Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/19/24

Area Forecast Discussion

National Weather Service Louisville KY

 1115 PM EDT Thu Apr 18 2024

.KEY MESSAGES...

*   Strong to severe storms possible Thursday night. Highest risk of
    severe storms will be generally west of I-65.

*   Much cooler weather this weekend. Next chance of rain arrives in
    the Tuesday/Wednesday timeframe.

&&

.UPDATE...
Issued at 1114 PM EDT Thu Apr 18 2024

The northern edge of Severe Thunderstorm Watch #129 has been
spatially extended to the east a row or two of counties to account
for a section of the ongoing broken convective line that might
continue moving into an environment still marginally conducive for
damaging winds, as highlighted by the latest SDF ACARS. In addition,
watching for storm mergers and boundary collisions that could help
mix down momentum aloft. Overall, ML-based HRRR model guidance still
hints at a decreasing severe threat for the coming hours as the line
progresses to the east.

&&

.MESOSCALE...
Issued at 947 PM EDT Thu Apr 18 2024

A few discrete warms sector cells have been firing off ahead of the
main convective line, which has been expected and picked up well in
the earlier CAM runs. It appears these cells are popping up in an
area of localized theta-e advection and deep moisture convergence
axis, and underneath a pocket of positive vorticity advection. SPC
Mesoanalysis suggest these storms are firing along a gradient of
SBCAPE, but have struggled to become severe. Will keep an eye on
these.

Severe thunderstorm line is charging across eastern Illinois at this
hour, and is noticeably accelerating as the cold pool pushes it
further east. At this pace, believe the line will be arriving into
Dubois County by 0230z. ACARS sounding out of SDF does show some
SBCAPE lingering, but thinking MLCIN will help weaken the line as it
approaches the I-65 corridor by 04-05z. HRRR 00z data supports this
too, with low level stable layer expected to help weaken this
convective line in a few hours. Will need to keep tabs on additional
convection across south-central KY later tonight though, where there
is potential to remain unstable within the warm sector prior to the
cold front arrival.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 346 PM EDT Thu Apr 18 2024

Currently, satellite imagery is showing a warm front stretching to
the northwest through southern Indiana and central Kentucky. This
front arches to the west into a surface low in western Missouri. To
the north of this front, dew points are in the 40s and 50s. To the
south of the front, mid 60s, and as we head through the afternoon
and evening hours, the surface low, part of a larger cold front
extending to the north and south, will begin moving towards
Indianapolis. This will cause the warm front and cold front to
develop an inverted "V" look by 0z over southern Illinois, eastern
Missouri and western Kentucky. Dew points over southern Indiana and
central Kentucky will likely drop into the 50s as the region becomes
better mixed.

As 1-2z approaches, the surface low will be moving from Illinois
into central Indiana. The area under the aforementioned inverted "V"
will see dew points in the mid 60s. Again, this is the area in
between the warm and cold fronts. On the leading edge, the warm
front will likely kick off convection over western Kentucky and
southward while the cold front running through Chicago arches
southward through southern Illinois. As these two lines continue
eastwards. The front line could become the dominate line for
southern part of the cold front over Missouri and could combine with
the northern half of the cold front, or it could remain as two
separate lines and join with the cold front over southern Indiana.
It doesn`t make much of a difference, except some over central
Kentucky could get one or two lines of convection.

The timing is going to help us from a severe weather standpoint.
Since the fronts won`t move through until after sunset, an inversion
is expected to develop and make any convection elevated. This will
limit potential wind energy from reaching the ground. Overall shear
is fairly weak. Think the current SPC outlook is a little bullish
over our CWA.

Winds tonight will remain out of the south to southwest around 5-10
mph. A few gusts around 30 mph will be possible as the line of
convection passes, and as the cold front begins to move through
during the morning on Friday, winds will quickly veer towards the
north-northwest increasing cold air advection into the area. Winds
tomorrow will stay around 10 mph as they gust to 15-20 mph.

WAA will keep temperatures warm tonight, only dropping into the 50s
to low 60s. Tomorrow, the sun is expected to return, but CAA will
limit temperatures to the 60s. A few in the Lake Cumberland region
could hit the low 70s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Issued at 346 PM EDT Thu Apr 18 2024

Friday Night through Monday Night..

