Mesoscale Precipitation Discussion 0190
NWS Weather Prediction Center College Park MD
522 PM EDT Thu May 14 2020

Areas affected...Southern IA...far northern MO

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

Valid 142120Z - 150200Z

SUMMARY...Storms training over areas that received heavy rainfall
earlier today could pose a flash flood threat through late this
afternoon into early this evening.

DISCUSSION...The GOES-16 visible loop showed a line of towering
cumulus forming along and just north of a stationary boundary
across portions of southern IA. The formation zone lies on the
northern edge of the instability gradient, with SBCAPE over 3000
J/KG over northernmost MO into far southern IA.

The storms are developing on the northern edge of the better
moisture source, and the combination of moisture and instability
allowed storms over Atlantic and Guthrie Center counties to
produce hourly rainfall rates in excess of 2.25 inches (though the
DMX HCA product does indicate the potential for hail
contamination) within the last 90 minutes.

The 850/300 mb mean wind is generally aligned with the propagation
vectors across southern and central IA, which could foster an
environment conducive to continued training. However, without a
clear source of lift over the boundary, it is not clear just how
extensive the convection becomes along and south of the boundary
through 15/00z. Both the latest HRRR/parallel HRRR solutions do
have a handle on the initial convective placement, but do not
necessarily have a handle on the intensity of the rainfall with
the storms themselves.

Each model shows a general increase in coverage as higher
instability is slowly advected along the front into southern IA.
The best coverage (based on the simulated radar imagery from the
HRRR/parallel HRRR is expected across southwest IA, where an area
of 1.00/2.00 inches of rainfall occurred in earlier convection.
Storms training over this area could produce an additional
1.00/2.00 inches or train, which pose a flash flood threat through
late afternoon and early evening.

Since the coverage of storms in the area that received heavy
rainfall earlier today is still unclear, flash flooding is
considered possible.

Hayes

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

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

LAT...LON   42129233 42019023 41439016 40809106 40049534
            40839630 41449511