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AWUS01 KWNH 271951
FFGMPD
NEZ000-SDZ000-COZ000-MTZ000-WYZ000-280100-

Mesoscale Precipitation Discussion 0680...Corrected
NWS Weather Prediction Center College Park MD
351 PM EDT Sat Jul 27 2019

Corrected for time on graphic

Areas affected...southeastern Montana...eastern Wyoming...western
South Dakota and Nebraska...north central Colorado

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

Valid 271950Z - 280100Z

Summary...Showers and thunderstorms are expected to increase in
coverage and intensity through the next several hours. Rainfall
amounts of 1-2 inches per hour are possible, which could lead to
localized instances of flash flooding.

Discussion...A moist and moderately unstable air mass is in place
along/just north of a surface front from the High Plains of
eastern Wyoming and Montana eastward into South Dakota and
Nebraska. PWs in the 1.0-1.2 inch range were indicated across the
outlined area per the latest RAP mesoanalysis data, with MUCAPE in
the 1000-2000 J/kg range. A mid/upper-level vorticity maximum was
noted in the latest satellite imagery extending from southwestern
Wyoming to western Colorado and moving eastward. Meanwhile,
another more substantial shortwave was observed quickly moving
into the Pacific Northwest and northern Great Basin this
afternoon. The combination of these features is resulting in
increasingly diffluent flow through the afternoon at the
upper-levels across the outlined area. Scattered to numerous
showers and thunderstorms have already developed, some of which
have produced rainfall rates of 0.75 in/hr. Latest IR imagery show
gradually cooling cloud tops in convection across eastern Wyoming
and far western South Dakota, and visible imagery suggests
increasing updraft strength with several overshooting tops
observed.

As the synoptic environment continues to gradually improve through
the afternoon, showers and thunderstorms may demonstrate somewhat
increased levels of organization, with multi-cell clusters
potentially resulting in locally enhanced rainfall amounts of 1-2
in/hr. The strongest upper diffluence and the strongest deep layer
wind shear should occur across the northern portion of the
outlined area, where some hi-res guidance (e.g. WRF-NSSL) shows
the potential for cold pool development and organization of an
MCS. This would result in increased heavy rainfall potential
before the complex begins to more quickly propagate eastward by
late afternoon/early evening. Due to the potential for localized
amounts approaching 2 inches, flash flooding is possible.

Ryan

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

ATTN...WFO...BOU...BYZ...CYS...UNR...

ATTN...RFC...CBRFC...MBRFC...

LAT...LON   46250456 45800397 45270324 44120266 43250284
            42580356 41920391 41290437 40850491 40440548
            40440610 41020659 41550653 42230600 42800571
            43470578 44460587 45580574 46230518


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