Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 212254
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
554 PM EST Sat Jan 21 2017

...Updated Aviation Discussion...

.Short Term (Now through Sunday Night)...
Issued at 300 PM EST Sat Jan 21 2017

A visible satellite loop showed a clearing trend west of I-65 this
afternoon, which should gradually push east through late
afternoon. After a relatively brief window for some sun with only
scattered clouds, mid and high level clouds will spread back in from
the southwest from mid to late evening. Surface temperatures were in
the mid to upper 60s this afternoon. Some locations mainly near and
west of I-65 should be able reach 70 this afternoon with a little
sunshine boost.

The trend in the 12z guidance has been to delay onset of showers and
isolated thunderstorms tonight into early Sunday, so have opted for
a dry forecast through 06z Sunday. Areas north of the Western
Kentucky and Bluegrass Pkwys may end up dry through 12z Sunday.

On Sunday, a mid-level closed low will deepen slightly as it rotates
east through the northern Gulf Coast states. A surface cyclone is
forecast to be over northern Arkansas by 12z Sunday and will proceed
east across the Lower OH/TN valleys during the Sunday-Sunday night
time frame before occluding over the Appalachians early Monday.
Periods of showers with embedded, isolated storms are expected
during the Sunday-Sunday night time frame. An initial east-west
oriented wave will spread into central KY from south-to-north
Sunday morning, with a lull possible immediately following this
first round.

While mainly isolated thunder is forecast, scattered storms are
possible Sunday afternoon and evening, especially south of the
Western KY/Bluegrass Pkwys. Lapse rates are steeper, yielding a bit
more instability. Severe weather is not expected. Gusty winds won`t
be much of an issue with this low pressure system, given the
proximity of the surface low to the forecast area on Sunday.

A mild night is in store with lows only in the upper 40s to low 50s.
Temps will be slow to rise on Sunday given widespread clouds/rain,
with highs in the upper 50s to low 60s. Cold advection returns
Sunday night, with lows falling into the mid to upper 40s.

.Long Term (Monday through Saturday)...
Issued at 325 PM EST Sat Jan 21 2017

A progressive weather pattern is in store for the week ahead as
a series of closed upper lows move across the CONUS.  The large low
in place over the Appalachians at the start of the work week will be
replaced by a short-lived ridge for Tuesday.  By Wednesday, the next
upper low will be heading toward the Great lakes, with a positively
tilted long wave trough stretching back to the desert southwest. A
surface low associated with the second upper low will move northeast
in the vicinity of the Great Lakes, though the exact route and
timing is where the main hemispheric models start to diverge.

The GFS takes the low through faster and farther north than the
ECMWF, with the Canadian slower and farthest south. Consequently,
the precip shield associated with this system varies greatly, but
the GFS and Euro trend together in minimizing the precip chances
compared to the CMC, with lower QPF. For now have leaned toward
the GFS/Euro consensus but do include some low POPs reflecting the
Canadian solution, especially given it`s success in highlighting
the wet Friday along the Mid Atlantic yesterday vice the GFS/Euro
dry solution at this time last weekend.

Rain showers will end from west to east Monday as the first system
moves out, with mainly dry weather (save for a few sprinkles)
Tuesday and Wednesday.  The second system brings slight shower
chances back for Thursday and Friday, mainly in the form of
sprinkles or flurries.

More significant than the precip - since any amounts that do
occur will be minimal - are the temperatures for the week.  Since
the current warm spell has belied the fact that we are currently in
the climatologically coldest week of the year, the plunge into the
"normal" range for Thursday through Saturday will be a shock to
anyone already acclimated to the mid-April-like readings of the past
week. Numbers-wise, highs will for Monday through Wednesday will be
in the 50s, then drop into the lower 40s Thursday and the 30s Friday
and Saturday.  Low temperatures will be mainly in the 30s Tuesday
morning, warm into the 40s for Wednesday, then drop into the 20s by
Friday and Saturday.

&&

.Aviation (00Z TAF Update)...
Issued at 550 PM EST Sat Jan 21 2017

VFR conditions will prevail through the evening, with just a mid-
level deck continuing to scatter out and south winds backing to SE.
Upper low will dig into the Red River Valley tonight, ejecting an
impulse out ahead of it, and that feature will spread a rain shield
into the Tennessee and Ohio Valley. Continued slower trend of both
synoptic and hi-res models suggests that prevailing rain and
associated cig/vis restrictions will only reach BWG just before
daybreak, and SDF/LEX by mid-morning.

Once the rain shield moves in, ceilings will quickly drop into IFR,
although SDF may be a couple hrs slower than LEX or BWG. Will also
mention VCTS/CB, though thunder is still a low-confidence forecast
at this point.  Forcing weakens a bit in the afternoon as the
leading wave lifts off to our north, so will end the thunder threat
and lift the ceilings into MVFR, though SDF and LEX will likely
remain in fuel-alternate even beyond the valid TAF period and into
Sunday night.

&&

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

$$

Short Term........EBW
Long Term.........JBS
Aviation..........RAS



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