Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 131121

Area Forecast Discussion
National Weather Service Louisville KY
621 AM EST Fri Jan 13 2017

...Updated Aviation Discussion...

.Short Term (Now through Sunday)...
Issued at 255 AM EST Fri Jan 13 2017

Cold front has pushed into the Tennessee Valley, with northerly
winds and cold air advection now well established over the Ohio
Valley. Main concern in the short term is the potential for ice
glaze around daybreak today and again early Saturday morning, mainly
over southern Indiana.

Post-frontal precip remains fairly widespread along and south of the
Western Kentucky and Bluegrass Parkways, but flat ridging over the
Deep South is keeping the mid-level flow just WSW enough that we
could see precip wave slightly northward from its current
trajectory. Surface temps over southern Indiana are just above
freezing, but with just enough room for both diurnal and wetbulb
cooling that any precip this morning could fall at freezing or below
in Indiana and north of I-64 in Kentucky. However, POPs are low
enough, and roadway temps still high enough, that ice accumulations
will be barely more than a trace, if anything. Given the limited
impacts, will just cover it with a Special Weather Statement.

Intermittent light rain is a good bet today across the region,
initially south of the WK/BG Parkways, but the focus will wave to
the north as the day progresses. Not a washout by any means, but
most locations will measure a few hundredths of liquid. The window
for freezing rain is a narrow one, with temps into at least the mid
30s by late morning. Not much more recovery than that, and max temp
forecast follows the low end of guidance.

Axis of precip shifts farther north in Indiana this evening, but
will wave back southward toward daybreak Sat, opening another window
for freezing rain. Temps should be a couple degrees warmer, so
precip type issues should just graze our CWA boundary with IND.
Again impacts will be limited given light QPF and temps just briefly
at or just below freezing. A bit quicker and stronger temp recovery
expected Sat afternoon with 50s punching into south central Kentucky.

.Long Term (Sunday night through Friday)...
Issued at 255 AM EST Fri Jan 13 2017

Waves of precip will continue to impact the Ohio Valley Saturday
night into Sunday, until a warm front lifts north into Indiana on
Sunday afternoon. Precip type will again be in question around
daybreak on Sunday, but should be limited to locations in Indiana
from Paoli to Salem to Madison and north, or roughly along and north
of Highway 56.

Unseasonably mild temps will arrive on Sunday night as we pop into
the warm sector in response to upper ridging downstream of a closed
low lifting out of the Sonoran desert. After a break in the precip
Sunday night and Monday, warm advection showers develop again late
Monday with coverage increasing on Tuesday. Could see a few rumbles
of thunder Tue/Tue night as the low lifts into Canada and drives a
slow-moving cold front into the Ohio Valley.

Latest GFS and ECMWF are pointing to another break in precip Wed
night into Thu as the front could finally clear the area. Not quite
ready to jump on this solution as it remains an unseasonably warm
and moist pattern, but have trended POPs lower in this time frame
given the agreement between models, and later shifts can continue to
cut POPs if continuity is established.

QPF is not looking as impressive as in previous forecasts, with 5-
day totals coming in the 1-2 inch range and spread out over much of
that time. Will continue to monitor for potential flood concerns,
but know that it will take a few days before the expected rainfall
catches up with us.


.Aviation...(12Z TAF Issuance)
Updated at 620 AM EST Fri Jan 13 2017

Cold front still remains stalled out south of the region and we`ll
be dealing with low stratus and passing showers throughout much of
the TAF period.  Overnight guidance has come in a bit more
pessimistic for aviation conditions today.  In general, ceilings are
probably going to run in the 700-1500 ft AGL range at all the
terminals.  MVFR to low end VFR visibilities are expected with
reductions due to light rain and mist.  Surface winds will generally
be out of the northeast at 5-10kts.

Ceilings look to lower tonight with ceilings possibly dropping into
the LIFR range at all the terminals.  Winds will remain out of the
northeast at 5-10kts and will likely shift to the east very late in
the period as the front to the south start to retreat northward as a
warm front on Saturday.




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