204
AWUS01 KWNH 301641
FFGMPD
UTZ000-NVZ000-302200-

Mesoscale Precipitation Discussion 1154
NWS Weather Prediction Center College Park MD
1239 PM EDT Tue Sep 30 2025

Areas affected...East-central Nevada...West-central Utah...

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

Valid 301640Z - 302200Z

SUMMARY...Scattered to numerous small-cored convection within a
favorable repeating flow regime and possible back-building may
result in a few streets of .75-1.25" in 1-3 hours resulting in an
isolated incident or two of localized flash flooding is possible.

DISCUSSION...GOES 7.3um WV suite depicts a subtle shortwave at the
right entrance to a 50kt S-N jet along the northern NV/UT border
lifting northeast with typical back-arched upper-level cirrus
indicative of the very favorable divergent flow aloft.  Upstream
the well defined drying also denotes the elongated main trough
axis extending from SE OR through central NV; with the core of the
west to east jet starting to nose southward delineating the mean
trough axis.

Low level response has been for enhanced return flow out of the
Lower Colorado River bending eastward along a surface to boundary
layer trough between the Salt Lake surface low and the southern NV
low.  Pooled moisture mainly below 700mb has supported total Pwats
to 1" across the Salt Flats into SLC vicinity just along/ahead of
the leading shortwave; though enhanced values up to .8-.9" still
remain along the upwind edge.  Some mid-level drying and clearing
over east-central NV has provided some insolation/heating to
support SBCAPEs nearing 1000 J/kg.  In response to the DPVA, and
low level convergence at the nose of the low level moisture flux
feed; numerous small cored convective cells have begun to cluster
across S White Pine county, NV with hints of further Cu field
development across NE Lincoln county, NV into Millard county, UT.
 While the cores are shallow (-45 to -50C tops) and narrow, there
is increasing coverage to support better moisture flux convergence
for enhancing rates to near .75"/hr over the next few hours.

Deep layer flow is broadly southwest to southeast parallel to the
surface trough and considering the overall longer wave trof is
filling at the base and shifting northeast, the deeper layer flow
should remain similar to allow for repeating environment.  This
concurrent for upstream instability pool and low level moisture
flux/convergence to support some back-building potential... all of
which will slowly shift eastward.   Given all this, a few repeat
streets may allow for localized .75-1.25" totals in 1-3 hours.
Naturally low FFG values are about .75-1"/hr and 1-1.5"/3hrs
suggesting an isolated incident or two of localized flash flooding
may be possible through the afternoon/early evening while
instability pool remains viable.

Gallina

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

ATTN...WFO...LKN...SLC...VEF...

ATTN...RFC...RSA...STR...NWC...

LAT...LON   40831256 40821165 40001141 39451159 38801201
            38191282 37701405 37931487 38881502 39621464
            40311387 40591326