Tornadoes and Damaging Winds in Florida, January 22, 2016

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
847 PM EST THU JAN 21 2016

...Tornado Watch in effect until 09Z for western portions of the
region...

.Near Term [Through Tonight]...

As of 01Z, the low is located in central Mississippi with a cold
front draped through southern Mississippi and southern Louisiana.
Rain and thunderstorms are starting to move into the western part of
the region. Rain will spread eastward tonight as a cold front
approaches. Thunderstorms will become more likely after midnight.
The storms will be nearing Tallahassee and Albany by 12z.
Thereafter, the line should clear the forecast area shortly after
15z.

While rain is a certainty, it's the severe weather potential that's
more uncertain with this system. On the dynamical side, this system
is quite impressive. 500 mb height falls in the 90-120m range
overspread the area by Friday morning as an upper low moves into
Central Mississippi. 0-6 km wind shear increases to 60 to 65 kts
ahead of the cold front early Friday morning, with 0-1 km shear as
high as 35 kts across the Florida Panhandle. Each of these are very
favorable parameters for severe weather. But is often the case with
our wintertime storm systems, instability is at a premium. Surface
data shows deeper moisture return occurring across the Central Gulf,
but the low level flow further east is expected to remain
sufficiently backed through the evening hours, which keeps a
peninsula or eastern Gulf trajectory to our flow - transporting only
mid 50 degree dewpoint air into the region. It's not until after 06z
that low level flow switches to a SSW direction and transports 60-65
degree surface dewpoints toward us. That coupled with weak lapse
rates, surface-based CAPE in the GFS and Euro struggles to exceed
250 J/kg just inland from the coast and less than 50 J/kg well
inland at DHN/ABY. So while instability is a significant limiting
factor here, should better instability occur, the deep layer shear
will be more than sufficient to support a damaging wind threat with
the primary line - and possibly even an isolated tornado or two
ahead of the squall line. Given the uncertainties (and the
impressive nature of the shear) will include mention of severe
storms generally along and south of the US-84 corridor in GA/AL down
into the Gulf of Mexico. The threat for severe weather should
continue past 12z, but be ending as the cold front sweeps through
the area.

&&

.Aviation...
[Through 00Z Saturday]...

Conditions will be mostly MVFR tonight and into the morning
hours. Thunderstorms will move in late tonight into the morning
hours ahead of a cold front. A few of these storms may be severe.
The primary threat will be damaging winds and possibly a brief
tornado. Southerly winds will increase tonight as a cold front
approaches. During and after the storms move through winds will be
gusty. Outside of thunderstorms gusts could reach 30 knots in the
morning and throughout the day.

&&

.Prev Discussion [416 PM EST]...

.Short Term [Friday Through Saturday Night]...

High temperatures will occur in the morning (just ahead of a
strong cold front), with temperatures slowly falling through the
50s across the region Friday afternoon (except falling through the
40s in the FL Panhandle and southeast Alabama). Gusty winds and
cloudy skies will make it feel even cooler. Some of the NWP models
and MOS continue to "squeeze out" light QPF across south GA and
south AL Friday night. This could present a problem because low
layer thicknesses would become supportive of snow during this
time. However, from a Q-G perspective, our entire forecast area
will be under a region of sinking motion. From an ageostrophic
standpoint, there are no apparent frontogenesis bands or jet
streak circulations that would suggest ascent. The numerical
guidance does forecast high RH values in the lower troposphere,
but this moisture only extends up to 10k ft...below the -10 C
isotherm, the point at which ice typically begins to develop in
clouds through heterogeneous nucleation. In other words, we do not
think there will be snow in our forecast area Friday night or
Saturday morning, even though it will be cold and cloudy.

With the expected cloud cover continuing well into Saturday
afternoon, we leaned more toward the colder, non-MOS temperature
guidance, which tends to perform better in these types of situations.
Despite non-zero wind speeds Saturday night, a light freeze
appears likely.

.Long Term [Sunday Through Thursday]...

A light freeze is possible Sunday night, as our forecast area will
be near a surface high pressure center and the airmass still cool
and dry. A warming trend will begin Monday afternoon as deep
layer ridging develops over the Southeast. The next chance of rain
will be Tuesday and Wednesday as an upper level, semi-phased,
positive tilted, long wave trough approaches slowly from the west.
This system does not appear to be as energetic as the recent
systems which have impacted our area.

.Marine...

It's difficult to discern what may be convective and what is not,
but several of the high resolution models forecast 34 kt wind
gusts beginning late tonight. Even after the squall line moves
well to the east by Friday afternoon, there is good agreement
among the various NWP guidance that there will be frequent gusts
to 34 kt across most of our marine area through Saturday
afternoon.

.Fire Weather...

A soaking rain is expected tonight into Friday morning for all
locations. Cold dry air will move in by Saturday. RH values will
be low from Saturday through Monday, but are not expected to reach
critical thresholds. No fire weather concerns.

.Hydrology...

The Apalachicola River at Blountstown rose to flood stage yesterday
after dam releases upstream. The rest of our area river sites are
currently below flood stage, although some remain in or near action
stage.

Light to moderate rain will affect the area through the day today
with periods of heavier rain expected late tonight through Friday
morning as a cold front moves across the forecast area. Rainfall
accumulations from this system are expected to be around 1-2" total,
with the highest totals west of the Apalachicola and Flint Rivers.
These totals are expected to cause continued flooding on the
Apalachicola River at Blountstown and cause the Choctawhatchee River
at Caryville and Bruce to rise to flood stage Sunday night. At this
time, no additional flooding is forecast, though some rivers may
remain in or return to action stage.

For more detailed information, please visit:
http://water.weather.gov/ahps2/index.php?wfo=tae

&&

.Preliminary Point Temps/PoPs...

Tallahassee   56  63  37  45  31 /  90 100   0   0   0
Panama City   61  62  37  46  34 / 100  50   0   0   0
Dothan        56  58  34  41  28 / 100  60   0   0   0
Albany        52  61  36  43  29 /  90 100  10  10   0
Valdosta      53  65  37  45  31 /  60 100   0  10   0
Cross City    54  65  39  46  30 /  40 100  10  10   0
Apalachicola  61  64  39  48  34 / 100  70   0   0   0

&&

.TAE WATCHES/WARNINGS/ADVISORIES...
FL...High Rip Current Risk until 1 AM EST /midnight CST/ Friday FOR
     Coastal Bay-Coastal Franklin-Coastal Gulf-South Walton.

GA...NONE.
AL...NONE.
GM...Gale Warning until 4 PM EST Saturday 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 Suwannee
     River to Keaton Beach out 20 NM-Coastal waters from
     Apalachicola to Destin FL out 20 NM-Waters from Suwannee
     River to Apalachicola FL from 20 to 60 NM-Waters from
     Apalachicola to Destin FL from 20 to 60 NM.

&&

NEAR TERM...GODSEY/MCDERMOTT
SHORT TERM...FOURNIER
LONG TERM...FOURNIER
AVIATION...MCDERMOTT
MARINE...FOURNIER
FIRE WEATHER...MCDERMOTT
HYDROLOGY...MOORE