803
AWUS01 KWNH 061557
FFGMPD
MNZ000-IAZ000-NEZ000-SDZ000-NDZ000-062155-

Mesoscale Precipitation Discussion 1214
NWS Weather Prediction Center College Park MD
1155 AM EDT Sun Sep 06 2026

Areas affected...Central/Eastern SD...Far Northeast NE...Northwest
IA...Southwest MN

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

Valid 061555Z - 062155Z

SUMMARY...A gradual increase in the concentration of heavy showers
and thunderstorms can be expected going through the afternoon
hours. A growing threat for scattered areas of flash flooding will
exist which may include some urban impacts.

DISCUSSION...The mid to late-morning GOES-E IR satellite imagery
shows broken areas of heavy showers and thunderstorms impacting
portions of central/southern SD and northeast NE, with separate
activity also noted more recently over parts of southwest MN and
adjacent areas of northern IA.

Much of the activity is associated with an ejecting shortwave
trough out across the central Plains which is gradually moving off
to the east while also interacting with a quasi-stationary front.
Warm air advection ahead of the shortwave coupled with a corridor
of strong elevated instability and the arrival of DPVA should set
the stage for a more expansive convective footprint by early to
mid-afternoon.

MUCAPE values near and just northeast of the stationary front are
on the order of 3000 to 4000 J/kg, and PWs are quite high with
values near 1.75 inches. This combination of moisture and
instability will support showers and thunderstorms with
increasingly heavy rainfall rates as stronger forcing/lift arrives
with the shortwave dynamics/divergent flow aloft.

The 12Z hires CAMs as a consensus supports rainfall rates capable
of reaching 2 to 3 inches/hour with the expanding corridors of
stronger storms. However, the growing concern over the next
several hours will be slow cell-motions and a favorable
environment for backbuilding and locally training convection as
suggested by the Corfidi upwind propagation vectors.

Some rainfall totals by mid-afternoon may reach as high as 3 to 5+
inches given the high rainfall rates and slow cell-motions, and
this is supported by the consensus of the 12Z hires CAMs. These
high rainfall totals will generally favor 1 and 3-hour FFG
exceedance (30 to 50+ percent probabilities).

Therefore, the threat for at least scattered areas of flash
flooding is expected to increase with time, with an emphasis on
eastern SD into southwest MN and northwest IA. This will include
concerns for urban impacts, and especially for areas near Sioux
Falls.

Orrison

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

ATTN...WFO...ABR...BIS...DMX...FGF...FSD...LBF...MPX...OAX...

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

LAT...LON   46079883 46029690 45589570 45129506 44289445
            43219412 41579445 41119605 42279765 43539904
            44370051 45540070