Mesoscale Precipitation Discussion 1219
NWS Weather Prediction Center College Park MD
424 AM EDT Mon Sep 07 2026

Areas affected...Northwest Iowa...Extreme Southeast South
Dakota...

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

Valid 070825Z - 071300Z

SUMMARY...Near stationary over-running cells capable of 1-1.5"/hr
rates and highly focused 2-4" totals across areas of reduced FFG. 
Localized flash flooding remains possible through early morning.

DISCUSSION...A narrow window of weak but sufficient isentropic
ascent has broken out elevated convection across the narrow stripe
of recently affected areas where FFG values remain well below
normal and less than <1.5"/hr and <2"/3hrs.  GOES-E 10.3um and
3.9um SWIR IR loops combined with VWP out of FSD/OAX denote rapid
veering with westerly 700mb winds at 20kts from the west are
fairly orthogonal to the SSE to NNW surface to 850mb frontal zone
across eastern NEB resulting in convergence around or just below
the 700mb level with increase in congestus eventually blossoming
to a few CBs in NW IA with further weaker more scattered
convection further south into SW IA.  The orientation of the
boundary also resides on the NE side of a 500-1000 J/kg MUCAPE
(per RAP soundings) gradient that also aligns with the compromised
soil conditions.  RAP CINH fields are still showing more CINH
further south and higher CAPE upstream into SE SD.  A few TCu
exist there, but FFG values also rapidly increase across Yankton
to Miner counties; so have limited the areal extent for potential
additional flash flooding to those areas where FFG values remain
low.

Westerly winds are expected to remain but weaken slightly over the
next few hours, so most of the expected weakening past 12z will be
due to exhausting the remaining uncapped mid-level unstable air
upstream.  With limited cell motion and inflow generally equal and
opposite to the mean steering from 700-400mb, cells are likely to
remain somewhat stationary with slight back-building possible.  As
such, highly focused areas of 2-4" over the next 3-4 hours are
possible and given the low FFG, localized flash flooding.

Gallina

ATTN...WFO...DMX...FSD...OAX...

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

LAT...LON   43509698 43339595 42979523 42399451 41579402
            40939447 41079541 42429639 43179712