Weather Prediction Center issues Mesoscale Precipitation Discussion #768 concerning HEAVY RAINFALL...FLASH FLOODING LIKELY292
AWUS01 KWNH 210006
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KYZ000-INZ000-ILZ000-MOZ000-IAZ000-210605-
Mesoscale Precipitation Discussion 0768
NWS Weather Prediction Center College Park MD
805 PM EDT Sun Jul 20 2025
Areas affected...North-Central to Northeast MO...Central
IL...Southern IN
Concerning...Heavy rainfall...Flash flooding likely
Valid 210005Z - 210605Z
SUMMARY...Heavy showers and thunderstorms will be developing and
expanding in coverage going through the evening hours. High
rainfall rates and some cell-training concerns are expected to
drive an increasing threat of flash flooding.
DISCUSSION...The late-afternoon GOES-E IR satellite imagery shows
a few convective clusters beginning to organize and grow upscale
across portions of central IL through southern IN. The convection
is initiating along a well-defined surface trough/outflow boundary
where there is a substantial pool of moisture and instability.
MLCAPE values along and just south of the boundary are as high as
2000 to 3000+ J/kg from eastern MO through southern IN, with PWs
across the region of 2.0 to 2.25 inches. The environment is also
somewhat sheared with as much as 20 to 30 kts of effective bulk
shear in place. Some weak mid-level vort energy is also aligned in
a west to east fashion across the region from earlier convective
activity.
Going through the evening hours, a gradual increase in convection
is expected as additional upstream vort energy arrives and couples
with increasingly convergent low-level flow near this outflow
boundary. A nearby front just to the north will also be aiding in
the overall convergent low-level flow regime, and this will be
supported by some increase in right-entrance region upper jet
dynamics by late this evening.
In the near-term the convection should tend to be more focused
over central IL and southern IN, but gradual development is
expected farther west across areas of north-central to northeast
MO and into west-central IL by later this evening.
Concerns will tend to grow in time for there being multiple
clusters/bands of heavy showers and thunderstorms that will be
capable of training over the same area. Rainfall rates are
expected to be very high given the thermodynamic environment and
relatively organized nature of the thunderstorms. Some rates may
reach 2 to 3 inches/hour, with rainfall totals by 06Z (1AM CDT) of
as much as 3 to 5 inches possible which is supported by some of
the 18Z HREF and 12Z REFS guidance. These rains are likely to
produce areas of flash flooding, and some potential for locally
significant urban flash flooding may grow in time, and especially
after this period as additional heavy rainfall threatens the area.
Orrison
...Please see www.wpc.ncep.noaa.gov for graphic product...
ATTN...WFO...DVN...EAX...ILN...ILX...IND...LMK...LSX...PAH...
ATTN...RFC...KRF...MSR...TIR...NWC...
LAT...LON 40559143 40418990 40178850 39788678 39148507
38308519 38088675 38098837 38379036 38979313
39489405 40219407 40509293
Source:
Weather Prediction Center issues Mesoscale Precipitation Discussion #768 concerning HEAVY RAINFALL...FLASH FLOODING LIKELY---------------
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