECT UPPER HIGH
PRESSURE OVER THE TN VALLEY TO RETROGRADE...AS LOW PRESSURE BUILDS
IN FROM THE SE. AS A RESULT...ATMOSPHERIC MOISTURE WILL GRADUALLY
INCREASE...AND EXPECT ISOLATED TO SCATTERED SHWRS AND TSTMS THRU
THE PERIOD. AS DISCUSSED IN THE AFTERNOON DISCUSSION...PCPN MAY
BE TIED TO A WESTWARD-MOVING INVERTED TROUGH...BUT TIMING OF THIS
FEATURE IS STILL HIGHLY QUESTIONABLE EVEN RIGHT NOW AND WILL JUST
BROAD-BRUSH MAINLY SCT POPS FOR THIS TIME PERIOD.

&&

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

07

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE NASHVILLE TN
130 PM CDT THU MAY 20 2010

TNZ008>011-027>034-058>066-075-077>080-093>095-211030-
SUMNER-MACON-CLAY-PICKETT-DAVIDSON-WILSON-TROUSDALE-SMITH-JACKSON-
PUTNAM-OVERTON-FENTRESS-LEWIS-WILLIAMSON-MAURY-MARSHALL-
RUTHERFORD-CANNON-DE KALB-WHITE-CUMBERLAND-BEDFORD-COFFEE-WARREN-
GRUNDY-VAN BUREN-WAYNE-LAWRENCE-GILES-
130 PM CDT THU MAY 20 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR MIDDLE TENNESSEE.

.DAY ONE...THIS AFTERNOON AND TONIGHT

A WARM FRONT IS EXPECTED TO PUSH INTO MIDDLE TENNESSEE TONIGHT.
SHOWERS AND THUNDERSTORMS ARE EXPECTED...SOME STRONG TO SEVERE.
ONE TO THREE INCHES OF RAINFALL IS POSSIBLE.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS AND LOCAL EMERGENCY MANAGEMENT OFFICIALS ARE ENCOURAGED
TO REPORT HEAVY RAINFALL AMOUNTS TO THE NATIONAL WEATHER SERVICE
IN NASHVILLE.

TNZ005>007-022>026-056-057-211030-
STEWART-MONTGOMERY-ROBERTSON-BENTON-HOUSTON-HUMPHREYS-DICKSON-
CHEATHAM-PERRY-HICKMAN-
130 PM CDT THU MAY 20 2010

...FLASH FLOOD WATCH IN EFFECT UNTIL 6 PM CDT THIS EVENING...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR MIDDLE TENNESSEE.

.DAY ONE...THIS AFTERNOON AND TONIGHT

A WARM FRONT WILL MOVE NORTH INTO WEST MIDDLE TENNESSEE. ISOLATED
SEVERE STORMS ARE EXPECTED...WITH DAMAGING WINDS AND RAINFALL UP
TO 3 INCHES.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

REPORTS FROM TRAINED WEATHER SPOTTERS MAY BE NEEDED.

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

07

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE NASHVILLE TN
927 AM CDT THU MAY 20 2010

TNZ005>007-022>026-201530-
BENTON-CHEATHAM-DICKSON-HOUSTON-HUMPHREYS-MONTGOMERY-ROBERTSON-
STEWART-
927 AM CDT THU MAY 20 2010

...SIGNIFICANT WEATHER ADVISORY FOR BENTON...CHEATHAM...DICKSON...
HOUSTON...HUMPHREYS...MONTGOMERY...ROBERTSON AND STEWART COUNTIES...

AT 925 AM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A
STRONG THUNDERSTORM 7 MILES SOUTH OF ERIN...MOVING NORTHEAST AT 30
MPH.

PEOPLE IN DICKSON...HOUSTON...MONTGOMERY...NORTHEASTERN BENTON...
NORTHERN HUMPHREYS...NORTHWESTERN CHEATHAM...STEWART AND WESTERN
ROBERTSON COUNTIES...INCLUDING THE CITY OF CLARKSVILLE...SHOULD
MONITOR THE WEATHER SITUATION CLOSELY. LISTEN FOR POSSIBLE WARNINGS
AND BE PREPARED TO TAKE APPROPRIATE ACTION SHOULD SEVERE WEATHER
THREATEN.

HALF INCH SIZE HAIL...AND WINDS UP TO 40 MPH ARE EXPECTED WITH THIS
STORM. BRIEF PONDING OF WATER ON ROADWAYS IS ALSO LIKELY.

07

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE NASHVILLE TN
1252 PM CDT THU MAY 20 2010

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1119 AM     FLASH FLOOD      CLARKSVILLE             36.56N 87.35W
05/20/2010                   MONTGOMERY         TN   TRAINED SPOTTER

            ONE AND A HALF FEET OF WATER OVER MEADOW GREEN DRIVE AND
            CLOVERDALE DRIVE. THERE WAS ALSO WATER PONDING IN SEVERAL
            YARDS.

&&

RLH