Severe Thunderstorm Warning 45, NWS Louisville, KY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
858 PM EDT SAT MAY 1 2010

...FORECAST UPDATE...

BASED ON THE 18Z MODEL GUIDANCE I HAVE MADE SEVERAL CHANGES TO THE
ONGOING FORECAST. FIRST I HAVE ADJUSTED CURRENT HOURLY TEMPERATURES
DOWN BUT I EXPECT THEM TO RISE OVERNIGHT AS THE SURFACE LOW TRACKS
TO THE NORTH FROM ARKANSAS INTO ILLINOIS. HAVE ALSO LOWER POPS
THROUGH 06Z AS IT LOOKS AS FOR WE WILL CONTINUE TO SEE A GAP IN
CURRENT RAINFALL AND EXPECTED RAIN AS LOW APPROACHES. I HAVE ALSO
ADJUSTED QPF DOWN SOME..

AS FAR AS SEVERE STORMS THE TIMEFRAME BETWEEN 07 AND 14Z LOOKS BEST
WITH WINDS AND POSSIBLY A FEW TORNADOS THE MAIN ISSUE. AS FAR AS
FLOODING GOES SUNDAY LOOKS TO BE THE BEST DAY ESPECIALLY ACROSS
SOUTH CENTRAL KENTUCKY.

FORECAST ALREADY OUT.

.SHORT TERM (TONIGHT AND SUNDAY)...

...EXCESSIVE RAINFALL WITH LIKELY FLOODING AS WELL AS A SEVERE
WEATHER EPISODE FOR TONIGHT AND SUNDAY...

A MAJOR WEATHER EVENT IS IN STORE FOR US AS A POTENT WAVE RIDES UP A
FRONTAL BOUNDARY TO OUR WEST TONIGHT.  THIS BOUNDARY WILL THEN
SLOWLY PUSH THROUGH THE REGION THROUGHOUT THE DAY SUNDAY.  THE
SYSTEM WILL CREATE A DOUBLE THREAT...FLASH FLOODING AND SEVERE
THUNDERSTORMS.

SEVERE THREAT...

OCCASIONAL SHOWERS AND THUNDERSTORMS WILL BE COMMON FOR THE REST OF
THE AFTERNOON INTO THE EARLY EVENING HOURS.  AFTER
MIDNIGHT...CONVECTIVE ACTIVITY WILL STRENGTHEN AS STRONG SYSTEM
DYNAMICS OVERTAKE THE REGION. LATEST SPC DAY 1 OUTLOOK INDICATES A
MODERATE RISK OF SVR OVER THE WESTERN ONE QUARTER OF OUR FA WITH A
SLIGHT RISK TO THE EAST OVER MUCH OF THE REST OF OUR AREA. PRIMARY
CONCERN IS DAMAGING WINDS AND ISOLD TORNADOES WITH AN INCREASINGLY
VOLATILE ENVIRONMENT THAT FCST SOUNDINGS IN THE MODERATE RISK AREA
SHOW AFTER MIDNIGHT TNGT. THEY INCLUDE:

MEAN LAYER CAPE UP TO AROUND 2000 J/KG

STRONG LOW/DEEP LAYER SHEAR WITH THE LOW LEVEL JET INCRSG TO 60-70KT

STRONG/DEEP ASCENT/FORCING AS UPR/SFC WAVES MOVE ALONG A QUASISTNRY
FRONT ACRS SRN IL/SE MO AND THEN FRONT MOVES TOWARD OUR REGION AS
WAVES PASS TO THE NORTH.

CONTD MOIST INFLOW AS PRECIPITABLE WATER VALUES APPROACH 2 INCHES.

THIS DEEPLY MOIST/SHEARED ENVIRONMENT WITH UNIDIRECTIONAL MID/UPR
LEVEL FLOW WILL SUPPORT BOTH MULTICELL/SUPERCELL TRAINING STORMS AND
LEWPS THAT WILL COULD RESULT IN WIDESPREAD WIND DAMAGE AND ISOLD
STRONG TORNADOES...ESPECIALLY FOR THAT PART OF SOUTH CENTRAL
KENTUCKY TO THE WEST OF I-65 LATE TNGT.

