274 
FXUS62 KJAX 120812
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
412 AM EDT Sat Jun 12 2021

...STRONG TO ISOLATED SEVERE THUNDERSTORMS POSSIBLE THIS AFTERNOON
ACROSS SOUTHEAST GA AND THE SUWANNEE VALLEY...
...HOT AND BREEZY CONDITIONS PREVAIL ALONG THE I-95 CORRIDOR 
TODAY...
...WIDESPREAD SHOWERS AND THUNDERSTORMS EXPECTED ON SUNDAY
AFTERNOON...

.CURRENTLY...

Overnight surface analysis depicts low pressure (1005 millibars)
centered over eastern portions of North Carolina and situated
along a "backdoor" cold front that was dropping southward down the
Carolina coastal plain. This feature has pushed the axis of
Atlantic ridging southward across the Florida Straits. Aloft...a
series of shortwave troughs were diving southward from the Ohio
Valley through the southern Appalachians, which was digging a
longwave trough over the eastern third of the nation. Latest
GOES-East derived Total Precipitable Water imagery indicates that
the unseasonably dry air mass that was in place along and south
of the Interstate 10 corridor on Friday has been suppressed
further southward into north central and central FL, with PWAT
values from the I-10 corridor northward now around 1.8 - 1.9
inches, which values south of I-10 remain in the 1.3 - 1.5 inch
range as of 08Z. Showers and embedded thunderstorms have been
traversing the Altamaha River overnight, while a few pockets of
stratocumulus have been migrating eastward along the I-10
corridor, while fair skies prevail elsewhere. Temperatures at 
inland locations were falling through the low and middle 70s, with
coastal locations remaining in the upper 70s to around 80.
Dewpoints at 08Z were mostly in the lower 70s. 

.NEAR TERM [Through Tonight]...

Shortwave energy will continue to drop southward from the southern
Appalachians through inland southeast GA late this afternoon and
this evening, which will sharpen the longwave trough over the
southeastern states, allowing for deeper moisture to continue to
overspread our region to the south of a backdoor cold front that
will be approaching the GA coastal plain overnight. Low pressure
along this front near the Outer Banks will move offshore this
afternoon, but a tight local pressure gradient in place this
morning will be slow to loosen through tonight, resulting in
breezy west-southwesterly winds developing over our area shortly
after sunrise. These breezy winds will likely keep the Atlantic
sea breeze pinned near or just offshore from area beaches this
afternoon, resulting in another hot and breezy day along the I-95
corridor, where highs will soar to the low and mid 90s. A
lingering dry air mass should result in dewpoints dropping to the
upper 60s this afternoon along the I-95 corridor and across north
central FL, keeping maximum heat index values around 100. 

Deepening westerly flow in the mid levels will push the Gulf coast
sea breeze inland late this morning, and this boundary should
initiate scattered convection before noon over the northern
Suwannee Valley, while cooling temperatures aloft associated with
the digging trough also develop convection over inland southeast
GA. Activity will move east-southeastward at a quick 20-25 mph
pace, with scattered coverage continuing south of I-10 and
numerous showers and thunderstorms expected from I-10 northward
this afternoon and evening. Model soundings indicate that ML CAPE
values will reach the 2,000-3,000 j/kg range over inland southeast
GA and the northern Suwannee Valley, and these locations have been
placed within a Marginal risk for severe thunderstorm development
for today. Downdraft CAPE values around 1,000 j/kg at these
locations will promote a risk for downburst winds of 40-60 mph
within stronger convection that develops and potentially pulses
up towards severe limits. 

Highs should climb to near 90 in these locations towards noon 
before convection and cloud cover overspreads the area. An 
additional round of convection ahead of the aforementioned 
"backdoor" cold front may cross the Altamaha River later this 
evening, and isolated convection may continue to develop elsewhere
overnight as mesoscale boundaries continue to collide within a 
moist and increasingly unstable environment due to the upper 
trough moving overhead. Lows tonight will generally fall to the 
low and mid 70s. 

.SHORT TERM [Sunday Through Monday]...

Showers and storms will carry over on into Sunday due to
instability associated with the trailing end of the upper level 
trough. An advancing frontal boundary from out of the north and 
southwest to westerly flow brings moist air with PWAT values 
upwards of 2.25 inches through the region. Diurnal convection will
develop on Monday as an upper level shortwave crosses over the 
southeastern US. Highest likelihood for for thunderstorms and 
heavy rainfall are expected to occur over northeast Florida, south
of the I-10 corridor. Temperatures for this period will reach up 
into the upper 80s and lower 90s, with the highest temperatures 
occuring in areas that receive less rainfall.

.LONG TERM [Tuesday Through Saturday]...

Daily bouts of showers and thunderstorms will develop throughout
next week as a frontal boundary ahead of a drier air mass extends
south over southeastern Georgia by midweek, with the frontal
boundary currently expected to stall somewhere near the Florida-
Georgia border. Instability and moist air flowing from west to
east ahead of the stalled frontal boundary will result in
increased chances of storms and rainfall for northeast Florida and
reduced chances for southeast Georgia. 

&&

.MARINE...

Low pressure situated along a southward moving cold front over the
Carolinas will push offshore of the Outer Banks today. Breezy 
offshore winds will prevail ahead of this cold front through
tonight, with scattered showers and thunderstorms impacting the 
waters this afternoon and evening. Outside of thunderstorm
activity, southwesterly winds will increase to Caution levels of
15-20 knots this evening before diminishing after midnight. Showers
and thunderstorms will likely move over the Georgia waters 
overnight as the front approaches from the north. Seas of 3-5 feet
will prevail both near shore and offshore through tonight. The
front will then stall just to the north of the Georgia waters 
from Sunday through midweek, resulting in prevailing southwesterly
winds and scattered to numerous showers and thunderstorms each 
day. Seas of 2-4 feet will prevail over our local waters from
Sunday night through at least midweek.

Rip Currents: Prevailing offshore winds and low wave heights will
keep a low risk in place at area beaches this weekend through
early next week.

&&

.FIRE WEATHER...

Breezy westerly surface and transport winds today will promote
good dispersion values area-wide outside of thunderstorm activity.
Strong to isolated severe thunderstorms will be possible this
afternoon and evening across southeast GA and the Suwannee Valley.
Westerly transport winds will remain breezy on Sunday across north
central FL, with lighter winds elsewhere resulting in marginally
low dispersion values. Numerous afternoon and evening showers and
thunderstorms are expected throughout our region on Sunday.

&&


.PRELIMINARY POINT TEMPS/POPS...

AMG  89  71  88  69  90 /  70  80  70  20  30 
SSI  89  75  88  74  88 /  60  60  70  40  30 
JAX  92  72  91  71  89 /  50  60  80  50  50 
SGJ  93  74  89  72  87 /  40  40  70  60  50 
GNV  90  73  88  70  87 /  40  40  80  60  70 
OCF  90  73  89  72  87 /  30  40  70  60  70 

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...None.
AM...None.
&&