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AWUS01 KWNH 281635
FFGMPD
MNZ000-IAZ000-SDZ000-NDZ000-282100-

Mesoscale Precipitation Discussion 0684
NWS Weather Prediction Center College Park MD
1235 PM EDT Sun Jul 28 2019

Areas affected...eastern SD...extreme southwestern ND...west
central MN

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

Valid 281634Z - 282100Z

Summary...Increasing synoptic scale ascent along with a
strengthening low-level jet is expected to support the potential
for heavy rainfall, with 2-3 inches possible through the next
several hours. Flash flooding is possible.

Discussion...A mid-level MCV evident is evident in radar imagery
late this morning across eastern South Dakota, and was aiding in
the production of a stratiform rain shield with a few embedded
elevated thunderstorms in a relatively stable air mass north of a
quasi-stationary frontal boundary from eastern South Dakota into
Minnesota. South of this frontal boundary, moderate instability
was in place across much of Iowa, with MUCAPEs in the 1000-2000
J/kg range. Ahead of a developing surface low across southeastern
South Dakota, a highly moist air mass was in place along the
surface front, with PWs in the 1.7-1.9 inch range (+2 to +3
standard deviations). Latest GOES-16 visible imagery suggests that
development of a low-level jet crossing the surface front has
begun, with a new burst of convective cells just north of the
front and ahead of the surface low across eastern South Dakota.
Dual-pol radar data from these cells indicate the existence of
warm-rain processes in some of the more robust cells, producing
estimated rainfall rates approaching 2 in/hr. Model data show a
50-60 kt upper-level jet streak extending from eastern North
Dakota into northern Minnesota, and GOES-16 infrared imagery
support this, with some degree of banding observed in high-level
clouds across this area. This places the region where the
developing LLJ is crossing the surface front in the divergent
right entrance region of the upper-level jet streak.

Hi-res models show general consensus that the low-level jet should
continue to strengthen over the next few hours, into the 40-50 kt
range, lifting moist and increasingly unstable air across the
surface front. Deep-layer wind shear of 35-45 kt along with the
divergent upper-level flow should aid in convective maintenance
and support occasional high rainfall rates in excess of 1 in/hr by
early afternoon, with the potential for 2 in/hr in some areas if
multiple convective cells are able to train over the same areas. A
broad consensus of hi-res guidance including the HRRR, WRF-ARW,
WRF-NMM, and NSSL-WRF all show areas of 2-3 inch rainfall amounts
across the outlined area through 21Z. These rainfall rates and
amounts could lead to areas of flash flooding.

Ryan

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

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

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

LAT...LON   46449596 46419519 46179454 45949389 45579357
            45089384 44759422 44139523 43289656 43129760
            43429872 44109881 44949818 45619758 46189667



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