NWS Area Weather Forecast Discussion
Louisville, KY
LMK

000
FXUS63 KLMK 291126
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
626 AM EST Tue Nov 29 2022

...Updated Aviation Discussion...

.Short Term...(Today and tonight)
Issued at 317 AM EST Tue Nov 29 2022

...RISK OF STRONG/SEVERE THUNDERSTORMS THIS EVENING...

=======================================
Near Term      Now through 800 AM EST

Impacts:   None
Confidence: High
=======================================

Early morning satellite imagery shows high level cloudiness
increasing across the region. Temperatures varied across the region
with a ridge/valley split in progress along with some good
radiational cooling in our typical cold spots.  Where skies were
clear and in the valleys, temps were in the mid-upper 30s.  On the
ridges, temps were in the low-mid 40s.  High level cloudiness will
continue to increase throughout the remainder of the night and no
significant weather is expected.  Temps may drop a few degrees more
and then become steady as high level cloudiness puts a cap on
radiational cooling.

=======================================
Today            800 AM to 800 PM EST

Impacts:   Gusty Gradient Winds
           Late Afternoon Showers/Storms

Confidence: Medium-High
=======================================

After sunrise, winds will start to increase across the region mainly
out of the SE and SSE.  Wind speeds of 15-20 mph with gusts of 25-30
mph will be possible by mid-late morning.  Gusts during the
afternoon may increase somewhat but will be dependent on how the
boundary layer evolves.  Current high resolution models show a
relatively shallow mixed layer with a temperature inversion up
around 1Kft.  The challenge here is whether that PBL will extend
upward into the higher momentum air and be able to mix it down.
Ongoing cloud cover is likely to keep insolation down a bit which
makes us believe that the boundary layer heights may be a bit lower.
Nonetheless, sustained winds of 15-20 mph and gusts of 35-40 mph
will be possible.  Given the gradient winds expected, we will
highlight this with a Special Weather Statement with the morning
package.

Moving into the afternoon period, southerly flow will continue to
increase across the region as low-level 850 hPa jet streak
approaches from the southwest.  Afternoon temps should warm into the
low-mid 60s over southern IN with mid 60s over much of KY.  The
southerly flow will bring moisture into the region but it will take
some time to moisten up the initially dry lower levels.  Model
soundings from the high resolution datasets continue to show a
rather shallow boundary layer with a temperature inversion aloft.
Elevated instability with generally marginal lapse rates aloft will
promote elevated convection mainly in areas along and west of I-65
through the early evening with the activity spreading east of I-65
by 29/23Z to 30/00Z.  Overall severe weather risk through the late
afternoon appears to be rather limited due to the strong low-level
temperature inversion, rather marginal lapse rates aloft, and
uncertainty of northward moisture advection given the anticipated
upstream convection across AR/MS/TN/LA.

=======================================
Tonight          800 PM to 800 AM EST

Impacts:   Gusty Winds
           Strong/Severe Storms Possible

Confidence: Medium
=======================================

As we move into the evening hours, winds aloft will continue to
increase across the region and the overall convective environment
will be a high shear/low instability environment.  Moisture
advection should continue across the area with surface dewpoints
increasing int the low-mid 50s.  Some lower 60 dewpoints may get as
far north as the KY/TN border region.  We should see an uptick in
convection in the 800-1000 pm time frame as stronger synoptic scale
forcing overspreads the region.  Model soundings from the high
resolution consensus continue to show a low-level inversion holding
strong during the evening hours.  Cooler air aloft pushing in from
the west will allow lapse rates aloft, above the inversion to
steepen with time.  So we`ll have elevated instability in place. The
expected lift and shear will likely result in elevated convection
and this elevated convection may be rotating a bit given the ambient
environmental shear.  Lapse rates aloft are slightly weaker than in
previous models so a marginal severe hail threat can`t be ruled out.

The main question with regards to severe potential this evening will
be whether or not we`ll see this low-level inversion mix out prior
to frontal passage.  Earlier model runs suggest the possibility of
this mix out occurring prior to frontal passage. In this case, strong
slab forced ascent along the frontal interface would generate strong
convection which would be able to transfer the higher momentum air
down to the surface resulting in wind damage.  However, the latest
data rolling in seems to be a bit more strong in holding the
inversion place, especially across southern IN and northern KY.
There still seems to be a risk that we could mix out this inversion
across southern KY.  The other complicating factor is that upstream
convection across MS/AL/TN may impede the northward transport of
higher moisture into the Ohio Valley resulting in lesser instability
either at the surface or aloft for storms to work with.

Our current thinking is that the highest threat of strong/severe
storms would be in the 30/03-10Z time frame.  This time frame is
coincident with the cold front pushing through the region and that
feature being the main focus for convection.  Model spread with the
frontal passage is still a bit large with the HRRR solutions being
quick and the NAMs being slightly slower. The main hazardous weather
threat would be damaging winds given the high momentum of air aloft.
A low probability tornado threat is still on the table given the
shear profiles.  However, the tornado threat will depend on the
erosion of the low-level temp inversion.  Current indications that
the highest tornado risk would be confined to areas south of the
Cumberland Parkway.  A risk of marginally severe hail is also in the
cards and that will be dependent on the elevated instability profile
and strength of the convective cores moving through the region.

