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141
FXUS63 KEAX 180758
AFDEAX

Area Forecast Discussion
National Weather Service Kansas City/Pleasant Hill MO
258 AM CDT Sat May 18 2024

.KEY MESSAGES...

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- Above Normal Temperatures

- Scattered Showers/Storms Saturday and Sunday

- Active Pattern Sunday Night through Wednesday, Severe Storms
  Possible
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&&

.DISCUSSION...
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Issued at 258 AM CDT Sat May 18 2024

Mid-level split flow regime continues with trough along the Gulf
Coast and negatively titled short-wave trough axis entering the
Northern High Plains early this morning. Strong surface cyclone has
been deepening across the Northern Plains in response to stronger
dCVA associated with the surface trough. A cold front is trailing
this system and will be propagating across the Central Plains into
portions of the Upper Midwest and middle Mississippi River Valley
this afternoon. This will present scattered shower and isolated
thunder potential later Saturday evening. Prior to that, secondary
short-wave perturbation over Colorado will help to push ridge axis
across the region during the late morning and early afternoon hours.
During the period of H5 height rises, subsidence should help to keep
skies mostly clear, while insolation slowly begins to destabilize
the boundary layer. Increased mixing, along with southwesterly 850mb
flow promoting WAA will allow temperatures to reach the mid to upper
80s across most of the area this afternoon. Inner-quartile spread
amongst NBM members and other ensembles remains narrow, and even the
10th-90th percentile differences are only around 4 to 5 degrees for
most forecast points. The H5 ridge axis clears the area by the late
afternoon, and subtle mid-level vort max is progged by some
deterministic model guidance to move over eastern Kansas and western
Missouri by 00z-02z timeframe. While this is approaching, the
northern short-wave trough will begin to lift into Canada, but
continued deepening will eventually result in surface pressure falls
this evening across the northwestern two-thirds of the CWA, and the
cold front travels to around the Iowa-Missouri stateline. This will
be enough to create modest convergence against a conditionally
unstable boundary layer that could force a few showers or storms.
Current HREF mean CAPE shows a narrow axis of 2000 J/kg directly
along the cold front across our area. The main question will be
moisture transport throughout the afternoon. While mixing may help
to steepen boundary layer lapse rates, it may lower dewpoints too
drastically. As a result, this would result in meager updrafts along
the narrow axis convergence, and only modest deep layer shear may
result in convective shower activity failing to organize. With the
potential for steeper boundary layer lapse rates, SWODY1 does put
our area in a marginal risk, as thunderstorm could produce a wind
gust to around 60 MPH. This is a very conditional threat. The HRRR
simulated reflectivity fields show weak convection between 01z-02z
across our area but does not continue much past sunset. The NAMNest
and FV3 core CAMs keeps the convection for longer but seems to be to
high with the moisture content that there will be to work with.
Overall, synoptic scale ensemble guidance probabilities for
measurable rain are generally around 20 percent but below 10 percent
for a threshold of 0.10 inches of QPF. Will maintain some
mentionable POPs in the forecast for early this evening, given the
forcing and boundary layer mixing that is anticipated.

