938
FXUS62 KJAX 091833
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
233 PM EDT Thu May 9 2024

...New AVIATION...

For the latest NE FL and SE GA Daily Key Messages please visit:
https://www.weather.gov/media/jax/briefings/nws-jax-briefing.pdf

.AVIATION...
(18Z TAFS)
Issued at 232 PM EDT Thu May 9 2024

VFR conditions will prevail at the regional terminals through at
least 20Z. A Mesoscale Convective System (MCS) is expected to race
southeastward towards the terminals late this afternoon through
around sunset, bringing the potential for strong to severe
thunderstorms to SSI and the Duval County terminals after 21Z. We
have included TEMPO groups for wind gusts of 30-45 knots, along
with IFR visibilities and MVFR ceilings as this squall line
potentially moves across these terminals through 01Z. The
MCS/broken squall line will then weaken after 01Z, with confidence
too low to indicate anything other than vicinity thunderstorm
coverage at GNV and SGJ at this time. MVFR to IFR ceilings will
then overspread the regional terminals after 04Z through the early
morning hours on Friday. Another MCS is then expected to impact
our region after 12Z Friday, with this convective complex expected
to move rapidly eastward during the morning hours. We included
PROB30 groups from 13Z-18Z at each terminal for the potential of
20-40 knot wind gusts, along with MVFR to IFR conditions during
heavier downpours. Gusty southwesterly surface winds sustained
around 15 knots, with surface winds shifting to southerly at 10-15
knots at SGJ after 19Z due to a pinned Atlantic sea breeze
boundary near the coast. A period of breezy northerly surface
winds can be expected in the 00Z-04Z time frame in the wake of the
squall line/MCS passage. Otherwise, southwesterly winds of 5-10
knots will resume around or after 06Z Friday. Outside of
thunderstorm activity on Friday morning, west- southwesterly
surface winds will increase to 15-20 knots and gusty before 15Z.

&&

.UPDATE...
Issued at 1232 PM EDT Thu May 9 2024

Early afternoon surface analysis depicts a wavy frontal boundary
extending from the Mid-Atlantic states westward across the Ohio
Valley and then southwestward across the Tennessee Valley, the
Ozarks and northern Texas. Meanwhile, Atlantic high pressure
centered to the east of Bermuda continues to extend its axis
westward across the FL peninsula. Aloft...stout ridging centered
over Mexico`s Yucatan Peninsula continues to flatten in response
to a longwave that was digging southeastward from the Great Lakes
and Upper Midwest. Otherwise, cutoff troughing continues to slowly
retrograde westward across the Rockies. A strengthening jet streak
at 250 millibars (around 35,000 feet) positioned to the south of
the digging longwave trough was migrating from the Mid-Mississippi
Valley towards the Tennessee Valley, and this jet streak and
associated shortwave troughing was energizing a Mesoscale
Convective System (MCS) that was progressing across AL, GA, and
SC. Widespread low stratus ceilings across southeast GA this
morning have lifted to a healthy cumulus field, while a more flat
cumulus field exists across northeast and north central FL early
this afternoon, where a drier and more subsident air mass resides
closer to the northern periphery of the ridge axis. Temperatures
have already soared to the upper 80s and lower 90s in this drier
air mass, while temperatures across southeast GA were generally in
the mid 80s. Dewpoints range from the upper 60s to lower 70s.

