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AWUS01 KWNH 210447
FFGMPD
KSZ000-NEZ000-COZ000-211045-

Mesoscale Precipitation Discussion 0646
NWS Weather Prediction Center College Park MD
1246 AM EDT Sun Jul 21 2019

Areas affected...Eastern CO, Western KS, Southwest NE

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

Valid 210445Z - 211045Z

Summary...An MCV/weak surface low moving out of eastern CO will
lift northeast along a stationary boundary. Thunderstorms
developing ahead of this feature will continue to expand to the
east-northeast and train along this boundary where moisture
convergence will be maximized. Rainfall of 1-3" with isolated
higher amounts is possible, which may produce flash flooding.

Discussion...Goes-16 IR imagery tonight shows expansion of cooling
cloud tops across CO and western KS, atop a surface low and MCV
evident as rotation in reflectivity. Extending northeast from this
sfc low, a stationary boundary was analyzed extending through NW
KS and across southern NE. South of this boundary, a robust
southerly LLJ approaching 40 kts is driving moist unstable air
northward, while drier more stable air is wrapping back from the
north behind the surface low. Along this stationary front,
moisture has pooled with PWATs analyzed by the RAP to be 1.8-2.0
inches, and MUCape is in excess of 2000 J/kg. Modest upper
diffluence ahead of the convectively enhanced shortwave will
combine with the low-level convergence to unzip convection to the
northeast through the night.

In this favorably forced environment, thunderstorms will blossom
to the northeast, and likely train along the front where 0-6km
mean flow becomes parallel to the boundary and the Corfidi
vectors. Guidance is in very good agreement that a narrow ribbon
of convection will expand along the front, with training producing
1-3" of rainfall due to rain rates exceeding 1"/hr. Across this
discussion area, FFG is generally 2-3"/3hrs, however some
locations which have received above normal rainfall over the last
14 days and exhibit NWM 40cm soil moisture above 75% of saturation
have FFG of less than 2"/3hrs. This is where flash flooding may be
most likely, especially if training occurs across these areas.

Further east, and somewhat displaced from the stationary front,
outflow from prior convection may align N-S as is currently
exhibited across SW KS. Where this persists, it will become
aligned parallel to the LLJ, producing Corfidi vectors which will
be anti-parallel to the 0-6km mean flow. Backbuilding of echoes
within this regime could produce a secondary flash flood risk, but
the slow motion in a somewhat less unstable and forced environment
should lead to slow dissipation across this area. The primary
focus should then return to the boundary for much of the MPD valid
time.

Weiss

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

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

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

LAT...LON   41509995 41409956 40919956 40329986 39840008
            39260028 38620001 38289985 37889979 37469986
            37179999 37010038 37040084 37140145 37280210
            37670312 38020336 38520349 38980344 39350323
            39790285 40260235 40670180 40930121


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