FLASH FLOODING THREAT...

WITH SUCH A RICH MOIST ENVIRONMENT IN PLACE AND SOAKED GROUNDS FROM
THE 1-3 INCHES OF RAINFALL THAT FELL TODAY...THE SETUP FOR
PARTICULARLY DANGEROUS FLASH FLOODING IS IN PLACE.  THE SURFACE
BOUNDARY/S SLOW MOVEMENT EASTWARD WILL CAUSE STORMS TO TRAIN AND
REDEVELOP OVER THE SAME AREAS TONIGHT THROUGH SUNDAY NIGHT.
ADDITIONAL RAINFALL AMOUNTS OF 2-6 INCHES ARE EXPECTED TONIGHT
THROUGH SUNDAY NIGHT.  THIS WILL BRING STORM TOTALS FOR THE ENTIRE
EVENT UP TO 3-5 INCHES OVER SOUTHERN INDIANA...AND 5-7 INCHES OVER
CENTRAL KENTUCKY.  SOME AREAS OVER SOUTH CENTRAL KY MAY SEE 7+
INCHES OF RAIN BY THE TIME THIS STORM IS DONE!

EVERYONE SHOULD STAY ABREAST OF THE LATEST FORECASTS AND WARNINGS
FROM THE NATIONAL WEATHER SERVICE OVER THE NEXT 36 HRS.  USE NOAA
WEATHER RADIO OR VISIT OUR WEBSITE AT WWW.WEATHER.GOV/LMK.

.LONG TERM (SUNDAY NIGHT - SATURDAY)...

CONSENSUS IS BUILDING THAT THIS UPCOMING WORK WEEK WILL SEE A VAST
IMPROVEMENT OVER OUR WET DERBY WEEKEND. EXPECT A MAINLY DRY AND WARM
WEEK WITH OUR ONLY REAL CHANCES OF RAIN ARRIVING MONDAY EVENING AND
FRIDAY.

THE FORECAST UPPER AIR PATTERN ON MONDAY INDICATES A WEAKENING
POSITIVELY TILTED TROUGH CENTERED OVER THE SOUTHERN PLAINS. A STRONG
JET WILL HAVE EXITED THE BASE OF THIS TROUGH BY THIS TIME...AND WILL
EXTEND FROM TEXAS THROUGH NEW ENGLAND. MORE IMPORTANTLY...THE AXIS
OF VERY HIGH PRECIPITABLE WATER RESPONSIBLE FOR SUNDAY'S HEAVY RAINS
WILL HAVE SAGGED SOUTHEAST ACROSS EASTERN TENNESSEE AND WEST
VIRGINIA. AS DRIER AIR WORKS ITS WAY ACROSS THE COMMONWEALTH DURING
THE DAY...EXPECT AT LEAST PARTIALLY CLEARING SKIES WITH ANY
LINGERING RAIN ACROSS OUR SOUTHEASTERN COUNTIES ENDING DURING THE
MORNING HOURS. BY LATE MONDAY...SOME SCATTERED SHOWERS MAY DEVELOP
DURING THE AFTERNOON OR EVENING HOURS ACROSS SOUTHERN INDIANA AND
NORTHERN KENTUCKY AS THE AXIS OF THE ABOVE MENTIONED 500MB TROUGH
MOVES ACROSS THE OHIO RIVER.

