Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 271058

Area Forecast Discussion
National Weather Service Louisville KY
658 AM EDT Thu Jul 27 2017

...Updated Aviation Discussion...

.Short Term...(Today through Friday)
Issued at 245 AM EDT Thu Jul 27 2017

...Strong Storms Producing Heavy Rainfall Possible Today...

Early morning regional radar mosaic shows complex of storms across
portions of southern Illinois, moving into southwest and central
Indiana. This area of storms is working in an environment
characterized by high dewpoints /mid to upper 70s/ and within a belt
of high precipitable water /2.4 to 2.5 inches/ in an axis of
marginal elevated instability. Otherwise, a warm front denoted
mostly by a dewpoint gradient lies across eastern Indiana and
northern Kentucky. Generally mild and muggy conditions prevailed
across the region with a mix of clouds.

Near term concern is current complex over Illinois and Indiana.
Current thinking is that it will continue to track eastward into
southern Indiana toward dawn but work into a less favorable
environment and should weaken somewhat. Overall the environment
isn`t supportive of strong wind gusts but rather torrential rainfall
which could produce minor but quick flooding problems. The latest
runs of the HRRR seem to be capturing reality the best, so leaned on
it for the next 3-6 hours. Precipitation chances through mid morning
will be highest along/north of the Ohio River. Areas to the south
should stay mainly dry through at least mid morning.

A lot of what happens the remainder of the day depends on how this
complex unfolds and what surface boundaries are draped across the
region plus the opportunity for destabilization with peak
heating. Several ongoing complexes of storms should bring overcast
high clouds across the entire area, which should help to limit
daytime heating. If there is some clearing across southern
Kentucky and outflow boundaries, a few stronger storms may be able
to develop this afternoon.

Otherwise, scattered to numerous showers and storms should traverse
the forecast area throughout the afternoon and evening hours. High
moisture pooling ahead of the front will bring near record to record
PWATs and dewpoints should easily stay in the mid 70s. With warm
cloud depths well over 4 km through tonight, very efficient rain
producing thunderstorms are expected. Basin average total rainfall
amounts may be between 1 and 2 inches, though certainly locally
higher amounts are possible in areas with repeated training storms.

Flash Flood Guidance remains quite high and overall antecedent
conditions are dry. Confidence in repeated rounds of training storms
is low, so in collaboration with surrounding offices, will continue
to highlight flood threat through a SPS, weather story graphics, and
hazardous weather outlook.

Showers and storms will continue through tonight, especially along
and south of the KY Parkways as the surface low tracks east into the
Appalachians. Some of the meso, hi-res models show an organized
complex racing across southern Missouri into northern TN or southern
KY early Friday morning.

The surface front will begin to push through and south of the area
on Friday. Ahead of it, the environment will continue to be moisture
rich and scattered to numerous thunderstorms are possible during the
morning and early afternoon hours with improving conditions expected
int he late afternoon and evening hours.

Overall, temperatures will stay more or less around normal or even
slightly below normal the next 2 days thanks to more widespread
precipitation and clouds.

.Long Term...(Friday night through Wednesday)
Issued at 300 AM EDT Thu Jul 27 2017

Upper troughing over the Great Lakes and Ohio Valley will bring
seasonably cool temperatures and weather for this upcoming weekend.
Expect highs in the upper 70s to lower 80s Saturday and Sunday with
steady northerly breezes. Dewpoints should mix down into the upper
50s to lower 60s in the afternoon hours and overall there should be
plenty of sunshine. Morning temperatures Saturday are likely to be
in the lower to middle 60s, coolest across southern Indiana and
northern Kentucky. Sunday morning will be the coolest of the
forecast period with most locations dropping below the 60 degree
mark. Mid 50s are possible in the typical cooler rural locations.

Much of next week the upper level pattern will feature troughing
over the eastern US with ridging over the western US. At the
surface, high pressure will generally dominate the weather pattern
so the forecast will stay dry and mainly seasonable through at least
mid week. Temperatures and humidity will moderate back to near
normal levels but overall a quiet end to July and start to August
for the lower Ohio Valley.


.Aviation...(12Z TAF Issuance)
Issued at 657 AM EDT Thu Jul 27 2017

The complex of storms that was moving towards the Ohio River
overnight has weakened and is now just rain. This rain will affect
SDF off and on this morning. Some storms have begun to pop up,
though not near any of the TAF sites at this time. The best chance
for storms still looks to be this afternoon into the evening hours
during daytime heating. Therefore, will keep just showers in the
forecast for this morning and will introduce thunderstorms this
afternoon. Confidence is lower for the overnight hours with regards
to storms so will keep them out during the overnight hours for now
at SDF and LEX.

Ceilings are expected to lower tonight with MVFR ceilings and
possibly some light fog towards dawn tomorrow morning. Winds will be
out of the southwest today becoming light and variable overnight.




Short Term...ZT
Long Term...ZT
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