-- Discussion containing changed information from previous version are highlighted. --
923
FXUS63 KEAX 202348
AFDEAX

Area Forecast Discussion
National Weather Service Kansas City/Pleasant Hill MO
648 PM CDT Fri Sep 20 2024

.KEY MESSAGES...

- Warm and Humid

- Storms Overnight into Saturday Morning

- Stronger Storms Possible Sunday

- Cooler Temperatures Next Week

&&

.DISCUSSION...
Issued at 250 PM CDT Fri Sep 20 2024

There are three primary H5 features that will contribute to active
weather through the remainder of this weekend. A 592dam high is
centered over Texas, that has been amplified toward the lower
Mississippi River Valley due to a deeper trough starting to come
ashore the southwestern CONUS. Meanwhile, another trough is moving
across the Canadian Prairie Provinces. The surface cyclone with the
Canadian system is starting to move toward Hudson Bay, with the cold
front stretching across much of the CONUS, and is currently moving
across Central Missouri as of the late morning and afternoon hours.
A brief period of H5 height rises has provided weak subsidence on
the backside of this cold front, which has been keeping conditions
dry through much of this afternoon across the forecast area. A weak
vort max is expected to eject ahead the deeper mid-level trough over
the southwestern CONUS later this evening, providing modest H5
height falls across our area and may interact with the cold front
that will be parked somewhere in the southeastern third of our
forecast area. The surface cyclone associated with this wave likely
stays over the High Plains, but surface southerly flow south of the
cold front should increase instability overnight for the
southeastern third of the forecast area, and we may see some
elevated instability develop further northwest. Current CAMs depict
thunderstorm development after 04z this evening and entering our
western counties around the 06z-07z timeframe. MUCAPE values off the
12z HREF are progged around 1500-2000 J/kg, with 0-6km bulk shear
values in the ball park of 25-30 kts. This may be enough to support
a few isolated severe storms producing wind gusts around 60 MPH and
hail around quarter size early Saturday morning. Steeper lapse-rates
between 700mb-500mb may foster a few stronger updrafts. However,
current HRRR and RAP soundings are very dry in middle portions of
the troposphere, which may be detrimental to deep convection
initiation as the forcing is moving through. This may even be a
potential source of later initiation time then what current CAMs are
depicting in simulated reflectivity fields. This first wave pushes
east by late morning. For the remainder of Saturday afternoon,
another short-wave trough and vort max eject out of the southwestern
CONUS and continue to develop a broad surface cyclone across the
Plains. This enhances low-level southerly flow as far east as the
Mississippi River Valley, and will start to push the cold front back
northward as a warm front. Along the warm front, expecting
isentropic ascent to promote additional shower development. If there
is any lingering elevated instability, a few thunderstorms may
become possible, though current CAM guidance suggest this travels
further north, impacting only far northwestern portions of the
forecast area. Regardless of storm mode, heavier rain showers are
expected most of the day as ensemble probabilities for measurable
rainfall are above 80 percent for most of the forecast area, and for
a threshold of .50 inches of QPF is nearly 50 to 60 percent.
Temperatures Saturday afternoon are expected to be generally in the
80s, with cloud cover keeping conditions slightly cooler, but WAA
will prevent a drastic cool down through most of the day.

Sunday, H5 trough lifts out of the southwestern CONUS into the High
Plains. Stronger dCVA occurs in the southern Plains as this moves
eastward, but mid-level height falls expand further eastward and
inverted surface troughing should extend into eastern Kansas through
Central Missouri. Stronger AVA over the Northern Rockies develops a
surface anticyclone that will push southward out of the Northern
Plains, and should set the stage for a stronger cold front to
develop across the Missouri River Valley heading into Sunday
afternoon. Amongst deterministic guidance, there is still discrepancy
in how far north the primary H5 kinematic forcing travels, and this
also impacts how far northward favorable surface pressure falls
occur with the surface cyclone, and how quickly the front moves
through the area. Overall ensemble probabilities for rainfall remain
high, with over 80 percent probabilities for any measurable
rainfall, and continued 50-60 percent probabilities for at least
0.50 inches of rainfall. Between Saturday and Sunday activity, some
areas may see as much as 2-3 inches of rainfall by the end of this
active pattern, which will be welcomed due to current drought
conditions across the region. The main uncertainty is with how
strong storms will be, and what the severe threat could look like.
Instability should not be an issue to come by, with high
probabilities for exceeding 1000 J/kg of MUCAPE. However, if the
cold front and forcing sink further south, stronger updrafts could
initiate closer to the Interstate 44 corridor Sunday afternoon into
evening. If the system takes track that is further north, areas up
to Interstate 70 or even Hwy. 36 could experience stronger deep
layer shear as well as better surface convergence that could
generate a few storms. Hail and wind would be the primary threat. If
the surface cyclone ends up in a spot where surface winds back
considerably, could see a concentrated corridor of enhanced SRH that
presents a brief tornado threat if storms were to be discrete.
However, uncertainty remains too high to confidently pinpoint any of
these mesoscale details at this time. In addition, instability
recovery from Saturday activity and cloud cover could also play a
large role in boundary strength and differential heating. Again,
even if severe storms fail to go, there should be enough forcing and
moisture around to still provide rain showers across much of the
area. With respect to any flooding concerns, most areas will be able
to handle 2-3 inches of rainfall, especially if it is spaced out
over 36 hours. Will only need to monitor a few urban areas for fast
responding creeks, but even these will be able to handle a decent
amount of rainfall given the dry conditions over the past few weeks
across the region.

Heading into next week, our area will be under prominent troughing,
with potential for a closed-low to remain directly overhead. This
will keep temperatures substantially cooler. Most points in the
forecast area next week have an inner-quartile temperature range
between the upper 60s and mid 70s. While there will be some lift in
the presence of the troughing overhead, the front from the weekend
likely pushes most of the moisture out of the area. Ensemble
probabilities for measurable rainfall through most of next week
remains lower. If we see long periods of cloud cover, we may see
multiple periods of light sprinkles move through. Overall
probabilities for any measurable rainfall after Monday are between
10 and 15 percent.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
-- Changed Discussion --
Issued at 630 PM CDT Fri Sep 20 2024

VFR conditions will likely prevail through much of this TAF
cycle, but a threat of thunderstorms will be present for much of
that time also. The nocturnal low level jet is expected to push
storms in Kansas east into Missouri this evening, arriving in
the vicinity of Kansas City between 03Z and 04Z. The storms are
rather high based, so VFR conditions will prevail expect if a
storm directly impacts a terminal. Additionally, once the storms
get in the vicinity the same LLJ might keep storms bubbling
across the region late tonight and again in the morning.
-- End Changed Discussion --

&&

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

&&

$$

DISCUSSION...Krull
AVIATION...Cutter