638
AWUS01 KWNH 261506
FFGMPD
SCZ000-GAZ000-262105-

Mesoscale Precipitation Discussion 1067
NWS Weather Prediction Center College Park MD
1106 AM EDT Thu Sep 26 2024

Areas affected...South Carolina and Eastern Georgia

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

Valid 261505Z - 262105Z

SUMMARY...Extremely heavy rainfall in heavy banding will persist
into the afternoon over eastern Georgia and central South Carolina
including Columbia. Widespread flash flooding with locally
significant impacts is likely through the mid-afternoon.

DISCUSSION...Regional radar imagery at 15Z showed an axis of heavy
rainfall extending north-south over southern to central SC. This
band is redeveloping on the south end and shifting north, nearly
along its axis causing hourly rates of 2.5"/hr. This particular
band is tracking into Columbia which is rather flood prone. The
axis of heavy rain has been co-located with an area of strong low
level moisture flux convergence in a plume of 2.2 to 2.5" PW which
is the core of moisture streaming ahead of Helene on southerly
35kt low level flow. Instability is rather limited decreasing from
1500 J/kg near the SC coast to less than 500 J/kg near Columbia,
but this is overcome from strong dynamics where the mean layer
southerly flow is 40kt and oriented with the activity, causing
training.

Recent HRRR runs are under doing this band and feature more
scattered convective modes through the mid-afternoon. However, the
channeling of this flow between the upper low that remains over
western TN and the ridge east of FL will maintain redeveloping
advection and banding ahead of Helene. Given little change in the
forcing mechanisms in place, heavy rain potential will continue
into the mid-afternoon across many of the same locations already
seeing heavy rain. While FFG was rather elevated over these areas,
it is quickly dropping as heavy rain spreads in. The extreme rates
warrants likely wording for the flash flood risk.

There should be some break in heavy rain here later this afternoon
before banding from Helene returns this evening as the system
passes to the west.

Jackson

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...CAE...CHS...FFC...GSP...ILM...JAX...

ATTN...RFC...SERFC...NWC...

LAT...LON   35078146 34428010 33737988 32777985 32068065
            31248119 31618254 32388283 32908317 33288314
            33428275 33828248 34488209 35048177