Special Weather Statement, NWS Louisville, KY

Area Forecast Discussion
National Weather Service Louisville KY
129 PM EDT Sun Apr 16 2017

...Updated Aviation Discussion...

...Forecast Update...
Issued at 1210 PM EDT Sun Apr 17 2017

Outflow boundary sinking southward from morning storms to our north
is very evident on radar at this hour. Meanwhile, SPC mesoanalysis
shows steady destabilization in the airmass ahead of this boundary,
combined with some surface moisture convergence along it. The end
result, which agrees with latest hi-res model solutions, suggests
increasing coverage of showers and storms as we move through the
afternoon and early evening. In reality, the cold front is still
well off to the north and west, so the main triggering mechanism
will need to come from boundaries coincident with destabilization
until the front gets closer. Still like the idea of scattered
coverage increasing to numerous coverage. Chances for a stronger
storm also go up in areas that stay dry the longest.

Issued at 829 AM EDT Sun Apr 17 2017

Current radar imagery shows two distinct areas of precipitation. The
first is a lead batch of scattered to numerous showers with a few
embedded rumbles of thunder over east central KY. These showers are
associated with the low level jet and isentropic lift beneath modest
mid level lapse rates. They will continue to push off to the east
this morning. Meanwhile, we'll see a quiet dry stretch across
southern Indiana and west central KY until second batch of
precipitation ahead of the front moves in and develops on increasing
instability. The second wave should be more widespread with a better
chance at thunderstorms, some of which could be stronger.

Updated the grids to better reflect current precipitation
placement/chances, and highlight areas that will be dry for a while.

.Short Term (Now through Monday)...
Issued at 230 AM EDT Sun Apr 16 2017

...Strong storms possible this afternoon and evening...

Surface analysis reveals broad southerly flow and very warm
temperatures across the region. AMDAR soundings from earlier in the
morning revealed a LLJ taking shape, and model soundings indicate it
will persist through the morning hours. Current water vapor imagery
reveals a subtle shortwave beginning to now cross into the western
Kentucky. Should start to see some showers and thunderstorms form
out ahead of it in the next few hours, and these will persist
through most of the morning.

A line of convection that formed over the Plains yesterday evening
will make a run for the region this morning ahead of a cold front.
Most high-res short term guidance have the line falling apart by the
time it reaches southern Indiana and north-central Kentucky this
morning. Might see a lull in the showers and storms starting late
morning into early afternoon before additional convection fires off.
This setup will be very dependent on mesoscale features that coarse
resolution models often have a hard time capturing, so am putting
more weight into models like the HRRR/ARW/NMM/4km NAM that should
have a better handle on things. The high-res models seem to imply
that multiple boundaries will be present across the CWA by early
afternoon, including the outflow boundary associated with the dying
convection that will come through later this morning. Those
boundaries will serve as focal points for convective initiation, as
well as a cold front that will move into southern Indiana by late
afternoon.

Regarding severe weather parameters, previous discussions have
mentioned deep layer shear being marginal. That is still looking to
be the case, with 0-6km shear generally 20-25kts, although the 00z
NAM came in with pockets of higher deep layer shear in the 30-35kt
range. Instability values generally in the 1000-2000J/Kg range are
still being advertised by the models, though there remains some
uncertainty on how much of that will be realized given the potential
for lingering cloud cover from the morning's showers and
thunderstorms.

Given the parameters and setup, believe there will be some strong to
severe multi-cell clusters that develop Sunday afternoon and evening
starting first in southern Indiana and north-central Kentucky,
before spreading southward into south-central Kentucky by late
afternoon and evening. Main threats with these storms would be
strong wind gusts and small to low-end severe hail.

Models have come in a bit slower with the progression of the cold
front through the CWA tonight into Monday, and as a result it looks
like showers and thunderstorms will be widespread through much of
that period. Might have to keep an eye on severe weather parameters
as a slower frontal passage will keep central and southern parts of
the CWA in the warm sector longer where the atmosphere will be
potentially unstable.

.Long Term (Monday Night through Saturday)...
Issued at 245 AM EDT Sun Apr 16 2017

Medium to long range models keep the region well within the warm
sector starting Tuesday as a warm front lifts north of the region
and a series of low pressure systems eject off the Plains through
most of next week. As mentioned in the previous discussion, shower
and thunderstorm activity look to be diurnally driven, so will keep
higher PoPs during daytime periods.

It's not until Thursday that we start to see significant changes to
the weather as a strong low pressure system and associated cold
front move into the Ohio River Valley. Too early to get into any
details, but might have to watch this in the coming days as the
GFS/ECMWF/Canadian have a line of showers and thunderstorms along
the cold front moving into the CWA where an unstable atmosphere will
be present late Thursday afternoon/evening.

Cold front clears the CWA by Friday morning but stalls out just
south and east of the region. Both the GFS/ECMWF show strong CAA at
the surface behind the front as daytime temperatures struggle to get
into the 70s for northern sections of the CWA. Widespread cloud
cover and shower activity will also help to keep temperatures cool
through most of the day Friday.

The weekend looks to have active weather as yet another area of low
pressure ejects over the southern Plains and pushes toward our
region. As expected, the GFS/ECMWF have some differences regarding
timing and placement of the low, but those with outdoor plans next
weekend may want to keep a close eye on weather forecasts in the
coming days as mother nature may want to put on her own fireworks
display.

