Weather Prediction Center issues Mesoscale Precipitation Discussion #64 concerning HEAVY RAINFALL...FLASH FLOODING POSSIBLE299
AWUS01 KWNH 151850
FFGMPD
OHZ000-INZ000-152230-
Mesoscale Precipitation Discussion 0064
NWS Weather Prediction Center College Park MD
249 PM EDT Sat Mar 15 2025
Areas affected...Central and Eastern Indiana into Adj. Northwest
Ohio...
Concerning...Heavy rainfall...Flash flooding possible
Valid 151850Z - 152230Z
SUMMARY...A very narrow band of thunderstorms ideally oriented to
the moisture gradient and deep layer steering flow and of
sufficient length for training to exceed lower FFG values in the
region suggest an incident or two of localized flash flooding is
possible.
DISCUSSION...GOES-E WV overnight into early this morning noted the
strong cyclone across the Upper Great Lake region resulted in a
strong, elevated mixed layer (EML) extending well northwest into
the Ohio River Valley and central Great Lakes region, with
dust/soil and smoke particulates noted with it in the visible
imagery. This mixed layer has a surface reflection noted by a
frontal/dewpoint gradient across central IL into NW IND, with 40s
quickly becoming upper 50s and mid 60s across central and southern
IND. Clear skies this morning provided short-duration but ample
insolation for instability to build with SBCAPEs reaching near
1000-1500 J/kg mainly along and south of the boundary.
The WV suite also notes a broadening baroclinic shield of high
cirrus moving across the area associated with a broadening
diffluent region across the Ohio River Valley as a 130kt 250mb jet
streak continues to wrap along the interface of the older cyclone
and the approaching strengthening one from the Southern Plains.
This has provided strong divergence aloft along the broad right
entrance region of the jet and in turn lead to the acceleration
and backing of the low level jet across the TN Valley into the
region. Southerly winds intersecting with the SW to NE gradient
within the area of surface based instability provided sufficient
moisture convergence to generate thunderstorms along and south of
this axis within the area of deeper surface to boundary layer
moisture. Initial thinking was the cores of updraft would be
narrow given limited instability/surface heating. Strong steering
flow would also result in quicker SSW to NNE cell motion and the
probability of intersection of narrow updrafts would be limited.
However, recent trends note the stronger heating and moisture flux
convergence has resulted in slightly broader up/downdrafts while
also expanding longer along the convergence axis. Combined with
nearly parallel deeper layer steering and all 3 components are
start to result in a narrow axis of intense thunderstorms with
hourly rates of 1-1.5"/hr.
Given the length is about 80 miles, there is solid potential for
spots of 1.5-2" totals within 1-2 hours. FFG values are already
low from slower green-up with 1hr values between 1-1.5 and 3hr
values less than 2" along the training axis. As such, localized
flash flooding is considered possible, even if only a few
neighboring watersheds are impacted. The risk for flash flooding
is likely to be limited in time given quick erosion of remaining
downstream unstable area and may only exist for a few more hours
before weakening.
Gallina
...Please see www.wpc.ncep.noaa.gov for graphic product...
ATTN...WFO...ILN...IND...IWX...
ATTN...RFC...OHRFC...NWC...
LAT...LON 41248449 40808418 39948506 38878650 39058701
40478589 41238521
Source:
Weather Prediction Center issues Mesoscale Precipitation Discussion #64 concerning HEAVY RAINFALL...FLASH FLOODING POSSIBLE---------------
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