Mesoscale Precipitation Discussion 0903
NWS Weather Prediction Center College Park MD
245 AM EDT Mon Aug 11 2025

Areas affected...Southern Kansas and far Northern Oklahoma

Concerning...Heavy rainfall...Flash flooding likely

Valid 110644Z - 111200Z

Summary...An MCS moving across southern Kansas will interact with
an outflow boundary/stationary front to enhance convection through
early morning. Rainfall rates of 2-3"/hr are expected, which
through training could produce 3-4" of rain with locally more than
6" possible. Flash flooding is likely.

Discussion...The regional radar mosaic early this morning shows
expanding thunderstorms with heavy rainfall stretching across much
of southern Kansas and far northern Oklahoma. Within this
convection, dual MCVs are noted moving eastward, with a potent MCS
associated with the leading MCV pushing into central KS. This MCS
will continue to track eastward through the morning, interacting
with downstream convection, and leaving a residual outflow
boundary, to persist and intensify rainfall.

Thunderstorm activity is being driven by an impressive overlap of
synoptic and mesoscale ascent. A large-scale mid-level trough axis
is advecting eastward from the High Plains to produce broad height
falls, while an upper jet streak intensifies downstream to place
favorable RRQ diffluence atop the Central Plains. This deep layer
ascent is being enhanced by a strengthening southerly 850mb LLJ
measured via VWPs at KICT/KVNX to be 30-35 kts. This LLJ has
exhibited rapid strengthening and broadening the past few hours,
which is helping to intensify the thermodynamic environment by
drawing PWs of 1.8-2.0 inches and MUCAPE of 2000 J/kg northward to
support ongoing convection. Additionally, this LLJ is
isentropically ascending the hybrid outflow boundary/stationary
front analyzed by WPC to provide enhanced mesoscale lift.

While the CAMs are struggling to resolve the exact evolution of
the current radar, the recent HRRR and ARW have at least a better
handle on the positioning/timing of the features leading to
increased confidence in their output the next several hours. These
suggest that the LLJ will remain primarily from the south
overnight, with some local acceleration possible immediately
downstream of the MCV. As this occurs during the MCS translation
to the east, it will result in persistent and slow moving
thunderstorms downstream (Corfidi vectors collapsed to just around
5 kts) until the MCS sweeps through by morning. Additional
convective development is likely along other outflow boundaries as
well, further lengthening the duration of rainfall in some areas.
With thermodynamics supporting rainfall rates of 2-4"/hr (30-40%
chance of 3"/1hr from the WoFS, and HRRR 15-min rainfall as much
as 1"), rapid runoff is likely even despite 0-10cm soil moisture
from NASA SPoRT that is below the 20th percentile.

Most concerning, however, is the threat for training or slowing of
these intense rain rates. The HREF PMM and WoFS 90th percentile
rainfall by 12Z are quite well aligned with a maxima across
Kingman, Barber, and Harper counties, KS. Here, both these systems
predict as much as 6-7 inches of rainfall, with a broad swath of
2-5" (10-30% chance from the HREF) surrounding it and stretching
as far east as the KS/MO border. This indicates that flash
flooding is likely in many areas overnight, with an isolated
significant impact possible if these higher amounts occur over a
more vulnerable location.

Weiss

ATTN...WFO...AMA...DDC...ICT...OUN...SGF...TOP...TSA...

ATTN...RFC...KRF...TUA...NWC...

LAT...LON   38759928 38669773 38549705 38339627 38089551
            37779511 37419496 36919484 36559505 36059620
            36169750 36389914 36440071 36530111 36850170
            37400139 38060091 38550011