AWUS01 KWNH 122103
FFGMPD
NEZ000-SDZ000-MTZ000-WYZ000-130230-

Mesoscale Precipitation Discussion 1076
NWS Weather Prediction Center College Park MD
503 PM EDT Fri Sep 12 2025

Areas affected...Northeastern WY...Far Western SD...Southeast MT...

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

Valid 122100Z - 130230Z

SUMMARY...Stationary to slowly repeating cells near Big Horns,
likely to expand in coverage with approach of shortwave. 
Localized totals of 2"+ are possible but very isolated.  Flash
flooding is possible, particularly near burn scars and/or complex terrain.

DISCUSSION...GOES-E WV suite shows an anti-cyclonically arched
outflow band of cirrus along/ahead of embedded shortwave now
entering southeast WY.  Along an north of the outflow band,
divergence has been driving deep layer ascent across the Big Horn
mountain range, where a few cells developed over the last few
hours.  Deep layer steering generally resulted in northeasterly
motion and initial downdrafts were generally drier or hail
producing.  However, low level response has strengthened
northeasterly flow from deeper low level moisture across SE MT
banking it up against the Big Horns while, mid-level moisture from
the approaching shortwave, along with initial up/downdrafts having
moistened the profile.  While some instability was lost to this
moistening, RAP profiles and instability fields still strongly
suggest ample 750-1250 J/kg of instability along the left exit of
the outflow jet.  Recent Visible and EIR imagery from GOES-E
suggest continued updraft vigor across the central Big Horns with
increasing rainfall rates likely.  Lightning from GLM/NLDN
suggests a few stronger embedded rotating updrafts will likely
keep the heavy rainfall footprint to be more isolated in nature. 
Total PWat values increase to 1" and given Tds in the low 50s, and
solid moisture flux convergence, rates of .75"/hr are probable.  
This appears likely to continue for an additional hour or two.

Upstream, the main shortwave is providing even further broader
scale DPVA and therefore ascent.  Banded Cu fields are starting to
sprout stronger TCus and CBs across central WY.  The increase in
coverage and further deepening of mid-level moisture will
eventually expand overall coverage of convection capable of
localized .5-1" hour totals.  Some flanking development may allow
for some enhanced streaks of higher totals.   As such, overall
coverage is not likely to be high, but isolated totals of 1.5-2"+
are probable and in proximity to terrain or steep river
valleys/bluffs may result in localized flash flooding conditions.

Gallina

ATTN...WFO...BYZ...CYS...RIW...UNR...

ATTN...RFC...KRF...NWC...

LAT...LON   45970457 45710372 45280334 44650311 43710317 
            42790416 42130578 42210690 42930746 44200744 
            45370685 45930560 

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