167
FXUS63 KEAX 220506
AFDEAX

Area Forecast Discussion
National Weather Service Kansas City/Pleasant Hill MO
1206 AM CDT Sun Sep 22 2024

.KEY MESSAGES...

- Showers/Storms Continue This Evening

- Conditional Severe Threat NE KS to NW MO Late Tonight

- Conditional Severe Threat South of I-70 Sunday Morning/Afternoon

- Cooler This Week

&&

.DISCUSSION...
Issued at 240 PM CDT Sat Sep 21 2024

The forecast continues to have several moving parts to it that
leaves conditional threats and periods of higher uncertainty through
Monday morning. The mid and upper-level pattern has not seen a
drastic change over the past 24 hours. There is trough moving
through the Canadian Prairie Provinces. There are still some
influences on the mid-level pattern from this system, but the
primary feature driving the rain shower activity this afternoon has
been the trough currently centered just west of the Four Corners
Region. Jet streak with this system has positioned stronger dCVA
into the Front Range and High Plains, and has resulted in broad
surface cyclone across much of the Central Plains, with secondary
area of cyclogenesis in the TX/OK Panhandle Region. This has
de-amplified the ridge axis across much of the Gulf Coast and lower
Mississippi River Valley, and in the lower portions of the
troposphere has turned flow southerly. The thermal boundary that been
traversing eastern Kansas and most of Missouri the past few days
has started to push back northward already as a warm front. With
this, has also come isentropic ascent with some kinematic support
form weak vort max passing overhead. This has helped to provide the
expansive cloud cover as well as widespread shower activity across
the forecast area. Elevated instability, primarily with stronger WAA
has allowed the development of a few isolated thunderstorms.
However, wind shear has not been overly impressive across the warm
sector this morning and therefore organization for any convection
has been hard to come by. Expecting this to be the case through the
remainder of the evening. While there are few breaks in cloud cover
that could support additional updraft development, the lack of
stronger flow should continue to inhibit any robust organization.
The primary threat with any thunderstorms this afternoon will be
lightning, and wind gusts to around 40 MPH.

Later this evening, mid-level trough will start to lift out of the
Four Corners Region and will send another vort max across the
Plains. This should provide another shot of dCVA and promote surface
cyclogenesis primarily across the southern Plains this evening.
Current deterministic guidance along with several CAMs this morning
has an inverted surface trough that extends into the Ozarks and
southern Missouri River Valley that should provide increasing
convergence heading into the remainder of the evening. Meanwhile, an
area of subsidence over the Northern High Plains will develop a
stronger surface anticyclone that drops southward on the backside of
the ejecting trough out of the desert southwest. This will push the
thermal boundary back southward as a cold front as we head into the
overnight hours, and will be the focus point for stronger updraft
development from eastern Kansas into northwest and northern
Missouri. The main question will be if we will see enough clearing
for more robust destabilization on the warm side of this boundary
through the remainder of the afternoon. 12z HREF mean CAPE values
are in the ballpark of 1000-1500 J/kg across most of the forecast
area heading into the late evening hours. However, there could be
potential to push above 2000 J/kg if we are able to realize greater
insolation. With the rain activity today, the column is more moist
than it was yesterday, meaning dry air entrainment will not be as
prevalent. As the mid-level vort max moves through, deep layer shear
should continue to increase into the evening along the thermal
boundary, with 0-6km bulk shear values reaching between 30-40 kts.
The combination of forcing and deep layer shear, along with
instability will lead to the potential for thunderstorms to
organize, and present a threat for wind gusts to around 60 MPH and
hail around quarter size. Given the strong forcing, along with low-
level jet development, not expecting any storms to remain discrete
for a long period of time, and although hodographs are quite lengthy
the curvature will be very limited, thus limiting ability for SRH to
be realized and limiting any kind of tornado threat. Given the cloud
cover, we may not be able to mix out an inversion present around
900mb, meaning that most convection, even along the cold front, will
more elevated and not surface based. This almost limits how much of
wind shear updrafts can realize. Heavy rainfall may lead to stronger
cold pools with convective clusters along the front, further
supporting localized wind gusts if a line is able to develop. The
cluster then moves primarily east-southeast through the remainder of
the overnight hours. With respect to rainfall amounts, HREF mean
values are generally around 1.0 to 1.5 inches across a large portion
of the forecast area. There are few pockets of probability matched
mean values that exceed 2.5 inches. Will need to watch rainfall
rates for issues related to flooding. However, antecedent dry
conditions the past few weeks should help to mitigate most flooding
effects. Expecting the thermal boundary to also remain progressive
enough with stronger mid-level trough moving through that should
limit training showers/storms across most of our area. If the
stronger thunderstorm threat does not unfold as currently
anticipated, the amount of moisture and forcing present will still
result in rainfall across a large portion of the forecast area. Both
CAM and coarser ensemble suites continue depict probabilities above
70 percent for at least 0.50 inches of QPF along the cold front
through the overnight hours.

