Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 150515

Area Forecast Discussion
National Weather Service Louisville KY
1215 AM EST Fri Dec 15 2017

...Updated Aviation Discussion...

.Short Term...(This evening through Friday night)
Issued at 300 PM EST Thu Dec 14 2017

The short term period will feature mainly quiet conditions as high
pressure builds in from the west.  Temperatures this afternoon will
remain in the 30s with partly to mostly cloudy skies.  We should see
the clouds break up later tonight with temperatures falling into the
lower-mid 20s.

A short wave trough axis will swing through the region.  Moisture
looks to remain fairly limited.  We`ll probably see an increase in
cloudiness across southern IN and northern KY.   Highs look to warm
into the upper 30s with a few lower 40s down across southern KY.
Lows Friday night look seasonally cold with lows in the mid-upper

.Long Term...(Saturday through Thursday)
Issued at 300 PM EST Thu Dec 14 2017

Saturday through Thursday...

Surface high pressure is forecast to move through the southeastern
US on Saturday which should keep our region fairly dry with slightly
milder temperatures.  Current data suggests highs in the upper 40s
to the lower 50s.   Clouds will increase Saturday night as a
southern stream system approaches from the southwest.  Current
thinking is that precipitation will likely hold off until after
sunrise on Sunday.  Lows of 30-35 look decent for Saturday night.

Precipitation will rapidly expand in coverage on Sunday.  It appears
that we should see precipitation break out by mid-morning.  Thermal
profiles are a little colder here, so a wintry mix could be seen at
onset, if profiles remain cold enough.  That would not last all that
long as strong warm air advection allows the column to warm fairly
quickly.  Plenty of clouds and precipitation should keep temperatures
down a bit.  We plan on going a little cooler than the guidance with
highs in the upper 30s to the lower 40s north of the WK/BG Parkways,
and mid-upper 40s across the southern 2/3rds of KY.  Scattered
showers look to continue into Sunday night with lows in the upper
30s to the lower 40s.

It still appears that we`ll see a little bit of lull in the weather
for Monday.  However, that lull won`t last long as a secondary wave
should pass into the region late Monday into Tuesday bringing
another round of rain showers.  Highs on Monday look to warm into
the lower 50s with overnight lows in the 40s.  Some showers may
linger into Tuesday morning with a drying trend expected into the
afternoon.  Highs on Tuesday look to warm into the lower 50s with
lows Tuesday night falling into the lower 30s.   An area of high
pressure looks to then move into the region on Wednesday with highs
generally into the upper 40s to the lower 50s.  Lows Wednesday night
look to cool back into the 30s.  A return to a southwest flow looks
to begin in earnest on Thursday with highs warming into the lower-
middle 50s.

Friday into the Week of Christmas...

The latest data still suggests a highly active period of weather
coming for the holiday weekend and into the week of Christmas.  The
latest data suggests that a storm system will affect the region late
Thursday and into Friday in the form of a cold front.  We`ll be on
the warm side of this system with a period of showers (possibly a
few storms) pushing through the region.  That front looks to push
off to the east with colder conditions pushing into the region by
Saturday.  Highs may push into the upper 50s to around 60 very early
Friday before falling in the wake of the cold front.  Highs by
Saturday look to cool back into the 30s.

As we`ve been highlighting for the last few days, long range signal
analysis has been strongly advertising a signal passage in the Dec
23-24th time frame.  This is in the range of the long range
dynamical models and both the GFS and Euro both show this system
possibly impacting the region in the above time frame.  However, the
details as to the sensible weather with this system have yet to be
worked out.

The upper level pattern is forecast to be very amplified across NOAM
during this period.  The pattern is forecast to have a strong
eastern Pacific ridge just off the US coast extending into Alaska
with a corresponding downstream trough axis across the Plains and
another ridge in the western Atlantic.  The crux of the forecast
looks to depend on how strong the ridge over the Pacific and off the
east coast of the US will be.

In general terms, if the Pacific/AK ridge is strong, the
corresponding SEUS/SW Atlantic ridge will likely be strong,
resulting in a warmer pattern over the eastern US with the bulk of
the cold in the western US and in the Plains.  On the other hand, if
the east Pacific/AK ridge is not as strong, the corresponding
SEUS/Atlantic ridge will probably not be as strong and the cold air
over the Plains and west may be displaced further east.

Depending on the upper level configuration, there is a very good
possibility that an active storm track will be seen on the western
edge of the SE ridge.  Good moisture transport and low-level cold
air instruction would likely set the stage for a major wintry event
mainly on the poleward side of the storm track.  At this time, the
Ohio Valley looks to be within the path of the storm track, but the
thermal profile forecast is far, far from certain.  The dynamical
models will continue oscillate over the coming days producing
various, if not wild solutions.  It is important not to lock into
any one solution.  Our advice is that if you have travel plans for
late next week and into Christmas, that you keep abreast of the
latest forecasts over the next week.


.Aviation...(06Z TAF Issuance)
Issued at 1209 AM EST Fri Dec 15 2017

Through the early morning period a VFR stratus deck will persist over
the region. Some of the models do suggest this deck will lower right
to the MVFR threshold at BWG before dawn, but confidence on this is
low, so will keep ceilings on the higher side. Clouds should scatter
out a bit this morning, though a broken ceiling may develop again in
the afternoon before things clear out tonight. Winds will be light
and variable early this morning then pick up after sunrise. Some
gusts to 17-20 knots out of the west are expected through the
afternoon hours.




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