Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 241721
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1221 PM EST Wed Dec 24 2014

...Updated Aviation Discussion...

...Forecast Update...
Issued at 1020 AM EST Wed Dec 24 2014

The forecast is in good shape -- no significant edits needed.

At 10am EST low pressure was centered in the vicinity of Madison,
Indiana, and was drifting to the northeast.  Patchy light rain will
continue to accompany this feature and its trailing cold front this
afternoon.  As the system pushes east and we get into a tighter
pressure gradient, winds will pick up.  The highest gusts will be
east of I-65, especially along the I-75 corridor. These winds will
come in from the west and northwest, causing temperatures to drop
into the 40s.

Thunder chances appear slim, but we could hear a few rumbles of
thunder this afternoon east of I-65 with chances increasing as one
heads east into eastern Kentucky.

.SHORT TERM (Now through Christmas Day)...
Issued at 300 AM EST Wed Dec 24 2014

Low pressure will travel along a frontal boundary stretching
north/south across our western forecast area this hour. Have a thin
band of low clouds and some fog reports along this band. Flow aloft
should push this boundary slowly eastward through the day today as
the surface low gets into the eastern Great Lakes. Winds should
start gusting behind the surface low as the pressure contours are
packed more tightly behind the system. Decided to issue a wind
advisory for later this afternoon and a few hours into the evening
over the Bluegrass region after collaboration with neighbors.
Advisory criteria is sustained 30 mph for a couple of hours and/or
40 mph gusts any time.  Do not have close to either criteria in my
current forecast for the rest of the region, so did not want to
issue a blanket areawide advisory.

Precip chances will linger even behind the front, as an elongated
vortmax behind it takes its time passing through the forecast area.
There is still some question about if there will be deep enough
moisture available tonight to get more than drizzle, but if it does,
we could see some light snow showers. Forecast liquid equivalent
look to be too light and ground temperatures too warm to have snow
accumulations in the grids, so this does not look like an impactful
snow.

Clouds should linger into the day Christmas. Highs should get to
near normal levels despite the cloud cover.

.LONG TERM (Thursday night through Tuesday)...
Issued at 304 AM EST Wed Dec 24 2014

Thursday Night - Friday Night...

The upper pattern will feature amplified troughing over the western
CONUS with low amplitude and broad ridging over the eastern CONUS to
end the week. At the surface, high pressure will generally hold over
the mid Atlantic Coast. This upper ridge/surface high pattern over
the Ohio Valley will result in dry conditions and pleasant
temperatures. Thursday night will actually feature good radiational
cooling conditions with lows around 30 east to the mid 30s west.
Expect milder temperatures Friday night in the mid 30s to around 40.
Expect highs on Friday to range between 50-55.

Saturday - Sunday...

Upper level flow flattens out over the CONUS through the weekend,
with SW flow dominating over the eastern US. The general model
agreement is that low pressure will slide through the Great Lakes on
Saturday with the trailing cold front sliding through our area
sometime Sunday. Ahead of this feature, expect warm advective rain
chances to pick up across our west as early as Saturday morning and
peaking Saturday night and Sunday just ahead of and along the front.
At this point, highest chances look to be across south central KY,
with lesser chances along and north of the Ohio River as northward
advance of deep moisture gets cut off.

Temperatures will again be mild on Saturday with low to mid 50s
expected. Lows will mostly be in the upper 30s and low 40s Saturday
night. Sunday temperatures will be tricky and dependent on frontal
passage, but will generally go with a cool down and highs in the 40s.
Temp profiles support all rain through this point in the forecast.

Sunday Night - Tuesday...

Confidence lowers as we enter the new week, however there is a
general consensus on the overall pattern. This pattern will feature
the surface boundary that had passed through our area waffling in
the vicinity of the Ohio Valley as it remains nearly parallel to the
upper flow. Meanwhile, there is a signal that the southern stream
will become active with a surface low developing over the Gulf Coast
states, and then travel up the Appalachians to our SE. This could be
a wet pattern for us if the placement of the boundary is correct.
This pattern could also bring a wintry mix into play along and on
the north side of the surface boundary so we will need to pay
attention to the evolution of this setup over the coming days. That
said, not too excited about the model performance of late, and given
the complexity of the setup won`t mention more than rain chances
across the southern half of the CWA and periods of rain/snow mix
across our north through Monday. Monday night and Tuesday could
bring better chances for scattered snow showers across much of the
area as colder air filters in behind the departing low. In fact,
there is a signal for a shot of much colder air just in time for the
new year. Stay tuned.

&&

.AVIATION (18Z TAF Update)...
Issued at 1220 PM EST Wed Dec 24 2014

A surface front and upper trof will slowly cross the region from
west to east this afternoon and evening.  Patchy light rain will
continue, especially this afternoon, with low ceilings continuing
through tonight into Christmas morning.  Ceilings should be mostly
MVFR (as opposed to the earlier IFR ceilings), though it is
difficult to determine exactly which side of 2000` they will be.
For now will go on the pessimistic side and keep them just below
fuel alternates through tonight.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...WIND ADVISORY until 9 PM EST this evening FOR KYZ033>037-039>043-
     046>049-055>057-066-067.

IN...NONE.
&&

$$

Update.........13
Short Term.....RJS
Long Term......BJS
Aviation.......13




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