Mesoscale Precipitation Discussion 1033...Corrected
NWS Weather Prediction Center College Park MD
648 PM EST Sat Dec 01 2018

Corrected for typos

Areas affected...FL Panhandle & nearby areas of AL/GA

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

Valid 012342Z - 020542Z

Summary...Thunderstorms with heavy rainfall continue to exist in
and near the FL Panhandle.  Hourly rain totals to 2.5" with local
amounts to 4" are expected.

Discussion...The 23z surface analysis reveals a mesoscale wave of
low pressure in the western FL panhandle between Paxton FL and
Geneva AL.  This is along a convective band which had previously
been moving eastward, but appears to be slowing its forward
progress as another wave of showers and thunderstorms moves into
southernmost AL and other activity attempts to fill in the gap
between these two convective areas.  Water vapor imagery shows a
variety of upper level shortwaves enhancing upper level
divergence: in the subtropical stream, one extends southwest from
central AL while others approach from the west across MS and LA. 
A significant southern stream trough/ vorticity lobe moving across
the Mid- Mississippi Valley is moving by to the northwest. 

Precipitable water values of 1.6-1.9" lie in this region per GPS
data.  Inflow at 850 hPa is convergent out of the WSW-SW at 35-50
kts per VAD wind profiles, near the direction/magnitude of the
mean 850-400 hPa wind and the effective bulk shear.  MU CAPE
values of 1000-2000 J/kg exist in the region per SPC mesoanalyses;
CIN has partially set in across the eastern FL panhandle and
southwest GA.  Winds are unidirectional with height.  The above
quantities have led to short training bands of convection,
occasional cell mergers, and mesocyclones, all of which carry
heavy rain potential.

The mesoscale guidance has had issues thus far, with random runs
of the HRRR, as well as the 12z ECMWF, 18z 4 km NAM CONEST, and
18z Canadian Regional (perhaps the best of the bunch) performing a
bit better than the other guidance.  With shortwaves moving into
the region, mesocyclones and short bands of convection are
expected to produce hourly rain totals to 2.5" with additional
local amounts to 4"; near and just beyond the 5 year recurrence
interval for the region.  Increasing CIN could allow for greater
convective elevation over the warm front with time, with heavy
rain pushing farther into southern GA with time.  With soils
slowly saturating, flash flooding is a growing concern within and
beyond the period of this MPD. 

Roth

ATTN...WFO...JAX...MOB...TAE...

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

LAT...LON   31788387 31648302 31148235 30608237 30168271
            29738327 29788353 29998402 29748492 30328612
            30278695 30158787 30298804 30628755 31098660
            31338594 31668504