307
AWUS01 KWNH 182105
FFGMPD
COZ000-WYZ000-UTZ000-IDZ000-190230-

Mesoscale Precipitation Discussion 1325
NWS Weather Prediction Center College Park MD
504 PM EDT Fri Sep 18 2026

Areas affected...Northern UT...Southeast ID...Southwest
WY...Northwest CO...

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

Valid 182100Z - 190230Z

SUMMARY...Multiple SW to NE bands of thunderstorms slowly
progressing eastward capable of short-term repeating and localized
1.5-2" totals continue to present an isolated to widely scattered
risk of localized flash flooding through the remainder of the
evening into early overnight hours.

DISCUSSION...GOES-E WV suite continues to show strong closed low
just west of the OR/ID/NV corner still advancing eastward while
strong southwest to northeast deep layer flow continues to present
broad area of enhanced moisture flux across the remaining warm
sector across much of N UT into SE ID and W WY.  CIRA LVT analysis
shows a narrower core of 850-700mb plume across W UT to SE ID with
50-75 kg/m/s while overlayed with the broader 700-500 moisture
flux at similar ranges.  Total PWats in the plume range from
.75-1" or about 1.5-2 std dev from normal helping to increase
rainfall efficiency/moisture loading to the convective cores that
are present.   GOES-E Visible imagery shows a weaker line back
near the advancing cold front just west of the NV/UT border with
much stronger line advancing toward/through the N UT I-15 corridor
back into the E Bonneville Flats; advancing eastward slowly within
the broad height-falls aloft at 5-10kts though individual cells
are lifting north-northeast at 25-30, presenting short-term
opportunities for localized repeating of stronger cores.  Strong
diffluence and speed divergence will further help to maintain the
clusters/convective lines with back-sheared outflow anvils
expected and with bulk shear over 50kts, weak rotation may further
enhanced localized rainfall rate/efficiency due to increased
moisture flux convergence in speed and direction.

Instability is maximized around 1250-1500 J/kg (MLCAPE) across N
UT, but an west to east axis also remains along/north of the Unita
Range before broadening again near the leading SW-NE convective
line across north-central CO into south-central WY (500-1000
J/kg).  Stronger cells lead this line, but remain quickly moving.
GOES-E Visible, notes a small gap from this initial line, but 2-3
more lines of cells across the Unita Range exist.  Each with a
capability of a quick .25-.5" before moving through, but random
repeating may allow for localized 1-1.5" totals before the main
line adds up to another .5".  So a scattered/buck-shot appearance
of 1-2" localized maxima should dot N UT/SW WY and NW CO for the
remainder of the evening.  So isolated to scattered incidents of
localized flash flooding will remain possible this evening
especially in urban, rugged/steep terrain and recent burn scar
areas.

Gallina

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

ATTN...WFO...CYS...GJT...PIH...RIW...SLC...

ATTN...RFC...KRF...PTR...STR...NWC...

LAT...LON   43200970 42640907 42290852 41940759 41040713
            40280719 40040852 39371086 39181163 39151269
            39471371 40331389 42381281 43041122