Severe Thunderstorm Warning 451, NWS Louisville, KY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
334 PM EDT TUE OCT 18 2011

.Short Term (Tonight and Wednesday)...

Short term models overall in good agreement handling a complicated
weather system tonight and Wednesday. Strong mid-level shortwave
will close off over the lower OH Valley Wednesday morning as an
upper-level (300 mb) jet streak digs southeast into the southern
Plains and then pivots across the Gulf states and into the TN Valley
tonight and Wednesday. Surface reflection of these features aloft
will include a surface low which will deepen and move north-
northeastward along a pronounced surface front over middle TN and
KY. The front has continued to lift slowly northward over southern
and southeastern KY this afternoon in response to the approaching
system aloft. At 19z, according to the KY Mesonet and ASOS obs, the
front was just southeast of BWG (but north of OHX) to between LEX
and Richmond (Madison County). It is probably very near LEX given a
calm wind on latest LEX observation. The front may lift a bit
farther north late this afternoon and evening as the low pushes
northeast along it.

Along and south of the front, latest SPC mesoanalysis page shows
500-1000 J/kg CAPE and -2 to -4 surface-based LI values. Models
still show some elevated instability/steeper lapse rates north of
the front over central KY as well. As forcing for lift increases
late this afternoon and tonight with approaching mid-level system
and jet streak, increasing rains over southern IL to western TN will
expand northeastward into our forecast area. Also, scattered to
numerous thunderstorms will develop over middle TN to central KY.
Latest NWS Doppler radar is now showing convective cells beginning
to develop quickly over middle TN. They will expand and propagate
across south-central and central KY over the next few hours. Along
and south of the front, a few cells could produce strong wind gusts,
hail, and very heavy rain. North of the front, small hail is still
quite possible.

Rain and embedded convection will continue tonight over much of the
forecast area as the mid-level system closes off and starts to take
on a negative tilt. Locally heavy rain will continue.

By Wednesday morning, models suggest an upper dry slot will
propagate into parts of central KY within or just left of core of
upper jet streak. This may cause rain to diminish somewhat, although
low clouds and at least scattered showers and drizzle will continue.
GFS is faster than NAM with this evolution, but both show it. By
Wednesday afternoon, deformation rains within the isotach gradient
zone left of the upper jet core should rotate eastward into central
KY resulting in additional rainfall and cool dreary temperatures.
The clouds and rain will continue into Wednesday night. High
temperatures Wednesday will be tricky, as the coolest air associated
with this system will not be here til Thursday, but temperatures
Wednesday should reach no higher than lower to perhaps mid 50s.

.Long Term (Wednesday Night - Tuesday)...

Wednesday Night - Friday Night...

...Windy Conditions Expected Wednesday Night through Thursday
Evening...

The latest suite of deterministic and ensemble model runs continue
to be in good agreement with developing a very large full latitude
trough over the eastern United States.  Strong mid-level wave
currently moving through the plains will hook up with a northward
advancing tropical-hybrid system to develop a large area of surface
low pressure over the eastern U.S.  The surface low will deep and
potentially bomb out over the eastern Great Lakes.  As this occurs,
we'll be on the western side of the system within the deformation
and trowl zone.  Widespread showers, some heavy at times will be in
the area Wednesday night and continuing into Thursday.  Initial
thinking was that the system would pull off rather quickly, however,
with the slower and deeper solutions, this system will likely move
off slower than the models anticipate.  Rainfall amounts of 0.25 to
0.75 inches will be possible through the period with the bulk of the
heaviest rain falling across the northeastern half of the forecast
area.

In addition to the rain, as the system closes off aloft and moves
northeastward, really cold air will work into the region Wednesday
night and Thursday.  Thermal profiles show that while the colder air
is still forecast to come in, the near surface warm layer is
forecast to remain thick enough for rain.  However, in previous
cases like this, we have seen heavier (convective) showers actually
put down some sleet.  We believe this is still possible, but
forecast uncertainty remains high enough to keep it out of the
forecast for now.  As the low cranks up, the pressure gradient will
increase rapidly throughout the day on Wednesday.  Sustained winds
of 20-25 MPH will be common across the region Wednesday night and
Thursday with gusts up to 40 MPH being possible.  Should further
data continue this trend, a Wind Advisory may be required in
subsequent forecasts.  Temperatures will fall into the lower 40s
Wednesday night but it will feel like the mid 30s when one adds in
the wind chill.  Temperatures are not really going to go anywhere on
Thursday as readings will likely top out in the 42-46 degree range.

