Area Forecast Discussion
Issued by NWS Louisville, KY

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020
FXUS63 KLMK 041715
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1215 PM EST Sun Dec 4 2016

.Forecast Update...
Issued at 840 AM EST Sun Dec 4 2016

88D showing only lighter returns across the area at this time.
Cannot rule out some patches of drizzle over the next few hours, but
a better area of moisture will come in from the west this afternoon.
Thus have continued the trend of drying out the rest of the morning
forecast before spiking rain chances back up again. These changes do
not affect the zone forecast, but will be reflected in our hourly
web forecasts.

&&

.Short Term (Now through Monday)...
Issued at 230 AM EST Sun Dec 4 2016

An early morning analysis showed surface high pressure centered over
Ohio and West Virginia while aloft the latest water vapor imagery
and 500 mb heights had a closed low over the Gulf of California and
a shortwave trough moving across the central Plains. A plume of
moisture streaming out of Mexico and the southern Plains combined
with steady isentropic lift has resulted in light rain showers
across the TN and lower OH river valleys. Locally, temperatures
ranged from the mid 30s across southeast Indiana to low 40s near the
TN border. Regional radar shows the light rain showers slowly moving
north/northeast and with surface wet-bulb temperatures expected to
remain at or above freezing, the threat of any frozen precipitation
is very low. A cold rain is in store for most folks this Sunday
morning.

Available hi-res guidance in good agreement showing this southern
stream precipitation skirting across middle TN into south-central
and southeast Kentucky through the morning while the aforementioned
shortwave trough over Kansas/Nebraska makes a move toward Indiana
later today. There will likely be a gap or break in the light rain
for parts of central Kentucky and southern Indiana mid/late morning
into early afternoon, and just very spotty showers are possible. As
the next wave approaches mid/late afternoon, better coverage of rain
is expected to break out across southern Indiana and northern
Kentucky. This will continue into the early evening hours. Overall,
light rain amounts are forecast through tonight with most areas
picking up around 1/10 to 2/10 of an inch. Some spots near the TN
border may see up to 1/4 of an inch of rain.

Rain will taper off mid/late evening and will likely end as drizzle
as soundings show drying aloft while low-level saturation and lift
lingers. Low stratus or fog is possible during the overnight into
the Monday morning commute.

Plan on highs today to top out in the low to mid 40s while lows
tonight will fall into the lower 30s.

For Monday, surface high pressure will quickly move across the area.
Soundings show a fairly deep dry layer in the mid levels but a low
level inversion may keep a stratus deck in place for most of the
day, so don`t expect a lot of sunshine to start the new work week.
Highs will range from the upper 40s across southern Indiana to lower
50s across southern Kentucky.

.Long Term (Monday Night through Saturday)...
Issued at 240 AM EST Sun Dec 4 2016

The weather highlights in the long term forecast are rainfall Monday
night and Tuesday, precipitation chances and types Wednesday night
and Thursday and then the first significant cold outbreak of the
winter season to end the work week.

The upper level shortwave currently over Mexico will kick toward
Tennessee late Monday night and Tuesday. As it does so, it will
surge higher Gulf moisture northward into the area. Strong forcing
for ascent will bring widespread rain to the area beginning late
Monday afternoon or evening across southern Kentucky, and up to
southern Indiana after midnight. Rain chances remain in the 80 to
100 percent range. There continues to be some weak elevated
instability across south-central KY so an isolated rumble of thunder
is not out of the question. Rain will be most widespread from
midnight to noon then begin to exit out of the area during the
afternoon Tuesday. Total rainfall amounts are forecast between 3/4
and 1 inch across the entire area, the highest amounts around the
TN/KY border.

High pressure builds in for Wednesday which will provide a dry day
but with below normal temperatures. Highs are forecast to range from
near 40 across southern Indiana to the mid 40s across southern
Kentucky.

The forecast Wednesday night and Thursday remains challenging with
the 04.00z guidance still not coming into agreement. The GFS and GEM
solutions are much drier, showing a moisture limited cold front
passage late Wednesday night. Meanwhile, the ECMWF continues to
advertise a more phased system, bringing a surface low toward
central Kentucky with much more precipitation. The GFS/GEM solution
would favor lower precipitation chances with just some very light if
at all snow potential while the ECMWF is warmer but with the
potential for rain to change to snow on the backside before ending.
Kept a model consensus of low rain to snow chances Wednesday night
and Thursday morning, but did lower QPF from the consensus after
coordination with PAH.

It looks like either way Thursday will be the transition day to a
much colder weather pattern as a deep upper level trough dives
southeast from the northern Plains and Upper Midwest. Strong
Canadian high pressure will usher in the coldest air of the season,
and temperature anomalies are up to 3 SD below normal. Thursday may
be a non-diurnal day with temperatures steady or falling in the
afternoon into the upper 20s or low 30s. There`s good consensus that
lows Thursday and Friday nights will be in the teens while Friday`s
highs may struggle to break 30 in most places. The cold temperatures
continue into Saturday with highs only in the 30s.

&&

.Aviation...(18Z TAF Issuance)
Issued at 1215 PM EST Sun Dec 4 2016

Upper trough axis will push into the region from the northwest. This
will bring another round of moisture to the region leading to a
reduction in ceiling height/vsbys along with widespread rainfall. It
appears that rainfall will redevelop later this afternoon and
continue into the evening hours.  After the rain diminishes late
tonight, low clouds will remain along with drizzle and some fog.
Ceilings will likely fall below IFR levels this evening and into the
overnight hours with vsbys remaining in the IFR to MVFR range.
Ceilings look to improve Monday morning.

Winds are looking to be rather erratic as they will be shifting
around over the TAF period.  The will start off out of the
southeast/south this afternoon and then veer to the southwest and
then to the northwest tonight after the trough passage.  A shift
again to the northeast is expected on Monday.

&&

.LMK Watches/Warnings/Advisories...
IN...None.
KY...None.
&&

$$

Update...RJS
Short Term........ZT
Long Term.........ZT
Aviation...MJ



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