Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 200657

Area Forecast Discussion
National Weather Service Louisville KY
257 AM EDT Thu Sep 20 2018

.Short Term...(Today and tonight)
Issued at 254 AM EDT Thu Sep 20 2018

Quiet and calm weather ongoing this morning thanks to a large upper
level ridge currently over the TN Valley. GOES-16 IR products show
mostly clear skies across the region, and very pronounced
valley/river fog just to our east in the Appalachians. Winds have
generally been light to calm so far this morning, so can`t rule out
some patchy ground fog developing in the usual fog-prone areas later
this morning before sunrise. Any fog that does form should burn off
quickly after sunrise.

Another hot and mostly sunny day will be on tap, with temperatures
generally reaching the upper 80s to low 90s. When combined with
dewpoints in the upper 60s to low 70s, heat indices west of I-65
could approach 100 degrees for a few hours this afternoon. Doesn`t
look like we`ll get much relief from the heat in the form of rain,
as warm air aloft due to the presence of the upper level ridge will
keep most convection suppressed. A few high-res models hint at some
very isolated storms developing late this afternoon north of I-64,
but coverage of said showers looks to be too low to include in grids
at this time.

Another warm, muggy night will be in store tonight. Winds will pick
up some overnight as a weak LLJ develops and the pressure gradient
tightens in response to a deepening low near the Great Lakes region.


.Long Term...(Friday through Wednesday)
Issued at 255 AM EDT Thu Sep 20 2018

Vigorous storm system moving across the northern Great Lakes into
Ontario on Friday will drive a cold front SE into the Ohio Valley.
We`ll have plenty of instability ahead of the front to support
strong updrafts. Stronger deep-layer shear to organize a potential
squall line will remain to our north and northeast, but not out of
the question that we could catch the tail end of the line. Marginal
SVR risk for southern Indiana and north-central Kentucky looks to be
reasonable, given the potential for a line or pulse threat. That
could increase if the shear were to extend farther SW.

Cold front becomes oriented parallel to the upper flow on Friday
night, and a weak wave ejecting out of the southern Plains will
support renewed precip chances on Saturday, especially across
southern Kentucky. To the north of that precip shield, high pressure
over the Great Lakes will bring cool and cloudy conditions with
temps more typical of October.

Sunday forecast will be largely dependent on just where the stalled
front remains hung up under flat upper flow. Additional waves of
showers and storms along the front will keep at least south-central
Kentucky unsettled, and perhaps even more of the area if the ECMWF
is correct in its frontal position, which is farther north than the
GFS. That front will lift north on Sun night as upper flow backs SW
in response to downstream ridging, with broad and moist southerly
flow setting up on Monday. GFS and ECMWF paint a lot of QPF, but
this is often overdone in the warm sector.

Unsettled weather continues Tue-Wed as a longwave upper trof pushes
a cold front at least well into the Ohio Valley, if not all the way
through. Too early to get too detailed with severe potential, but
the system looks dynamic enough to support at least some stronger
storms. Expect above normal temps and borderline summertime humidity
through the first half of next week, with clouds and precip limiting
diurnal ranges.

Widespread QPF totals over the period will likely average 2-3
inches. However, depending on the placement of any heavier and/or
repeated rainfall, higher amounts will likely result in flooding
along some streams.


.Aviation...(06Z TAF Issuance)
Issued at 101 AM EDT Thu Sep 20 2018

With mostly clear skies and light to calm winds, some patchy ground
fog may develop before sunrise near the HNB/LEX terminals.
Otherwise, any fog that develops should burn off quickly after
sunrise, with VFR conditions expected the rest of the day.




Short Term...DM
Long Term...RAS
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