Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
801 PM EDT Wed Oct 2 2024

Day 1
Valid 01Z Thu Oct 03 2024 - 12Z Thu Oct 03 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Pereira

Day 2
Valid 12Z Thu Oct 03 2024 - 12Z Fri Oct 04 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

The consensus for locally moderate to heavy rainfall remains
steadfast within the latest ensemble and deterministic
interpretations with a bit more emphasis on the Southeast LA
Parishes as the 12z CAMs output. Latest HREF continues to signal a
focused area of 3-5" potential tomorrow afternoon and early evening
in areas along and south of I-10 from near New Orleans through
Biloxi towards Mobile. There's still some discrepancy on the
placement of the local maxima with the highest potential likely
over either St. Bernard or Plaquemines Parishes, both areas that
are very difficult to flood due to the swampy land structures and
sandier soils that limit flash flood potential. A modest theta-E
advection pattern with PWATs running close to 2-2.1" will likely
allow for some convective elements promoting rates between 1-3"/hr,
but the current FFG indices are very pronounced in those parts,
attributing to very low FFG exceedance probabilities in either
1/3/6 hr time frames. Decided against a MRGL addition and
maintained the nil forecast across the CONUS, but this will be an
area to monitor in the next succession of updates as the threat is
non-zero, but currently below 5%.

Kleebauer


Day 3
Valid 12Z Fri Oct 04 2024 - 12Z Sat Oct 05 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Broad cyclonic flow over the Western Gulf will allow for a modest
advection of deeper moisture and accompanying shower/thunderstorms
activity to protrude inland of Deep South TX on Friday. Current
signature within guidance notes a tongue of elevated instability
within a deep moist layer on the western periphery of the low
pressure pattern over the Gulf. The area of interest resides across
the Lower RGV, mainly within the coastal plain encompassing
Brownsville/South Padre Island/Harlingen. Recent trends maintain
some rainfall in the area with totals bordering 0.75-1.5" with a
few deterministic outputs flirting with the 2"/24-hr marker. The
current signal is likely too "light" to allow for any enhanced
flash flood concerns, however the threat is likely non-zero. Unless
the precip forecast evolves into something greater, this will
likely lie outside the MRGL risk threshold, but wanted to make
mention as this is an area we will continue to monitor. The nil ERO
over the CONUS was carried over in this forecast cycle.

Kleebauer

Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt