Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 292025

Area Forecast Discussion
National Weather Service Louisville KY
325 PM EST Wed Nov 29 2023

.Short Term...(This evening through Thursday)
Issued at 315 PM EST Wed Nov 29 2023


Key Messages

- Mostly clear and milder temperatures tonight

- Mix of sun and high clouds Thursday, clouds increase late in the

- Breezy conditions return on Thursday; SSW winds 12-18 mph with
gusts 20-30 mph


Across the region this afternoon, sunny skies abound with
temperatures considerably warmer than yesterday thanks to a
combination of ample sunshine and milder SW winds. These SW winds,
which have at times gusted over 20 mph, are thanks to a strong low-
level pressure/height gradient between a high over the Deep South
and a low over Hudson Bay. As we head later into the afternoon and
evening hours, winds will gradually weaken thanks to boundary layer
decoupling limiting downward transfer of higher momentum air aloft.

Tonight, mostly clear skies are expected with upper level moisture
providing scattered high clouds mainly after sunset. In spite of
aforementioned boundary layer decoupling, temperatures will still be
considerably warmer than the past few nights, with lows expected to
range from the upper 20s in the coldest valleys to the mid-to-upper
30s in urban heat centers and elevated ridge tops.

Tomorrow should be another breezy day across central Kentucky and
southern Indiana as a strong gradient in low level pressures/heights
continues. A transient northern stream wave will move across the
upper Midwest and Great Lakes region, with a trailing southern
stream shortwave lagging behind over the southern Plains. The
combination of these two upper level systems will be associated with
a surface low and northeastward-extending cold front stretching from
the lee of the southern Rockies up to the upper Peninsula of
Michigan. East of this system, broad low-level SSW flow will
continue to bring warmer air into our region, and temperatures
tomorrow afternoon should be 5-10 degrees warmer than today across
the area. Moisture, especially in the lowest layers of the
atmosphere, will be slow to return over our area as the influence of
the low-level high keeps the deepest moisture over the Mississippi
Valley and points west. Expect the daytime hours to remain dry over
much if not all of the area tomorrow, with morning sunshine/high
clouds gradually giving way to more cloud cover late in the day
(especially west of I-65). If any one area did see a light rain
shower Thursday afternoon, the best chance (5-15%) would be north of
the Ohio River.


.Long Term...(Thursday night through Wednesday)
Issued at 310 PM EST Wed Nov 29 2023


Key Messages:

 - Widespread rainfall Thursday night into Friday. Expected rainfall
amounts 0.25-0.75"

 - Breezy conditions expected on Friday

 - Above normal temperatures expected through this weekend, closer to
normal values early next week


Thursday Night through Friday Night...

Southern stream system still on target to affect the region Thursday
night and Friday.  Model cross sections continue to show a good
amount of Gulf moisture being advected north into the region
courtesy of a 55-60kt low-level jet axis.  Model proximity soundings
still show PWAT values of 0.90-1.00 inch so widespread moderate rain
showers are expected.  Will continue to keep PoPs >90% from late Thu
through Fri morning.  Rainfall amounts of 0.30 to 0.75" still look
likely, though a few spots may be able to squeeze out an inch of
rainfall.  Lows Thursday night will be in the lower 40s with highs
on Friday warming into the upper 50s to lower 60s with breezy
conditions expected.

By Friday night, surface low will move off to the northeast with a
decent deformation band of moderate to heavy precipitation extending
from northern IL thorugh Michigan.  Locally, our moisture will get
shut off fairly quickly with rain ending from west to east during
the evening.  Lows Friday will feature a gradient with lower 40s
across our SW Indiana counties with upper 40s/lower 50s across
central/SE KY.

Saturday Through Wednesday...

For the weekend, we`ll remain in a broad southwest flow aloft and
temperatures will stay above normal.  Saturday should feature mainly
dry conditions across much of the region, with the exception of a
few showers down across the far south/southeast (Lake Cumberland
area).  Highs on Saturday will be in the mid-upper 50s across
southern Indiana and northern KY with lower 60s in areas south of
the Cumberland Parkway.  On Sunday we should remain fairly dry
though we`ll have a weak northern stream system that will pass
through late in the day and could produce a few rain showers.  Highs
on Sunday will be similar to Saturday with upper 50s across southern
IN and northern KY with lower 60s across southern KY.

By late Sunday and into Monday, our southwest flow aloft will
transition over to more of a trough with the core of the cold going
into the NE US.  A couple of small perturbations within the flow
will pass through and mainly skirt just to our northeast.  This
could bring some rain chances to our northeast sections on Monday.
With the cold trough in place, we`ll see colder temps on Monday with
highs in the lower 50s and overnight lows in the mid 30s.  Latest
29/12Z model suite still is in agreement with a stronger clipper
system dropping southward and affecting the region Tuesday night
into Wednesday.  Thermal profiles will warm up well above critical
thresholds ahead of the approaching clipper so this one will bring a
cold rain to the region with the bulk of wintry weather staying
across WI/MI/northern IN/northern OH.  Behind that clipper, another
surge of colder air will infiltrate the region.

Extended Forecast Discussion...

Looking into the extended, the cool blast behind the above mentioned
clipper will be rather short lived as a warmer pattern is likely to
redevelop across much of the CONUS.  Much of this will be driven by
the MJO which will be heading into phases 3/4/5 during this period.
While the NAO and AO are forecast to remain negative, the MJO and
the expected +EPO pattern will likely help sustain the warm pattern.
Updated signal analysis from last week suggests the next signal
passage coming in the 12/10-12 time frame.  Given the MJO and
teleconnection pattern the main storm track looks to be from the
southern Plains into the Great Lakes.  Another bout of moderate
rainfall looks likely here with another possible cool down behind

Longer range data continues to be in pretty good agreement with a
colder pattern developing toward the late part of December as those
models suggest that a ridge will develop across the western US with
deeper troughing setting up across the east.  The timing to this
pattern remains uncertain due to uncertainties on how large the
upcoming MJO pulse will be.  While the ensemble mean from the GFS
and Euro push the MJO into phases 4/5 and then collapse it rather
quickly, there are some ensemble members that have larger orbits
through phases 4/5/6 and do not get over to phase 7/8 until late
month.  Additionally, the Pacific Jet will play a major role in the
possible pattern change for late month.  As of this writing, the
Pacific Jet is forecast to remain extended and strong through the
month which will greatly diminish the probability of a west coast
ridge popping up.  On the other hand, if the Pacific Jet were to
retract a bit more to the west, then the possibilities of the west
coast ridge developing will increase.


.Aviation...(18Z TAF Issuance)
Issued at 1230 PM EST Wed Nov 29 2023

VFR conditions are expected through the current forecast period.
This afternoon, southwest gradient winds will gradually relax toward
sunset, though gusts of 20+ kt will be possible through around 22Z.
Tonight, a 30-35 kt jet at 925 mb will lead to marginal LLWS
conditions, particularly between 09-14Z Thursday. For now, have
withheld inclusion in the forecast due to how marginal the wind
shear will be relative to critical thresholds, though this may need
to be added in subsequent forecasts (primarily at SDF/BWG/HNB).
Tomorrow morning, stronger winds aloft will once again mix down to
the surface, with 10-15 kt sustained winds and gusts around 20 kt
expected after 14-15Z.




Short Term...CSG
Long Term...MJ
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