BY EARLY WEDNESDAY...UPPER AIR FLOW WILL BECOME ZONAL ACROSS THE
CONUS AS A STRONG JET MOVES ASHORE ACROSS THE PACIFIC NORTHWEST.
MILD WESTERLY FLOW WILL MOVE ACROSS THE LOWER OHIO VALLEY WEDNESDAY
THROUGH EARLY FRIDAY. AT THE SURFACE...EXPECT LIGHT WINDS WEDNESDAY
AS HIGH PRESSURE MOVES OVERHEAD. SOUTHERLY FLOW WILL DEVELOP
THURSDAY AS HIGH PRESSURE BECOMES ESTABLISHED ACROSS OUR
SOUTHEASTERN STATES. MOSTLY SUNNY SKIES AND WARM TEMPERATURES IN THE
MID 70S TO THE LOWER 80S ARE EXPECTED WEDNESDAY AND THURSDAY.

THE ZONAL UPPER AIR PATTERN IS EXPECTED TO BEGIN TO AMPLIFY EARLY
FRIDAY AS LOW PRESSURE IS FORECAST TO DEVELOP ACROSS THE LOWER
MISSOURI VALLEY. THIS WILL DEEPEN AS IT MOVES TOWARDS THE GREAT
LAKES LATE IN THE DAY. SHOWERS AND THUNDERSTORMS MAY ACCOMPANY A
PRETTY STOUT COLD FRONT FRIDAY AS IT MOVES SOUTHEAST ACROSS THE OHIO
RIVER. HIGH PRESSURE WILL BUILD SOUTHEAST TOWARDS THE LOWER OHIO
VALLEY EARLY SATURDAY. THIS WILL BRING DISTINCTLY COLDER
TEMPERATURES FOR NEXT WEEKEND.

&&

.AVIATION (00Z TAF ISSUANCE)...

ALL AND ALL IT WILL NOT BE A GOOD NIGHT TO FLY ACROSS CENTRAL
KENTUCKY.

AN AREA OF LOW PRESSURE LOCATED OVER SOUTHWEST ARKANSAS THIS EVENING
WILL TRACK TO NORTHERN ILLINOIS BY 12Z. AS THIS LOW MOVES TO THE
NORTHEAST LOW LEVEL WINDS ACROSS CENTRAL KENTUCKY WILL INCREASE WITH
A 50 TO 60KT LOW LEVEL JET DEVELOPING OVER THE REGION. IN ADDITION
HEAVY THUNDERSTORMS WILL MOVE INTO THE AREA WITH THE POTENTIAL FOR
DAMAGING WINDS. THE STRONGEST WINDS AND THUNDERSTORMS SHOULD OCCUR
BETWEEN 06 AND 14Z. HEAVY RAIN AFTER THIS TIME WILL GRADUALLY TAPER
OFF BY LATE IN THE FORECAST PERIOD BUT CIGS WILL REMAIN IN THE MVFR
CATEGORY.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...FLASH FLOOD WATCH THROUGH MONDAY MORNING FOR KYZ023>043-045>049-
     053>057-061>067-070>078-081-082.

IN...FLASH FLOOD WATCH THROUGH MONDAY MORNING FOR INZ076>079-083-084-
     089>092.

&&

UPDATE.........JA
SHORT TERM.....AML
LONG TERM......JSD
AVIATION.......JA

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE LOUISVILLE KY
900 PM EDT SAT MAY 1 2010

INZ076>079-083-084-089>092-KYZ023>043-045>049-053>057-061>067-
070>078-081-082-022030-
ORANGE IN-WASHINGTON IN-SCOTT IN-JEFFERSON IN-DUBOIS IN-
CRAWFORD IN-PERRY IN-HARRISON IN-FLOYD IN-CLARK IN-HANCOCK KY-
BRECKINRIDGE KY-MEADE KY-OHIO KY-GRAYSON KY-HARDIN KY-BULLITT KY-
JEFFERSON KY-OLDHAM KY-TRIMBLE KY-HENRY KY-SHELBY KY-FRANKLIN KY-
SCOTT KY-HARRISON KY-SPENCER KY-ANDERSON KY-WOODFORD KY-
FAYETTE KY-BOURBON KY-NICHOLAS KY-NELSON KY-WASHINGTON KY-
MERCER KY-JESSAMINE KY-CLARK KY-LARUE KY-MARION KY-BOYLE KY-
GARRARD KY-MADISON KY-BUTLER KY-EDMONSON KY-HART KY-GREEN KY-
TAYLOR KY-CASEY KY-LINCOLN KY-LOGAN KY-WARREN KY-SIMPSON KY-
ALLEN KY-BARREN KY-MONROE KY-METCALFE KY-ADAIR KY-RUSSELL KY-
CUMBERLAND KY-CLINTON KY-
900 PM EDT SAT MAY 1 2010 /800 PM CDT SAT MAY 1 2010/

