Mesoscale Precipitation Discussion 0479
NWS Weather Prediction Center College Park MD
1105 AM EDT Fri Jun 21 2024

Areas affected...Northern NE...South-Central to Southeast
SD...Northwest IA...Southern MN

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

Valid 211505Z - 212105Z

SUMMARY...Redeveloping bands of heavy showers and thunderstorms
are expected going through the early to mid-afternoon hours. These
rains are expected to largely fall over areas that have seen very
heavy rainfall recently, and are therefore extremely sensitive to
additional rains. Given the wet/saturated conditions on the
ground, instances of renewed flash flooding are likely heading
into the afternoon hours.

DISCUSSION...A wavy quasi-stationary front remains draped across
the region from central NE through northern IA with multiple waves
of low pressure riding east along it. In the wake of overnight
convection, there has been a relative lull in activity over the
last couple of hours, but the latest GOES-E IR satellite imagery
and dual-pol radar data does show a couple of new linear bands of
elevated convection beginning to focus across northern NE and also
southeast SD, far northwest IA, and southwest MN.

Some additional expansion of elevated convection north of the
front is expected going through mid-afternoon as shortwave energy
gradually ejects east out across the High Plains and helps
facilitate some larger scale ascent/divergent flow aloft along
with a persistent southerly to southwest low-level jet of 20 to 30
kts overrunning the front and yielding isentropic ascent and
frontogenetical forcing.

MUCAPE values in vicinity of the regenerating rounds of convection
are on the order of 500 to 1000 J/kg, with a very moist
environment (PWs around 1.75 inches) in place that is supportive
of efficiently heavy rainfall rates. Going through the
mid-afternoon hours, some of the stronger elevated storms may
drive rainfall rates upwards of 1.5 to 2 inches/hour. Some
cell-training is expected given the orientation of the convection
with the deeper layer west-southwest mean layer flow.

The new 12Z HREF guidance is suggesting the potential for as much
as an additional 2 to 4 inches of rain with isolated heavier
amounts going through mid-afternoon. Given the wet/saturated soil
conditions, elevated streamflows, and lingering impacts from heavy
rainfall last night, these additional rains over the next several
hours are highly likely to renew areas of flash flooding. This
will especially be the case along portions of the I-90 corridor
from southeast SD through southern MN including the Sioux Falls
vicinity.

Orrison

ATTN...WFO...ABR...ARX...DMX...FSD...LBF...MPX...OAX...UNR...

ATTN...RFC...MBRFC...NCRFC...NWC...

LAT...LON   44799457 44699254 44239183 43699208 43249344
            42919612 42399845 42170010 42340135 42930149
            43490063 44019907 44469696