Tornadoes and Flooding in Georgia, December 1 to 2, 2018

Area Forecast Discussion
National Weather Service Jacksonville FL
337 AM EST Sat Dec 1 2018

...UNSETTLED, WET WEEKEND WEATHER WITH ISOLATED SEVERE
THUNDERSTORM POTENTIAL...

NEAR TERM...Today and Tonight...

Widespread rainfall along a lifting warm front will impact the
forecast area today, with the most persistent shield of rainfall
expected to focus across SE GA. Forecast models continued to
diverge with placement of highest rainfall amounts, with general
consensus of 1-3 inches across SE GA, with less than 1 inch across
NE FL south of the I-10 corridor through tonight. Decreasing rain
chances are expected across NE FL by afternoon, especially east
of the Highway 301 corridor and toward the Atlantic coast, as the
best forcing will focus north near the warm front, and to the west
ahead of the approaching surface cold front. Late this afternoon
into tonight, rain chances will remain elevated across SE GA and
and actually begin to increase from the west ahead of the slow
moving, approaching surface cold front. The entire forecast area
will be within the warm sector by tonight as dew pts surge into
the mid to upper 60s, near 70s toward the Suwannee River Valley,
bringing an increasing potential for a few strong to severe storms
tonight.

The potential for isolated strong to severe storms will increase
across SE GA and the western Suwannee River Valley late morning
through the early evening where the warm front will focus the best
low level convergence as it meanders over these zones under a
strong 50 kt 850 mb jet and unseasonably high PWAT of 1.8-2" under
SW steering flow 30-35 kts. High 0-1 km helicity values are
expected to rise to 300-500 m2/s2, favoring rotating cells, however,
despite high moisture content and strong dynamics, the limiting
factor for severe storms will be the lack of elevated surfaced
based instability with the HRRR indicating barely 300 J/kg of MU
CAPE by 00Z. Based on limited instability, continued with only
isolated thunderstorms in the forecast for today. After sunset,
the greater potential for strong to severe storms will focus
across inland SE GA (west of Waycross) and across the Suwannee
River Valley (generally west of I-75 corridor) through 12Z Sunday
as instability noses inland from the Gulf Coast region ahead of
the approaching cold front under strong dynamical forcing.
Potential severe thunderstorm hazards including damaging wind
gusts and isolated tornadoes.

A warming trend in temperatures will continue through sunrise as
the warm front approaches, with high temperatures today warmer
than yesterday despite cloud cover due to warm air advection.
Highs will near the upper 60s across SE GA to near 80 across our
southern FL zones. Tonight, lows will only fall into the 60s, with
muggy overnight conditions as dew pts continue to rise.

.SHORT TERM /Sunday through Monday/...

Showers and thunderstorms will continue to be prevalent on Sunday
and Monday as a system of low pressure pushes past towards the
northeast, moving ahead of the encroaching cold front boundary.
Models currently show the heaviest rainfall occuring across
southeast Georgia and west of I-75 on Sunday, with more broad
pattern on Monday as storms develop ahead of the cold front and
press down from the northwest in a band across the region. High
temperatures during this span will reach into the upper 70s and
low 80s, with overnight low temperatures dropping to the mid to
upper 60s.

.LONG TERM /Tuesday through Friday/...

The cold front to the northwest will have completely pushed into
the area by Tuesday morning, with the most southern counties
experiencing storms and showers. The rains will have cleared by
Tuesday afternoon, with the northwesterly flow bringing in cool
dry air for the next couple of days. On Thursday the high pressure
system associated with the front will move off to the northeast,
resulting in a change of the prevailing flow to out of the
northeast bringing in moist air, warmer temperatures, and possible
showers. The lowest temperatures during this span will be on
Wednesday night and early Thursday morning, with lows dropping as
low as the mid to low 30s. Tuesday and Friday's high temperatures
will range from the mid 60s to mid 70s, which will bookend the
cooler max temps on Wednesday and Thursday which will be in the
50s and 60s.

&&

.AVIATION...

VFR conditions early this morning under mid/high clouds with
increasing coverage of light showers/drizzle under ESE flow
generally 5 kts or less. Best rain chances will focus near SSI
through the day where temporary restrictions due to heavy rainfall
are possible, with less coverage of showers across NE FL by
afternoon. Expect increasing southerly winds with gusts near 15-20
kts at times by late morning. Potential for thunderstorms today,
although isolated coverage still supports refraining from
including in the TAFs at this time.

&&

.MARINE...

Southerly winds will increase over the local waters today ahead
of an approaching cold front. Light ESE winds this morning near 10
kts will increase through midday into the 15-20 kt range over the
near shore waters, with 20-25 kts over the outer waters where an
advisory was issued. The front will begin to stall across the
local waters Sunday into Monday with the local pressure gradient
gradually relaxing, causing winds to decrease. The advisory for
the outer waters extends through midday Sunday, then expect
exercise caution conditions through mid-week for the outer waters
as the cold front settles south of the waters Tuesday, then high
pressure builds across the Gulf Coast region through mid-week.

Rip Currents: Moderate risk today under increasing ESE winds into
the afternoon of 15-20 kts with swells near 1 ft and swells
periods of 9-11 seconds. Low risk Sunday as winds transition to
SW.

&&

.HYDROLOGY...

Locally heavy rainfall of 1-3 inches possible across portions of
the Suwannee River Valley of inland North Florida and portions of
inland Southeast Georgia this weekend. This will produce localized
flooding issues along with expected river rises along the
Alapaha, Satilla, Altamaha and Suwannee River Basins.

&&

.CLIMATE...

Deep southerly flow will push near record humid airmass into the
region with dewpoint temperatures reaching the lower 70s in NE FL
on Sunday and Monday:

Record High Dewpoints for JAX, 71F on 12-2-1991, 70F on 12-3-1968.

Record High Dewpoints for GNV, 72F on 12-2-1985, 71F on 12-3-1991.

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  69  66  78  66 / 100  50  60  60
SSI  69  66  76  66 / 100  30  30  40
JAX  74  68  79  67 /  80  20  20  20
SGJ  76  69  80  66 /  50  20  30  10
GNV  75  69  81  68 /  50  30  40  30
OCF  78  68  83  67 /  30  40  40  20

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...None.
AM...Small Craft Advisory from 11 AM this morning to 1 PM EST Sunday
     for Waters from Altamaha Sound GA to Fernandina Beach FL
     from 20 to 60 NM-Waters from Fernandina Beach to St.
     Augustine FL from 20 to 60 NM-Waters from St. Augustine to
     Flagler Beach FL from 20 to 60 NM.

&&

Enyedi/Corless