Mesoscale Precipitation Discussion 0575
NWS Weather Prediction Center College Park MD
1202 PM EDT Wed Aug 01 2018

Areas affected...Florida Panhandle and Big Bend, and adjacent
areas

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

Valid 011601Z - 012100Z

Summary...A mixture of rain and thunderstorms should continue to
affect the Florida Panhandle and Big Bend region into the
afternoon, as well as adjacent parts of Alabama and Georgia. On a
localized basis, rain rates will exceed 2 in/hr, which could lead
to flash flooding.

Discussion...A deep plume of tropical moisture continues to be
channeled into the Florida Panhandle region via deep southerly
flow. This is evident in CIRA layer precipitable water products,
with a prominent and continuous swath of higher values in the
700-500mb and 500-300mb layers extending back into Central America
and the ITCZ. This moisture source in the tropics is yielding PWs
around 2.2 to 2.3 inches per the blended total PW product, as well
as several GPS-PW observations near the coast. This should support
heavy rainfall in the stronger convective cells and bands in the
region. 2-3 in/hr rain rates would be possible in such an
environment, and rain rates this high could lead to flash
flooding, especially if they align with areas that have seen heavy
rainfall in recent days.

The main limiting factor at this time is the unfocused nature of
ongoing convection. Small convective bands exist on KMOB and KEVX
radars in the Florida Panhandle, but these seem to be drifting
enough to limit the duration of the very heavy rain rates at any
one location. Other than some frictional convergence near the
surface along the Gulf coast, there is a lack of a surface
boundary to focus the rainfall in a particular area at the present
time. GOES-16 visible satellite does show some partial clearing in
the Florida Panhandle, and this could allow both instability to
build (potential for stronger or more organized convection) and
differential heating boundaries to develop (which could focus
convection in a more sustained way). Therefore, the potential for
flash flooding could still increase this afternoon. To the north
of that, into southeast Alabama, dense cloud cover may limit
further destabilization, but sustained moderate to occasionally
heavy rainfall with low-topped convection supports a small chance
of flash flooding in this area as well.

Further to the east, KTLH radar showed a prominent arc of
convection extending through the Big Bend region and into the
eastern Gulf of Mexico. Although the squall line may have a
tendency to drift with time, the potential for very heavy rain
rates may allow for a localized threat of flash flooding further
east in the region.

Lamers

ATTN...WFO...BMX...FFC...JAX...MOB...TAE...TBW...

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

LAT...LON   32708552 32338482 31498511 31168378 30148286
            29308260 28958310 29778391 29538480 29538535
            30038595 30288669 30298743 31378733 32388664