768
FXUS63 KEAX 231737
AFDEAX

Area Forecast Discussion
National Weather Service Kansas City/Pleasant Hill MO
1237 PM CDT Thu May 23 2024

.KEY MESSAGES...

- Warm Today, Isolated Shower Possible

- Shower/Thunderstorm Complex Overnight; Severe Storms Possible

- Severe Storms Forecast Saturday Evening

&&

.DISCUSSION...
Issued at 351 AM CDT Thu May 23 2024

GOES-16 water vapor satellite imagery shows the PV anomaly over the
northwest CONUS that has provided persistent troughing over the past
week and has been responsible for sending multiple short-wave
troughs and mid-level vorticity maxima across the Central CONUS.
Surface anticyclone that brought mild weather conditions on
Wednesday has pushed into the southern Great Lakes Region during the
overnight hours. Currently watching a short-wave perturbation around
H5 that is starting to eject across the Rockies away from the main
troughing region in the northwest United States. Early this morning,
the dCVA associated with this has been lowering surface pressure
from the Front Range into the High Plains of Kansas. This should
allow pressure falls to continue and foster surface cyclogenesis.
Through the morning and afternoon, downstream over our forecast area
H5 heights should rise through a good portion of the afternoon. As
the surface cyclone in the High Plains deepens, mass response is
expected into the lower Missouri River Valley that should enhance
low-level meridional flow in our area. Expecting this to boost
temperatures back into the mid 80s this afternoon, and should help
bring in an airmass with dewpoints in the mid 60s. Dewpoints this
morning have been sitting in the 50s across most of our forecast
area. As WAA kicks in, expecting a wing of isentropic ascent into
our area that will try to force a few light showers. However, 850-
700mb flow turns more southwesterly as the mid-level short-wave
begins to move eastward, and helps to setup a stronger EML from
eastern Kansas into Central Missouri. The drier air may be enough to
prevent shower activity as isentropic ascent occurs, given the
antecedent lower dewpoints this morning. GEFS and other ensemble
members do have around 30-40 percent probabilities for rain of at
least 0.01" through the afternoon, but are less than 10 percent for
a threshold of 0.10 inches of QPF. Have added in slight chance POPs
through this afternoon the strongest theta-e advection is on going.
00z HREF mean QPF is very low. Strong EML should create a strong cap
through most of the afternoon, so even as convergence increases with
the deepening cyclone, should inhibit most convective potential in
our area. The HRRR along with other CAMs do hint at some light
activity, but do not produce much in the way of QPF within the wing
of WAA. The main event for our area will be the arrival stronger H5
height falls, increased cyclonic vorticity advection and approach of
the cold front developing a QLCS/MCS. CAMs have been developing
convection over Central Nebraska around 01z and then gradually
expands southward into Kansas, and reaches our western and
northwestern counties after 06z and continues eastward into Friday
morning. Warm sector SBCAPE will likely be in the realm of 1750-2250
J/kg, per HREF mean, though could potentially be as high as 3000
J/kg as indicated by recent runs of the RAP. Using the 0-6km layer
as a proxy for deep layer shear, looking at values along the cold
front around 30-40 kts, with the vector oriented parallel to it. 0-
3km CAPE values steadily increasing to over 100 J/kg ahead of the
cold front (prior to any outflow boundaries shooting ahead of any
QLCS/MCS). Therefore, both the synoptic pattern and potential
mesoscale environment late Thursday into early Friday morning should
support upscale growth, and enough shear to keep it organized over
the Plains. Once again, our forecast area finds itself in a scenario
where the QLCS may start to weaken, given the cold pool may start to
get ahead of the better deep layer shear environment, which may be
mostly post-frontal by the time it gets to our area. However if it
is not outflow dominant, may be able to tap into some of the energy
and have enough convergence to overcome the cap. If storm mode
remains linear and and is not quite outflow dominant, severe winds
of 60 MPH would be the primary concern. With preceding EML in place
and if there is a large degree of boundary layer mixing, which a few
model soundings have been hinting at, perhaps localized RIJ
development could foster some wind gusts of 70 MPH+, especially for
our northwest MO counties. However, a stabilizing layer boundary
layer may greatly reduce this. Perhaps localized hail could be
realized with steeper mid-level lapse rates but thinking linear
storm mode inhibits this. With respect to tornado potential, the 0-
3km bulk shear magnitude sits right around 30-35 kts immediately
ahead of the progged line and is oriented mostly parallel it, thus
overall would make mesovortex genesis hard to come by unless a
stronger RIJ surge can oriented a portion of the line from northwest
to southeast. While typing this discussion, the 06z HRRR has been
coming in, and noticing at least in the simulated reflectivity
field, that most of the activity in southeast Nebraska dissipates
while remaining portion of the QLCS moves into Iowa. However, will
not buy yet into just one solution given the increasing synoptic
support, LLJ this evening, and expected moisture transport preceding
the cold front arrival.

