WPC Met Watch |
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Mesoscale Precipitation Discussion: #0692 (2018) |
(Issued at 458 AM EDT Sun Aug 19 2018
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MPD Selection |
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Mesoscale Precipitation Discussion 0692
NWS Weather Prediction Center College Park MD
458 AM EDT Sun Aug 19 2018
Areas affected...Eastern North Dakota, Northeast South Dakota,
Northwest Minnesota
Concerning...Heavy rainfall...Flash flooding possible
Valid 190856Z - 191440Z
Summary...Thunderstorms had rapidly developed between 2 AM and 4
AM CDT across eastern North Dakota, near a front in the low levels
of the atmosphere. As the front is expected to move very little in
the next several hours, these storms should stay anchored in the
region and could produce locally heavy rainfall where they can
persist. Rain rates 2 in/hr are likely, and that could lead to
flash flooding over the eastern Dakotas.
Discussion...KMVX radar showed a significant uptick in convective
coverage and intensity between 07Z and 09Z, and GOES-16 showed
cooling cloud tops (IR channels) and increasing lightning activity
(GLM). All these signals were consistent with increasingly
organized thunderstorm activity just ahead of a surface front, and
along a low-level deformation zone. RAP analysis places an 850mb
low in east-central South Dakota, with a deformation zone
extending northeast from there. Precipitable water values in this
region to the northeast of the low were elevated, and generally
around 1.6 to 1.7 inches. A ribbon of instability also existed in
the same region, with MUCAPE values around 2000 j/kg. The low is
expected to be nearly stationary into the mid-morning hours, and
the associated deformation zone may only shift slightly to the
southeast. This should maintain fairly strong low-level forcing in
a corridor with a moist, unstable air mass, and thus convection
should be able to persist for at least several more hours. As
convection becomes focused along the deformation zone, it could
begin to train over some areas and lead to swaths of heavy
rainfall. MRMS and KMVX dual pol estimates showed rain rates
approaching 2 in/hr already and KJMS reported 1.70 inches of rain
in just 23 minutes (0820-0843Z), so the rain rates could
conceivably exceed 2 in/hr in the heaviest rain bands. These rain
rates could produce flash flooding, particularly if they were
sustained in an area for longer than an hour. Although the
greatest concentration of convection is in eastern North Dakota at
the moment, additional convection may fill in across northeast
South Dakota in the next few hours as the low becomes better
established.
Lamers
ATTN...WFO...ABR...BIS...FGF...
ATTN...RFC...MBRFC...NCRFC...
LAT...LON 48489610 47049601 45319685 44739841 44969992
46349994 47709825
Last Updated: 458 AM EDT Sun Aug 19 2018
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