671
AWUS01 KWNH 211202
FFGMPD
MNZ000-SDZ000-NDZ000-211800-

Mesoscale Precipitation Discussion 0296
NWS Weather Prediction Center College Park MD
802 AM EDT Tue May 21 2024

Areas affected...Eastern SD...West Central MN...Far Southeast ND

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

Valid 211200Z - 211800Z

SUMMARY...Several hours of heavy and efficient rainfall rates that
can approach 1"/hr may result in flash flooding this morning,
especially low lying spots and in areas with sensitive soils.

DISCUSSION...A potent 500mb trough over eastern CO is taking on a
negative tilt this morning, resulting in a blossoming baroclinic
leaf signature over the Midwest on GOES-16 water vapor imagery.
This is further enhanced by the region lying beneath a dual-jet
structure at 250mb with the divergent right-entrance region of a
130kt jet streak over south-central Canada paired with the
divergent left-exit region of a 110kt jet streak in the southern
High Plains. Exceptional synoptic scale forcing will work in
tandem with 925-850mb frontogenesis that is oriented from SW-NE
from southeast SD to central MN and becoming more and more
pronounced by the hour according to RAP mesoanalysis.

The frontogenesis is a byproduct of not only strengthening WAA
within that layer, but also a quickly strengthening IVT over the
Nation`s Heartland. NAEFS shows IVT values in southern MN and
eastern SD that are as high as 500 kg/m/s around 12Z this morning.
By 18Z, the IVT values in central MN will surpass 750 kg/m/s and
be well above the 99.5 climatological percentile. As the morning
unfolds, the moisture out ahead of the developing 850mb low will
eventually wrap around the northern and western flanks of this
low, eventually leading to a robust deformation axis that will
envelope most of the highlighted region. Instability will
generally be elevated and not in abundance given the thick cloud
cover and the precipitation shield occurring on the opposite side
of the where the warm sector will be. That being said, model
soundings from the RAP/HRRR/3kmNAM all suggest warm cloud layers
will be 9,000ft deep or even deeper in some cases with low-mid
level RH values >90%. This will support highly efficient rainfall
rates despite the absence of deep convection this morning and
through midday.

The 06Z HREF`s 6-hr LPMM between 12-18Z that depicted >2" amounts
near the border of northeast SD and western MN. Note that for some
areas, especially the area just referenced, the pivoting axis of
the deformation zone will likely continue beyond 18Z and may
require a follow up MPD depending upon how much rainfall will have
occurred this morning. FFG`s may not be surpassed in the 1-hr
timescale, but 3-hr FFGs in some areas are 1.5-2.0" and hourly
rainfall rates could range between 0.75-1.00"/hr this morning.
Storms in central MN have already produced as much as 0.60"/hr
rainfall rates and the best moisture advection has yet to occur.
With all that said, there is the potential for flash flooding in
the more flood prone areas where soils are more sensitive and in
lower lying areas.

Mullinax

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

ATTN...WFO...ABR...DLH...FGF...FSD...MPX...

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

LAT...LON   46759453 46269378 45679409 45089490 44519578
            43539665 43029715 43099811 43769828 45029781
            45979676 46609548