Area Forecast Discussion
Issued by NWS Louisville, KY

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470
FXUS63 KLMK 221055
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
655 AM EDT FRI JUL 22 2016

...Forecast Update...
Issued at 655 AM EDT Thu Jul 21 2016

Did a quick update this morning to increase pops across our NW. New
development has occurred along the remnant outflow of overnight MCS
and as boundary continues to slide south see no reason to think it
won`t continue. In fact, as we move toward midday, expect new
development all along the boundary. Expect brief heavy rainfall,
cloud to ground lightning and perhaps a few gusts of wind with the
morning storms. Some stronger, but pulse, storms are then possible
this afternoon where torrential rain, continuous lightning, and
gusty winds are expected.

Other concern is the impact the clouds/storms will have on
temperatures and eventual heat indices. Overall thinking is that
criteria will not be reached in most spots, but with prolonged
duration of expected heat and humidity through the weekend won`t
make any changes to the headline at this time. Coordinated this
decision with surrounding offices earlier.

.SHORT TERM (Now through Saturday)...
Issued at 318 AM EDT Fri Jul 22 2016

...Hot, Humid, and Unsettled Weather for the Weekend...

Main focus for this morning is a weakening MCS currently moving into
central IL/IN, and its eventual impact on today`s weather. More
specifically, the impact on temperatures and resultant heat indices,
and potential for redevelopment of scattered showers and storms on
the remnant outflow later this afternoon. Deterministic models
continue to struggle mightily with evolution of the system for
today, but latest runs of the HRRR have caught up to what is
currently going on. More importantly, they paint a reasonable
picture of what could occur this afternoon. Latest IR satellite
imagery continues to show warm cloud tops, and latest radar
presentation clearly shows weakening of the line of storms to our
north. So, fully expect only a few showers and/or storms to impact
our NW CWA shortly after sunrise, if they even survive at all. Will
have small chances mentioned in this area in the morning. Think the
HRRR does a pretty good job of placing where remnant outflow and/or
differential heating will occur this afternoon, and have scattered
coverage (40-50%) of showers and storms developing by early
afternoon mainly east of I-65 and across southern KY. This is an
aggressive forecast given some of the other data offered by models,
but would like to have some chances in because folks that do see T-
storms will see slow moving heavy rainers given the lack of deep
flow and high PWAT airmass.

If the above scenario plays out, it could have significant impacts
on the going temp/heat index forecast as convective debris from this
morning and afternoon could limit heating. Bottom line is that we
will not change the going Heat Advisory in case the upstream system
really weakens and we are still able to realize good heating this
afternoon. That being said, have backed off max heat indices a bit,
which will put most areas along and west of I-65 in the 100 to 103
degree range. Highs should range from around 90 in our east where
highest coverage is expected, to the mid 90s SW where the
longest/best heating should occur.

Will keep isolated to widely scattered chances mainly across our N
for the overnight where the best overlap of better flow aloft and
displacement from the upper ridge center occurs. May have to contend
with some lingering showers and storms in our E/SE around sunset,
but those should quickly diminish with the loss of heating. Expect a
mild overnight with lows in the 72 to 77 range.

Weakening upper ridge becomes "dirty" by Saturday, and with plenty
of instability in an relatively uncapped environment should see 30-
40% chances of storms mainly afternoon and evening. Any remnant
outflow and differential heating will serve as additional triggers.
Hot and humid conditions will continue with max heat indices
reaching into the 100 to 107 range across the Heat Advisory Area.

Will not be extending the going headline into Sunday at this time as
we are struggling to hit criteria to this point, and convective
chances continue to lower confidence. Potential is certainly there
for an extension, but still have plenty of time to decide this if
need be.

.LONG TERM (Saturday Night through Thursday)...
Issued at 320 AM EDT Fri Jul 22 2016

...Continued Hot, Humid, and Unsettled Through This Weekend...

Saturday Night - Sunday Night...

Elongated upper ridge axis will stretch from the desert SW through
the mid Atlantic Coast to end the weekend. The relatively weakened
state of the ridge will allow for scattered, and mainly diurnally
driven convection on Sunday, but should see mostly quiet overnight
periods on either side of Sunday. Instability will be plentiful, but
the lack of deep flow of any note will mitigate chances for
organized storms. So, expect mainly a heavy rain threat with slow
moving storms in a moist airmass. The strongest updrafts could
produce a pulse severe wind threat, but very localized in nature.

Continued heat and humidity will still be a topic of discussion on
Sunday as low 90s temperatures combine with dew points in the mid
70s. The big question mark is with coverage/timing of convective
chances which will impact our temp forecast, and overall heat indice
values. Don`t plan on extending the Heat Advisory at this time,
mainly due to convection and the uncertainty of impacts from it.
Lows on Saturday and Sunday nights will be in the mid 70s.

Monday - Wednesday...

An upper disturbance will move through eastern Canada to start the
new week, with a trailing weak cold front likely sliding into our
region. This will provide a bit of additional focus for showers and
storms on Monday into Monday evening. Depending on how much progress
the front makes, chances may linger into Tuesday and even Wednesday
mainly across southern KY. Will taper chances a bit on these days
due to uncertainty, but Monday looks like the wettest/best coverage
day of the long term. Again, not expecting severe at this point,
although strong pulse storms are possible given the amount of
instability. Heat/humidity could continue to be a problem into
Monday, especially if the front is slow and storms erupt later. Heat
Adviory could be extended through Monday as well with later
forecasts.

Will try to depict a few degrees cooler for the Tuesday/Wednesday
time frame in anticipation of the front making some progress through
the area. Still, temps in the upper 80s to around 90 are reasonable.

Wednesday Night - Thursday...

The mid week portion of the forecast should remain active as
shortwave troughing finally tries to win out over the eastern CONUS
as western ridging retrogrades. This should put temperatures back
toward the normal range for this time of year, but at least
scattered coverage of showers/storms seems warranted during this
stretch.

&&

.AVIATION (12Z TAF Update)...
Issued at 618 AM EDT Fri Jul 22 2016

Light MVFR fog will continue at BWG through about 13z before burning
off. A complex of showers and storms from near Bloomington to
Evansville will drop southward this morning. This may impact SDF for
a few hours this morning.

As the line drops further, it will likely lay out an outflow
boundary across the region which may be the lift for redevelopment
of showers/storms later this afternoon. The greatest focus/coverage
of activity looks to be around SDF/LEX.

Any storms that do form will be diurnal and dissipate with the loss
of daytime heating. Light fog will once again be possible in the
favored locations late tonight into Saturday.

&&

.LMK Watches/Warnings/Advisories...
KY...Heat Advisory until 8 PM EDT /7 PM CDT/ Saturday for KYZ023>030-
     045-053-061>063-070>075.

     Heat Advisory from noon EDT /11 AM CDT/ today to 8 PM EDT /7 PM
     CDT/ Saturday for KYZ031>034-038-046-054-064-065-076-077-
     081.

IN...Heat Advisory until 8 PM EDT /7 PM CDT/ Saturday for INZ076>078-
     083-084-089>092.

     Heat Advisory from noon today to 8 PM EDT Saturday for INZ079.

&&

$$

Update.........BJS
Short Term.....BJS
Long Term......BJS
Aviation.......ZT



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