722
FXUS63 KEAX 201743
AFDEAX

Area Forecast Discussion
National Weather Service Kansas City/Pleasant Hill MO
Issued by National Weather Service Louisville KY
1243 PM CDT Mon May 20 2024

.KEY MESSAGES...

- Isolated to scattered showers and storms possible today, but
  timing and overall coverage are highly uncertain.

- There is an enhanced risk of severe thunderstorms on Tuesday
  across the entire region, with all severe hazards possible.
  Currently, the greatest chances for severe weather are
  generally east of Interstate 35.

- Locally heavy rainfall may occur with storms on Tuesday night,
  especially south of Interstate 70. A few instances of flooding
  may occur (about a 20 percent chance).

- The pattern remains active later this week through Memorial
  Day weekend.

&&

.DISCUSSION...
Issued at 337 AM CDT Mon May 20 2024

Busy night here with the severe storms that moved through the KC
metro during the late evening hours. Unfortunately, this
abridged the forecast process quite a bit tonight, so main focus
of the morning update was on the first 48 hours.

Objective 00z upper-air analysis indicated a broad trough in
western North America, with an elongated 250-mb jet streak from
the Great Basin to the Upper Great Lakes. Meanwhile, a
southern-stream anticyclonic jet streak extended from the Baja
region to western Texas, with difluent flow in the Missouri
Valley. A midlevel perturbation was present in the central
Plains, collocated with regionally strong 850-mb southerly flow.
Evening soundings exhibited environments quite supportive of
the severe storms that moved through Kansas and western
Missouri, with substantial CAPE and deep-layer shear atop fairly
dry low- and midlevels (resulting in highly favorable DCAPE). A
strong bow echo developed in southern Kansas and raced eastward
into the CWA during the late evening, producing substantial wind
damage in the KC metro and surrounding areas before dissipating
as nocturnal stabilization continued and cold-pool dynamics
gradually waned as outflow outpaced the existing convection.
The mesoscale convective system (MCS) developed a very
pronounced mesoscale convective vortex (MCV), which traversed
the northwestern half of our CWA overnight (and has now
progressed into southern Iowa as of 4 am).

The immediate forecast question today is to what degree the MCS
has curbed our region`s ability to generate new convection. The
progression of the MCV to our north and northeast suggests its
influence in our region may be confined to our far eastern
counties. However, as diurnal heating and destabilization
commence, the presence of the MCV and associated
convergence/lift may provide additional support to generate
convection with relatively little diabatic heating. Based on
current progression of the MCV, think chances of convective
regeneration in our CWA associated with it are diminishing, and
PoPs have been lowered somewhat in the eastern CWA today (after
the remnant precipitation from the MCS traverses to eastern
Iowa/Missouri early this morning).

However, convection-allowing models (CAMs) have been reasonably
consistent in developing convection early this morning in
eastern Kansas, supported by isentropic ascent on the poleward
side of the nocturnally maximized low-level jet. Less consistent
is the progression and persistence of this convection through
the day, with the latest HRRR simulations, for example, anywhere
from keeping convection mostly to our west before its
dissipation to lingering it into at least mid-afternoon in
northern/western Missouri. Given some support from the NAM Nest,
higher PoPs are warranted in the western half of the CWA today
(generally 30 to 60 percent).

Confidence lowers further during the late afternoon and evening,
with at least some hints of scattered convection developing in
northern/central Missouri. CAMs are all over the place regarding
coverage, specific geographic placement, and timing. Thus,
maintenance of some low PoPs through the overnight hours is
warranted (primarily north of I-70). Sufficient capping should
be in place farther south to keep these areas mostly dry
tonight.

Multiple rounds of convection will be occurring to our north
from this afternoon through Tuesday morning, in the stronger
southwesterly mid- and upper-level flow. However, on Tuesday, a
strong vort max will eject from the western U.S. trough
northeastward into the central Plains. This will translate into
eastern South Dakota and Nebraska and adjacent portions of
Minnesota and Iowa during the afternoon. Large-scale ascent
attendant to the shortwave trough will result in the development
of convection in advance of the progressive vort max. The
southern-stream jet streak will advance to Kansas and Missouri
during the afternoon, providing upper divergence support via the
left-exit region to areas mostly to our north. Such forcing
weakens farther south into our CWA, casting some uncertainty on
when convection develops along the approaching front given a
strong elevated mixed layer and associated capping. Development
should occur from north to south, with gradually sparser
coverage with southern extent. With this in mind, there is a
chance that the northwestern portions of the CWA see little in
the way of convection from the Tuesday system, with
probabilities increasing as one gets farther east from I-35.

Regarding the overall environment, severe weather is certainly
supported, with moderate to strong buoyancy (MLCAPE > 2000
J/kg), strong deep-layer and low-level shear (0-6 km bulk wind
differences exceeding 50 kt; effective SRH exceeding 150 J/kg),
and increasingly orthogonal upper flow to the approaching front
(more supportive of discrete/supercellular storms, at least
initially). The primary limiting factor is strength of capping,
as mentioned above, and also how quickly storms congeal/grow
upscale. Even if upscale growth is rapid, a severe MCS with an
environment supportive of QLCS tornadoes would be present.

Another consideration is heavy rain potential. With gradually
diminished forcing on the southern side of the system/front,
convection may tend to become more oriented parallel to upper
flow, especially during the evening/overnight hours. CAMs are
hinting at upward propagation becoming favored on the south side
of the developing MCS, which may lead to a favored zone of
training storms and potential flash flooding. This threat looks
greatest south of I-70 at this time. We will be monitoring this
potential closely as the event approaches.

A reinforcing vort max will move through the Midwest on
Wednesday, which may keep storm chances lingering through the
day in our eastern and southern CWA, especially. Otherwise,
there should be a brief period of quiet weather Wednesday and
Wednesday night. Yes, brief. The wavetrain of vorticity maxima
in favorable zonal to southwesterly upper flow continues
thereafter, with frequent bouts of active weather apparent
Thursday right through the holiday weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1241 PM CDT Mon May 20 2024

Low-confidence forecast continues due to varying model guidance and
conditionally unstable environment. Latest surface analysis places a
low pressure center over southern MN with a warm front extending
east and a cold front extending to the SW, placing TAF sites within
a warm sector with general S-SW flow. Current radar shows a few
areas of convection moving eastward across the area. So far these
have been short lived, modest cells that have produced little
lightning. Began all TAF sites with VCTS to account to potential for
convection to generate this afternoon. Otherwise, VFR conditions
should prevail outside of convection with winds backing to SE this
evening and overnight. Winds do pick up by Tuesday morning out of
the south with gusts around 20kt. Enough models are also suggesting
the possibility of a layer of MVFR stratus to advect over the TAF
sites Tuesday morning, which could linger into the late morning
hours.

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
MO...None.
KS...None.

&&

$$

DISCUSSION...CMS
AVIATION...CG