The morning sounding at Jacksonville revealed a substantial 3
degrees Celsius inversion based just above 850 millibars (around
5,000 feet), depicting the capped atmosphere that exists across
northeast and north central FL. However, plenty of sunshine will
likely heat temperatures up to levels where this atmospheric cap
will be broken, especially across southeast GA as the upstream MCS
approaches from the northwest this afternoon. Steep lapse rates
and the development of a low level jet of 40-50 knots at 850
millibars should maintain a southeastward moving squall line, with
a cold pool from the upstream MCS progressing southward and
pushing convective coverage across the Altamaha/Ocmulgee Rivers
during the mid to late afternoon hours. This broken squall line
will then race southeastward during the late afternoon and early
evening hours, with weakening likely as the line pushes across the
I-10 corridor towards sunset as it encounters the drier and more
stable air mass that remains in place across north central FL.
Damaging straight line wind gusts of 50-70 mph will be the primary
threat for locations north of I-10, but a few isolated incidents
of hail and tornadoes cannot be ruled out across southeast GA. The
Storm Prediction Center has placed an Enhanced Risk (level 3 out
of 5) for severe thunderstorms across southeast GA, where a 10%
probability of downburst wind gusts in excess of 74 mph exists,
in addition to 5% probabilities for tornadoes along with enhanced
probabilities for large hail. A Slight Risk was maintained for
locations along and south of I-10 into the early evening hours.
High temperatures will soar to the low and mid 90s nearly area-
wide, with maximum heat index values climbing to around 100.

The longwave trough will continue to dig southeastward across the
Tennessee and Ohio Valleys tonight, with strengthening westerly
flow to the south of this feature propelling another shortwave
trough and associated MCS across the Deep South during the
overnight and predawn hours. The prior weakening MCS will push
across north central and coastal northeast FL during the early to
mid evening hours, with a break in between MCSs expected through
the overnight hours. Short-term, high resolution guidance is in
relatively good agreement in positioning this next MCS and
associated strong to severe thunderstorm threat at the doorstep of
the Ocmulgee/Alapaha/Suwannee Rivers around sunrise on Friday,
with this activity then sweeping eastward across our area through
the morning hours. Breezy west-southwesterly boundary layer flow
in advance of this upstream MCS is expected to advect a stratus
layer across the Suwannee Valley and inland southeast GA
overnight, with these low clouds possibly crossing the I-95
corridor around sunrise. Cloud cover and warm air advection
downstream of the approaching cold front should keep lows in the
70-75 degree range overnight.

&&

.SHORT TERM...
(Friday through Saturday night)
Issued at 329 AM EDT Thu May 9 2024

The second round of severe storms associated with a prefrontal
MCV darting from the west is expected during the morning hours
Friday. There remains substantial uncertainty yielding a fairly
low-confidence forecast. That stated, scattered severe storms
will be possible once again for the second time in about a 12 hour
stretch and similarly the primary threat being damaging straight-
line winds up to 50-70 mph. If this prefrontal complex of storms
fizzles out or under performs, it is more likely that stronger
convection will fire off later in the day as the cold front begins
to press in from the north during the afternoon and evening
hours. Though damaging winds will be the mostly likely form of
severe weather, potential for hail and isolated tornadoes cannot
be ruled out. The cold front and associated convection is expected
to exit to the south Friday evening with a drier airmass clearing
the skies in its wake. Temperatures will be on the warm side
again Friday ahead of the frontal passage with highs in the
low/mid 80s in SE GA and mid/upper 80s to near 90 in NE FL.

Dry northwesterly flow working around a ridge of high pressure
building from the west will lead to fair weather conditions
through the weekend with high temps spanning the 80s each day and
lows dropping down into the upper 50s for inland areas Sunday
morning under clear skies and light drainage winds.

&&

.LONG TERM...
(Sunday through Wednesday)
Issued at 329 AM EDT Thu May 9 2024

A wet and unsettled pattern is setting up for next week as a
parade of disturbances lined up one after the next track across
Florida and areas of the Southeastern US. Guidance is fairly
consistent on the first system arriving Monday afternoon and
evening as a wave of low pressure rides along a lifting warm
front. As that warm front lifts across the region, a moist and
unstable airmass will become established which will support an
increasing thunderstorm potential throughout next week. Though
there is increasing spread among guidance by Tuesday, there is
general consensus that an upper trough will swing into the
Southeast, enhancing forcing and shear to perhaps invoke strong to
severe convection. Uncertainty increases further Wednesday and
Thursday but it appears another upper level system will track
across the northern GOMEX and bring additional rain to the region.
Soils are fair receptive to rain and should be able to soak up
the predicted precip; however, the potential for flooding will be
increasing given the back-to-back nature of the systems.
Temperatures will trend near normal through Tuesday and then trend
upward thereafter.

