405
AWUS01 KWNH 210228
FFGMPD
WIZ000-MNZ000-IAZ000-210800-

Mesoscale Precipitation Discussion 0293
NWS Weather Prediction Center College Park MD
1027 PM EDT Mon May 20 2024

Areas affected...Southern MN...Northern IA...

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

Valid 210230Z - 210800Z

SUMMARY...Slow moving thunderstorms continue to proliforate with
strengthening moisture flux to increase rainfall efficiency.
Localized rates of 1.5-1.75"/hr and slow motions may support
widely scattered 2-3" totals resulting in localized flash flooding
incidents overnight.

DISCUSSION...As stronger shortwave continues to exit through the
Great Lakes, generally flat west-southwesterly flow exists across
the Upper Mississippi Valley with the approach of stronger
height-falls emerging from in the Central High Plains.  Between, a
subtle shortwave in the Missouri Valley supports a weak surface to
boundary layer wave in proximity to NW IA with well defined
stationary front across N IA toward a wave in SE MN.  Moisture and
instability has pooled along the boundary with 1.25" total PWATs
and 2000 J/kg of MLCAPE.  Localized convergence sparked widely
scattered cells along the front from near Dodge county to Kossuth
to Clay and Cherokee counties in IA.  Favorable environment with
upstream back-building (as upstream shortwave approaches) helps to
replace updrafts just upstream resulting in very slow effective
cell motions.  Given unobstructed south to southeasterly (even
easterly in SE MN) inflow of this modestly moist and unstable air
to sustain the updrafts; flow is expected to increase as noted by
regional VWP already seeing a 5-10 increase across IA/W WI/SE
MN... to allow for increasing moisture flux and rainfall
production.  Rates of 1.5-1.75" should be expected and with slow
motions to allow for widely scattered but localized 2-3+" totals
that would exceed the 3hr lower FFG in the region (generally
1.7-2.2"/3hr).

Upstream, the shortwave in the Missouri valley is providing
further DPVA and strengthened inflow resulting in broader vertical
ascent across NW IA into SW MN. Cells will continue to strengthen
but are also likely to have increasing forward (east-northeast)
cell motions as the wave lifts out.  Still rates of 1.75-2"/hr are
possible resulting in streaks of 2-3" as they pass.  Additionally,
this may allow for cell repeating or even merge with downstream
slower moving cells resulting in the higher localized rainfall
totals with increased potential for higher run-off and possible
flash flooding.

Gallina

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

ATTN...WFO...ARX...DMX...FSD...MPX...

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

LAT...LON   44739317 44649192 44009142 43669160 43349199
            42669339 42059450 42259570 43499639 44019593
            44419494 44589436