By Thursday night, the upper low and surface low will be on its way
through the northeastern US.  Quite a bit of low-mid level moisture
will remain in the area to keep skies mostly cloudy early with
partial clearing occurring late.  With the pressure gradient staying
up, the threat of frost for Friday morning looks less at this time.
Should more clearing take place and winds die down faster than
forecast, the southwestern/western sections would have the best shot
of seeing frost.  Skies should really clear out during the day on
Friday as highs warm back into the lower to middle 50s.  Good
radiational cooling looks on tap for Friday night/Saturday morning
with temperatures falling to near freezing.  At this time, Saturday
morning looks to be the best time for us to see a decent
frost/freeze event.

Saturday - Tuesday...

Surface high pressure is forecast to hold sway across the region on
Saturday and Sunday providing mostly sunny days and mostly clear
nights.  As the high heads east Saturday night, some mid-high level
clouds may advect in from the west.  Surface winds will likely veer
around to the south/southwest which will keep temperatures from
falling as much.  Highs Saturday should top out in the lower 60s
with overnight lows cooling into the mid 30s in the east with upper
30s to the lower 40s in the central and western sections.  Highs
Sunday should warm into the lower to middle 60s.  A weak upper
trough will work through the region Sunday night and Monday, but
with moisture quite limited, only think an increase in clouds will
be noted.  lows Sunday night will cool into the lower-middle 40s
with highs on Monday in the middle to upper 60s.  Another mid-level
wave looks to enter the region on Tuesday.  This wave is a bit more
deeper and moisture may have increased enough that a few isolated
showers will be possible.  Latest consensus guidance suggests very
low pops in this period, thus plan on increasing the clouds but
keeping the forecast dry.  Highs Tuesday look to be even milder with
upper 60s to lower 70s expected.

Finally, a look ahead reveals more unsettled weather for the end of
next week. Both the 18/12Z runs of the GFS and Euro show yet another
large amplification of the flow over the CONUS.  It does appear that
a large upper trough will crash into the eastern US as high latitude
blocking develops over the north Atlantic.  This will likely bring
another round of precipitation to the eastern US along with a shot
of cold air out of Canada, which could be colder than what we see
this week.  It certainly will be something to watch over the coming
days.

&&

.Aviation (18Z TAF Issuance)...

Rain and embedded convection from southeastern MO to western TN will
expand and track north-northeast this afternoon and tonight ahead of
a deepening shortwave aloft, which will close off over the lower OH
Valley late tonight and Wednesday. The rain will push into BWG and
SDF late this afternoon and especially tonight. Scattered
thunderstorms will develop within and ahead of the area of rain,
along and north/west of a surface front oriented from between BWG
and OHX northeast to eastern KY at this time. Increasing lift and
developing surface-based instability over middle TN to southeast KY
(south of the front) will fuel storm development as the air lifts
northward above the front. Have included VCTS in all TAFs for this
afternoon and evening as low pressure moves northeast along the
boundary. This front should make it to or slightly north/west of LEX
so will start their winds off as south-southeast, becoming variable
and then north tonight as the low approaches and passes by. LEX
surface winds will need to be monitored given the close proximity of
the front.

With rain expected at all TAF sites tonight, cigs will lower
considerably. All models show cigs lowering into IFR category
tonight, which are reflected in TAFs. For now, will keep values out
of LIFR until there is more evidence that this may occur, which it
could. Wednesday morning, steadier rains should diminish to
scattered showers at TAF sites, with additional light rain and
drizzle moving in later in day on back side of surface low. IFR cigs
should continue. Kept vsbys in MVFR category tonight and Wednesday.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
KY...NONE.

Short Term.......TWF
Long Term........MJ
Aviation.........TWF

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE LOUISVILLE KY
402 PM EDT TUE OCT 18 2011

INZ076>079-083-084-089>092-KYZ023>043-045>049-053>057-061>067-
070>078-081-082-192015-
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-
402 PM EDT TUE OCT 18 2011 /302 PM CDT TUE OCT 18 2011/

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

.DAY ONE...TONIGHT.

SCATTERED TO NUMEROUS THUNDERSTORMS WILL DEVELOP LATE THIS AFTERNOON
AND TONIGHT OVER MUCH OF CENTRAL KENTUCKY AND INTO SOUTH-CENTRAL
INDIANA. SOME OF THESE STORMS WILL PRODUCE SMALL HAIL...OCCASIONAL
CLOUD-TO-GROUND LIGHTNING...AND HEAVY RAIN. OVER SOUTH-CENTRAL
KENTUCKY...THE STRONGEST STORMS COULD ALSO PRODUCE ISOLATED WIND
DAMAGE AND ISOLATED QUARTER-SIZE HAIL THROUGH THIS EVENING ALONG
AND SOUTH OF A STATIONARY FRONT.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY.

