341
AWUS01 KWNH 180026
FFGMPD
WIZ000-MNZ000-IAZ000-SDZ000-180600-

Mesoscale Precipitation Discussion 0456
NWS Weather Prediction Center College Park MD
826 PM EDT Mon Jun 17 2024

Areas affected...Southern Minnesota, eastern South Dakota

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

Valid 180019Z - 180600Z

Summary...Showers and thunderstorms will increase in coverage this
evening and begin to train along a surging warm front. Rainfall
rates in excess of 2"/hr are likely at times, which could produce
2-4" of rain with locally higher amounts. Flash flooding is
possible.

Discussion...Showers and thunderstorms are expanding across
portions of MN this evening as reflected by rapidly cooling cloud
tops in the GOES-E IR imagery collocated with strengthening
reflectivity via the regional radar mosaic. This activity is
building in response to pronounced ascent due to the favorable
positioning of the RRQ of an upper jet streak, a shortwave noted
lifting out of SD, and increasing isentropic upglide atop a
surface warm front analyzed by WPC from northern NE through
western WI. Together these are producing strong lift into a
favorable thermodynamic environment characterized by PWs of around
1.7-1.8 inches, and a sharp SBCAPE gradient to as high as 4000
J/kg over northern NE. Rainfall rates within ongoing convection
are already estimated to be 1-1.5"/hr.

The CAMS are struggling to initialize the current activity, as the
latest reflectivity is much more widespread than the models
indicate it should be. This reflects how potent the environment is
for thunderstorm development, and the ingredients based approach
indicates thunderstorms will continue to develop through the
evening as the front begins to lift northward. The setup supports
widespread development along and north of the warm front, with
activity becoming more intense as the 850mb LLJ rises to 50-60 kts
from the south, pegged above +6 sigma from the SREF, surging
extreme moisture flux into the region. This will reinvigorate
convection generally along the warm front where lift is most
intense, while the additional synoptic lift results in widespread
thunderstorms across the discussion area. Additionally, this
surging LLJ will result in veering and collapsing Corfidi vectors
in the next few hours, and signals are strong for back-building
convection to the SW along the warm front, with cells then
training N/NE at 15-25 kts. The lack of model support for the
current activity indicates that the HREF probabilities are likely
too low, but even they already suggest rain rates will eclipse
2"/hr at times, and where backbuilding/training occurs this has a
10-20% chance for as much as 5" of rainfall in the next 6 hours.

Despite the uncertainty in the model output, the ingredients
suggest instances of flash flooding are likely due to the heavy
rates and training potential. Additionally, soils across this
region are saturated from recent rainfall that has been 2-4" in
the last 24 hours, and around 300% of normal the last 7 days. This
has compromised FFG to 0.75-1.5"/3hrs, which will likely be
exceeded, causing at least scattered instances of flash flooding.


Weiss

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

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

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

LAT...LON   45939554 45909406 45469317 44849275 44259297
            43769420 43379537 43169668 43239804 43759887
            44179886 44539855 45119790 45669678