Mesoscale Precipitation Discussion 0604
NWS Weather Prediction Center College Park MD
912 PM EDT Mon Aug 06 2018

Areas affected...Enter areas affected

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

Valid 070112Z - 070600Z

SUMMARY...Solid atmospheric elements suggestive of heavy
rain/isolated flash flooding due to training may be limited by
very dry/absorptive hydrological environment. 

DISCUSSION...00z ILX sounding supports very high instability but
also a slightly richer low level moisture profile with Total PWAT
near 2".  RAP analysis appears to have assimilated a small pocket
of deeper low level moisture confirmed by CIRA LPW (advected
northward) in the 850-7H layer with a pocket of 18C Tds oriented
from vicinity of AAA to north of DNV and intersecting with
convectively expanding cells enriching rainfall efficiency.  00z
surface analysis, along with ILX/LOT RADAR denotes the southward
sag of the frontal boundary across central IL becoming nearly
parallel from UNI to BMI to the mean unidirectional cloud bearing
flow from 8H-3H...including speed shear supporting mass loading of
downdrafts for rates in excess of 2-2.5"/hr. 

Below 8H, the boundary layer flow from the SW to WSW supports some
moisture convergence to support upstream redevelopment, suggesting
training is more likely further south north/along I-74 into
Central IND, especially being a bit further from the core of the
jet and mean cell motions are slightly reduced to 15-20kts vs. the
20-30kts further north with the strongest convergence/low level
forcing near the surface wave along the MI/IND border.  As such
rates to 2-2.5"/hr with these motions and back-building/training
potential suggest 2-4" totals are possible over the next 2-4 hours
especially along 40N.

This setup would generally suggest flash flooding is possible to
potentially likely in places.  However, given the dry antecedent
conditions, through an area of naturally better draining soils
near the Wabash valley; FFGs are quite high over 3" in 3hrs, and
2-2.5"/1hr... so setup/training must be ideal for exceedance to
occur and hence focused further south (though included FWA due to
hydrophobic runoff on impermeable surfaces)   Hi-Res CAMs are much
more bullish further north given better synoptics but it appears
observations are a bit more moist than assimilated in the 12z
cycles.  The RAP/HRRR have been more suggestive of greater/more
intense development with time providing some additional
confidence.  As such, flash flooding is considered possible but on
the lower end of coverage and magnitude.

Gallina

ATTN...WFO...ILX...IND...IWX...LOT...

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

LAT...LON   41108526 40238524 39828588 39888736 40008875
            40518871 40678793 40868675