Mesoscale Precipitation Discussion 0551
NWS Weather Prediction Center College Park MD
633 PM EDT Sat Jul 28 2018

Areas affected...far southeastern WY into western NE, northeast CO
and western KS

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

Valid 282230Z - 290430Z

SUMMARY...Flash flooding is expected across portions of the
central High Plains later this evening as storms move
southeastward and grow in coverage. Localized totals of 2-4 inches
are expected despite a general overall movement of convection
toward the southeast.

DISCUSSION...22Z radar imagery showed a couple of organized
storms/supercells over southeastern WY moving toward the
southeast, while less organized activity was noted farther south
over the CO/WY border and into east-central CO. These cells were
occurring within an axis of 1500-2500 J/kg MLCAPE via the latest
SPC mesoanalysis (...in agreement with RAP analyses plus 18Z
soundings from from DNR and LBF) and within an area of increasing
total precipitable water. Both GOES 16 derived total precipitable
water and RAOB data showed a general 0.1 to 0.2 inch increase
across western NE/KS between 12Z and 18Z. The development of 10-20
kt easterly 850 mb flow across the High Plains near and beyond 00Z
is expected to continue the advection of moisture into the region
while likely forming additional convection in conjunction with the
translation of ongoing activity.

Flow in the mid-upper levels is broadly diffluent across the
region, and while easterly to southeasterly low level flow and
west-northwesterly steering flow supports forward propagation of
convection toward the southeast, above average rainfall across the
region over the past week and the increasing of precipitable water
values to near 1.5 inches supports a flash flood threat. Rainfall
rates of 1-2 in/hr, increasing to near 3 in/hr are expected
through 04Z with cell mergers and brief stalling of heavy rain
cores. The 18Z NAM_conest and recent HRRR runs seem to be handling
ongoing convection the best and support the potential for 2-4
inches of rain through 04Z.

Otto

ATTN...WFO...BOU...CYS...DDC...GID...GLD...LBF...PUB...

ATTN...RFC...ABRFC...MBRFC...

LAT...LON   42660424 42180266 41420139 40589991 39669925
            38779936 37909986 37490046 37550168 38410209
            39030266 39770376 40920503 42360524