996
FXUS63 KEAX 140900
AFDEAX

Area Forecast Discussion
National Weather Service Kansas City/Pleasant Hill MO
400 AM CDT Wed Aug 14 2024

.KEY MESSAGES...

- Showers/Thunderstorms This Morning

- Conditional Chances for Afternoon Redevelopment; More Overnight

- Hot and Humid Wednesday Afternoon

&&

.DISCUSSION...
Issued at 359 AM CDT Wed Aug 14 2024

H5 ridge axis is shifting into the eastern Plains this morning with
multiple short-wave perturbations and vort maxima upstream from the
main axis. This has been promoting an extend period of dCVA from the
Front Range into the High Plains over the last couple of days, with
steady surface pressure falls extending eastward from the area of
cyclogenesis in the Front Range. Low-level flow has been south-
southwesterly the past few days and has provided several thermal
boundaries to push through the area. Current surface analysis
indicates a slow moving warm front oriented from near Salina, KS to
Fayetteville, AR. This has setup a strong theta-e gradient from east-
central Kansas into Central Missouri. Ahead of this warm front
isentropic ascent along the 305K level has been promoting shower
activity in the southwestern and southern portions of our forecast
area. While there is plenty of heat and moisture around, strong WAA
around 700mb has kept a stronger cap in place, which has largely
limited updrafts from deepening. Meanwhile, a stronger convective
cluster has been moving through southeast Nebraska during the
overnight hours associated with stronger mid-level vort max and
large scale lift under an area of strong upper-level divergence. As
we head into the remainder of the morning hours Wednesday,
anticipating more showers/storms to fill in along the area of
isentropic ascent as well as increasing upper-level kinematic
support for lift. The CAMs have not been handling this morning`s
convective trends well. Early CAM runs developed very robust storms
across our area for this morning, but then more recent runs have
kept conditions very dry. It appears that although the cyclone was
deepening over the Front Range, surface pressure falls stalled for a
bit and thus pulled the thermal boundary further west. In addition,
it looks like the CAMs were not depicting the timing of the mid-
level short-waves riding through the ridge well. As a result,
convection initiated further west than originally expected, and the
CAMs also may have been struggling with the CINH present. With
current radar trends, have kept rain showers and thunderstorms in
the forecast for this morning, as the moisture and forcing is
around. However, there is large uncertainty with how intense
convection gets this morning, as well as how much QPF it will end up
producing. Coarser synoptic scale ensembles still paint
probabilities around 30 percent for seeing at least 0.50 inch of QPF
with morning activity along the warm front and first passing mid-
level vort maxima. The 00z HREF outputs a mean QPF for areas east of
Interstate 35 of around 0.75 inches for the first round of rainfall,
but keep in mind its inputs include the 00z HRRR run along with
other CAMs that filled in much more robust convection compared what
we have realized so far. As the low-level jet kicks in, expecting
more to develop east of Interstate 35 during the mid and late
morning hours, which could still drop around 0.75 inches of QPF, but
confidence in this is low-medium. With respect to the severe threat,
a higher CAPE environment should start shifting eastward, with
current MUCAPE values between 500-750 J/kg. Effective bulk-shear
values around 30-45 kts. This may support a few stronger updrafts
this morning that could produce small hail and maybe wind gusts up
to 60 MPH. However, with the large amount of CINH in place, updrafts
may continue to struggle unless it can tap into the large scale
ascent from the short-wave moving through. Overall, very uncertain
how the remainder of the morning plays out. HREF probability matched
means for morning convection QPF max out around 2 inches in some
pockets. Not sure if storms will last long enough in any one
location to achieve this, but if they do could result in some
flooding issues. Thus have kept the Flood Watch in place for areas
mainly east of Interstate 35, but will acknowledge that overall QPF
trends have been downward the past several hours.

