Mesoscale Precipitation Discussion 0790
NWS Weather Prediction Center College Park MD
1044 AM EDT Fri Sep 07 2018

Areas affected...SE KS, Nrn/Ctrl MO, C IL, WC IN

Concerning...Heavy rainfall...Flash flooding likely

Valid 071442Z - 072040Z

Summary...An extensive area of rain with embedded thunderstorms is
likely to develop along a front that stretches from the Plains
into the Mid-Mississippi River Valley. Moderate to heavy rain is
expected across much of the region. Slow-moving rain bands and
thunderstorms are also likely to produce smaller swaths of heavier
rainfall, which should lead to flash flooding. Rain rates of 1-2
in/hr would be relatively common in these sort of rain bands, but
localized rates up to 3 in/hr would be possible.

Discussion...Regional radar mosaic this morning shows a large
ribbon of rain stretching from Indiana, curling southwest into the
southern Plains. This was largely situated along and north of a
stalled, extensive low-level front. Tropical Depression Gordon was
centered in Arkansas, and the strongest winds in the 925-850mb
layer were generally east of the center. Therefore, there was
stronger northward moisture flux into Missouri this morning, in
addition to the pooling moisture already existing along the
quasi-stationary front. Precipitable water values were generally
between 2.0 and 2.2 inches, as shown by the CIRA blended TPW
product, GPS-PW observations, and some of the regional 12Z
soundings. These were around the 99th percentile for this time of
year for this region. Of particular note is the depth of the
moisture plume. CIRA layer PW products shows a prominent channel
of higher PW values in the 700-500mb layer, and especially in the
500-300mb layer, connecting back into the ITCZ in the eastern
Pacific and suggesting deep saturated or nearly-saturated profiles
right along the stalled front. The depth and magnitude of
available moisture should easily support heavy rainfall. The 12Z
SGF sounding also showed modest CAPE values just under 1000 j/kg,
with a tall narrow profile and a freezing level approaching 16,000
feet -- a hallmark of environments with efficient warm rain
processes.

Given the abundance of moisture in proximity to a low-level
boundary, the expectation is for fairly widespread moderate rain
and embedded heavier rain bands and thunderstorms. Most convective
bands should be limited in vertical extent, and dominated by
collision-coalescence processes with limited ice. This should keep
rain rates high in any convective bands that develop. 1-2 in/hr
rates would be relatively common, but slightly higher rain rates
couldn't be ruled out in the presence of stronger and more focused
forcing. In the next couple hours (14-17Z), one location that may
see higher rain rates and a more focused flash flood threat would
be in southeast Kansas, where a nearly stationary rain band
appears to be increasingly organized and growing in size based on
recent scans from the KICT radar. Dual pol and MRMS rain rate
estimates have been locally as high as 3 in/hr east of Wichita.
The area from near Winfield, northeast to near Yates Center, and
Paola, would be at particular risk for flash flooding from this
nearly stationary rain band.

After 17Z, hi-res models show increasing amounts of convective
banding developing from central Missouri into central Illinois as
low-level inflow increases to the east of Gordon. This may enhance
low-level convergence along the front and lead to a greater flash
flood threat developing in the 18-21Z time frame across Missouri
and Illinois.

Lamers

ATTN...WFO...DVN...EAX...ICT...ILX...IND...LOT...LSX...SGF...
TOP...

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

LAT...LON   40788788 40268617 39398681 38848948 37909268
            37059603 37689717 38879553 40009312 40569095