Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 232202

502 PM EST Tue Dec 23 2014

...Forecast Update...
Issued at 455 PM EST Tue Dec 23 2014

Web cams reveal light drizzle and patchy dense fog may briefly
reduce visibilities near the Ohio River in the Louisville metro
through rush hour.  Thus, issued an SPS through 7pm.

.SHORT TERM (Now through Wednesday Night)...
Issued at 305 PM EST Tue Dec 23 2014

Low pressure taking shape along the Louisiana Gulf Coast this
afternoon, with an inverted surface trof extending well north,
across the Pennyrile region of Kentucky and into southern Indiana.
Precip shield is filling in as it expands from the Deep South into
the Tennessee Valley, and will make for a wet night across the Ohio
Valley. Already seeing some showers in south central and east
central Kentucky, but thus far the lightning strikes have remained
over the Cumberland Plateau.

Coverage and intensity of precip will increase through the evening,
with the heaviest precip expected after midnight as the deepening
low cuts north through central Kentucky. With the dynamic setup,
will retain mention of thunder roughly along and east of I-65, with
the main window from 06-18Z. Temps will remain nearly steady through
the night, except our westernmost counties in Indiana where the
light north winds may help drop readings into the mid 40s.

Surface low will lift into Indiana by mid to late morning, after
which the thunder threat will decrease from west to east. Strong
winds not too far off the deck will have the potential to mix down
in showers or T-storms, mainly across the Bluegrass and farther
east. Will continue to mention near-severe gusts in the Hazardous
Weather Outlook. Temps will continue to hold steady through the
morning, with cooler air filtering in from the west during the

WSW winds will crank up as the exiting surface low really starts to
deepen. Expect a steady 15-25 mph, with 30-35 mph gusts in the
afternoon. The wind forecast bears watching as any substantial delay
in the cold advection could provide a window for stronger gusts,
which could be enough to push us into a Wind Advisory.

Wraparound precip will warrant keeping POPs well into the evening,
if not beyond midnight Wednesday night. Could see a changeover to
snow before it shuts off, but forecast soundings are looking
marginal for having ice in the cloud layer. Temps will remain just
above freezing, so even a dusting of snow will likely be limited to
grassy surfaces.

.LONG TERM (Thursday through Tuesday)...
Issued at 300 PM EST Tue Dec 23 2014

After a wet and unsettled Christmas Eve, residents of central
Kentucky and southern Indiana will wake up Christmas morning to much
improved conditions as the storm system currently impacting the area
will have rapidly lifted north of the Great Lakes. Plan on leftover
clouds quickly clearing out west to east as a modified Pacific
airmass surface high takes hold over the region. This will make for
a seasonable and dry Christmas and plan on highs in the mid to upper

The upper level flow becomes zonal to southwesterly between
Christmas night and Friday night as a western CONUS trough begins
to deepen. Surface high pressure off the North Carolina coast will
keep a light but southerly wind in place, and overall Friday looks
pleasant with highs in the low/mid 50s after starting off the
morning in the low 30s.

23.12z guidance continues to advertise a front crossing the region
Saturday while a surface low tracks across the Great Lakes. However,
there remains some timing difference between the models. The GFS is
a faster solution, bringing rain into the area Saturday morning
while the ECMWF/GEM holds off until Saturday night. For now, will
advertise 30-40 percent rain chances, but the ECMWF/GEM trend is
favored so Saturday, at least the morning period, may end up drier.
Another mild day as highs should reach the low/mid 50s. This could
be on the low-side if precip/clouds hold off until the evening.

There are signals that the surface front stalls along the Gulf coast
late in the weekend, which complicates the forecast Sunday onward.
The upper level jet strengthens significantly from Texas to
Michigan, reaching 160+ kts by Sunday. The sensible weather impacts
between the models are large, some develop another surface low
tracking along the spine of the Appalachians. Others are shunted
further south, some have no reflection at all. Basically, confidence
Sunday onward is below average but a wet period is possible. A model
consensus of chance POPs is reasonable at this point. Temperature
profiles warmed considerably compared to model runs 24 hours ago, so
this appears to be more of a rain scenario, but will keep a
rain/snow mix Sunday night.

As we head into next week, there are some signals for a colder
airmass to move through the region. For now, we`ll trend
temperatures downward to slightly below normal which will show highs
in the upper 30s to lower 40s and lows in the 20s for Monday/Tuesday
next week.


.AVIATION (18Z TAF Update)...
Issued at 1230 PM EST Tue Dec 23 2014

Inverted sfc trof draped NE-SW across Kentucky has kept low clouds
in all morning, and we expect IFR conditions for most of the valid
TAF period. The only real question mark is the timing of any precip,
and chances for thunder as the deepening sfc low lifts north through
the Ohio Valley late tonight and Wednesday morning.

Will initialize with unrestricted visibility as the relative lull in
precip continues. Still just enough drizzle around to merit VCSH,
but operational impacts will be brief and limited.

Precip shield taking shape over the Tennessee Valley will spread
northward late this afternoon into this evening, so will go back to
prevailing SHRA with visibilities starting to drop. However,
ceilings will remain the determining factor in our IFR. After
midnight we get into a better dynamical setup as the surface low
approaches, so will go for heavier rain and also include VCTS. Could
even drop into LIFR ceilings in the heavier showers. Light winds
this evening will increase after midnight, but still just around 10
kt and southerly direction will nearly parallel the long runways at

By late morning the surface low should be solidly to our north, so
will look for slight improvements to conditions. Visibility
restrictions should end but will continue to carry VCSH for
lingering precip. Ceilings will lift to MVFR but will remain below
fuel-alternate thresholds.

Main afternoon concern at SDF will be wind, as WSW winds pick up to
around 15 kt with gusts around 25 kt. Will be a close call for
forcing SDF to the shorter crossing runway.




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