A STRONG LOW PRESSURE SYSTEM IS FORECAST TO MOVE NORTHWARD ACROSS
THE EASTERN SECTIONS OF THE MIDDLE AND UPPER OHIO VALLEY. THIS
SYSTEM WILL BRING WIDESPREAD RAINFALL AND WINDY CONDITIONS TO THE
OUTLOOK AREA. SUSTAINED WINDS OF 20 TO 25 MPH WITH WIND GUSTS UP
TO 40 MPH CAN BE EXPECTED FROM WEDNESDAY EVENING THROUGH THURSDAY
AFTERNOON. MUCH COOLER AIR WILL FILTER IN BEHIND THIS SYSTEM.
AREAS OF FROST ALONG WITH NEAR FREEZING TEMPERATURES WILL BE
POSSIBLE BY SATURDAY MORNING.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS ARE ENCOURAGED TO REPORT ANY INSTANCES OF HAIL AND STRONG
WINDS THROUGH TONIGHT TO THE NATIONAL WEATHER SERVICE IN
LOUISVILLE.

TWF/MJ

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE LOUISVILLE KY
425 PM EDT TUE OCT 18 2011

KYZ045-046-054-182100-
MARION-NELSON-WASHINGTON-
425 PM EDT TUE OCT 18 2011

...STRONG THUNDERSTORM WITH DANGEROUS LIGHTNING...HEAVY RAIN...AND
PENNY SIZE HAIL...

AT 423 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A
STRONG THUNDERSTORM 11 MILES WEST OF LEBANON...AND MOVING NORTHEAST
AT 35 MPH.

FREQUENT CLOUD TO GROUND LIGHTNING...HEAVY RAIN WITH RAINFALL RATES
OF AROUND ONE INCH PER HOUR REDUCING VISIBILITIES TO LESS THAN ONE
MILE...AND PENNY SIZE HAIL...ARE EXPECTED WITH THIS STORM.

* THIS STORM WILL ALSO IMPACT...
  SPRINGFIELD...
  LORETTO AND NERINX...
  BURKES SPRING AND GANDERTOWN...
  BEARWALLOW AND CISSELVILLE...
  SAINT CATHARINE AND FREDERICKTOWN...

PRECAUTIONARY/PREPAREDNESS ACTIONS...

IF YOU ARE IN THE PATH OF THIS STORM...SEEK SHELTER INDOORS AND STAY
AWAY FROM WINDOWS. STAY TUNED TO NOAA ALL HAZARDS RADIO...
WEATHER.GOV/LOUISVILLE ON THE INTERNET...OR LOCAL MEDIA FOR LATER
UPDATES AND POSSIBLE WARNINGS.

&&

LAT...LON 3751 8549 3754 8550 3756 8553 3756 8555
      3754 8555 3752 8556 3754 8560 3793 8529
      3780 8506 3747 8538 3748 8544 3747 8546
TIME...MOT...LOC 2026Z 215DEG 30KT 3757 8543

MJ

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LOUISVILLE KY
426 PM EDT TUE OCT 18 2011

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

0420 PM     HAIL             HOLLAND                 36.70N  86.07W
10/18/2011  E1.00 INCH       ALLEN              KY   BROADCAST MEDIA

&&

EVENT NUMBER LMK1101139

RL

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE LOUISVILLE KY
459 PM EDT TUE OCT 18 2011

KYZ034-038>040-045>048-054-055-066-182130-
ANDERSON-BOYLE-CASEY-JESSAMINE-MARION-MERCER-NELSON-SHELBY-SPENCER-
WASHINGTON-WOODFORD-
459 PM EDT TUE OCT 18 2011

...STRONG THUNDERSTORMS WITH DANGEROUS LIGHTNING...HEAVY RAIN...AND
HALF INCH HAIL...

AT 456 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING
STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM 9 MILES NORTH OF
SPRINGFIELD TO 12 MILES SOUTHEAST OF SPRINGFIELD...AND MOVING
NORTHEAST AT 40 MPH.

FREQUENT CLOUD TO GROUND LIGHTNING...HEAVY RAIN WITH RAINFALL RATES
OF AROUND ONE INCH PER HOUR REDUCING VISIBILITIES TO LESS THAN ONE
MILE...AND HALF INCH HAIL...ARE EXPECTED WITH THESE STORMS.