Sunday, PV anomaly maintains troughing over the northwestern CONUS
providing continued southwesterly mid-level flow across our area.
Saturday`s short-wave perturbations moves toward the Great Lakes
Region, with another compact vort max ejecting out of Colorado into
the Central Plains. For the start of Sunday morning, this will
provide a period of subtle H5 height rises, and will stall the
thermal boundary likely somewhere in our northern forecast area. A
few weak showers may develop along this if there is still some
convergence but overall large scale ascent will remain absent for a
few hours. Current HRRR has some development between Hwy. 36 and the
Iowa border during Sunday afternoon along this boundary. Overall
ensemble probabilities Sunday afternoon for measurable precipitation
are around 20 percent for our northern CWA. Continued WAA will keep
temperatures in the 80s across most of the area, and inner-quartile
spread amongst members of most ensemble suites remains narrow. By
Sunday evening, mid-level vort max moves across our region providing
enhanced kinematic forcing within he area of H5 height falls. The
associated dCVA will support cyclogenesis across the Plains and will
turn low-level flow southerly across our forecast area, which should
provide more moisture support. This will also push the thermal
boundary further north into Iowa and will function as a warm front.
Increasing dCVA from Kansas into the lower Missouri River Valley
should increase large scale ascent through Sunday evening and into
Monday morning. New development is possible from far eastern Kansas
into Central Missouri, with steeper mid-level lapse rates from EML
potentially supporting a few storms that could produce hail around 1
inch and winds gusts to 60 MPH. Deep layer shear should be better
with this kinematic forcing and could help with further
organization. The main question though is how convection develops in
Kansas, where dryline activity could develop discrete storms that
eventually becomes and MCS and propagates eastward. Current HRRR
runs congeal convection into a strong MCS that crosses I-135 by 00z.
If this holds together, could produce wind gusts into the early
morning hours of Monday in our CWA. A lot of uncertainty though as
to how long this maintains itself, at least with respect to a wind
and hail threat for severe weather. Expecting heavier rainfall to
fall out of this, with ensemble probabilities for measurable
precipitation above 60 percent for the northwestern two-thirds of
the CWA by Monday morning. Deterministic guidance has a few pockets
of over 1" of rainfall across our north, though greater totals will
be closer to the warm front in portions of southeast Nebraska and
southern Iowa. Will need to watch for areas of training convection
and MCS propagation speed, which could lead to hydro/flooding issues
if this trends southward. Currently, SPC SWODY2 places our area in a
marginal risk, mainly for the the MCS coming in Monday morning
though activity Sunday afternoon across northern Missouri could
become problematic should there be a larger degree of
destabilization.

Monday afternoon, thermal boundary still lingers close to the area
as another vort max ejects out of Colorado as dCVA provides more
lift to continue surface cyclone development over the High Plains,
maintaining a stream of theta-e advection into our area. Isentropic
ascent with increasing moisture transport may support additional
shower development through the middle of the afternoon on Monday,
and ensemble probabilities for measure precipitation remain above 60
percent for much of the area through Monday afternoon. There may be
some diabatic processes that help bring in larger degrees of
destabilization on Monday afternoon that if shear remains strong on
the backside of exiting short-wave could support more organized
activity. However, confidence is rather low given that is will
largely depend on how the Monday morning MCS plays out.

Monday Night and into Tuesday, stronger short-wave trough and mid-
level vort max moves through the region, that provides deeper
surface pressure falls across most of the area and increases low-
level convergence. Deep layer shear will continue to increase as
this feature moves through and Tuesday early evening cold front
approaches the area that will support stronger organized activity.
Currently, mid-level lapse rates are shaping up to remain steep with
this environment. However, the timing of the main H5 trough axis
lifting still remains uncertain, and this will likely influence
storm mode for our area heading into Tuesday. Earlier  lifting
further west of the area may result in waiting for a linear
convective mode to develop along the cold front, present mainly a
wind threat. However, if the trough axis progresses further eastward
before lifting, may see more surface wind backing and and deep layer
shear oriented more perpendicular to the cold front that could
support a discrete a storm mode. For now, expecting active severe
weather on Tuesday but specific details remain to be seen. Given the
active days of convection expected Sunday and Monday, this may
greatly modify the eventual mesoscale environment through the
middle of the week. Regardless of convective hazards, ensemble
probabilities remain high for at least 0.25 inches of QPF through
Tuesday, with some deterministic guidance producing pockets of 1 to
1.5 inches of rainfall Tuesday into Wednesday. In addition to severe
thunderstorms concerns, this could also present flooding and other
hydrology related issues.

Additional short-waves continue to eject across the Central CONUS
through the middle of next week, that will bring additional
precipitation chances heading into the end of May.
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&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1228 AM CDT Sat May 18 2024

Overnight and during the morning skies will remain clear. There
is potential for some daytime cumulus development but bases will
remain VFR. Winds during the afternoon will be between 5 and 10
kts. Cold front starts moving toward the area later this
evening, and may force a few showers. Coverage at this time
appears limited, so will just place VCSH into the TAFs, and will
continue to monitor trends through the day.

&&

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

&&

$$

DISCUSSION...Krull
AVIATION...Krull