Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 211655

1155 AM EST Sun Dec 21 2014

...Updated Aviation Discussion...

...Forecast Update...
Issued at 1035 AM EST Sun Dec 21 2014

Morning fog burning off and temperatures have climbed above
freezing, so freezing fog / slick roadway threat largely over.
Forecast for this afternoon remains on track and we`ll have a fair
amount of sunshine, outside of some high level clouds coming in from
the west. Lowered high temperatures a couple of degrees due to
little boundary layer mixing and the slow climb this morning. Still
on track for 40s, but more likely to range from the low 40s across
southern Indiana to mid/upper 40s across southern Kentucky.

Issued at 800 AM EST Sun Dec 21 2014

Localized freezing fog developed overnight as many automated
observations show light fog/mist with visibilities in the 3-5 mile
range. This resulted in some slick roadways, especially bridges and
overpasses around river valleys. With temperatures in the low/mid
20s still, the threat could linger for a couple more hours until the
sun works to burn off fog and melt any icy spots. Added patchy
freezing fog to the forecast for the remainder of the morning and
highlighted threat with a SPS. Adjusted hourly temperatures as we`re
running a bit too warm this morning. Otherwise, forecast largely on
track with highs in the mid/upper 40s.

.SHORT TERM (Now through Monday)...
Issued at 251 AM EST Sun Dec 21 2014

The influence of high pressure has brought mostly clear skies to the
region early this morning with temperatures in the lower to mid 20s.
This high pressure will slowly shift to the northeast tonight and
tomorrow as a low pressure system drops into the Midwest. For today
dry weather is expected with mainly high clouds streaming across the
area. Temperatures will be warmer than yesterday, topping out in the
mid 40s to around 50.

For tonight and early Monday a southern stream system moving up the
east coast could spread a few showers into east central KY. However,
coverage of these showers will not be too high so have kept chances
around 20%. Lows tonight will drop into the lower to mid 30s.

Winds will shift to southerly by Monday with warm air advection
continuing. A few showers will be possible across western portions
of the forecast area late in the day as the aforementioned low nears.
Temperatures will be warmer still despite thickening cloud cover.
Highs will top out in the lower to mid 50s.

.LONG TERM (Monday Night through Saturday)...
Issued at 304 AM EST Sun Dec 21 2014

Monday Night through Wednesday Night...

...Active Weather Pattern Still Likely for Christmas Eve...

Deep latitudinal trough will be just out to our west at the start of
the forecast period with a surface low pressure system up over
Iowa.  Widespread rain showers will likely be in progress across the
region as we will remain in a deep southwesterly flow aloft with
plenty of lift and moisture available for precipitation.

The deep trough axis will shift eastward on Tuesday.  The models
continue to be fairly deep with this trough axis.  Some of the
models are now showing some surface based instability developing
during the day on Tuesday.  Given the model soundings, it appears
that we may have some isolated/embedded thunderstorms with this
activity as it presses through the region. However, current thinking
is that more widespread thunderstorm development will be to our
south across the northern Gulf coast states.  After coordinating
with our surrounding offices, we will be adding some thunder into
the forecast for Tuesday.

Temperatures Monday night and Tuesday will be mild with lows only
dropping into the lower-middle 40s and highs warming into the upper
50s to possibly near 60 in some locations.  Current thinking is that
the best shot of 60 degree readings will be out across our east and
southeastern sections.

By late Tuesday, we still expect to see a secondary low pressure
system develop along the frontal boundary pushing through the
region.  In the past few days, the models have been aggressive with
this low developing and shift north while strengthening rapidly.
The current data still supports this to some extent (GEM/GFS),
though the reliable ECMWF runs are noticeably weaker with this
system.  Not sure if this some one time solution from the model or
the emergence of a trend.  The GEM and GFS runs continue their
trends of a developing/strengthening storm system, so perhaps this
is just some off run by the Euro.  Nonetheless, the system of note
has not yet been fully sampled by radiosonde data yet, so things may
change over the next few days.

In keeping a consistent forecast going, we believe that we`ll see
the low slide up into Ohio and then into Ontario by late Wednesday.
An influx of colder air will push into the region.  The models have
maintained their westward tracks, so the cold air push may be a
little later than previously forecast.  In any case, rain showers
are expected for much of the day on Wednesday with a change over to
snow showers by Christmas Eve.  It will be quite blustery as well
given that the pressure gradient will increase quite a bit.  Still
thinking sustained winds of 10-20 MPH with gusts up around 30 MPH
will be likely Wednesday afternoon and Christmas Eve.  Temperatures
will have their daily high early in the day on Wednesday with
readings falling throughout the day.  Temperatures by Christmas Eve
will be in the middle 30s.   Temperatures will continue to cool into
the lower 30s later in the night with the snow showers continuing
but they are expected to diminish after midnight.

There is still a low risk of some minor accumulations with the snow
showers on Wednesday night...especially in areas that see more snow
squalls than snow showers and flurries.  However, the factors going
against accumulations will be the wet ground and surface
temperatures staying at or above freezing during that time period.

Christmas Day through Saturday...

Fairly large surface high pressure system is forecast to be centered
over the northern Gulf of Mexico on Christmas Day.  We will be on
the northern periphery of this ridge with an increasing
southwesterly flow.  We`ll probably have some morning clouds left
over from the departing storm system, but it looks more and more
likely that we`ll scour out clouds during the afternoon hours.
Combination of statistical and dynamical guidance suggests highs in
the lower 40s in the north with middle to upper 40s across southern
Kentucky.  Lows Christmas night will be a little milder due to the
continued southerly flow expected with lows in the middle 30s.

A fast moving frontal boundary will approach the region on Friday.
We`ll continue to see a mild southwest flow out ahead of this
feature with a chance of some isolated showers.  The front looks to
move through during the afternoon/evening hours with colder air
filtering back into the region.  Pre frontal highs will be in the
upper 40s to the lower 50s with temperatures Friday night cooling
back into the lower-middle 30s.  A colder airmass will likely hold
sway into Saturday with continued dry conditions.  Daytime highs on
Saturday look to only warm into the middle to upper 30s in most
areas.   A few lower 40 readings will be possible down across
southern KY.


.AVIATION (18Z TAF Update)...
Issued at 1150 AM EST Sun Dec 21 2014

VFR conditions expected for most of the TAF period as high pressure
to the northeast remains the main weather feature. Light easterly
flow today will become more southeasterly overnight. A fetch of Gulf
moisture and warmer temperatures will bring a low end VFR or MVFR
deck of clouds to the TAF sites after midnight. Current observations
across AL/GA show bases between 2500 and 3500 ft, and forecast
models are in good agreement showing this pivoting across Kentucky.
Introduced a MVFR group for BWG/LEX, however not as confident that
this will impact SDF.




Short Term.....EER
Long Term......MJ
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