&&

.MARINE...
Issued at 1232 PM EDT Thu May 9 2024

A squall line of strong to severe thunderstorms is expected to
traverse the GA waters during the mid to late afternoon hours
today, with this line reaching the northeast FL waters during the
late afternoon and early evening hours. This squall line is
expected to weaken after sunset as it approaches the waters south
of St. Augustine. Strong to severe thunderstorms will be capable
of producing damaging wind gusts, hail, and frequent lightning
strikes. Outside of thunderstorm activity, seas of 3-5 feet will
prevail both near shore and offshore through tonight. Otherwise, a
cold front will enter the southeastern states tonight and will
progress southeastward across our local waters on Friday afternoon
and evening. Southwesterly winds will strengthen to Caution
levels of 15-20 knots for the offshore waters tonight, with
Caution conditions then spreading to the near shore waters on
Friday.

Additional rounds of strong to severe thunderstorms will be
possible after sunrise and again during the afternoon hours ahead
of this front. Winds will shift to northwesterly in the wake of
the frontal passage on Friday night and Saturday morning, with
weak high pressure the expected to build eastward from the Ozarks
on Saturday night, reaching the coastal Carolina region by Monday
afternoon. Caution level winds of 15-20 knots on Friday evening
will begin to subside during the predawn and early morning hours
on Saturday. Onshore winds will develop on Sunday afternoon and
will then strengthen on Monday night ahead of an approaching warm
front. Showers and thunderstorms will overspread our local waters
by late Monday night as this warm front lifts northeastward
across our area.

Rip Currents: A lingering northeasterly ocean swell will combine
with strengthening southerly winds this afternoon to create a low
end moderate risk at the northeast FL beaches. Gusty offshore
winds should result in a low risk at all area beaches on Friday
and Saturday.

&&

.FIRE WEATHER...
Issued at 1232 PM EDT Thu May 9 2024

Breezy southwesterly surface and transport winds will combine with
elevated mixing heights to create high daytime dispersion values
for most locations along and east of Interstate 75 this afternoon.
Hot temperatures and breezy offshore winds will drive relative
humidity values down to around 35 percent for locations along and
east of the U.S. Highway 301 corridor this afternoon. Low cloud
cover is expected to overspread our region late tonight through
early Friday morning. Strong west-southwesterly surface and
transport winds on Friday will result in high daytime dispersion
values for north central FL, with good values expected elsewhere
across northeast FL despite abundant cloud cover and increasing
rain chances, with fair values forecast across southeast GA.
Rounds of strong to severe thunderstorms are possible during the
afternoon and early evening hours today, on Friday morning, and
again on Friday afternoon. Strong to severe thunderstorms will be
capable of producing damaging wind gusts, hail, and frequent
lightning strikes. An isolated tornado cannot be ruled out during
the severe weather potential this afternoon through early evening.
A cooler and drier air mass will then filter into our region
during the weekend, with minimum relative humidity values falling
to around 30 percent at most inland locations during the afternoon
hours on Saturday and Sunday. Breezy northwesterly transport
winds and elevated mixing heights on Saturday could result in
elevated daytime dispersion values.

&&

.CLIMATE...
Issued at 1232 PM EDT Wed May 8 2024

Daily record Maximum Temperatures at the local climate sites for...

Thursday, May 9th...JAX 96/1962...CRG 93/2008...GNV 95/2011...AMG 95/1962

Friday, May 10th...JAX 94/2017...CRG 95/2003...GNV 95/2011...AMG 95/2011

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  71  83  60  81 /  60  70  10   0
SSI  73  84  64  80 /  80  70  20   0
JAX  73  87  64  84 /  80  80  30   0
SGJ  74  91  67  83 /  20  60  30  10
GNV  73  88  64  87 /  20  60  30  10
OCF  72  89  68  89 /  20  50  30  10

&&

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

$$