Dry conditions are expected Friday night and into Saturday as a
surface high pressure system builds into the region with a dry zonal
flow pattern aloft.  A southern stream system may graze the far
southern part of KY Saturday night and Sunday morning, but the
latest trends in the data suggests a drier forecast may end up
prevailing.  Lows Friday night will dip into the upper 30s and lower
40s.  Highs Saturday will be cool highs in the 60-65 degree range.
Lows Saturday night should be a bit cooler with lows in the upper
30s across much of the region.  Areas south of the Cumberland
Parkway may only drop into the lower 40s.  Continued cool conditions
are expected for Sunday with highs in the upper 50s to near 60.
Depending on cloud cover conditions Sunday night, we could see some
patchy frost in southern IN and the KY Bluegrass region as lows dip
into the mid 30s.  Monday will see warmer conditions returning to
the area with temps warming up into the mid-upper 60s.

Tuesday through Thursday...

Forecast confidence continues to increase in another chance of
showers and storms coming into the region in the late Tuesday/early
Wednesday time frame as a shortwave trough aloft moves through the
region.  The previous forecast of solid PoP coverage still looks
good here.  Temperatures through the period will warm into the upper
60s to the lower 70s with overnight lows in the low-mid 40s.

&&

.AVIATION /00Z TAFS THROUGH 06Z SUNDAY/...
Issued at 744 PM EDT Thu Apr 18 2024

VFR conditions will deteriorate this evening as showers and
thunderstorms approach the region ahead of a cold front. Expect
impacts to ceilings and vis as thunderstorms roll through from west
to east, first at HNB in the next few hours, and later tonight at
LEX and RGA. The peak for convective activity will be from 02-09z
tonight. After the storms pass, ceilings will lower to MVFR and
likely below the 2k ft fuel alternate threshold near the pre-dawn
hours. There appears to be a short window where ceilings could drop
to IFR, so included a TEMPO group at all terminals for that as well.
We`ll gradually improve to VFR conditions again by late tomorrow
morning or early afternoon, with post-frontal winds from the north.

&&

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

&&

$$

MESOSCALE...CJP
UPDATE...ALL
SHORT TERM...KDW
LONG TERM...MJ
AVIATION...CJP



Area Forecast Discussion

National Weather Service Memphis TN

 952 PM CDT Thu Apr 18 2024

...New UPDATE...

.UPDATE...
Issued at 952 PM CDT Thu Apr 18 2024

The first batch of showers and thunderstorms has moved off to the
east but round 2 is approaching the Mid-South along a cold front
stretching from central IL into northern AR. A fair amount of
instability is still present across the region with MUCAPE still
on the order of 1000-2000 J/kg. Surface-based instability appears
to be largely capped at the moment. Deep-layer shear has increased
over the past few hours with effective bulk wind shear now in the
40-45 kt range along and west of the MS River.

The increasing low-level jet has also carved out a looping
hodograph which has enhanced storm-relative helicity across the
area. The NQA VAD hodograph indicates 0-1 km SRH of 440 m2/s2
which is significantly more than the RAP13 has been alluding to.
This could lead to some embedded supercell structures within the
approaching line. Fortunately, the 0-3 km bulk wind shear is
limited to 25-30 kts from the west-northwest. This would provide
only marginally sufficient wind shear to support mesovortex
formation along the line which should limit the potential for
tornadoes. Damaging wind and large hail look to the be the
primary threat should this convection remain rooted in the
boundary layer.

MJ

&&

.MESOSCALE UPDATE FOR SEVERE WEATHER...
Issued at 533 PM CDT Thu Apr 18 2024

We`re finally beginning to see more robust storm development north
of Interstate 40. This is where the greatest instability is
located. Farther south, the cap is stronger and showers/storms are
really struggling to maintain/gain intensity despite an
approaching shortwave trough near the Arklamiss. The latest
analysis indicates MLCAPE (instability) on the order of 2000 J/kg
from near Memphis into southeast Missouri (with 0-3 km MLCAPE near
or above 100 J/kg). Mid-level lapse rates are fairly steep across
portions of AR/MO/TN by Mid-South standards (near 7 C/km) which
will support stronger mid-level updrafts and hail growth. One of
the negatives is the lack of stronger deep-layer shear. Bulk shear
isn`t all that bad at 35 kts or so, but that is more marginal for
supercell development, especially with 0-3 km SRH at or below 100
m2/s2. This suggests more in the way of multicells with weak
supercell characteristics in general. Large hail and localized
damaging wind are the primary concerns. Weak low-level wind shear
will keep the tornado threat low for now.

Storms upstream are expected to grow upscale into a linear mode,
moving into the Mid-South later this evening. The greatest
uncertainty will be whether or not the air mass preceding this
line of storms is able to remain surface-based instability. If so,
damaging winds will be a larger concern. If not, storms may remain
elevated which will limit the severe weather potential.

