Mesoscale Precipitation Discussion 0934
NWS Weather Prediction Center College Park MD
359 PM EDT Sun Oct 07 2018

Areas affected...Central Missouri to Western Illinois

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

Valid 071958Z - 080158Z

Summary...Slow-moving and repeating showers and thunderstorms will
continue into this evening. The risk of flash flooding expand from
east-central MO to western IL (remaining west/north of the St.
Louis urban area).

Discussion...The anti-cyclonic branch of the warm conveyor belt
east of an expansive trough across the western CONUS with origins
in the tropical east Pacific with additional moisture feed from
the western Gulf crosses Missouri and western IL per GOES-16 water
vapor imagery. 1.75 to 2 inch PW in this moisture plume is across
east-central MO and western IL per recent RAP analysis which is a
2.5 standardized anomaly.

Activity this afternoon has been focused in vicinity of a
quasi-stationary frontal zone across east-central MO with modest
instability characterized by MLCAPE values of 1000 to 1500 j/kg
per recent RAP analysis. Rain rates of two inches per hour
triggered a flash flood warning for Miller and Morgan Counties in
MO an hour ago. A secondary swath of thunderstorms have developed
east of there which are now in the western St. Louis suburbs.
Surface, low level and deep layer southerly flow will allow
additional thunderstorms to repeat over these areas as indicated
by the 19Z HRRR.

Furthermore, activity that develops farther northeast into western
IL should be oriented closer to the front which could allow
particularly heavy rainfall in western IL. FFG in western IL is
not low, but 2-4" would cause local concerns into the lower IL
river valley.

Guidance is confident in the activity not shifting farther east
into St. Louis itself with the focus west to north of the city.
Activity from yesterday was west of St. Louis which is where FFG
is lowest.

Given the additional rainfall potential and with the ground
becoming increasingly saturated, the possible threat for flash
flooding is expected continue through this evening.

Jackson

ATTN...WFO...EAX...ILX...LSX...SGF...

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

LAT...LON   40188991 39668933 39149022 38939057 38419088
            38079149 38059258 38669306 39209230 39889106