Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 152045
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
345 PM EST Fri Dec 15 2017

.Short Term...(This evening through Saturday night)
Issued at 315 PM EST Fri Dec 15 2017

Mid-level short wave trough continues to push through the region
this afternoon.  After seeing some brief clearing this morning,
batch of low-mid level cloudiness has worked its way back into
southern Indiana and central Kentucky.  Where skies have remained
partly sunny, temperatures have warmed into the upper 30s and very
low 40s, mainly west of the Natcher Parkway.  Elsewhere across
southern Indiana and central Kentucky, readings were generally in
the 34-39 degree range.  In the near term, we expect cloudiness to
remain in place this evening with temperatures remaining in the low
to mid 30s.

For tonight, high pressure is forecast to build into the region.
This should allow some partial clearing to work into the region
later tonight. Lows will range from the upper 20s to the very low
30s.

For Saturday, high pressure is forecast to move off to the east and
we should get back into a southerly flow regime.  Under partly to
mostly sunny skies, we should see afternoon temperatures push into
the upper 40s to the lower 50s.  Clouds will increase Saturday night
ahead of the next weather system.  Lows look to cool into the 33-38
degree range.

&&

.Long Term...(Sunday through Friday)
Issued at 345 PM EST Fri Dec 15 2017

Sunday through Friday...

Latest model data continues to show a weakening short wave trough
axis moving northeastward through the region on Sunday.  This
feature will bring plenty of cloud cover and rain showers to the
region.  Thermal soundings remain warm, so precipitation looks to
remain rain throughout the event.  The precipitation looks to move
off to the east Sunday night.  It appears that we`ll see a bit of a
break in the action for Monday and perhaps into Tuesday as we get a
bit of a split flow pattern aloft.  A fast Pacific jet flow will
flood the northern US with modified Pacific air, with the southern
branch of the jet providing plenty of moisture to areas to our
south.  We`ll be on the confluent side of things, but the models
diverge in their solutions by Wednesday as to how the southwestern
US trough axis ejects.  The GFS is more progressive and slides
things to our south and east, while the Euro ramps up the trough and
allows it to drift further northward into the Ohio Valley.  For now,
have stuck close with our neighbors and leaned a little closer to
the GFS and its ensembles and kept Wednesday a bit drier.  Will need
to watch future runs to see if additional precip chances may be
needed in future forecasts.

Highs Sunday look to be on the cool side of things with highs in the
lower 40s.  Lows Sunday night look to cool into the upper 30s.
Monday through Wednesday continue to look mild with highs in the
40s/50s and overnight lows in the 30s.

By Thursday, the upper level flow pattern is expected to amplify
once again with a large scale trough axis centered in the western
CONUS and downstream ridge off the SE US coast.  This should place
the Ohio Valley in a southwest flow with a milder temperature
pattern setting up.  The models still suggest that a cold front will
push into the region by late Thursday and into Friday brining
another round of showers to the region followed by a cool down in
temperatures.

Saturday and into Christmas Week...

Latest model data continues to point to an active period of weather
during the upcoming Christmas holiday period.  The upper level
pattern looks to feature strong upper ridges on both sides of the US
coasts, with a corresponding trough axis in between.  The crux of
the forecast remains on where these features will be located next
weekend and how strong they will be.

The main impactful weather looks to be on the western periphery of
the SE ridge where abundant tropical moisture may flow northward and
over the top of an expanding low-level cold airmass.  The specific
details on the overall thermal structure of the atmosphere remain
unresolvable at this time period.  The deterministic model runs
continue to fluctuate with each passing run.  In addition, the
ensemble spread remains remarkably high at this time.  Therefore, it
will be another 5-6 days, perhaps longer, before the sensible
weather features come into focus.

In summary, our message remains consistent from yesterday.  It is
important to no lock into any one model solution over the next week.
Our advice is that if you have travel plans for late next week and
into Christmas, that you keep a close eye on the latest forecasts
over the next week.

&&

.Aviation...(18Z TAF Issuance)
Issued at 1202 PM EST Fri Dec 15 2017

Plan on breezy westerly winds this afternoon with gusts to around 20-
22 kts. Skies will vary from partly to mostly cloudy but ceilings
will remain VFR. More mid-level clouds are possible tonight,
especially at SDF, LEX, and HNB. For tomorrow, expect southwesterly
winds to increase ahead of an approaching cold front. Sustained 10
to 15 kts with gusts 20-22 kts are likely. Skies should remain
mostly clear outside of high cirrus.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&

$$

Short Term...MJ
Long Term....MJ
Aviation.....ZT



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