Area Forecast Discussion
Issued by NWS Louisville, KY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

380
FXUS63 KLMK 292332
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
732 PM EDT Sat Apr 29 2017

...Updated Aviation Discussion...

.Forecast Update...
Issued at 715 PM EDT Sat Apr 29 2017

Well... the cap ended up weakening late this afternoon and
allowing a few rogue storms to develop across eastern portions of
the CWA. Environment has been favorable for severe/rotating
storms, and hail up to ping pong ball size has been reported with
one of the storms. Storms will continue to persist for the next
couple of hours, with large hail and damaging winds being the main
threats. Not too worried about a tornado threat as 0-1km shear is
rather low (generally less than 10kts via the SPC mesoanalysis),
and with the sun setting and the boundary layer beginning to
decouple, lower levels of the atmosphere should begin to
stabilize.

&&

.Short Term...(This evening through Sunday night)
Issued at 255 PM EDT Sat Apr 29 2017

...Flash flooding and Strong to Severe Storms Possible Tonight
through early Monday morning...

Current satellite/surface analysis reveals the subtle remnants of an
outflow boundary over central Kentucky from this morning`s
convection. Areas north of the outflow boundary have remained
relatively stable and cool, with temperatures at this hour in the
upper 70s to lower 80s and no cumulus development. South of the
outflow boundary, temperatures are in the mid to upper 80s, and
satellite reveals a broad cumulus field. While SPC mesoanalysis
shows MUCAPE on the order of 2000J/Kg and effective bulk shear of 40-
60kts across most the region, there is a pretty strong cap in place
that is keeping a lid on any convective development. Expect the cap
to remain strong through the afternoon and keep the region dry.

Another round of strong to severe convection is forecast to develop
over IL/MO/AR this afternoon and push eastward. CAMs weaken the line
considerably by the time it reaches our region (03z-06z Sunday),
with some having it completely dissipated before it even reaches
western portions of the CWA. Current thinking is that the convection
will hold together long enough to reach at least the western half of
the CWA tonight, but don`t think we`ll be dealing with any severe
storms as instability will be pretty limited overnight.

By Sunday morning, might have some lingering showers and storms from
overnight convection. Models have sporadic showers and storms firing
off Sunday morning and afternoon over western portions of the CWA,
which seems feasible if outflow or other boundaries are present.
Severe weather chances will be largely influenced by how much
clearing we get Sunday morning and afternoon out ahead of the cold
front. Based on latest 12z guidance, does not look like we will see
much in the way of clearing, so anticipate a limited severe weather
threat much in line with the Day 2 SPC Outlook. Strong wind gusts
and hail look to be the primary severe threats with the beefier
storms.

The bigger threat tonight through Monday morning will be the flash
flooding potential. Last night`s showers and thunderstorms brought a
tremendous amount of moisture to southern Indiana and northern parts
of Kentucky, where reports indicated as much as 8 inches of rain
fell. Contemplated holding off on a flash flood watch until tomorrow
afternoon or evening since there are some questions regarding how
tonight`s convection will evolve and play out, but feel it`s best to
start it this evening. With the ground already saturated in these
areas, even decaying convection could be enough to get some
localized flash flooding going again. Best chance for precipitation
and flash flooding will be Sunday late afternoon into Monday morning
as a line of showers and storms form along the cold front.

.Long Term...(Monday through Saturday)
Issued at 303 PM EDT Sat Apr 29 2017

By 12z Monday, precipitation associated with cold front will be
ongoing across the CWA. Instability looks to be very limited so not
expecting any severe weather, though an isolated storm or two with a
strong wind gust can`t be ruled out. Cold front should clear the
region by late afternoon and filter in drier, cooler air. Winds will
be breezy out of the southwest behind the front, generally 20mph to
25mph with gusts near 35mph.

High pressure builds in from the west Tuesday and results in a
pleasant late spring day. Much like Monday, winds will still be
breezy during the afternoon.

Medium to long range guidance advertise a large trough in the
central/southern Plains swinging into the southeastern US starting
Wednesday through most of next week. Unfortunately, models diverge
on the evolution of the trough, with some model solutions developing
a cut-off low in the southeastern US that hangs around through the
weekend, while others swing the trough axis up the northeastern
coast by the weekend. Should the cut-off low solution win out,
expect most of next week and weekend to be wet and cool. If the
trough axis moves up toward New England, the mid to late work week
will be wet, but should dry out by the weekend (and still remain
cool). Given the model variability and no particular preference
toward one model or another, will take a blended solution for now.

&&

.Aviation...(00z TAF Issuance)
Issued at 725 PM EDT Sat Apr 29 2017

Isolated to scattered storms are ongoing near the LEX terminal but
are pushing off to the northeast. Should see the storms die down
over the next hour or two. Another round of storms from the west
will try to make it to our region, but most models have the storms
falling apart west of I-65. Will keep the forecast dry for the
terminals overnight. LLWS will be present at all TAF sites as LLJ
develops overnight and boundary layer decouples.

Tomorrow, expect isolated to scattered showers and thunderstorms
during the morning and afternoon, with more widespread precipitation
by Sunday evening. Given uncertainty in timing of precipitation,
will keep precipitation out of TAF forecast for now.

&&

.Climate...
Issued at 830 AM EST Fri Apr 28 2017

Temperature and rainfall records for the weekend:

            4/29 Warm L   4/29 Record H   4/30 Warm L  4/30 Record H
Louisville   67 (1951)      89 (1899)      70 (1899)    91 (1894)
Lexington    67 (1899)      86 (1899)      70 (1899)    91 (1942)
Bowling G.   67 (1899)      91 (1894)      68 (1899)    92 (1942*)
Frankfort    63 (1899)      89 (1914)      66 (1910)    91 (1942)

            4/29 Rainfall 4/30 Rainfall
Louisville   2.02" (1927)   2.37" (1983)
Lexington    1.31" (2014)   3.21" (1909)
Bowling G.   2.40" (1912)   3.00" (1911)
Frankfort    2.20" (2002)   2.62" (1909)

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...Flash Flood Watch from midnight EDT /11 PM CDT/ tonight through
     Monday morning for INZ076>079-083-084-089>092.

KY...Flash Flood Watch from midnight EDT /11 PM CDT/ tonight through
     Monday morning for KYZ023>025-030>033.

&&

$$

Update...DM
Short Term...DM
Long Term...DM
Aviation...DM
Climate...RJS



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.