094 
FXUS62 KJAX 151444
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
1044 AM EDT Tue Jun 15 2021

...ISOLATED STRONG TO SEVERE STORMS POSSIBLE THIS AFTERNOON INTO
EVENING...

...MAX HEAT INDEX VALUES TODAY WILL REACH 105 DEGREES IN SOME 
AREAS...

.UPDATE...

A cold front over central Georgia is shifting southward towards
the area today and tonight. Scattered showers and storms develop
ahead of the frontal boundary and along the sea breezes this
afternoon into evening. A pocket of drier air is spreading into
southeast Georgia with satellite PWAT estimates dropping into the
1.2-1.4". Best chance for storms this afternoon will be along and
south of the FL/GA border where there is better moisture (JAX 12Z
sounding PWAT = 2"). Moisture recovers over southeast Georgia
later this evening which could support isolated showers and
storms. Despite weak shear, there is ample CAPE and DCAPE to
support occasional downbursts with strong/damaging outflow winds
this afternoon into evening. Heavy downpours will also be possible
which could cause minor flooding. Otherwise, hot and breezy day
with highs in the low to mid 90s and heat indices between 100-105
possible. 


&&

.PREV DISCUSSION [724 AM EDT]...

.NEAR TERM [Through Tonight]...

Prevailing flow from out of the southwest ahead of the advancing  
frontal boundary will lead to showers and thunderstorms forming 
later this afternoon with a potential for strong isolated storms
potentially forming in conjunction with developing dynamics aloft.
Most likely areas for storms to develop span areas near the 
Florida-Georgia border and north and along the I-10 corridor. 
Storms are expected to clear out this evening. High temperatures 
for today are expected to lower to mid 90s with the highest 
temperatures expected to occur over southeast Georgia, with heat 
index values of 100 degrees expected throughout the forecast area.
Overnight low temperatures will be in the lower 70s.


.SHORT TERM [Wednesday through Thursday Night]...

A potent shortwave trough diving southeastward from the eastern 
Great Lakes region on Tuesday night will pivot eastward across the 
Mid-Atlantic states, emerging offshore by Wednesday evening. This 
feature will briefly deepen troughing along the southeastern 
seaboard, driving another frontal boundary southward across 
southeast GA during the afternoon hours. An unseasonably dry air 
mass, featuring PWAT values falling to around 1 inch, will filter 
into inland portions of southeast GA by late afternoon, which 
will keep thunderstorm activity mostly confined to northeast and 
north central FL. Breezy low level west-southwesterly flow south of 
the FL/GA border will likely advect widely scattered convection 
developing over the FL Big Bend and Nature Coast eastward into the 
the Suwannee Valley and north central FL during the morning hours. 
Outflow boundaries from this morning convection should then migrate 
northward towards the I-10 corridor by early afternoon, which should 
trigger scattered to numerous thunderstorms. Coverage will be 
limited over north central FL during the afternoon hours as a 
cirrostratus shield over the Gulf of Mexico and the FL peninsula 
lifts northward, which will limit instability. Model soundings 
depict cooling mid-level temperatures as the base of the eastern 
U.S. trough migrates through our area, and downdraft CAPE values may 
approach 1,000 - 1,200 j/kg along the I-10 corridor as drier air
aloft advects into our region. These factors should result in a
few storms pulsing and becoming strong or even briefly severe, with 
damaging wind gusts of 40-60 mph, small hail and frequent lightning 
strikes being possible along the I-10 corridor. Fast westerly flow 
will result in a quick eastward storm motion on Wednesday afternoon, 
which will limit the risk for localized flooding. The drier air mass 
will allow highs to skyrocket to the mid 90s across inland southeast 
GA, while highs elsewhere generally reach the upper 80s to lower 
90s. 

Upper troughing will depart the U.S. eastern seaboard by early 
Thursday, leaving our region with weakening northwesterly flow 
aloft. The aforementioned cirrostratus shield associated with 
widespread convection over the southern Gulf of Mexico and broad
low pressure development in the Bay of Campeche will continue to 
overspread our area. The departing trough will result in a frontal
boundary stalling near the FL/GA border on Wednesday night, with
this feature gradually weakening on Thursday and then dissipating
by Thursday night. An unseasonably dry air mass will remain in place
over southeast GA, allowing inland lows to fall to the mid and upper
60s at inland locations by early Thursday morning. Evening 
convection will move offshore for locations south of the frontal 
boundary, with widely scattered convection again developing along 
the FL Big Bend and Nature Coasts during the overnight and predawn 
hours. Isolated convection will be possible over the western 
Suwannee Valley towards sunrise. Lows will fall to the low and mid 
70s across northeast and north central FL. 

