Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Fri May 12 2023 19:39:02

AWUS01 KWNH 121938
FFGMPD
SDZ000-NDZ000-130130-

Mesoscale Precipitation Discussion 0275
NWS Weather Prediction Center College Park MD
338 PM EDT Fri May 12 2023

Areas affected...west-central SD/ND

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

Valid 121933Z - 130130Z

SUMMARY...Isolated flash flooding may occur across central and
western portions of the Dakotas through 01Z. Rainfall rates of 1-2
in/hr and storm totals of 2-4 inches are expected.

DISCUSSION...19Z radar imagery showed scattered showers and
thunderstorms over southern ND and northern SD, near and to the
north/west of a quasi-stationary front that was draped across the
region. Anomalous low level moisture near the front (dewpoints
between 60 and 70 F) along with breaks in cloud cover has allowed
MLCAPE to increase into the 500-1000 J/kg range from central SD
into southeastern portions of ND. Flow at 850 mb was generally
from the east/upslope at 15-30 kt (VAD wind plots) with some
surface convergence along the frontal boundary noted as well.
Aloft, flow was mildly diffluent to the north of a vertically
stacked cyclone located over NE.

Shower and thunderstorm coverage is expected to increase over the
next few hours with further daytime heating/expansion of
instability. While individual cells should generally be
progressive within the easterly flow, tall/skinny CAPE profiles
and cell mergers should support efficient rainfall rates of 1-2
in/hr within the main axis of instability. Farther west, low level
convergence should allow cells to merge into a more stable
environment over the western Dakotas but with slow movement and
potential for rainfall values to add up over time. Storm totals of
2-4 inches and flash flooding will be possible given low flash
flood guidance values across a majority of the MPD threat area.
There remains some disagreement in short term CAM guidance with
QPF placement, and while recent runs of the HRRR have focused
localized 2-4 inch totals in northwestern SD, it may be
underplaying potential further north given trends in satellite
imagery and subsequent increases in instability.

Otto

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!66QRdLCMAEzXgJgN0RKthHRGA9GNWwfKY73zKeoK0Yfn9Asq2dhmILlZiOzSq-mZqNpb=
wvZX7GRvZjrz2LdWhFQlzrk$  for graphic product...

ATTN...WFO...ABR...BIS...UNR...

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

LAT...LON   47580158 47070012 46419918 45719891 45179993=20
            44690056 44190082 43360098 43200174 43450230=20
            44320311 45600348 47290291=20

=3D =3D =3D
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