Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 210049

Area Forecast Discussion
National Weather Service Louisville KY
849 PM EDT Thu Apr 20 2017

.Forecast Update...
Issued at 845 PM EDT Thu Apr 20 2017

See the fine line that is the cold front well on latest radar
mosaic. Have some new cells developing still ahead of that line over
southeast Missouri, but also some newer development along in
southern Illinois. Cells over southeast Indiana are headed east now
out of our area. Have slowed the timing of greatest pops down based
on latest radar trends...however we still have quite a bit of
moisture getting pumped into the area. With that front providing
lift overnight, will keep in likely pops for most locations. Updated
products coming out now.

Issued at 735 PM EDT Thu Apr 20 2017

In a relative lull right now in storms, after wave one, based on
afternoon heating, went through. Now we are watching the cells
closer to the front move in, some over central IN and others over
southern IL and western KY. Expect new development over the next few
hours, along with those cells in central IN to clip Jefferson
county, IN in the next hour. Have adjusted pop grids and other grids
for latest trends. Best dynamics at this time clearly are with the
stronger cells to our north right now, where effective SRH are
analyzed (SPC) at around 200.  Another peak is over far western KY,
so will have to watch there too for any organized cells that form.


.Short Term...(This evening through Friday night)
Issued at 300 PM EDT Thu Apr 20 3017

...Strong Storms Possible This Afternoon and Evening...

Afternoon satellite imagery reveals partly sunny skies across the
region.  Temperatures have warmed into upper 70s to the lower 80s
across the region.  Convective coverage has increased over the last
hour in several hours.  One area of development has been down in the
Lake Cumberland region with a secondary area of development across
western KY and southwest Indiana.  Atmosphere is a bit unstable with
the best instability still located out to our west.  Mid-level lapse
rates are still rather weak contributing to CAPE values around 800-
1000 J/Kg.  Bulk shear values remain relatively low (25kts) with the
best shear located across northern IN and southern MI. DCAPE values
are approaching 1000 J/Kg which suggests that the strongest storms
this afternoon may produce brief periods of gusty winds along with
locally heavy rainfall.

In the near term, we expect convective coverage to pick up through
the remainder of the afternoon with the greatest concentration
across western KY into southwest/south-central IN.  Scattered
convection will also be seen across central KY.  Afternoon highs
should top out in the 80-84 degree range.

For tonight, convection from the evening will be ongoing and
dropping southeastward through the region.  Surface cold front to
the northwest of the area looks to reach the Ohio River after
midnight and then settling down into southern KY by dawn.  Strongest
storms of the period would be in the evening while diurnal
instability is the highest.  However, onset of nocturnal cooling of
the PBL will lower instability and the thunderstorm intensity will
decrease as the night wears on.  Influx of cooler air will push in
behind the front.  Lows tonight will range from the lower 50s across
southern IN and far northern KY with upper 50s to the lower 60s
across southern KY.

For Friday and Friday night, surface cold front is forecast to stall
out near the KY/TN border early in the period. The front is likely
to not move all that much during the day which will keep most
convection down south of the WK/BG Parkways.  Convection looks to
increase in coverage and strength during the afternoon and evening
as a mid-level wave approaches the region from the west.  Widespread
convection is expected during the overnight hours Friday night.
Highs Friday will exhibit a gradient with readings in the lower 60s
across southern Indiana, with upper 60s to lower 70s across much of
Kentucky. Lows Friday night will cool into the upper 40s over much
of the region with the exception of southern KY where lower 50s will
be seen.

.Long Term...(Saturday through Thursday)
Issued at 310 PM EDT Thu Apr 20 2017

Vigorous mid-level wave and associated surface low pressure center
is expected to move along the an east-west oriented baroclinic zone
on Saturday.  Widespread showers with a few thunderstorms are
expected throughout the day on Saturday.  The multi-model consensus
suggests much of the heavier rainfall will push east of the area
Saturday night.  However, plenty of rich low-level moisture will
remain in place along with a cool northeasterly flow.  The net
result for Saturday night will be plenty of low cloudiness with
periods of light rain and/or drizzle.  Highs on Saturday will top
out in the 50-55 degree range across southern Indiana with 55-60
across much of central KY.  Low-mid 60s will be possible across the
Lake Cumberland region.  Lows Saturday night look to drop into the
lower-mid 40s.

The upper level wave will likely close off over the region early
Sunday and then move across the region.  The GFS and Euro still have
some timing differences here.  Though it looks like much of the day
may end up being cloud with scattered showers being possible, mainly
east of the I-65 corridor.  Highs Sunday will be in the 60-65 degree
range with overnight lows cooling into the lower 40s.

Upper level low looks to move east/southeast of the region by Monday
with mid-level ridging building into the region.   This should
result in a much drier and milder period of weather for Monday
through Tuesday night.  The next weather feature of note looks to
cross the region on Wednesday which may bring our next round of
precipitation.  A sharp warm up in temperatures looks very likely by
the end of next week.  Highs Mon/Tue will be in the low-mid 70s with
upper 70s to low 80s by Wed/Thu.  Overnight lows look to settle into
the 50s during the period.


.Aviation...(00Z TAF Issuance)
Issued at 710 PM EDT Thu Apr 20 2017

In a bit of a gap at this time for storms, but still looking at some
new development as a cold front inches closer to us.  Have some
stronger storms over central Indiana now, and expect new development
over us later this evening. Tried to pin the best timing from
various model guidance. Behind the storm chances the front will come
and we may see some lingering showers overnight, along with lower
cigs. Latest hi-res guidance places the BWG/LEX on the edge of fuel-
alternate ceilings for most of the day Friday, so went pessimistic
for those sites. Rain chances return in the afternoon as the front
stalls just south of the region and showers develop behind it.




Short Term...MJ
Long Term....MJ
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