Weakening forcing along the decaying frontal boundary and a more 
subsident air mass overspreading our region from the south will 
limit convective coverage to widely scattered for northeast and 
north central FL on Thursday, with dry weather expected for most of 
southeast GA, where highs will soar to the mid 90s at inland 
locations. Our local pressure gradient will loosen, allowing for 
early development of the Atlantic sea breeze, which will keep 
coastal highs around 90. Highs will also remain around 90 for most 
of northeast and north central FL due to increasing cloud cover and 
afternoon convection. Convection will shift offshore before sunset, 
with thickening high cloud cover keeping lows in the upper 60s for 
inland locations north of I-10, with lows around 70 elsewhere, 
except mid 70s at coastal locations.


.LONG TERM [Friday Through Tuesday]...

Broad low pressure is forecast to only gradually organize late this 
week and early this weekend over the western or central Gulf of 
Mexico. Deep-layered southerly flow will develop locally as Atlantic 
ridging builds westward and extends its axis across south FL. Thick 
cirrostratus emanating from widespread convection that will be 
covering a good portion of the Gulf of Mexico should limit 
convective coverage on Friday to widely scattered, mainly for 
locations west of the U.S. Highway 301 corridor. Highs on Friday 
should reach the upper 80s to around 90 across northeast and north 
central FL, while a lingering dry air mass allows highs to climb to 
the lower 90s for inland southeast GA. 

We leaned on the wetter GFS solutions for the upcoming weekend and 
early next week, with widespread afternoon and evening convection 
expected along the I-75 corridor and throughout inland southeast GA 
on Saturday, followed by slightly higher coverage across all of 
southeast GA on Sunday as low pressure potentially gets steered 
eastward along the I-10 corridor in the Deep South. The forecast is 
low confidence due to uncertainty in how organized this low pressure 
center becomes before reaching the central Gulf Coast region this 
weekend. Cloud cover and inland convection should keep highs in the 
mid to upper 80s for most locations this weekend, with a tropical 
air mass advecting into our region on the heels of veering low and
mid level winds, which will keep lows in the 70s. High temperatures 
may climb back into the lower 90s on Monday, with southwesterly low 
level flow likely focusing afternoon and evening convection along 
the I-10 and I-95 corridors.


.AVIATION...
[Through 12Z Wednesday]

VFR conditions continue through the morning hours. Breezy southwesterly
winds develop by late this morning reaching speeds around 12 
knots and gusts near 20 knots through the day. Scattered showers 
and storms are expected to develop near the TAF sites this
afternoon with a chance for the formation of isolated severe 
storms. Stronger storms could cause strong wind gusts and lower 
visibilities due to heavy downpours. Storms are expected to 
dissipate in the evening hours.


.MARINE...

A trough will move into region from the north today with the 
frontal boundary stalling over the area Wednesday and into 
Thursday. Wind speeds are expected to reach into Small Craft
Advisory levels for offshore waters this Afternoon. A weak ridge 
will build to the east Friday into Saturday. Low pressure will 
track to the west then northwest of the region Sunday into Monday.

Rip Currents: SE GA: Low today, Moderate Wednesday
              NE FL: Low through Wednesday


.FIRE WEATHER...

Breezy west-southwesterly surface and transport winds will develop  
shortly after sunrise for locations south of Interstate 10, with 
breezy westerly surface and transport winds expected north of I-10. 
These winds will create good dispersion values area-wide by the late 
morning hours. Strong to isolated severe thunderstorms will be 
possible this afternoon, with strong wind gusts, lightning, and 
small hail possible within stronger activity. A drier air mass will
then filter into inland portions of southeast Georgia on Wednesday
and Thursday, resulting in only isolated afternoon and evening
thunderstorms for locations south of Waycross. Minimum relative
humidity values may approach critical thresholds on Wednesday and
Thursday afternoons for locations north of Waycross. Breezy
westerly surface and transport winds will continue on Wednesday
for locations south of Waycross.

&&

.PRELIMINARY POINT TEMPS/POPS...

AMG  96  69  93  66  95 /  30  30  10  10   0 
SSI  94  76  90  74  89 /  20  20  30  30  10 
JAX  95  73  93  70  92 /  60  30  60  30  30 
SGJ  92  73  92  74  90 /  50  20  60  30  30 
GNV  91  72  90  71  90 /  60  20  60  20  40 
OCF  90  74  89  71  89 /  60  20  40  20  40 

&&

.JAX WATCHES/WARNINGS/ADVISORIES...
FL...None.
GA...None.
AM...Small Craft Advisory from 6 PM this evening to 5 AM EDT 
     Wednesday for Coastal waters from Altamaha Sound to 
     Fernandina Beach FL out 20 NM-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.

&&