Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Thu Jun 22 2023 18:54:04

AWUS01 KWNH 221853
FFGMPD
MNZ000-SDZ000-NDZ000-230045-

Mesoscale Precipitation Discussion 0563
NWS Weather Prediction Center College Park MD
252 PM EDT Thu Jun 22 2023

Areas affected...Eastern SD...Southeast ND...Western MN

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

Valid 221850Z - 230045Z

SUMMARY...Blossoming thunderstorms along and ahead of a frontal
boundary may pose a flash flood threat this afternoon. Urbanized
locations and sensitive soils are most at-risk.

DISCUSSION...GOES-16 visible imagery and GLM overlay showed a
growing field of developing thunderstorms strteching along a front
extending from northern NE to western MN. The region also lies
beneath the diffluent right-entrance region of a 250mb jet streak
centered over lower Hudson Bay. The atmosphere has grown
increasingly unstable thanks to daytime heating and will continue
to destabilize. RAP forecasts suggest 1,000-2,000 J/kg of MLCAPE
will be at these storms disposal. Moisture is also plentiful
across the region. The 12Z ABR sounding sported a handful of
parameters that were at or above the 90th climatological
percentile that included PWATs, sfc-3km mixing ratio, and surface
dew point. RAP forecast show up to 1.75" PWATs in central SD but
1.25-1.5" will be more commonly observed along the front within
the highlighted area.

The combination of ample moisture at low levels and freezing
levels will result in unusually deep warm cloud layers. RAP
forecasts in northeast SD showed warm cloud layers could approach
9,000-10,000' in depth, providing these storms with adequate tools
necessary to contain warm rain processes. Mean 850-300mb wind are
also oriented parallel to the front, suggesting the potential for
repeating rounds of storms across the area. Vertical wind shear is
not overly impressive, but up to 20 knots of effective bulk shear
may be enough to maintain these storms long enough to allow storms
to generate 2"/hr rainfall rates.

Portions of central SD are most sensitive to possible flash
flooding where 1-hr FFGs are as low as 1.0-1.5". Most other
locations are closer to 2"/hr levels for 1-hr FFGs, making the
flash flood threat much more isolated. Aside from the sensitive
soils in central SD, urbanized communities that contain a greater
concentration of hydrophobic surfaces are also at a heightened
risk for flash flooding.

Mullinax

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!8Rqgro1EFcW2lddc_oASx0b2dTmKs41HaZfUtuIyjzg5qPJocxfLa80KGQOcJGd2H_yp=
EYetRRrxrcX6QPaiJ_GS3N0$  for graphic product...

ATTN...WFO...ABR...BIS...FGF...FSD...MPX...UNR...

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

LAT...LON   46909582 46179511 43489733 43140008 44050073=20
            45179998 46109857=20

=3D =3D =3D
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