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTH CENTRAL
INDIANA AND CENTRAL KENTUCKY.

.DAY ONE...OVERNIGHT.

IN RESPONSE TO DEEPENING LOW PRESSURE ACROSS THE MISSISSIPPI
VALLEY...ADDITIONAL THUNDERSTORMS ARE EXPECTED TO FIRE ALONG AND
EAST OF A COLD FRONT THAT WILL BE STRENGTHENING AS IT REACHES WEST
KENTUCKY BY SUNRISE.

STORMS ARE EXPECTED TO INCREASE IN STRENGTH AFTER 2 AM CDT AND WILL
LIKELY PRODUCE DAMAGING WINDS AND POSSIBLY ISOLATED TORNADOES...
MAINLY TO THE WEST OF INTERSTATE 65 ACROSS CENTRAL KENTUCKY AND
SOUTHERN INDIANA.

IN ADDITION...SHOWERS AND THUNDERSTORMS WILL POSE A FLASH FLOOD
THREAT OVER SOUTHERN INDIANA AND CENTRAL KENTUCKY. WITH GROUNDS
ALREADY WELL SATURATED FROM THE RAINS TODAY...ANY QUICK BURSTS OF
2 TO 3 INCHES OF RAINFALL WILL LIKELY CAUSE FLASH FLOODING.

SINCE THESE FLASH FLOOD AND POTENTIALLY SEVERE PRODUCING STORMS ARE
EXPECTED TO AFFECT THE OUTLOOK AREA AT NIGHT...WE HIGHLY ENCOURAGE
YOU TO SET YOUR NOAA WEATHER RADIO TO ALERT MODE SO THAT YOU CAN BE
AWAKENED IN THE EVENT THAT A WARNING IS ISSUED WHILE YOU ARE ASLEEP.
MANY FLASH FLOOD AND SEVERE WEATHER FATALITIES OCCUR LATE AT NIGHT.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY.

THE SEVERE WEATHER WILL CONTINUE THROUGH SUNDAY MORNING WITH MORE
STRONG TO SEVERE THUNDERSTORMS CAPABLE OF PRODUCING DAMAGING
WINDS...ISOLATED TORNADOES...AND VERY HEAVY RAINFALL. RAINFALL
TOTALS THROUGH THE WEEKEND ARE EXPECTED TO TOTAL BETWEEN 3 AND 7
INCHES....WITH THE HEAVIEST AMOUNTS IN EXCESS OF 7 INCHES ACROSS
SOUTH CENTRAL KENTUCKY.

THIS EXCESSIVE RAINFALL WILL LIKELY RESULT IN FLOODING
PROBLEMS...THEREFORE A FLASH FLOOD WATCH IS IN EFFECT. IF YOU LIVE
IN A FLOOD PRONE AREA...STAY ABREAST OF THE LATEST FORECASTS
THROUGH THE WEEKEND.

SCATTERED THUNDERSTORMS ARE POSSIBLE FRIDAY AND FRIDAY EVENING AS A
COLD FRONT IS EXPECTED TO MOVE ACROSS THE REGION.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS AND EMERGENCY MANAGERS ARE ASKED TO REPORT INSTANCES OF
HEAVY RAINFALL...FLASH FLOODING AND SEVERE WEATHER TO THE NATIONAL
WEATHER SERVICE IN LOUISVILLE.

DK/AML/JSD/JA

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