Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 220523

Area Forecast Discussion
National Weather Service Louisville KY
1223 AM EST Sun Jan 22 2017

...Updated Aviation Discussion...

.Forecast Update...
Issued at 955 PM EST Sat Jan 21 2017

Forecast is fairly well on track for the rest of tonight, but
confidence is diminishing in the timing of precip onset, which
affects the Sunday forecast more than overnight. Latest runs of NAM
and hi-res models suggesting we may have a hard time getting precip
into south-central Kentucky much before daybreak, and may be solidly
into the afternoon before rain spreads into the I-64 corridor.
However, the 18Z GFS is several hrs faster and lines up well enough
with the overnight forecast that any changes will be limited to
hourly trends. Temp forecast appears in good shape.


.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...(06Z TAF Issuance)
Issued at 1220 AM EST Sun Jan 22 2017

Trended back arrival and intensity of precipitation based on the
latest model guidance and downstream obs.  Although the convection
associated with a leading shortwave ahead of an approaching upper
low is strong to severe over the Gulf states this evening, it is
forecast to weaken significantly as it moves northward into our
region.  With the latest models indicating a slow arrival as well,
took precip into BWG at 14Z and SDF/LEX around 18Z with a small
chance for some showery activity and light br before that.  On
arrival of the rains, at least MVFR if not IFR will impact the TAF
sites.  The best chance for showers and isld t-storms for all TAF
sites looks to be this afternoon.  By tonight the pressure gradient
on the NW side of the strong low pressure system will create gusty
winds resulting in northerly wind gusts as high as 20-25 mph.




Short Term.....EBW
Long Term......JBS
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