As the first short-wave moves through, a stronger short-wave
upstream from the ridge axis ejects across the Plains and will start
to provide H5 height falls by the afternoon. A brief period of
height rises may be possible in response to the initial ejection of
the short-wave, and could perhaps clear conditions out from early
morning isentropic upglide. With another round of dCVA, surface
cyclone over the Front Range should continue to deepen with surface
pressure falls continuing from the Central Plains into the lower
Missouri River Valley through the afternoon, eventually sending the
warm front thermal boundary further to the east-northeast. If we
clear, we may see temperatures hit the lower 90s with dewpoints in
the mid lower to mid 70s, especially for eastern Kansas and western
Missouri. If we realize these higher temperatures, heat index values
may reach near 105 during the afternoon hours. Thus have maintained
the Heat Advisory for the southwestern third of the forecast area
through the early evening hours. However, if we get more showers and
cloud cover to backfill, temperatures may be cooler. Amongst NBM
members, inner-quartile range for max temperatures this afternoon
had larger spread then typically seen for a forecast less than 12
hours out, with temperatures ranging from the 85F to 93F in some
locations. This uncertainty is largely attributed to changes in some
members that have kept robust convection and lingering cloud cover,
and other members that were completely dry and clear. Attention then
turns into the late afternoon and evening hours as the main mid-
level vort max moves into the lower Missouri River Valley and the
associated surface cyclone begins to propagate eastward across the
Plains. This sends the warm front eastward out of the forecast area,
with a cold front coming in from the Central Plains. Both large
scale ascent from upper-level kinematics and surface convergence
along the cold front should start to initiate storms late into the
afternoon and through the evening. The timing of the mid-level
forcing is about 4-6 hours later than was originally depicted in
guidance from yesterday`s model runs. The CAMs has been focusing
development in our area starting between 02-03z now. However, will
note that with the struggles with this morning activity, not sure
how reliable the CAM output really is for late afternoon and evening
development. The warm sector ahead of the deepening cyclone appears
to be capped with stronger WAA between 850mb-700mb, which would
require longer daytime boundary layer heating and destabilization to
realize surface based parcels. However, if we see more convection
this morning that places an outflow boundary across the area, we may
see better forcing near the surface that could work through this
cap. With mid-level height falls and subtle cooling between 700-
500mb, could realize better SBCAPE that could get a few updrafts
going. Increasing mid-level flow should help to yield 0-6km bulk
shear values between 30-40 kts, which could lead to the organization
of storms, and present a hail and wind threat. But, if the boundary
layer needs more time to mix and destabilize, we may have to wait
until later in the evening with the approaching cold front for
enough forcing. Once we get past 00z though, mid-level lapse rates
are progged to steepen with the mid-level short-wave trough
approaching, and surface pressure falls and backing surface winds
should increase overall shear values, as well as low-level storm-
relative helicity values to close to the front. Not exactly sure how
far into the warm sector this will extend at this point, but initial
convection along the front could be discrete and take on a
supercellular mode, capable of hail at least quarter size and wind
gusts in excess of 60 MPH. Initial storms could present a brief
tornado threat, but it appears storm motions may be more parallel to
the boundary as low-level jet kicks in, and storms congeal into a
line. From there, main threats then become hail and gusty winds.
Important mesoscale features to watch this afternoon will be CINH
and CAPE environment during the afternoon hours IF there is an
outflow boundary hanging around. Then, as the cold front approaches,
watching how the shear evolves and storm motions relative the
boundary will determine convective mode. As for QPF, we are still
dealing with an environment with PWATs of 2.00 to 2.25 inches. HREF
mean QPF paints 1.25 to 1.75 inches for mainly our north-central
area, with 0.25 to 0.75 for central and southward. HREF probability
matched mean (PMM) values max out between 2.5 to 3.0 inches. If the
thermal boundary stalls early Thursday morning, areas east of
Interstate 35 could potentially see in excess of 2.0 inches of
rainfall, that could result in flooding issues if that same area
sees heavier rainfall from the Wednesday morning activity. Coarser
scale ensemble seems to favor heavier rainfall into Thursday
morning, likely with a more pronounced short-wave trough and surface
cyclone moving through. Again though, the CAMs struggle this morning
make the CAM output QPF hard to trust, along with what the 00z HREF
is has produced. If the cold front remains progressive and limits
training, this will help mitigate most of the hydro related
concerns.

Heading into the weekend, medium-range deterministic guidance
depicts a deep closed system dropping south form Hudson Bay will an
amplified mid-level ridge develops over the Rockies. Several vort
maxima may work through the flow that will bring additional rain
shower and thunderstorm chances. Differences in timing of the short-
waves though have resulted in large spread amongst ensemble suites,
which right depict low-end probabilities throughout much of the
weekend. For right now will keep the low-end NBM POPs toward the end
of the week, and will refine once this Wednesday-Thursday system
clears the area.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 1154 PM CDT Tue Aug 13 2024

A line of storms is likely to develop over eastern KS and
western MO in the next few hours and shift east with time in the
pre-dawn hours. This area of storms will likely affect all TAF
sites from 8-9Z through 11-12Z. Outside of the storms, IFR to
low MVFR conditions are expected through the overnight hours. As
a warmer and more humid air mass builds into the area, storms
shift east and ceilings begin to raise so that by the afternoon
hours, VFR conditions become likely. Easterly winds initially
will become southeasterly this afternoon and southerly this
evening.

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory from 1 PM this afternoon to 7 PM CDT this
     evening for MOZ028-037-043-044-053-054.
     Flood Watch until 3 PM CDT this afternoon for MOZ003>007-
     013>017-022>025-030>033-038>040-045-046.
KS...Heat Advisory from 1 PM this afternoon to 7 PM CDT this
     evening for KSZ025-057-060-103>105.

&&

$$

DISCUSSION...Krull
AVIATION...CDB