Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 221123

Area Forecast Discussion
National Weather Service Louisville KY
723 AM EDT Sun Oct 22 2017

...Updated Aviation Discussion...

.Short Term...(Today through Monday)
Issued at 255 AM EDT Sun Oct 22 2017

High pressure centered over the Mid-Atlantic region continued to
provide dry weather across the lower Ohio Valley early this morning
as the latest satellite imagery shows a stream of cirrus moving
overhead. This combined with southeast winds 5 to 10 mph has kept
readings elevated in the 50s to lower 60s.

For today, plan on one more seasonably warm day before unsettled
weather and large temperature changes arrive for most of next week.
A cold front, currently along a line from near Minneapolis to
Oklahoma City will slowly advance eastward toward our area today.
Ahead of this front, a well mixed boundary layer and tightening
pressure gradient will promote southerly wind gusts 20 to 25 mph at
times. This will also allow temperatures to rise well into the 70s,
with a few locations possibly hitting the 80 degree mark despite
some increasing high clouds.

The latest suite of hi-res models continue to slow the progression
of the rain showers this afternoon and evening. The bulk of
precipitation will likely hold off until after sunset, though a few
showers may develop ahead of the main line across southwest Indiana
and portions of west central Kentucky later this afternoon.

As the main upper level energy drops into Arkansas and Mississippi
tonight, widespread showers are expected to lift into south central
Kentucky then spread northward through the entire area overnight
into Monday morning. Will maintain the highest precipitation chances
from mid/late evening through Monday morning across the entire area
where 1 to 2 inches is likely. Locally higher amounts will be
possible across south-central Kentucky.

The atmosphere will be characterized by anomousoly high PWATs /1.5
to 1.7 inches/, strong moisture transport, and deeply saturated,
which all support the idea of efficient rain producing showers. This
could produce periods of heavy rain. The antecedent dry conditions
will help and while large scale flooding isn`t a risk, localized
short term issues could develop across central Kentucky where the
greatest rainfall rates are likely.

The upper shortwave and surface low will quickly lift to the
northeast of the area during the day Monday, bringing a southwest to
northeast end to the widespread showers. In its wake, a strong cold
front will sweep through Monday evening and Monday night, bringing a
surge of cold air and breezy northwest winds. Plan on lows MOnday
night in the 40s.

.Long Term...(Monday night through Saturday)
Issued at 256 AM EDT Sun Oct 22 2017

The Tuesday through Wednesday period will feature weather more like
November,  not October, with a large upper level trough across the
region bringing cool temperatures and cloudier conditions. Tuesday
will be a windy and noticeably colder day with northwest winds
gusting to 20-30 mph at times. There should be plenty of strato-cu
development and a chance of light rain showers or sprinkles during
the day mainly across southern Indiana and northern Bluegrass
region. Plan on highs to stay in the 50s.

On Wednesday a quick moving northwest flow system is forecast to
drop through the Upper Midwest into the lower Great Lakes region.
The 22.00z guidance points to the majority of its impact confined to
central Indiana and central Ohio, but will have to watch closely to
see if it brushes parts of southeast Indiana and northern Kentucky
with any showers. Highs on Wednesday will range from the low 50s
across the Bluegrass to mid 50s closer to the TN border.

Depending on timing and how winds/clouds materialize, Thursday
morning could be one of the coolest mornings so far in the autumn
season. A model consensus puts lows in the mid to upper 30s, which
could support patchy frost.

Beyond Thursday, forecast confidence drops off considerably with the
potential for another weather system next weekend. There are plenty
of timing, thermal, and spatial differences in the 22.00z guidance.
For now, leaned on the model consensus which advertises 20-40
percent rain chances. Temperatures could be seasonably cold in the
wake of that system but for now will show highs in the 50s and lows
in the 30s.


.Aviation...(12Z TAF Issuance)
Issued at 650 AM EDT Sun Oct 22 2017

Low-level jetting will be the main player in the near-term, as we`ll
initialize wind shear at all but LEX, LLWS will mix out by late
morning as sfc winds pick up, with southerly gusts in the 20-25 kt
range for most of this afternoon.

Rain will spread into the region shortly before sunset, with
ceilings just barely VFR into the evening. Ceilings will build down
through the night, going into fuel-alternate around midnight and
finally into IFR just before sunrise as precip picks up in intensity
and boundary-layer becomes saturated.

The outlier in all of this is LEX, where precip will not arrive
until solidly after midnight, and ceilings will remain VFR through
12Z Monday.




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