Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 301255
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
855 AM EDT Thu Oct 30 2014

...Forecast Update...
Issued at 850 AM EDT Thu Oct 30 2014

A quick update to remove the early morning wording. Had a chilly
start to the day, with several places down to around freezing as
well as a few reports of frost. Rest of today`s forecast pretty much
on track with only a few minor tweaks.

.SHORT TERM (Now through Friday)...
Issued at 305 AM EDT Thu Oct 30 2014

...Windy Conditions and Falling Temperatures Expected Friday...

Other than some patchy frost this morning in valley and sheltered
locations, we`ll start the day out fairly quiet with clear skies and
calm to very light winds as sfc high pressure sits over the region.
Temps today look to be cooler than yesterday with limited mixing and
increasing cloud cover throughout the afternoon hours.  Look for
high temps to top out in the mid 50s to low 60s this afternoon.

A weak upper shortwave trough will arrive tonight bringing scattered
rain showers to the region mainly after midnight and into the
morning early morning hours Friday.  Most locations can expect to
see rainfall amounts up to a tenth of an inch from light rain
tonight.

For Friday, a cold front will drop into the Ohio Valley bringing
more forcing for continued rain showers through early to mid
afternoon.  A break in precip is expected after the cold front
passage during the late afternoon or early evening hours before a
potent upper low barrels southward into our region bringing yet more
light precip chances (see long term discussion for details on Friday
night precip).  We`ll see windy conditions on Friday afternoon as
the cold front passes through.  NW winds of 15 to 20 mph will gust
up to 30 mph especially after the front passes and we perhaps see
some breaks in the clouds behind the front mid to late Friday
afternoon.  Temps will be tricky for Friday as well.  Friday morning
we`ll start out in the low to mid 40s.  We`ll warm into the upper
40s and low 50s by mid to late morning.  The cold front should pass
through the region quickly during the early afternoon hours
resulting in falling temps through the 40s for the rest of Fri
afternoon.

.LONG TERM (Friday Night through Wednesday)...
Issued at 310 AM EDT Thu Oct 30 2014

...First Blast of Cold Air Coming This Weekend with Wintry Precip
Friday Night East and Sub-Freezing Temps Sunday Morning Areawide...

Friday Night to Saturday Morning...

Latest GFS, NAM, and ECMWF are in pretty good agreement showing an
deep upper low diving SSE across the eastern OH Valley Friday night.
The GFE 18z ensembles showed the trough aloft being 3 to 4 standard
deviations below normal which is significant. With this system will
come cold air advection and dynamic cooling aloft. The model-
indicated pattern suggests possible development of a winter-like
deformation band within a tight isotach (lines of constant wind
speed) gradient in the left exit region of a 300 mb jet streak
diving south over the lower OH Valley. In these types of patterns, a
definitive mesoscale band of wintry precipitation normally occurs
assuming temperatures within the moist layer and at the surface are
sufficiently cold. In this system, the models suggest all this to
occur, which would suggest a band of snow over the eastern half of
the forecast area, especially east central KY late Friday night.
Model soundings show moisture extending up to between 500 and 600
mb, and cold enough in the moist layer for ice crystal formation
which would stay as mostly snow as it fell to the ground.

If this verifies, then scattered rain showers during the day Friday
likely would diminish or end in the evening, with a band of some
snow developing late at night which would move quickly southeast and
end by Saturday morning with up to an inch or so of snow possible
mainly across the Bluegrass, and especially on grassy areas.

The latest GEM, however, tracks the low and associated wintry
precipitation farther east, mainly east of our forecast area. For
now, will keep precipitation chances in the chance category over
eastern areas until the track of the system and potential band
formation is better known. Nevertheless, will indicate possibility
of all snow vs. a rain-snow mix in our previous forecast for late
Friday night into early Saturday morning.

Temperatures Saturday Morning and Sunday Morning...

The coldest air of the fall season will descend upon us over the
weekend. Temperatures Saturday morning will depend on cloud cover,
which should be widespread over the eastern half of forecast area.
Should see some clearing over western parts of central KY which will
allow readings to fall, although frost is less likely due to winds
remaining gusty from the northwest. Morning lows Saturday morning
will flirt with 32 F over many areas, but a widespread freeze is not
expected. High temperatures Saturday afternoon should remain in the
40s across the forecast area, with only lower 40s east where low
clouds will linger much of the day.

By Sunday morning, high pressure will be anchored over the OH Valley
with a mostly clear sky (although some clouds could linger over our
far southeast counties) and light wind. This will be a good setup
for temperatures to fall below freezing (mid 20s to around 30) over
much of southern IN and central KY, which would likely end what`s
left of the growing season in many locations. A freeze headline may
well be needed closer to that time, but will go with a special
weather statement for now to highlight the cold (plus the
possibility of some snow east late Friday night).

Sunday Through Wednesday...

The high pressure over us Sunday morning will move east Sunday and
Monday allowing a warming trend, especially by Monday afternoon when
highs should range from around 60 east to the 60s west across
central KY and southern IN. Expect similar temperatures Tuesday. Dry
weather will prevail Sunday through much of Tuesday, but a few
showers may move into western parts of south-central IN by late
Tuesday. The next weather system will then bring a band of numerous
rain showers across the area Tuesday night into Wednesday.

&&

.AVIATION (12Z TAF Update)...
Updated at 645 AM EDT Thu Oct 30 2014

VFR conditions are expected through the TAF period for the most part
as sfc high pressure remains in control of the region.  The only
exception might be some light br at BWG toward sunrise resulting in
a brief MVFR restriction.  Upper level clouds will be on the
increase late in the day as an upper level trough approaches the
region.  The upper level trough will bring rain showers and mid
level cigs tomorrow morning.  Winds should remain generally light
and variable or even calm at times throughout this TAF period.

&&

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

$$

Update.........RJS
Short Term.....AMS
Long Term......TWF
Aviation.......AMS





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