Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 211100
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
700 AM EDT Mon May 21 2018

.Short Term...(Today and tonight)
Issued at 255 AM EDT Mon May 21 2018

Largely a persistence forecast today as the Ohio Valley remains
under a warm and moist low-level air mass, weak flow aloft and weak
surface gradients. Ongoing convection over the Mississippi Valley is
on track to stay mainly to our north and west.

Expect at least scattered convection to fire later today, with hi-
res models pointing to the 18-20Z time frame, but a strong enough
outflow from storms to our west could initiate earlier west of
Interstate 65. Plenty of moisture and instability in place to
support typical pulse threats such as gusty winds and heavy
rainfall, but dynamics are too weak for organized severe weather.
Marginal risk in SPC`s Day 1 outlook seems to be on the money.

Convective temps are a bit lower than Sunday, so expect more clouds
to develop earlier and limit max temps to the mid 80s. Showers and
storms will continue into the evening before mostly dissipating.
However, both GFS and NAM suggest a sfc boundary could hang up near
the Ohio River, and continue to support precip chances through the
night.

.Long Term...(Tuesday through Sunday)
Issued at 235 AM EDT Mon May 21 2018

A weak cool front is expected to be across central Illinois and
central Indiana Tuesday morning and will drop into southern Indiana
and central Kentucky by late afternoon and into the evening hours.
Scattered showers or storms may be ongoing Tuesday morning across
parts of the area ahead of the front, and this could limit
destabilization for the afternoon. If skies do clear out by
afternoon ahead of the front, then modest instability would develop
on the order of 1500 to 2000 J/kg. Surface convergence along the
front and weak but present deep layer shear (25 to 30 kts) may be
enough of a trigger to fire convection by late afternoon or early
evening. The better setup for stronger storms lies northeast of the
area, but couldn`t rule out a stronger storm producing gusty winds
or hail north of I-64 and east of I-65.

The front then clears south of the Tennessee border Tuesday night
and any remaining showers should dissipate by early Wednesday
morning. With high pressure nosing in from north, northeast/east
flow will provide a couple of drier, slightly less humid, but still
warm days for the Ohio Valley. Dry conditions are expected Wednesday-
Friday.

Lower confidence going into the upcoming holiday weekend as the
suite of forecast models continue to show a complex pattern
featuring a couple of shortwave troughs moving through the flow but
also tropical moisture originating out of the Gulf. Depending on how
these two systems come together, or not, will dictate coverage of
showers and storms. A trend in the model consensus from the previous
forecast is for less chances on Saturday as any moisture from the
Gulf now looks to hold off until Sunday for the Ohio Valley.

Temperatures through this week and upcoming weekend will continue to
stay above normal with highs in the mid/upper 80s and lows in the
60s.

&&

.Aviation...(12Z TAF Issuance)
Issued at 645 AM EDT Mon May 21 2018

VFR conditions with light winds and cirrus ceilings this morning
across central Kentucky and southern Indiana. Convection remains
well to the west over the Mississippi Valley, and does not figure to
even impact HNB until around midday.

Expect scattered showers and storms to develop this afternoon, with
better coverage than Sunday given lower convective temps. Will
mention VCTS and CB across the board starting early in the
afternoon, with the potential for a direct impact on all but LEX
increasing enough to warrant a PROB30 after 21-22Z.

Confidence diminishes after sunset, but this pattern hasn`t shown
signs of sustaining organized convection too deep into the night.
Will go dry after 02-04Z with mid-level debris cloudiness.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&

$$

Short Term...RAS
Long Term...ZT
Aviation...RAS



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