&&

.Aviation (18Z TAF Update)...
Issued at 129 PM EDT Sun Apr 16 2017

At the beginning of the TAF period a cold front will extend roughly
along a TOL-STL-TUL line. This front will progress to the southeast
this afternoon and evening, bringing widespread showers and
scattered thunderstorms to the TAF sites. SDF stands the best chance
of seeing the most shower activity and also has the greatest risk of
a strong to severe storm.

Off-and-on shower activity will continue late this evening through
tomorrow. Winds will decrease significantly tonight and moisture
will increase, leading to MVFR ceilings late tonight into early
Monday morning.

&&

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

Update.........DM
Short Term.....DM
Long Term......DM
Aviation.......13

Hazardous Weather Outlook
National Weather Service Louisville KY
313 AM EDT Sun Apr 16 2017

INZ076>079-083-084-089>092-KYZ023>043-045>049-053>057-061>067-
070>078-081-082-170715-
Orange-Washington-Scott-Jefferson-Dubois-Crawford-Perry-Harrison-
Floyd-Clark-Hancock-Breckinridge-Meade-Ohio-Grayson-Hardin-Bullitt-
Oldham-Trimble-Henry-Shelby-Franklin-Spencer-Anderson-Woodford-
Fayette-Bourbon-Nicholas-Nelson-Mercer-Jessamine-Larue-Marion-Boyle-
Garrard-Madison-Butler-Edmonson-Hart-Green-Taylor-Casey-Lincoln-
Logan-Warren-Simpson-Allen-Barren-Monroe-Metcalfe-Adair-Russell-
Cumberland-Clinton-
Including the cities of Paoli, Salem, Scottsburg, Madison, Jasper,
English, Tell City, Corydon, New Albany, Jeffersonville, Lewisport,
Hawesville, Hardinsburg, Brandenburg, Hartford, Leitchfield,
Elizabethtown, Shepherdsville, Louisville, La Grange, Bedford,
Milton, New Castle, Shelbyville, Frankfort, Georgetown, Cynthiana,
Taylorsville, Lawrenceburg, Versailles, Lexington, Paris, Carlisle,
Bardstown, Springfield, Harrodsburg, Nicholasville, Winchester,
Hodgenville, Lebanon, Danville, Lancaster, Richmond, Morgantown,
Brownsville, Horse Cave, Greensburg, Campbellsville, Liberty,
Stanford, Russellville, Bowling Green, Franklin, Providence,
Scottsville, Glasgow, Tompkinsville, Edmonton, Columbia, Jamestown,
Burkesville, and Albany
313 AM EDT Sun Apr 16 2017 /213 AM CDT Sun Apr 16 2017/

This hazardous weather outlook is for portions of south central
Indiana and Central Kentucky.

.DAY ONE...Today and Tonight.

A line of showers and thunderstorms are expected to form ahead of
a cold front this afternoon and evening. Some of the storms could
produce brief heavy rainfall, gusty winds, and small hail.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Isolated to scattered storms are forecast through much of next week
as several weather systems move through the Ohio Valley. Details
regarding the evolution of these systems remains uncertain, but the
forecast will be monitored in the coming days for any severe weather
potential.

.SPOTTER INFORMATION STATEMENT...

Spotter assistance may be requested this afternoon and evening.

&&

More information, along with other weather, hydrological and
climate information can be found, at weather.gov/louisville.

DM

Special Weather Statement
National Weather Service Louisville KY
206 PM EDT SUN APR 16 2017

KYZ030-031-161830-
Jefferson-Oldham-
206 PM EDT SUN APR 16 2017

...A LINE OF STRONG THUNDERSTORMS IS AFFECTING LOUISVILLE AND
SOUTHWESTERN OLDHAM COUNTY...

At 204 PM EDT, radar indicated strong thunderstorms from Glenview to
Audubon Park. Movement was east at 30 mph.

Winds in excess of 40 mph are possible with these storms.

Locations impacted include...
Louisville, Jeffersontown, St. Matthews, Lyndon, Middletown, Douglass
Hills, Prospect, Hurstbourne, Graymoor-Devondale and Pewee Valley.

LAT...LON 3839 8539 3830 8541 3830 8542 3829 8543
      3830 8545 3828 8547 3827 8541 3812 8544
      3808 8567 3809 8571 3806 8581 3829 8570
      3830 8567 3835 8564
TIME...MOT...LOC 1804Z 247DEG 28KT 3832 8564 3820 8572

13

Special Weather Statement
National Weather Service Louisville KY
113 PM CDT SUN APR 16 2017

INZ089-KYZ023-024-161845-
Perry-Hancock-Breckinridge-
113 PM CDT SUN APR 16 2017

...A LINE OF STRONG THUNDERSTORMS IS AFFECTING SOUTHERN PERRY...
CENTRAL HANCOCK AND NORTHWESTERN BRECKINRIDGE COUNTIES...

At 112 PM CDT, radar indicated strong thunderstorms from near Tell
City to 6 miles southwest of Hawesville to near Rockport. Movement
was east at 25 mph.

Winds in excess of 45 mph are possible with these storms.

Locations impacted include...
Tell City, Hawesville, Cannelton, Cloverport, Skillman, Goering,
Gerald, Dodd, Tobinsport and Holt.

LAT...LON 3795 8677 3806 8650 3797 8640 3779 8671
      3778 8682 3779 8682 3784 8685 3784 8688
      3783 8690 3784 8691 3787 8691 3788 8689
      3789 8691 3791 8692
TIME...MOT...LOC 1812Z 249DEG 24KT 3794 8672 3786 8685 3786 8700

13