Flash Flooding in Florida, January 2, 2021

Area Forecast Discussion
National Weather Service Tallahassee FL
627 AM EST Sat Jan 2 2021

.AVIATION...
[Through 12Z Sunday]

A line of heavy rain is developing in the Gulf and will move
inland and become more expansive through the day. Expect IFR/LIFR
all day at TLH and VLD where multiple rounds of heavy rain are
expected. The remaining terminals will likely prevail at MVFR
until late this afternoon when more widespread rain fills in
across the region resulting in deteriorating conditions at
ECP/DHN/ABY.

&&

.PREV DISCUSSION [305 AM EST]...

.NEAR TERM [Through Tonight]...

Deep layer southwesterly flow resides atop a frontal boundary draped
through the Tri-State region. The deep-layer moisture transport has
resulted in record high PWAT values across the region in advance of
a strong northern stream shortwave. The shortwave currently over the
Southern Plains will advect into the Midwest through the night,
spreading upper-level diffluence across the region as the trough
takes on a negative tilt. While rain will continue along and ahead
of the front in the weakly convergent, but also upslope regime (over
the Big Bend coastal front), the heaviest rain will begin later this
afternoon as the more favorable dynamics overspread. Forecast rain
amounts from various deterministic sources suggest around 2-4 inches
to be a good estimate of widespread areal averages. Hi-res data
suggest that isolated locations could see up to double those values,
especially along the Forgotten Coast, Big Bend, and south-central
Georgia. For this reason, the Flash Flood Watch will remain in
effect through tonight. In addition to the threat for heavy rain,
there is a low-end threat for a severe storm or two. Deep-layer
shear and wind profiles become most favorable at the time of peak
destabilization today. However, instability is forecast to remain
rather limited in the cloudy pre-frontal zone and mid-level lapse
rates are forecast to be quite poor in the saturated environment.
Thus, widespread severe weather is not expected, but a storm or two
could produce strong winds or possibly a tornado.

Rain will gradually end from west to east through the night as the
frontal system departs, with cooler air advecting in behind it.
Expect lows to range from the low 40s in southeast Alabama, to
around 60 in the southeast Big Bend.

.SHORT TERM [Sunday Through Monday]...

Sunday will predominantly be much drier and cooler as the quasi-
stationary front draped across our region finally lifts to the
north and east late Saturday night. A surface high pressure system
is expected to build across the north Gulf coast Sunday, which
will lead to a cold Sunday night. Temperatures will fall into the
mid to upper 30s across the region, as calm winds and clear skies
lead to efficient radiative cooling processes across the region.
High temperatures on Sunday will be cooler as well, with much of
the region struggling to reach the low 60s.

.LONG TERM [Monday Night Through Saturday]...

The long term period will predominantly remain dry as surface high
pressure builds over the southeast through the early half of the
work week. As a quick shortwave trough exits off the mid-atlantic
coast Monday night, ridge building is expected to develop in the
upper levels across the southeast starting Tuesday. This upper
level ridge is expected to have a short residence time across the
southeast, as a rather robust upper level trough ejects
equatorward into eastern Texas and Oklahoma by late Wednesday
night. The upper level trough is expected to become separated from
the northern jet stream, and become a cut-off upper level trough,
which will make its progression eastward along the northern Gulf
coast slightly slower. The cold front associated with this system
is not expected to reach our area until late Thursday night into
Friday morning. Given that the previously discussed ridge will
have short residence time across the region, there will not be
enough time for appropriate moisture to return into the region.
This will likely limit the potential for severe weather across the
region, as instability will be lacking. Beyond this next system,
another brief reprieve is expected to end the work week. Overall,
temperatures will remain in the low to mid 60s for highs, and
upper 30s to low 40s for lows across the region.

.MARINE...

