Flooding in Georgia, March 5, 2020

Area Forecast Discussion
National Weather Service Jacksonville FL
557 AM EST Thu Mar 5 2020

.AVIATION...
[Through 12Z Friday]

Meandering front across north Florida this morning with cool
northerly flow impacting SSI, Duval county terminals and SGJ with
low stratus bringing restrictions of LIFR to MVFR with passing
light showers/drizzle. Fog near GNV and low stratus will lift
after sunrise, while low stratus at other terminals will gradually
lift through mid to late morning although SSI will remain under
restrictions through much of the day with more persistent rainfall
expected. Breezy SSW winds develop across NE FL by midday with
mostly rain free conditions until mid to late afternoon as broken
squall line of storms approaches from the west. Storms exit
offshore of the coast this evening, with just lingering showers
around midnight and low stratus advecting southward trailing
frontal passage with winds shifting NW through sunrise Friday
morning bringing IFR to LIFR ceilings.

&&

.PREV DISCUSSION [336 AM EST]...

.NEAR TERM [Through Tonight]...

Lull in widespread showers early this morning with shallow
isentropic lift along a stalled quasi-stationary front extending
zonally near the I-10 corridor. A few light showers were along
this boundary, with patchy fog and low stratus north and south of
the boundary. Not much change expected through sunrise other than
the stalled front to begin to lift northward across SE GA morphing
into a warm front ahead of a surface low tracking eastward along
the central Gulf Coast states. This pivoting of the trough axis
northward could trigger a few more showers across SE GA into the
early morning hours, otherwise, a dry morning commute for most
locations with temps ranging from the cooler mid/upper 50s north
of the front to the upper 60s to near 70 south of the front.

Deteriorating conditions expected through the day today as the
warm front lifts and lingers near the Altamaha River basin into
the afternoon as the surface low tracks east directly over the
local area into the early evening. The potential for flooding
rainfall will continue to focus across SE GA into the late morning
and through the afternoon with strong low level lift, upper level
forcing and unseasonably high deep moisture all coinciding over
already saturated grounds near the Altamaha River basin. Locations
from NW Wayne county to northern Coffee county received 3-4
inches of rainfall yesterday and an additional 1-2 inches is
forecast across the basin today, with locally higher amounts.

Rainfall less of a concern for zones south of Waycross, however,
severe storm potential will increase for all areas from the west
by late morning for SE GA, then across the entire forecast area
this afternoon into the early evening as t'storms develop near and
south of the surface low. Convective ingredients including very
strong speed shear and a strong baroclinic zone over SE GA along
the frontal axis will bring the potential for severe storms,
including tornadic cells this afternoon into this evening with 0-1
km Helicity 200-400 m2/s2 near the meandering frontal zone. Farther
south across NE FL south of the surface low, expect more of a
broken pre-frontal squall line of storms, some of which could be
strong to severe with damaging wind gusts.

General timing of greatest severe storm potential is roughly noon
to 7 pm for inland SE GA and the Suwannee River Valley to about 3
pm through 9 pm for coastal SE GA and the remainder of NE FL.
Storms will press offshore through 9-11 pm, trailed by lingering
low stratus and light showers through the early morning hours as
surface cold front presses south across the local area and lingering
850 mb trough lags through 09z. Dry conditions expected by
sunrise Fri with cooler conditions and progressively clearing
skies from NW to SE through the morning with breezier NW flow.

Temperature gradient will be quite impressive today across the
local area with highs ranging some 20-25 degF from the upper 50s/near
60 across the Altamaha River basin to the mid/upper 80s across
our southern FL zones near the St. Johns River basin under breezy
SW flow. Tonight trailing the cold front, minimum temperatures
will cool into the 40s across SE GA to the 50s to near 60 across
NE FL.

.SHORT TERM [Friday Through Saturday]...

The cold front will have completely moved across the southeastern
US by early Friday morning and will be followed by a cold air
mass which settle in over the forecast area resulting in clear
skies, dry weather, and cooling temperatures. Breezy northwesterly
winds are anticipated for Friday, with winds peaking in the
afternoon and reaching speeds of 15-20 mph with gusts up to about
25 mph. High pressure will persist through into Saturday, with
temperatures dropping into the 60s & lower 70s on Friday and into
the upper 50s and lower 60s on Saturday. Overnight low
temperatures will drop down into the mid to upper 30s in southeast
Georgia and in the upper 30s and lower 40s for northeastern
Florida during this period.

.LONG TERM [Sunday Through Thursday]...

A warming trend will kick off on Sunday as the center of the high
pressure air mass begins to drift off to the northeast, resulting
in the prevailing flow veering to become more out of the east and
then shifting about to be out of the southwest by Tuesday. High
pressure ridging will persist over the entire region through
Monday and will inhibit convective developments as temperatures
rise and humidity levels increase. Models show isolated to
scattered showers starting to develop over inland southeastern
Georgia in association with a weak short wave trough, on Tuesday
and Wednesday, however ridging over the Florida peninsula from out
of the east will restrict build ups from developing to the south.
Daily high temperatures are expected to increase from out of the
60s and lower 70s on Sunday up into the upper 70s and lower 80s by
midweek. Overnight low temperatures will similarly warm from out
of the 40s up into the mid 60s.

.MARINE...

A warm front lingering over the local waters early this morning will
lift north through the afternoon. Elevated south winds over the FL
outer waters will continue near Small Craft Exercise Caution
levels today. An area of low pressure will track across south
Georgia this afternoon into the evening with a broken line of
thunderstorms tracking offshore over the local Atlantic waters
late this afternoon and early evening. A cold front will move
south of the waters tonight trailed by clearing skies and strong
offshore flow late tonight with advisory conditions expected over
the outer waters and potential gusts to gale force. Issued a Small
Craft Advisory with the morning forecast for the outer waters
through Sun evening. Gusts to gale force will be possible Friday
night into Saturday morning, and a Gale Watch may be needed. High
pressure will build north of the waters Saturday then northeast
Sunday and Monday as winds and seas decrease with onshore flow.

Rip Currents: Low risk today and Fri. Elevated risk possible this
weekend for NE FL beaches as winds become onshore.

.HYDROLOGY...

Moderate river is expected to continue and/or forecast to re-
develop along the Altamaha River basin based on recent rainfall
and an additional 1-2 inches today across the basin. Recent
guidance continues to take the Alapaha at Statenville into Minor
flood late this weekend cresting very close to Moderate flood
early next week. The Satilla river at Atkinson is expected to
continue in Minor flood through early next week with guidance for
the Satilla near Waycross forecast to rise into Minor Flood Stage
early next week.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is requested. Spotters should safely report
significant weather conditions and/or damage by calling the office or
tweeting us @NWSJacksonville.

&&

.PRELIMINARY POINT TEMPS/POPS...

AMG  65  46  63  36  59 / 100  30   0   0   0
SSI  69  51  64  40  57 / 100  50   0   0   0
JAX  82  53  68  40  59 / 100  60   0   0   0
SGJ  84  55  68  43  58 /  90 100   0   0   0
GNV  83  54  69  38  61 / 100  50   0   0   0
OCF  84  56  70  40  63 / 100  80   0   0   0

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...Flash Flood Watch through this evening for Appling-Atkinson-
     Bacon-Coffee-Jeff Davis-Northern Ware-Pierce-Wayne.

AM...Small Craft Advisory from 1 AM Friday to 10 PM EST Saturday 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.

&&