Sunday morning, lingering showers and storms are expected especially
south of Hwy. 36, though most of the activity should eat into the
instability that greatly limits any kind of severe threat,
especially past 10-11z timeframe. The mid-level trough continues to
move eastward. Most guidance depicts the surface cold front being
somewhere in the southeastern third of the forecast area,
essentially from Bates County Missouri to Cooper County Missouri.
There is some potential for the boundary to stall during the late
morning hours here, that could result in some training. This time
frame late morning into the afternoon hours of Sunday is where most
of the forecast uncertainty still remains. A few CAM solutions keep
the boundary further to the northwest along the Interstate 70
corridor, while others push it much closer to Interstate 44 in
southern Missouri. Therefore, this is leading to spread in solutions
for recovery on the warm side of the boundary for the southern
portions of area. With the mid-level wave still nearby, the boundary
should still have decent deep layer shear present, that if there is
recovery and further destabilization on the warm side of the
boundary, new development could organize and produce a few stronger
to marginally severe storms. Once again, the main concerns would be
wind gusts around 60 MPH and hail around quarter size. With that
being said, ensemble probabilities seem to favor a more
southeastward position of the front and better surface convergence
closer to the Interstate 44 corridor for most of Sunday afternoon,
concentrating the more favorable severe threat outside of our
forecast area. As for rainfall amounts, our southeast counties still
hang onto elevated probabilities for at least 0.50 inches of QPF,
and HREF probability matched mean values have a few pockets of an
additional 2-3 inches of rainfall. This would be the higher end of
expected totals, but if the boundary does stall for a few hours
while activity is still ongoing, this could result in event totals
closer to 4 inches of rainfall. Current Flash Flood Guidance depicts
that most of the area can handle in excess of 3 inches, so this
amount spread over 36 hours would indicate only a minimal flooding
threat. However, if the higher end of the probability matched mean
values as indicated by the 12z HREF are realized over a shorter
time, localized flooding may become possible, and will need to be
monitored.

For the remainder of the week, medium range deterministic guidance
is quite spread with how the pattern evolves. GFS develops a
stronger closed-low system centered more over the Great Lakes
Region, while ECMWF keeps it much further west. This greatly impacts
timing of southerly flow vs northerly flow, and what this means for
temperatures during the middle of this week. Inner-quartile ranges
amongst various ensemble suites is large, between 68 and 81F for
many points across our forecast area. For now, will stick with
temperatures in the official forecast closer to the median of these
values. Regardless, with the passage of the Sunday cold front and
mid-level wave/low parked somewhere nearby if not directly overhead,
temperatures will be cooler this upcoming week then what was
experienced last week. The uncertainty is whether we will be well
below normal, or perhaps right around it depending on the
positioning of the closed-low system and how much progress any kind
of ridging along the western CONUS makes. Although there may be some
large scale lift available, most of of the moisture still gets
pushed southeastward of the area by Monday, setting up drier
conditions through the middle of this week. Though if we continue to
see a denser cloud shield, cannot rule out periods of sprinkles or
light showers through the middle of this week. Currently though,
ensemble probabilities for measurable rainfall in our forecast area
remain quite low through at least Thursday.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1159 PM CDT Sat Sep 21 2024

On going stormy weather will continue to impact the Kansas-
Missouri state line terminals through the rest of the night and
much of Sunday. VFR showers and thunderstorms continue to advect
east from Kansas into Missouri ahead of a cold front that will
sweep south Sunday morning. Thunderstorms and showers will
prevail ahead of the front with showers and lowering CIGs behind
the front as it settles south. Conditions should improve as we
move through the morning into the afternoon hours of Sunday.

&&

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

&&

$$

DISCUSSION...Krull
AVIATION...Cutter