Special Weather Statement, NWS Louisville, KY

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

.Short Term...(This evening through Monday night)
Issued at 315 PM EDT Sun Apr 16 2017

...Numerous Showers & Storms, A Few Strong this Afternoon/Evening...

Scattered to numerous showers and storms have developed in the
unstable airmass ahead of an old outflow boundary laying roughly
along the I-64 corridor. We'll continue to see an increase in
coverage into the evening hours as a warm advection arm from an MCV
over the MO bootheel swings into the CWA later. Modest instability
will combine with weak shear to create mostly general thunderstorms,
however the threat for some multicell clustering is possible. Main
threats should be brief heavy rainfall, cloud to ground lightning,
and small hail. A Severe T-Storm or two is possible for gusty winds
or marginally severe hail through the evening.

Frontal boundary slowly sinks south overnight as it becomes nearly
parallel to the upper flow. Best coverage (likely-categorical) will
be across south central KY overnight with a relative lull toward
dawn. Southern IN and northern KY should be mostly dry by dawn
tomorrow.

As we move toward Monday afternoon, a disturbance in the mid level
flow will track across the TN Valley and will spark off scattered to
numerous showers and storms mainly across southern and central KY.
Surface boundary should be into TN so expect that scattered
convection would be elevated by a stable layer near the surface. So,
expect mainly just showers and a few general T-storms. Loss of
forcing and frontal boundary identity allows for a mostly dry Monday
night.

Lows tonight should mostly be in the upper 50s and low 60s on Sunday
night with Monday highs only topping out in the upper 60s to near 70
behind the front. Steady NE surface flow is always a "cool" setup.
Overnight lows Monday night should be in the upper 40s and low 50s
in most spots.

&&

.Long Term...(Tuesday through Sunday)
Issued at 315 PM EDT Sun Apr 16 2017

Tuesday - Wednesday Night...

The majority of the latest data suggests that cool frontal boundary
will make it all the way through our CWA by Tuesday, with fairly dry
and benign zonal flow aloft over our region. Will still need to
leave some low chances down near the TN border nearest where the
boundary will be, but overall we should stay mostly dry Tuesday and
Tuesday night. Will also note a weak upper disturbance passing just
to our south, which serves as another reason to keep low chances in.

By Wednesday, a cool front trailing from a weak system over eastern
Canada will drop into northern OH/IN/IL, but should stay far enough
north to keep most of our forecast dry. Will have to keep some low
chances in, however, as a weak isentropic lift component kicks in
ahead of the next approaching wave and associated surface low out of
the central Plains. Overall, the mid week time frame looks a bit
drier than it did yesterday, but still not completely void of
showers or a few t-storms.

After highs in the mid and upper 70s on Tuesday, we'll be slightly
warmer on Wednesday with the added WAA component. The same trend
will hold for overnight lows. After Tuesday night min temps in the
lower 60s, Wednesday mins will be a tick warmer in the low and mid
60s due to steady WAA.

Thursday - Thursday Night...

Pretty good agreement in a strong shortwave and associated ~1000mb
surface low moving out of the upper Midwest into the Great Lakes
region during this time. Meanwhile, a trailing cold front will move
through, and could bring good coverage of showers and storms ahead
of it. 12Z GFS appears most aggressive with the system, yielding a
stronger upper shortwave and surface low to the point where some
stronger storms would be possible. At this point, prefer to lean
more toward the consensus and a slightly weaker overall system that
would have still have the potential to bring a broken line of
showers and storms, but less chance for stronger storms. Either way,
Thursday looks to be the best rain chance of the entire work week.
We should be able to warm to around 80 ahead of the front, with
temps dropping into the 50s later Thursday night.

Friday...

Aforementioned cold front makes it through our CWA by Friday, with
surface high pressure and transient shortwave ridging briefly taking
hold. This will allow for a dry Friday forecast with slightly cooler
highs in the low to mid 70s.

Friday Night - Sunday...

Confidence decreases significantly as we head into the weekend as
deterministic and ensembles struggle with the next ejecting
shortwave and the coincident amplification of the downstream
shortwave ridge. The faster and less amplified solutions bring
precipitation into the area by midday Saturday, while the slower
more amplified solution hold precipitation off until late Saturday
night/Sunday morning. It's unfortunate that the lowest confidence
portion of the forecast falls in the critical window of when outdoor
activities will be occurring in Louisville. Hopefully, trends become
more clear in the next 24-48 hours.

Confidence is higher that by Sunday morning into the day storm
system will be moving through the area with good shower and storm
chances likely accompanying it. Temperature forecast is dependent on
how the weekend evolves, but highs should generally be in the low to
mid 70s.

&&

.Aviation...(18Z TAF Issuance)
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...
IN...None.
KY...None.
&&

Short Term...BJS
Long Term...BJS
Aviation...13

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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

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

INZ089-090-KYZ023>025-028>030-033>036-038-161915-
Perry-Harrison-Jefferson-Shelby-Henry-Scott-Franklin-Spencer-Hardin-
Bullitt-Hancock-Meade-Breckinridge-
235 PM EDT SUN APR 16 2017

...A LINE OF STRONG THUNDERSTORMS IS MOVING THROUGH NORTHERN CENTRAL
KENTUCKY...

At 232 PM EDT/132 PM CDT/, radar indicated strong thunderstorms from
Owenton to Louisville to Hawesville. Movement was east at 20 mph.

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

Locations impacted include...
Louisville, Frankfort, Shelbyville, Shepherdsville, and Brandenburg.

Locally torrential rainfall is also occurring with these storms.

LAT...LON 3819 8563 3846 8491 3844 8493 3842 8488
      3838 8489 3834 8479 3849 8455 3838 8447
      3804 8527 3774 8678 3784 8685 3784 8691
TIME...MOT...LOC 1832Z 260DEG 16KT 3841 8487 3820 8555 3789 8678

13

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