377
AWUS01 KWNH 301644
FFGMPD
KSZ000-NEZ000-SDZ000-302215-

Mesoscale Precipitation Discussion 1032
NWS Weather Prediction Center College Park MD
1243 PM EDT Sat Aug 30 2025

Areas affected...central SD into east-central NE

Concerning...Heavy rainfall...Flash flooding possible

Valid 301640Z - 302215Z

SUMMARY...Slow moving cores of heavy rainfall are expected from
central SD into east-central NE over the next 3-6 hours. Hourly
rainfall of 1 to 2 inches can be expected at times, which may
produce a couple of areas of flash flooding.

DISCUSSION...Water vapor imagery from GOES East showed a complex
pattern across the central U.S. with a number of mid-level
vorticity maxima extending from the Dakotas into NE. Upstream, a
longwave trough axis was noted across WY to the UT/CO border,
advancing east with small scale vorticity maxima embedded within
the southwest flow out ahead across the High Plains. Low to
mid-level analyses showed a nearly stationary low over
west-central SD, associated with a slow moving cyclonic swirl of
heavy rain centered over Haakon County with MRMS-derived rainfall
rates of 1 to 2+ in/hr ending 14 and 15Z, though recent rates have
lowered to about 1 in/hr. A trough axis extended SSE from the low
into central NE with widely scattered showers and thunderstorms
over the NE Sandhills into portions of east-central NE.
Satellite-derived precipitable water imagery indicated that a
tongue of higher moisture extended northward through the central
Plains into central SD, ahead of the quasi-stationary low. OSPO
LPW imagery showed low level components of this moisture plume
from the southern Plains and mid to upper level components from
the Southwest, including remnant moisture from former T.S.
Juliette in the eastern Pacific. The remnant tropical moisture
could be a factor in enhancing rainfall efficiency this afternoon.

As the longwave trough axis passes across the central Rockies this
afternoon, downstream diffluence will increase over NE and
southern SD, helping to increase ascent. While the low over SD is
not expected to move through 22Z, the southern extension of the
trough into NE should swing east and possibly develop with a
secondary low center. Mesoscale circulations within this pattern
are expected to support slow moving cores of heavy rain.

One negating factor is the presence of weak instability with 16Z
SPC mesoanalysis data showing only 500-1000 J/kg MLCAPE over parts
of SD and western NE and less than 500 J/kg over eastern SD/NE.
Widespread cloud cover may limit the development of higher
instability over central to eastern SD/NE later this afternoon,
capping rainfall intensity. However, the favorable moisture axis
and slow movement of rainfall may still allow for localized
pockets of 1-2 in/hr rates and possible flash flooding over the
next 3-5 hours.

Otto

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...ABR...FSD...GID...LBF...OAX...UNR...

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

LAT...LON   45730200 45630108 44879969 43389808 41789709
            41009706 40149768 39939835 40019874 40279901
            40509918 40679930 41209947 41509951 41679949
            41799940 41799920 41739899 41679883 41579861
            41709841 41729829 41849810 42229811 42369826
            42559871 42699978 42950061 43430136 43590166
            44300289 45170313 45490274