Mesoscale Precipitation Discussion 0603
NWS Weather Prediction Center College Park MD
618 PM EDT Mon Aug 06 2018

Areas affected......SOUTHEAST NEBRASKA TO SOUTHWEST IA AND
NORTHWEST MO...

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

Valid 062300Z - 070500Z

Summary...Bands and clusters of showers and storms likely to
produce locally heavy rainfall in southeast Nebraska to southwest
Iowa and northwest MO this evening into early overnight...

Discussion...Latest radar/satellite trends indicate increasing
shower/thunderstorm coverage across central Nebraska moving east.
The models indicate a combination of mid level convergence and
upper level divergence is triggering ascent.  Ascent is aided by
steep lapse rates of 7-8 deg/KM on the 20z RAP analysis.

With dewpoints in the upper 60s to lower 70s and RAP forecasts of
pooling of precipitable water values of 1.75-2 inches, heavy
downpours are likely within the showers/storms.

The RAP and 18z NAM show 850-700 mb theta-e advection and the NAM
shows increasing convergence in this area, so showers/storms
should continue to increase.

The high res models indicate potential for 2-4 inches of rain this
evening through 06z, including the 20z HRRR, 12z WRF ARW and WRF
NMMB.  The NSSL WRF and 18z NAM have an axis further south into
northern MO but show potential for a band of heavy rain to occur.
The flash flood guidance values are on the order of 2-3 inches in
3 hours, so flash flooding was shown as possible instead of likely
given most areas have predicted rain under the flash flood
guidance.

Also, additional showers and storms may occur after this period,
so we will be monitoring for potential reissuance later this
evening into early overnight.

Petersen

ATTN...WFO...DMX...EAX...OAX...

ATTN...RFC...MBRFC...NCRFC...

LAT...LON   41159497 41159408 41109377 41029341 40929288
            40879274 40769266 40459277 40189319 40089387
            40049454 40069520 40079567 40069618 40079656
            40089694 40569678 40939617 41039568