NWS Louisville, KY wrote its last area forecast discussion before the first event at Mar 30, 6:30 PM EST, 1 hour 5 minutes earlier.
Area forecast discussion, Mar 30, 6:30 PM EST, 1 hour 5 minutes before
Area Forecast Discussion
National Weather Service Louisville KY
730 PM EDT Wed Mar 30 2022
...Updated Mesoscale and Aviation Discussions...
.Mesoscale Update...
Issued at 725 PM EST Wed Mar 30 2022
Very strong forcing for ascent noted ahead of the sfc cold front
just east of the Mississippi River, where a QLCS is advancing
eastward. The mid/upper level trough is pivoting northeastward over
MO/AR, with strong divergence just downstream. A 70-80 kt southerly
LLJ is developing over western TN/KY, and these winds quickly lift
northeast over central KY and southern IN this evening.
Given such strong forcing and at least a weakening QLCS pushing
through the region this evening, damaging winds are still very much
a concern due to downward momentum transfer of the intense LLJ.
Lightning activity has been decreasing along the northern portion of
the QLCS in western KY. Instability is expected to play a role as a
primary limiting factor to more widespread severe convection along
the QLCS. A large dewpoint gradient still exists across central KY
with values of 45-50 F west of I-65 and 40-45 F east of I-65. Low-
level moisture return will continue ahead of the line, and dewpoints
should push into the 50s prior to storm arrival. But instability
will remain meager at best, especially east of I-65 late this
evening. Current thinking is that the QLCS will continue to weaken
over central KY, but uncertainty remains on how rapidly that occurs.
But overall, this diminishing trend will result in a lower tornado
threat with time. Thus, a Severe Thunderstorm Watch has been issued
for southern Indiana and portions of central Kentucky. The watch
runs through 05z, and a downstream extension can be issued if the
line maintains itself longer than expected.
&&
.Short Term...(This evening through Thursday)
Issued at 350 PM EDT Wed Mar 30 2022
...GUSTY GRADIENT WINDS OF 45-50 MPH THIS AFTERNOON...
...LINE OF STRONG TO SEVERE STORMS EXPECTED THIS EVENING...
=====================================
Near Term
Now Through 600 PM EDT
=====================================
*Bottom Line Up Front*
- Dry and windy conditions for the rest of the afternoon
- Southerly wind gusts of 45-50 mph possible
- Enhanced fire danger in eastern portions of the CWA
Afternoon satellite imagery reveals partly to mostly sunny skies
across the region. Current surface temperatures are in the upper
70s to the lower 80s. We've hit 84 at KSDF which breaks the
previous record set back in 1977 and 1895. As expected, good
atmospheric mixing has taken place as we've scoured out a bit of
moisture. dewpoints across the region bottomed out in the upper 30s,
but with the cloud cover and continued moisture advection, the
dewpoints have risen a few degrees over the past hour or so.
Moisture did mix out a bit better out across our western CWA as well
as dewpoints have fallen into the lower-mid 40s. We still have a
decent dewpoint gradient out across far western KY where dewpoints
out toward Fulton county are near 60.
Currently surface winds remain out of the south with sustained
speeds of 20-25 mph with gusts in the 35-40 mph range. So far, we
have had gusts in the upper 40 mph range across the KY Mesonet. We
still could see some sporadic 45-50+ mph gusts over the next few
hours. However, as mid-high level clouds come into the region,
mixing will become more limited and wind gusts will likely remain
the 40s into the evening hours.
With the mix out occurring, we do have some lower RH values across
the region. A few spots out across our eastern areas did drop below
25% which necessitated a Red Flag Warning for eastern areas. RH
values are expected to increase a bit as we go through the
afternoon. However, the combination of low RH, gusty winds, and low
10h fuels will lead to dangerous fire conditions across the region
through early evening. Therefore, the Red Flag Warning will
continue.
Strong capping up near 700 hPa as evidenced on the 18Z ILN and OHX
special soundings looks to keep things dry through the early evening
hours.
=====================================
This Evening and Overnight
600 PM EDT Tonight to 600 AM Thursday
=====================================
*Bottom Line Up Front*
- Squall line expected to move into western KY this evening
- Best chances of strong to severe storms west of I-65
- Damaging wind gusts and isolated tornadoes main threats
Squall line out to the west continues to get better organized this
afternoon. Thus far, lightning has been confined to points in AR
and points south. Latest high res CAMs and ensemble guidances has
shown a slower progression of the squall line into the region.
Earlier thinking was that the squall line would enter our western
CWA near 00Z, but that may be a bit too fast given current trends
and current forecasts.
Severe threat remains quite elevated, especially across our western
CWA where we will have a high shear/low instability set up. Overall
trends continue to show the best combination of shear and available
instability remaining across western KY this evening and it may
develop a bit more eastward into our CWA. In any case, storms out
to the west will pose a damaging wind and isolated tornado hazard
this evening. Current high res and HREF guidance still does show
numerous 2-5km UH tracks over far western KY. However, these tracks
really diminish as you approach the I-65 corridor. This is likely
due to the lower moisture and instability expected in the I-65
corridor and points east. Additionally, model soundings do show a
slightly backed surface wind profile across our western CWA this
evening. However, as the night wears on, those SE surface winds veer
back to the south with time which reduces the directional shear
component. With the LLJ pushing into the region, any storms out to
our west should be able to tap into this and bring that higher
momentum air to the surface. Thus, the SPC ENH risk area was pushed
a bit further to the north and east with the 1630Z issuance to
account for this.