* THESE STORMS WILL ALSO IMPACT...
  SPRINGFIELD...
  LEBANON...
  LAWRENCEBURG...
  HARRODSBURG...
  TATHAM SPRINGS AND FAIRVIEW...
  ASHBROOK AND KLONDYKE...
  HICKORY GROVE AND SINAI...
  FOX CREEK AND ANDERSON CITY...

THESE STORMS WILL AFFECT THE BLUEGRASS PARKWAY BETWEEN MILE MARKERS
25 AND 59.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

IF YOU ARE IN THE PATH OF THESE STORMS...SEEK SHELTER INDOORS AND
STAY AWAY FROM WINDOWS. STAY TUNED TO NOAA ALL HAZARDS RADIO...
WEATHER.GOV/LOUISVILLE ON THE INTERNET...OR LOCAL MEDIA FOR LATER
UPDATES AND POSSIBLE WARNINGS.

&&

LAT...LON 3780 8463 3781 8466 3779 8465 3778 8466
      3779 8468 3783 8468 3782 8471 3774 8470
      3742 8507 3764 8552 3811 8524 3811 8496
      3810 8491 3786 8457
TIME...MOT...LOC 2059Z 224DEG 36KT 3783 8515 3764 8500

AMS

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LOUISVILLE KY
501 PM EDT TUE OCT 18 2011

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

0450 PM     HAIL             6 SW CAMPBELLSVILLE     37.29N  85.43W
10/18/2011  E0.75 INCH       TAYLOR             KY   TRAINED SPOTTER

&&

EVENT NUMBER LMK1101140

RL

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LOUISVILLE KY
511 PM EDT TUE OCT 18 2011

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

0508 PM     HAIL             CAMPBELLSVILLE          37.35N  85.35W
10/18/2011  E1.00 INCH       TAYLOR             KY   EMERGENCY MNGR

&&

EVENT NUMBER LMK1101141

RL

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE LOUISVILLE KY
529 PM EDT TUE OCT 18 2011

KYZ033>036-038>041-045>048-053>055-182200-
ANDERSON-BOYLE-FAYETTE-FRANKLIN-HENRY-JESSAMINE-LARUE-MARION-MERCER-
NELSON-SCOTT-SHELBY-SPENCER-WASHINGTON-WOODFORD-
529 PM EDT TUE OCT 18 2011

...STRONG THUNDERSTORMS WITH DANGEROUS LIGHTNING...HEAVY RAIN...AND
HALF INCH HAIL...

AT 528 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING
STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM 9 MILES NORTH OF
HARRODSBURG TO 9 MILES SOUTH OF BARDSTOWN...AND MOVING NORTHEAST AT
35 MPH.

FREQUENT CLOUD TO GROUND LIGHTNING...HEAVY RAIN WITH RAINFALL RATES
OF AROUND ONE INCH PER HOUR REDUCING VISIBILITIES TO LESS THAN ONE
MILE...AND HALF INCH HAIL...ARE EXPECTED WITH THESE STORMS.

* THESE STORMS WILL ALSO IMPACT...
  GEORGETOWN...
  FRANKFORT...
  VERSAILLES...
  SPRINGFIELD...
  SHELBYVILLE...
  NONESUCH AND TABLOW...
  MORTONSVILLE AND TROY...
  PINCKARD AND WITHROW...
  FIRMANTOWN AND GAYBOURN...

THESE STORMS WILL AFFECT INTERSTATE 64 IN KENTUCKY BETWEEN MILE
MARKERS 35 AND 69.

THESE STORMS WILL AFFECT INTERSTATE 75 IN KENTUCKY BETWEEN MILE
MARKERS 120 AND 136.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

IF YOU ARE IN THE PATH OF THESE STORMS...SEEK SHELTER INDOORS AND
STAY AWAY FROM WINDOWS. STAY TUNED TO NOAA ALL HAZARDS RADIO...
WEATHER.GOV/LOUISVILLE ON THE INTERNET...OR LOCAL MEDIA FOR LATER
UPDATES AND POSSIBLE WARNINGS.

&&

LAT...LON 3855 8501 3851 8502 3852 8498 3849 8498
      3846 8490 3844 8492 3842 8488 3838 8489
      3834 8479 3837 8471 3847 8459 3846 8453
      3824 8447 3756 8483 3754 8489 3763 8524
      3749 8528 3757 8567 3801 8536 3855 8503
TIME...MOT...LOC 2129Z 215DEG 32KT 3790 8485 3768 8550

AMS