BBS: TELESC.NET.BR
Assunto: MESO: Nws Weather Prediction Center College Park Md
De: COD Weather Processor
Data: Sat, 30 May 2026 21:56:43 +0000
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AWUS01 KWNH 302156
FFGMPD
NEZ000-SDZ000-NDZ000-MTZ000-WYZ000-310355-
Mesoscale Precipitation Discussion 0280
NWS Weather Prediction Center College Park MD
555 PM EDT Sat May 30 2026
Areas affected...Far Northwest Nebraska...Northeast
Wyoming...Western South Dakota...Central and Eastern Montana
Concerning...Heavy rainfall...Flash flooding likely
Valid 302155Z - 310355Z
SUMMARY...Broken clusters of heavy showers and thunderstorms will
continue to expand and organize across portions of far northwest
Nebraska, northeast Wyoming, western South Dakota, and into
central/eastern Montana this evening. Fueled by highly anomalous
moisture and enhanced surface convergence along an elongated axis
of surface low pressure, rainfall rates of 1 to 2 in/hr will be
capable of producing localized 2 to 3+ inch totals. Flash flooding
is likely, particularly across sensitive high-terrain basins.
DISCUSSION...Recent RAP mesoscale analysis and satellite imagery
depict a robust upper-level low centered over Wyoming, embedded
within an elongated trough stretching across the northern Rockies.
This low is projected to slowly lift northward through the evening
hours, providing widespread, deep-layer forcing and ascent.
Concurrently, a potent low-to-mid-level fetch is continuously
transporting a deeply anomalous moisture plume from the Central
Plains northwestward. Precipitable Water (PW) values within this
plume are exceptionally high for late May, running 2 to 3 standard
deviations above the climatological mean.
At the surface, the latest mesoscale guidance indicates the
organization of an elongated surface low pressure center
stretching from northeast Wyoming up through southeast and central
Montana. This feature is significantly enhancing low-level
convergence across the region. Along and east of this boundary, an
axis of moderate instability has materialized, with MLCAPE values
locally exceeding 1000 J/kg extending down into northeast Wyoming,
the Black Hills of western South Dakota, and far northwest
Nebraska.
Driven by this combination of deep synoptic lift, enhanced surface
convergence, and high moisture efficiency, broken to locally
organized convective clusters are expected to produce intense
hourly rainfall rates of 1 to 2 in/hr along this corridor. The
consensus of the latest high-resolution guidance, including the
18Z HREF, 18Z REFS, and recent RRFS runs, strongly favors
localized additional accumulations of 2 to 3 inches through the
late evening.
The 18Z HREF indicates areas of 40 to 60+ percent probabilities of
exceeding 3-hour Flash Flood Guidance (FFG), particularly across
central Montana and the Black Hills. Given some of the flashy
nature of the regional terrain and the high efficiency of these
convective cores, areas of rapid runoff are expected which will
tend to lead to at least some areas of flash flooding.
Orrison
...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!_7I_3W3cBH4sMFgh7FCFr6xlRXGPvPZy5pBUVynG0TWaOJz6oQA44_CoEtqXaSsqZUrI=
0uthYGrDFobxeObCh5ktqAo$ for graphic product...
ATTN...WFO...BIS...BYZ...CYS...GGW...LBF...RIW...TFX...UNR...
ATTN...RFC...KRF...NWC...
LAT...LON 49360786 48810655 47960486 45980291 45230218=20
43850163 42760206 42490315 42670366 43730460=20
44370529 44880727 44750918 45050999 45951047=20
47221004 48700989 49260913=20
=3D =3D =3D
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