Area Forecast Discussion
Issued by NWS Louisville, KY

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863
FXUS63 KLMK 231657
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1257 PM EDT Sun Jul 23 2017

.Forecast Update...
Issued at 1255 PM EDT Sun Jul 23 2017

Precipitation associated with MCS has exited the region to the east.
Some light showers and isolated thunderstorms have started moving in
from the west across northern portions of the CWA near the Ohio
River. Activity along and north of I-64 should remain isolated to
scattered in nature for the rest of the day. Will keep PoPs capped
around 20 to 30 percent for northern portions of the CWA, with
higher chances for showers and storms in the south where more
widespread development is expected.

Did drop the temperatures down a bit more for areas along and north
of I-64 given current temperature/model trends and expected activity
and cloud cover later this afternoon. Rest of forecast is on track.

Issued at 910 AM EDT Sun Jul 23 2017

The MCS is beginning to taper down this morning across the region,
though widespread showers and thunderstorms are prevalent across
northern portions of the CWA. This MCS will gradually move eastward
over the next few hours and give way to a brief lull in activity.
More storms are forecast to develop across south-central Kentucky
this afternoon along outflow/differential heating boundaries from
this morning`s convection. Because this area has yet to see much in
the way of rainfall recently, will not go forward with any flash
flood watches as FFG remains relatively high. Localized flooding
will still be possible this afternoon with any training convection.
Shear/instability will also support a few strong to severe storms.

Given current and upstream conditions, have also decided to drop the
northern half of the heat advisory over western portions of the CWA.
We should see temperatures warm up some later this morning as the
MCS departs, but satellite reveals a lot of cloud cover/convective
debris upstream of the region and feel like we will not hit advisory
criteria for many places. Best chance of hitting heat advisory
criteria will be around the Bowling Green area where heat advisory
is still in place.

&&

.Short Term (Now through Monday)...
Issued at 315 AM EDT Sun Jul 23 2017

Steady mid and upper level height falls have set in and will
continue today as a synoptic scale trough swings southeast over the
Great Lakes. Modest flow aloft will finally become cyclonic as the
upper ridge continues to establish itself over the Four Corners. At
the surface, a convectively-reinforced boundary was oriented east-
west across southern Indiana.

Two separate MCSs were ongoing early this morning, one over southern
IN/northern KY and another impacting southern OH/northeast KY. These
clusters of thunderstorms were moving to the ESE at 30-35 kts. The
strong convection over the northern CWA has pushed out an outflow
boundary, which was moving south through Bullitt, Hardin, Meade, and
Breckinridge counties, extending back northwest into Perry Co, IN.
Numerous thunderstorms will continue across mainly southern IN and
the northern half of central KY through 11-12z. While the convection
will become increasingly elevated, an axis of 1500-2500 J/kg MUCAPE
and a very warm, moist boundary layer should allow for robust
convection for another 2-3 hours. Convection is expected to
gradually diminish by 12z.

Isolated activity can`t be completely ruled out after 12z, but in
general, a lull in precipitation looks likely into the early
afternoon. With fairly strong heating once again today,
redevelopment over central KY along remnant boundaries is expected
during the second half of the day. Storms this afternoon and evening
could quickly become strong, capable of very heavy rain, frequent
lightning, and gusty winds. The strongest updrafts may produce small
hail.

A Heat Advisory remains in effect generally along and west of I-65,
where heat indices will peak in the 100-106 range. The hottest
conditions are expected in the southwest, including Bowling Green
and surrounding areas.

Rain and storms will push southeast late this evening into the
overnight period, with most areas dry after midnight. Lows will fall
into the upper 60s to lower 70s behind the cool front. Highs on
Monday will be near climatological normals, in the mid 80s to around
90 degrees. Models continue to suggest weak convergence associated
with the stalled boundary on Monday, so we may see isolated to
scattered showers/storms.

.Long Term (Monday Night through Saturday)...
Issued at 325 AM EDT Sun Jul 23 2017

Tuesday will feature mid-level height rises, with surface high
pressure over the Great Lakes. We`ll likely see mostly sunny skies
with a light northeast wind here in central KY and southern IN.
Highs will be in the mid to upper 80s. We`ll likely see a stretch of
dry weather and normal summertime temps that continues through
Wednesday night. Highs on Wednesday will likely warm to around 90.

The passage of a shortwave trough and its associated cold front
bring showers and thunderstorms back into the forecast for Thursday
and Thursday night. Post-frontal upper troughing, along with
Canadian high pressure, may provide some downright "cool" weather
Friday into the weekend. Highs in the low to mid 80s look possible,
with lows in the 60s.

&&

.Aviation (12Z TAF Update)...
Issued at 648 AM EDT Sun Jul 23 2017

A complex, challenging forecast.

First order of business is early morning storms. Convection from the
pre-dawn hours has decreased, but new convection is coming in from
southeast Illinois. Will use radar to time the new storms into SDF.
There is some question about whether or not they will make it all
the way to LEX...feeling right now is that they will have reduced to
scattered showers by the time they get that far east. This is a low
confidence forecast, though, so changes may be needed. BWG will stay
south of the early morning storms.

Then this afternoon new storms are expected to fire along various
boundaries left over from the morning convection plus a weak
synoptic surface trof. The models are hitting southern Kentucky the
hardest with new storms, and this has been a consistent solution
over the past several runs of local models. So, will go with this
idea in the TAFs.

Clearing tonight may lead to patchy fog.


&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...Heat Advisory until 7 PM CDT this evening for KYZ026-061-062-
     070>074.

&&

$$

Update...DM
Short Term.....EBW
Long Term......EBW
Aviation.......13



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