Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 060230
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
930 PM EST Mon Dec 5 2016

.Forecast Update...
Issued at 925 PM EST Mon Dec 5 2016

Making minor tweaks for timing tonight. Forecast in general is on
track with the upper low starting to generate precip over the
ArkLaTex region. Even though rain has been slow to move into western
and middle Tennessee, still expect the rain shield to really expand
northward overnight. Onset of precip may be a couple hrs slower than
advertised, but still expect rain into most of central Kentucky and
even southern Indiana by daybreak Tue. Will also reflect
steady/rising temps overnight, as mins appear to have already been
realized.

&&

.Short Term...(This evening through Tuesday night)
Issued at 250 PM EST Mon Dec 5 2016

...Widespread Rain Expected Tonight and Tuesday...

The low cloudiness mixed out up near the I-70 corridor this
afternoon.  The clearing line did make it briefly down to near the
Ohio River, but abundant mid-high level cloudiness associated with
next weather system has overspread the region.  Temperatures ranged
from the lower 40s over west and north-central Kentucky to the mid-
upper 40s over the eastern part of the state where some clearing did
take place earlier this morning.  Not expecting much of any further
rises in temperatures this afternoon, so readings should stay in the
upper 30s to the lower 40s this evening with mostly cloudy skies.

Later tonight, closed upper low in the southern stream over Texas
will lift northeastward and reach the Tennessee Valley by Tuesday
morning.  As this occurs, deep layer moisture will push northward.
Coincident deep layer forcing will spread northward and should help
precipitation shield expand rapidly to our south late this evening.
Precipitation looks to overspread KY later tonight.  Elevated
instability still looks rather marginal and a rumble or two of
thunder across southern KY can not be ruled out.  Otherwise, the
main sensible weather issue will be moderate to occasionally heavy
rainfall overnight into early Tuesday.  Overnight lows tonight will
drop to around 40 across southern Indiana and into the lower 40s
across Kentucky.  The rainfall should continue into the day on
Tuesday and then diminish in the afternoon.  Rainfall totals of 0.75
to 1.5 inches will be possible by the rains shift off to the
northeast.   Highs Tuesday will warm into the mid-upper 40s.  Temps
will fall into the upper 20s to around 30 by Wednesday morning.

.Long Term...(Wednesday through Monday)
Issued at 329 PM EST Mon Dec 5 2016

...Cold Weather To Invade Later This Week...

Wednesday through Friday Night...

Well advertised upper trough axis will shift into the region late
Wednesday. Overall model guidance has continued to trend drier
with the cold front swinging through the region. We could still
see some light QPF down state where better moisture will reside.
Depending on how much low-level moisture remains, some light snow
flurries will be possible late Wednesday and into early Thursday.
Strong northwest flow in the wake of the front will usher the
coldest air of the season into the region. Lows by Thursday
morning will range from the mid to upper 20s. Strong northwest
flow off the warm Great Lakes will fire up the lake effect snow
machine. However, low-level flow will steer the vast majority of
those snow showers into west- central IN and into central OH.
We`re not expecting much of a diurnal rise in temperatures on
Thursday with highs in the upper 20s to the low 30s. It will be
windy day with winds of 15-20 MPH and some higher gusts...which
will make it feel more like the teens in the afternoon and
evening.

High pressure will nose into the region Thursday night with lows
dropping into the mid-upper teens.  Highs Friday will basically be
in the upper 20s and lows Friday night will once again drop into the
teens.

Saturday through Monday...

Strong Canadian high pressure will hold sway across the region for
Saturday with little improvement in the temperature department.
Highs will range from the lower-mid 30s north of I-64 with mid-upper
30s found mainly south of the Parkways in Kentucky.

From Saturday night onward, the forecast becomes much more
complicated as the models struggle with the overal flow pattern.
Both models do have us in a slight return flow regime with the next
in a series of upper level waves coming into the region.  While both
models agree that another mid-level wave will push into the region,
they strongly disagree in terms of timing.  The GFS is rather quick
bringing moisture back into the region Saturday night.  On the other
hand, the Euro is much slower delaying the arrival by almost 24
hours. Given the GFS tendency to overpower the northern stream, its
solution is likely too fast, given the pattern.  Thus, we have split
the forecast to a compromise of the GFS and Euro.  This keeps a
decent amount of continuity in the forecast for now.

In this forecast, we`ll continue to intoduce some light preciptation
late Saturday night and early Sunday.  Low-level warm air advection
ahead of the system will likely keep precip in the form of a wintry
mix initially, quickly changing over to plain rain as temps warm
into the upper 40s.  Depending on how fast the system moves through
the region, precip may linger into Sunday night and Monday before
the front pushes through the region.  Another blast of cold air will
follow in the front`s wake.

&&

.Aviation...(00Z TAF Issuance)
Issued at 655 PM EST Mon Dec 5 2016

First area of isentropic lift associated with low pressure
developing over the Deep South ran into a wall of dry ENE flow near
the KY/TN line, allowing SDF and LEX to break out of stratus and BWG
to lift to high-end MVFR. However, the main low is still taking
shape over the Lower Mississippi Valley, and conditions will rapidly
deteriorate late this evening.

Expect IFR ceilings and light stratiform rain to spread into BWG by
03Z, and SDF and LEX after roughly 06-07Z. Vis will stay in the MVFR
range, and we could even see a bit of a dry slot toward daybreak.
However, greatest impacts will occur Tuesday morning, with LIFR
ceilings expected as a deformation zone lifts through the Ohio
Valley.

Surface low and upper trof axis will be to our east by early
afternoon, bringing an end to the rain and a wind shift to the W-NW.
However trapped moisture will keep ceilings in fuel-alternate until
near the end of the TAF period.


&&

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

$$

Update...RAS
Short Term...MJ
Long Term...MJ
Aviation...RAS



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