Mesoscale Precipitation Discussion 0788
NWS Weather Prediction Center College Park MD
428 AM EDT Fri Sep 07 2018

Areas affected...SE IA...NE MO...Central IL

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

Valid 070827Z - 071427Z

Summary...Showers and thunderstorms will increase in coverage
early this morning with periods of heavy rainfall likely. 2-4" of
rain with isolated higher amounts are possible, occurring on top
of already saturated soils which will produce a flash flood threat
through late morning.

Discussion...Showers are becoming more numerous on latest KILX
radar imagery as moisture at least peripherally associated with
T.D. Gordon streams northward and atop a stationary front. RAP
analyzed PWATs this morning are 1.7 to 2.0 inches, more than 2
standard deviations above the mean. Even higher PWAT air on the
latest blended-TPW product will advect into the threat area on
southerly 850mb winds around 20 kts. As this moisture surges
northward, strong low-level confluence will develop between 850
and 700mb, driving increasing omega through the morning. This
low-level confluence will act in tandem with a strengthening 700mb
E-W oriented axis of deformation and a subtle trough, as well as
increasing diffluence within an encroaching 50 kt upper level jet
(especially after 11Z) to further enhance lift.

RAP soundings depict 0-6km mean wind will be very light, 5 kts or
less, with corfidi vectors aligned to the left of this wind
supportive of training thunderstorms. Despite weak 0-6km shear
limiting storm organization, training and mergers are likely which
will allow efficient rainfall producing thunderstorms to persist.
High res guidance including the 00Z NMMB and HREF blended mean
show 2-4" of rainfall likely across the threat area, with the
focus potentially occurring across locations that have received
significant rainfall in the last 24-hours. Flash flood guidance is
low in these areas so the soils are very sensitive to further
rainfall.

Weiss

ATTN...WFO...DMX...DVN...EAX...ILX...LOT...LSX...

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

LAT...LON   41688984 41628909 41498855 41308815 41008796
            40668801 40328821 40118887 39938946 39759014
            39539053 39419091 39299136 39199179 39069236
            39099312 39559310 40099290 40599244 41089199
            41329148 41569094 41669041