Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 201712
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
112 PM EDT WED JUL 20 2016

...Updated Aviation Discussion...

...Forecast Update...
Issued at 910 AM EDT Wed Jul 20 2016

A few cells have popped up near the Wabash, lending some credence to
the HRRR solution showing showers/storms pushing south west of the I-
65 corridor. Have updated the pops and blended with current obs in a
zone update.

.SHORT TERM (Now through Thursday)...
Issued at 254 AM EDT Wed Jul 20 2016

As of early this morning, latest regional radar showed a weakening
complex of showers and storms across southeast Illinois and far
western Indiana, slowly moving to the south and east. This system
was moving on the edge of an upper level ridge that is centered over
Oklahoma. Locally, sky cover ranged from mostly clear across eastern
Kentucky to mostly cloudy west of I-65 thanks to convective debris
clouds. It was a mild and muggy morning with readings in the mid 70s
to around 80.

For today, the forecast is tied to what happens with the
aforementioned complex of storms and any associated outflow
boundaries that try to set up across the area. Hi-res models are in
good agreement showing it weakening and continuing to sag to the
south, mainly west of the forecast area, through mid-morning.

However, differential heating and/or outflow boundaries are likely
to be pushed east into part of our area. As readings climb into the
mid 80s to near 90, sufficient MLCAPE is expected to develop. The
weak pertubation aloft along with weak surface convergence could
bring isolated to widely scattered coverage of showers or storms
across southern Indiana and along/west of I-65. For now, chances
were kept in the 15 to 25 percent range. Otherwise, it will be
another warm to hot day with highs a few degrees either side of 90.

Any storms that do develop this afternoon should dissipiate early to
mid evening with the loss of daytime heating, giving way to a mainly
dry but mild to muggy night. Look for lows once again in the mid 70s.
The urban areas will likely stay up around 80.

On Thursday, forecast guidance shows the upper level ridge extending
its reach further east more while any weak shortwave troughs stay
well north into the Great Lakes region. This should keep the area
mainly dry but will bring in slightly warmer temperatures. Look for
highs in the 90 to 94 range with maximum afternoon to early evening
heat indices in the 100 to 105 range.

.LONG TERM (Thursday night through Tuesday)...
Issued at 255 AM EDT Wed Jul 20 2016

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

The main focus in the long term period continues to be on the
extended period of high heat and humidity forecast for the area
through the remainder of this week and into the weekend.

The synoptic pattern is expected to feature a large upper level
ridge centered over the south-central Plains but its reach will
spread through the lower Ohio Valley and mid-Atlantic. Overall storm
tracks through the weekend will largely stay to the north into the
Great Lakes region.

In general, look for high temperatures Friday through Sunday in the
90 to 95 degree range each day. It is forecast to be considerably
more humid those days as well with dew points in the low to mid 70s.
As a result, maximum heat indices in the afternoon and early evening
will range from 100 to 105.

Compounding the impacts from the heat will be the relative lack of
nighttime cooling characterized by lows only in the upper 70s to
even low 80s for the core of the urban areas. The repeated hot
afternoons are tough, but the lack of cooling at night for several
consecutive days is what makes heat waves dangerous.

Some relief may be in store with chances for afternoon to evening
storms Saturday and Sunday. The northwest flow aloft pattern over
the area does allow the opportunity for convective complexes to
initiate to our north and brush parts of the area at times.
Certainly the environment will have plenty of instability so will
continue to lean on the model consensus showing 20 to 30 percent
chances Saturday and Sunday. The greatest chances look to be across
southern Indiana, north-central Kentucky and the northern Bluegrass
region.

By early next week, forecast models suggest that the upper level
ridge is shunted back to the southwest, allowing more of a zonal
flow to set up across the area. This may allow more synoptic
features to drop into the area and bring greater chances of showers
and storms. For now, the Monday into Tuesday time frame has 40 to 50
percent chances as a front attempts to cross the region.

&&

.AVIATION (18Z TAF Update)...
Issued at 1211 PM EDT Wed Jul 20 2016

A few thunderstorms near BWG/SDF will be the main near-term concern.
A few storms have developed across west-central KY well west of BWG
and SDF.  Have timed these showers and a few rumbles of thunder into
SDF with a TEMPO group, but will leave any TEMPO group out of BWG
for now given that convection may just stay off to the west.
Outside of any storm, expect passing mid/high clouds with generally
light and variable winds.

Any storms will wane tonight, leaving just some passing mid/high
clouds.  Winds will be light, thus think we could see some fog
development at BWG, especially if it rains there this afternoon.
Otherwise expect a dry day tomorrow with just scattered cu/high
clouds and light winds.

&&

.LMK Watches/Warnings/Advisories...
KY...NONE.
IN...NONE.
&&

$$

Update.........RJS
Short Term.....ZT
Long Term......ZT
Aviation.......KJD


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