Cautionary conditions are expected to linger through the remainder
of the weekend as waveheights and winds remain elevated. During
the day today, shower and thunderstorm activity will likely remain
most of the day across a broad portion of our marine zones. These
showers and thunderstorms will be capable of producing gusty
winds at times. An isolated water spout can't be ruled out with
some of the more robust storms. As the front finally gets pushed
east by late Saturday evening, southerly winds will transition to
northeasterly for the remainder of the period. Slightly more
favorable boating conditions are expected to return by Monday as
surface high pressure builds over the southeast.

.FIRE WEATHER...

Red Flag conditions are not forecast over the next several days.
Widespread rain and low dispersions are forecast today.

.HYDROLOGY...

A very dynamical environment will lead to the potential for heavy
rain and robust rainfall amounts over the next 24 hours. Currently
at the surface, there is a quasi-stationary front that is draped
in a southwest/northeast orientation from the Florida Panhandle to
south central Georgia. This front is providing a focus for
moderate to heavy rainfall through today and tonight. In the upper
levels, a rather robust and energetic shortwave vorticity maxima
is expected to lift northward out of south Texas, and become
negatively tilted later this afternoon. This will provide a focus
for upper level divergence and forcing for ascent across our
area. The region will also be under the influence of the right
entrance region of a 135 knot jet streak across northern Alabama
and eastern Tennessee. This will only enhance the vertical lift
across the region.  Given that PW values across the area are
approaching 2 inches, there is the potential for very heavy
rainfall and the potential for flash flooding across this
frontogenetical axis. With the threat for flash flooding and heavy
rainfall, a flash flood watch has been issued for much of the
area. WPC has also expanded their slight risk for excessive
rainfall across our area. Currently much of the area has already
experienced 2-4 inches of rainfall over the last two days. This
rainfall coupled with forecast amounts of 2-4 inches with isolated
amounts near 6 inches possible today could lead to localized
flooding concerns as well as an increased potential for river
flooding.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not requested. However, spotters are always
encouraged to safely report significant weather conditions when they
occur (while following all local, state, and CDC guidelines) by
calling the office or tweeting us @NWSTallahassee.

&&

.PRELIMINARY POINT TEMPS/POPS...

Tallahassee   70  51  61  38  62 / 100 100   0   0   0
Panama City   66  49  61  42  62 / 100  90   0   0   0
Dothan        66  42  56  35  60 /  80  60   0   0   0
Albany        67  47  58  37  60 /  90 100   0   0   0
Valdosta      72  55  62  38  60 /  80  90   0   0   0
Cross City    75  59  68  40  63 /  20 100  10   0   0
Apalachicola  69  54  61  41  61 / 100 100   0   0   0

&&

.TAE WATCHES/WARNINGS/ADVISORIES...
FL...Flash Flood Watch through late tonight for Calhoun-Coastal Bay-
     Coastal Franklin-Coastal Gulf-Coastal Jefferson-Coastal
     Wakulla-Gadsden-Inland Bay-Inland Franklin-Inland Gulf-
     Inland Jefferson-Inland Wakulla-Jackson-Leon-Liberty-
     Madison-Washington.

     High Rip Current Risk through late tonight for Coastal Bay-
     Coastal Franklin-Coastal Gulf-South Walton.

GA...Flash Flood Watch through late tonight for Baker-Ben Hill-
     Berrien-Brooks-Calhoun-Colquitt-Cook-Decatur-Dougherty-
     Early-Grady-Irwin-Lanier-Lee-Lowndes-Miller-Mitchell-
     Seminole-Terrell-Thomas-Tift-Turner-Worth.

AL...None.
GM...Flash Flood Watch through late tonight for Apalachee Bay or
     Coastal Waters From Keaton Beach to Ochlockonee River FL
     out to 20 Nm-Coastal Waters From Ochlockonee River to
     Apalachicola Fl out to 20 Nm-Coastal waters from Mexico
     Beach to Apalachicola FL out 20 NM-Coastal waters from
     Mexico Beach to Okaloosa Walton County Line FL out 20 NM.

&&

NEAR TERM...Harrigan
SHORT TERM...Bunker
LONG TERM...Bunker
AVIATION...Harrigan
MARINE...Bunker
FIRE WEATHER...Harrigan
HYDROLOGY...Bunker