Once the cold front moves through the region, the threat of
strong/severe convection will greatly diminish.  Winds are expected
to veer around to the west and strong cold advection will result in
a quick temperature drop.  Given the spread in the models, we used
the blend for hourly temps late tonight.  A strong gradient of
temperature will be seen with lower 30s in the west and upper 40s to
near 50 in the east by 30/12Z.

.Long Term...(Wednesday through Monday)
Issued at 310 AM EST Tue Nov 29 2022

By sunrise Wednesday morning, the bulk of the precipitation and all
of the severe threat will have pushed east of the area as
temperatures plummet behind the cold front. Cold advection will
continue through the day on Wednesday as breezy conditions linger,
with WNW winds generally between 10-15 mph and gusts to 25 mph.
Unlike many post-frontal setups in the Ohio Valley, the progressive
nature of this system combined with deep dry air rushing in behind
the front should allow skies to completely clear out by Wednesday
afternoon. High temperatures on Wednesday should occur before or
right around sunrise, with temperatures staying in the upper 30s and
lower 40s during the afternoon hours. High pressure will quickly
move into the region Wednesday night, helping to ease winds and
allowing temperatures to drop into the 20s for lows Thursday
morning.

The mid- and upper-level flow pattern will become much more zonal
for the end of the week as sfc high pressure moves from being
overhead Thursday to east of the Appalachians on Friday. On
Thursday, temperatures will remain cool in the 40s as low-level warm
advection remains west of the Mississippi River. Guidance continues
to suggest that a fairly transient area of upper-level moisture will
traverse the region on Thursday, bringing some additional high cloud
cover as it does so. This additional cloud cover will likely also
hold temperatures in check as warming via insolation is limited. By
Friday, high pressure across the mid-Atlantic and developing sfc
cyclone over the northern Plains will facilitate a local pressure
gradient conducive for warmer southerly flow. Temperatures will
generally be 10-15 degrees warmer than Thursday, with highs expected
to reach the mid-to-upper 50s. Deeper moisture will begin to move
across central Kentucky and southern Indiana by Friday afternoon,
with cloud cover expected to increase again as we head into the
weekend.

Looking ahead to the upcoming weekend and the beginning of next
week, latest ensemble guidance supports two separate chances for
precipitation across the region. The first chance looks to arrive
Friday night into Saturday as a transient mid-level shortwave moves
across the Great Lakes and upper Midwest. While the sfc low should
remain well north of the area, a trailing cold front is progged to
strengthen as it approaches the area from the west. Isentropic
analysis on the 300 K surface shows that moist isentropic upglide
will strengthen ahead of the front across the Ohio and Tennessee
valleys Friday night, which should allow for some light
precipitation to develop ahead of what will initially be a fairly
precipitation-starved front. Generally expecting light totals of
less than 0.25" with this system, with lesser amounts expected north
of the Ohio River and greater amounts expected the farther south and
east you go.

The second, and likely more significant chance for precipitation
will impact the region Sunday night into the first few days of next
week. The aforementioned cold front which moves through the region
on Saturday will lift back to the north as a warm front Sunday night
into Monday as the mid- and upper-level flow pattern starts to
amplify once again. Current medium-range deterministic guidance
depicts an extensive plume of moisture which is currently progged to
setup over the region in conjunction with the aforementioned warm
front. At present, the position of the warm front would facilitate
broad moist upglide over central KY and southern IN for an extended
period of time next Monday into Tuesday, which would favor the
development of widespread precipitation. Current EPS/GEFS ensemble
means paint a broad swath of greater than 1" QPF with this system,
with probabilities of greater than 1" QPF in a 24-hour period
generally in the 30-50% range across central KY and southern IN next
Monday and Tuesday. Uncertainty in the magnitude of precipitation
totals still remains high given the lead time; however, odds are
fairly high that most of us will see a decent amount of
precipitation early next week. All precipitation with the
aforementioned system should be liquid, with temperatures expected
to remain well above freezing.

&&

.Aviation...(12Z TAF Issuance)
Issued at 626 AM EST Tue Nov 29 2022

IMPACTS:
 -Light fog at KBWG early
 -Gusty winds mid-morning through tonight
 -Widespread showers and storms this evening into the overnight

DISCUSSION:

Patchy light fog has been lingering down at KBWG this morning.  As
boundary layer mixing takes place after sunrise, we expect this fog
to mix out quickly.  Otherwise, VFR conditions are expected for much
of the daytime hours.  Winds will start to pick up out of the SE/SSE
and increase in speed.  Sustained winds of 15-20kts with gusts of 25-
30kts will be possible through the afternoon and into the evening
hours.  Scattered convection is expected to impact KHNB/KBWG by late
afternoon and then KSDF/KLEX during the evening and overnight hours.
Based on multi-model consensus, will go with prevailing TSRA at
KBWG/KSDF this evening, mainly in the 30/00Z-06Z time frame.  Will
keep showers and VCTS at KHNB/KLEX. Cigs will likely be MVFR but
some tempo drops to IFR could occur within storms. Look for a wind
shift behind the front, though the models still vary on timing the
front through the region.  The HRRR runs have been faster with the
NAMs being a little slower. Current thinking is front will be east
of the terminals prior to 30/12Z with gusty WSW winds continuing.

CONFIDENCE:

Medium on all elements.

&&

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

$$

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

Forecast Discussion from:
NOAA-NWS
Script developed by: El Dorado Weather
Adapted by FrankfortWeather.us