MJ

&&

.SYNOPSIS...
Issued at 333 PM CDT Thu Apr 18 2024

Scattered showers and thunderstorms will continue over the
Midsouth tonight, in advance of an upper level trough lifting
through the mid-Mississippi River Valley. Severe thunderstorms
will be possible, especially north of a Jonesboro Arkansas to
Jackson Tennessee line. Damaging winds and large hail will be the
primary threats. A few short-lived tornadoes will also be possible
through the early overnight hours, mainly to north and west of the
Memphis metro area.

Additional showers are expected across the Midsouth through early
Sunday, with isolated thunderstorms over north Mississippi. Severe
thunderstorm chances will be low. A reinforcing cold front will
push through the Midsouth Saturday night and early Sunday,
bringing low humidity and cool conditions for Sunday night through
early Tuesday.

&&

.DISCUSSION...
(This evening through next Wednesday)
Issued at 333 PM CDT Thu Apr 18 2024

Primary forecast concern remains severe thunderstorm chances
through tonight. SPC/RAP mesoanalysis showed mixed-layer CAPE of
1500-2000 J/kg along and west of the MS River. Mixed layer CINH
was estimated at zero across the Midsouth, but early afternoon
convective trends suggest consequential CINH remains. 12Z
soundings from LZK, SGF and JAN showed a stout elevated mixed
layer (EML) and underlying inversion. 17Z aircraft sounding from
LIT showed this EML remained strong, and based at 750mb. GOES
visible imagery showed multiple standing wave clouds over
northwest AR, suggestive of an overlying capping inversion.
Immediately west, frontal convergence was evident over far
northeast OK and southwest MO, but deep convection was limited to
areas further north along the front, over central MO.

To our south, thunderstorms persisted through most of the morning
and early afternoon. This convection initiated on an elevated
boundary, near the base of a relatively low (900mb) EML. This
convection was not initialized on early morning runs of the HRRR,
despite a pronounced upstream shortwave evident on GOES water
vapor imagery. The Arklamiss/central MS storms persisted into
central MS at midafternoon and have spread considerable high
cloudiness over north MS. This has limited surface heating and
ability to sustain deep convection - at least to this point.

Should a storm or two manage to break through the low level
capping inversion, robust CAPE and steep midlevel lapse rates will
support large hail over any portion of the Midsouth. Any of three
following features may aid in the breaking the convective cap: height
falls associated with aforementioned shortwave exiting the Arklatex,
strong surface heating, and general height falls associated with
the longwave trough passage over the mid-MS River Valley. None of
these are a sure bet, hence the lower typical Day 1 confidence
level in severe storms.

Should severe storms fail to materialize this afternoon, it
doesn`t mean we`re out of the woods. NAM and HRRR depict a
pronounced strengthening of 925mb SSW winds late afternoon and
evening. This is likely a contributing factor the looping model-
derived hodographs over eastern AR late this evening. If storms
manage to become surface-based, a mid to late evening QLCS
tornado threat may be realized over eastern AR. After midnight,
severe threat should diminish with strengthening low level
inversion, weakening elevated instability and weakening/veering of
the low level jet.

Comparatively tranquil weather will prevail Friday and Saturday,
as a surface cold front stalls over north MS, parallel to the
upper level flow. An open southern branch trough will lift into TX
on Saturday, with downstream moisture bringing showers mainly
south of I-40. A few thunderstorms will be possible over north MS,
but similar to yesterday, NBM thunder probabilities appear too
high/too far north Friday night through Sunday morning.

A reinforcing cold frontal passage Sunday night will bring dry and
cool conditions, with temperatures Sunday and Monday more typical
of early March.

PWB

&&

.AVIATION...
(00Z TAFS)
Issued at 615 PM CDT Thu Apr 18 2024

Showers and thunderstorms along a pre-frontal trough will move
east of MKL/TUP over the next few hours. Another round of showers
and thunderstorms will be possible later this evening into early
Friday morning along a cold front. Latest probabilistic guidance
shows a high potential for post-frontal MVFR/IFR low stratus to
develop across the area overnight into Friday morning. Conditions
will gradually improve later Friday morning into Friday afternoon.

&&

.MEG WATCHES/WARNINGS/ADVISORIES...
AR...None.
MO...None.
MS...None.
TN...None.
&&

$$

PUBLIC FORECAST...PWB
AVIATION...CJC