Friday morning into Friday afternoon, cold front continues to move
through and is expected to continue to produce precipitation, though
main QLCS/MCS complex at this point should be breaking apart and not
posing a severe weather hazard. GEFS and other ensemble suites
continue to paint 90+ percent probabilities for rainfall into Friday
afternoon, with 40-50 percent probabilities for exceeding 0.10
through about 22z on Friday. 00z HREF mean QPF values hold generally
around 0.75 to 1.00 inches for a 24 hour total from Thursday Night
through Friday evening across our area, with our northwest counties
with the heavier pockets. Localized probability matched mean values
from the 00z HREF produce about 2.00 inch of QPF, which seems a
reasonable high end if a few isolated cores become efficient
rainfall producers. There may be some low end severe potential later
into the afternoon on Friday mainly east of Interstate 35 if there
is any kind of clearing that could help destabilize the boundary
layer, our if a remnant outflow boundary promotes stronger
differential heating. However, any severe threat for winds around 60
MPH and hail to around quarter size will be conditional on mesoscale
factors modifying the environment. This is highlighted by the SWODY2
marginal risk for roughly the southeast third of our CWA. Main cold
front should completely clear our area Friday evening. Another short-
wave perturbation ejects across the Rockies and should help promote
H5 height rises through the early afternoon on Saturday, providing a
break from precipitation. However, heading into Saturday evening,
this short-wave trough will be another opportunity for active shower
and thunderstorm activity across our area.

Short-wave trough Saturday morning over the Front Range results in
compact mid-level vorticity maxima likely to promote stronger dCVA
and robust ageostrophic motions developing a stronger surface
cyclone across the Central Plains. Flow ahead of this will turn
southerly again and provide stronger theta-e advection into our
forecast area through Saturday afternoon. The bulk of the afternoon
right now appears dry, as most deterministic model guidance depicts
localized subsidence within the area of H5 height rises. Perhaps
some light precipitation could be squeeze out within the WAA wing
earlier in the day, but GEFS and other ensemble suites maintain very
low probabilities for any measurable precipitation during this time
frame, and focus higher probabilities late in the evening on
Saturday through Sunday morning. Mid-level height falls and cyclonic
vorticity advection should pick up in pace through Saturday evening,
as surface cyclone tracks eastward across the Central Plains.
Surface pressure falls and convergence increases late into the
evening. Once again, a strong EML likely sits atop a moist boundary
layer, with warm front positioned between Interstate 70 and Hwy. 36.
If this positioning does not change, this could lead to some
discrete convection that develops. However, this late in the
evening, LLJ likely results in faster upscale growth into some kind
of MCS. With the stronger kinematics and deep layer shear
overspreading the progged warm sector though, would think an
organized MCS could bring stronger winds and longer hodographs that
could support maintenance for a longer period of time. We will have to
see how the mesoscale pans out and the timing of the short-wave
trough ejecting out of the Plains to better pinpoint the threat, but
for right now would be concerned about the potential for warm front
with stronger low-level vorticity being present at the onset of
storms, and then robust upscale growth through the evening. Will
also have to be on the lookout for hydrologic issues should an MCS
stall, though with the stronger mid-level flow may help in making
any kind complex progressive and reduce storm training. For right
now, expect adverse weather late Saturday, and once we see how the
Friday activity clears out may be able to better pinpoint more
mesoscale details.

In the extended, deterministic guidance continues to depict rather
progressive flow through the middle of the week that will bring
additional rain shower and thunderstorm chances. Deterministic GFS
currently places a robust vorticity maxima with H5 trough Monday,
though speed and phasing the the system is not totally in line with
deterministic ECMWF. There are multiple periods of increase
probabilities amongst ensemble members through next week. A box and
whiskers and plot for temperatures through next week shows wider
spread, which is likely attributed to timing differences in
convection timing and when diabatic heating and evaporation cooling
are dominant.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1237 PM CDT Thu May 23 2024

VFR conditions continue thru midnight. TSRA expected starting
near sunrise through Fri AM. Conditions are expected to
deteriorate rapidly as a line of TSRA moves thru the terminals
around sunrise Fri morning. High winds are expected with storms.
Once the line passes, winds shift NW remaining gusty thru the
period. VFR conditions return midday into early Fri PM.

&&

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

&&

$$

DISCUSSION...Krull
AVIATION...Pesel