Storms look to enter our CWA between 00-02Z and should progress
eastward toward the I-65 corridor by 04-05Z and into the I-75
corridor in the 06-07Z time frame. Overall confidence for severe
weather remains high in our western third of our forecast area.
However, confidence drops considerably as you get closer to the I-65
corridor for several reasons. 1. Later arrival of storms as the
atmosphere starts to stabilize. 2. Substantial uncertainty about
whether strong moisture advection ahead of the squall line will be
able to moisten the atmosphere enough to support deep convection
from I-65 and points east. 3. How quickly will the line deteriorate
given the progressively unfavorable environment.
Confidence in how well CAMs can handle the complex environment
remains uncertain, but given the strong shear and environmental wind
profiles, there remains a risk of damaging wind gusts with even
shallow convection that may be diminishing in strength as it heads
eastward into central KY overnight. Surface cold front will be on
the heels of this convection and some additional showers may develop
right along the frontal interface late tonight. So, we will plan to
keep high PoPs going for the overnight period.
For Thursday, we'll be in the post frontal flow and we'll get into
the dry slot for a time. However, with steepening lapse rates due
to colder air coming in aloft, some scattered showers will be
possible in spots in the afternoon. Highs will range from the low-
mid 50s over southern IN and central KY, with daily highs in the
upper 60s in the east, but temps falling throughout the day.
.Long Term...(Thursday night through Wednesday)
Issued at 336 PM EDT Wed Mar 30 2022
Thursday night
An upper closed low, embedded in an upper trough, swings through
northern Indiana. This will provide southern Indiana and central
Kentucky with a chance for stratiform rainfall and drizzle. There is
still some variation in the models. The DGZ may or may not be
saturated. A lack of ice crystals would lead to more drizzle. In
reality, the region will probably see a little of both. Parts of
southern Indiana could even see a flurry mixed in for an hour or two
which would have zero impact on anything.
Friday
Temperatures begin the day near and just above freezing, but skies
clear throughout the day as high pressure and upper ridging advance
from the Ozarks into the Lower Ohio Valley. Anticyclonic flow around
the surface high keeps a northern component to the winds which will
limit highs to the upper 40s to mid 50s, but as the high passes
overnight, winds veer towards the south.
Saturday
WAA from the southern winds will help to lift temperatures from
previous days as they reach into the upper 50s to low 60s. A surface
low, associated with an upper trough, will drag a weak trailing cold
front towards the CWA. Clouds are expected to be thicker over
southern Indiana and thinner towards southern Kentucky. Afternoon
hours bring low rain chances (around 20% or less) to southern
Indiana and areas mainly north of the parkways in Kentucky. Any
light rainfall that does develop will move east of the CWA during
the first half of the night.
Sunday
Even with light northern winds in place, upper ridging and surface
high pressure will bring clear skies to the region, keeping
temperatures mostly in the 60s.
Monday - Wednesday
Upper flow becomes more zonal as a front, extending from a surface
low over the western Great Lakes, sets up along the Ohio River. The
front could stay north of the river across southern Indiana or sink
just south of the river. Either way, light precipitation is expected
near the front, but it could take some time for the lower levels to
saturate, so Monday will likely remain mostly dry.
A better chance of rain and possibly storms will arrive on Tuesday
as a digging shortwave strengthens an upper trough. This will result
in a strong surface low forming over Texas, before getting quickly
ejected towards the CWA. This will bring more widespread heavier
rain to the area. It's still early, so expect timing and details to
change as the event nears.
&&
.Aviation...(00Z TAF Issuance)
Issued at 720 PM EDT Wed Mar 30 2022
IMPACTS:
- Strong and gusty south winds through late evening
- Line of strong to marginally severe storms late evening to just
after midnight
DISCUSSION:
Strong southerly winds will continue well into the evening as a dry
column is allowing for very efficient mixing. Will keep prevailing
gusts generally in the 35 kt range, but more like 30 kt for HNB
where it's already clouding up ahead of the line.
Main convective line will bring brief IFR cig/vis in very heavy
rain, and while winds won't be much stronger than the pre-storm
gradient winds the direction will be erratic. Will run the worst
conditions in 2-hr TEMPO groups, even though the strong storms are
unlikely to cover the whole TEMPO period, with SDF hitting in the 03-
05Z time frame. Main source of uncertainty is how well these storms
hold up as they push eastward toward LEX.
Storms exit to the east after midnight, or more like 07Z for LEX,
giving way to lighter rain showers and winds still gusting near 25
kt out of the SW. Ceilings will initially be VFR, albeit just
barely, but will build down into MVFR and likely below 2000 feet for
a decent chunk of Thu morning. Look for improving ceilings and WSW
winds Thu afternoon, with gusts around 20-25 kt.
CONFIDENCE:
High on storms occurring, medium on exact impacts and timing.
High on winds.
Medium on ceilings Thursday.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...Wind Advisory until midnight EDT /11 PM CDT/ tonight for
INZ076>079-083-084-089>092.
KY...Wind Advisory until midnight EDT /11 PM CDT/ tonight for
KYZ023>043-045>049-053>057-061>067-070>078-081-082.
Red Flag Warning until 8 PM EDT /7 PM CDT/ this evening for
KYZ035>037-039>043-046>049-054>057-064>067-075>078-081-082.
&&
Mesoscale...EBW
Short Term...MJ
Long Term....KDW
Aviation...RAS