Area Forecast Discussion
Issued by NWS Jacksonville, FL

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FXUS62 KJAX 292018
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
418 PM EDT Mon May 29 2017

...INCREASING CHANCES FOR AFTERNOON AND EVENING THUNDERSTORMS
BEGINNING TUESDAY...

.Currently...
Afternoon surface analysis depicts high pressure (1019 millibars)
centered over the southeast Gulf of Mexico, extending eastward
across south Florida and into the western Atlantic waters.
Meanwhile, a stalled frontal boundary extends from coastal Texas
northeastward through the lower Mississippi and Tennessee Valleys.
Aloft...deep layered ridging prevails over our region and is
centered just northeast of the Bahamas, while a trough was
deepening over the western Great Lakes and digging southward
through the upper Midwest. A large Mesoscale Convective System
(MCS) generated along the frontal boundary over Texas earlier
today has pushed into the west central Gulf waters, with
convection associated with shortwave energy on the edge of this
MCS developing a batch of convection that is progressing quickly
northeastward across central and northern Georgia. A generally
flat cumulus field and some patches of cirrus debris are found
over our region, with another hot day in progress for locations
along and west of Interstate 95. Temperatures as of 20Z are in the
low to mid 90s inland, with the sea breeze cooling coastal
locations east of I-95 back into the upper 80s. Inland dewpoints
have fallen to the mid 60s, with lower 70s at the coast.

.Near Term /This Afternoon through Tuesday/...
Short-term high resolution guidance suggests that an outflow
boundary originating from convection over central Georgia will
propagate southeastward into interior southeast Georgia around
sunset. We remain in a largely dry and suppressed environment, so
this outflow will probably have to collide with the Atlantic sea
breeze early this evening to break our atmospheric cap to develop
isolated convection, and this would probably be for locations
between Alma/Waycross and Interstate 95. Since confidence remains
low, we have only placed isolated POPs in the forecast grids for
early this evening in these locations. Otherwise, we expect fair
skies to prevail, with low level moisture increasing enough for
some patchy fog formation possible in north central Florida and
the Suwannee Valley. Lows will range around 70 inland to the mid
70s at the beaches.

The trough aloft currently digging into the upper Midwest will
expand and dig southeastward, covering the rest of the Great
Lakes States and the Ohio Valley. The ridge to our east will push
a little further into the Atlantic waters, forcing cyclonic flow
to overspread our region and resulting in southwesterly flow aloft
strengthening. This flow will advect a shortwave trough currently
associated with the MCS over the western Gulf into the Florida
panhandle and southwest Florida by late afternoon. This weather
pattern will also push the frontal boundary into central Georgia
and southern Alabama by late afternoon. Deep layered moisture will
be slow to increase, which should keep coverage scattered for much
of our region despite increasing forcing arriving from the
southwest late in the day. Convection will probably be generated
along the Atlantic sea breeze, which should push west of U.S.
Highway 301 corridor by the late afternoon hours. Highs will top
our around 90 at coastal locations before the sea breeze moves
inland during the early afternoon, with another hot and
increasingly humid day inland, where highs will likely reach the
mid 90s before convection develops. Lingering dry air in the mid
levels will enhance the downburst potential tomorrow afternoon,
with DCAPE values progged to be in excess of 1100 j/kg per model
soundings over much of our area tomorrow afternoon. Storms may
pulse into the severe category as mesoscale boundary collisions
increase, with damaging wind gusts, small hail, and frequent
lightning strikes being the primary hazards.

.Short Term /Tuesday Night through Thursday/...
Tuesday evening...a few afternoon thunderstorms will linger into
the evening hours along the I-95 corridor, with warm and muggy
conditions expected for most areas. There could also be additional
thunderstorm development during the early morning hours across
southeast Georgia due to increased upper level support.

Wednesday and Thursday...seasonably hot and humid conditions will
prevail. Storms will increase to at least scattered coverage each
afternoon and evening as seabreeze/outflow boundaries interact and
take advantage of an increasingly moist and unstable atmosphere.
There will also be some upper level support in the form of embedded
shortwave troughs migrating through the eastern periphery of the
broad longwave trough aloft. A few severe storms will be possible
both days. Locally heavy rainfall, damaging wind gusts, large
hail, and intense lightning will all be possible with the
strongest storms.

.Long Term /Friday through Monday/...
Daily summertime convection will continue, with scattered to
numerous diurnal thunderstorm coverage expected each afternoon and
evening. Broad upper troughing aloft along with cooler 500 MB
temps and plenty of instability and adequate moisture each
afternoon will also provide a continued threat for a few strong to
severe storms each afternoon, especially where seabreeze/outflow
boundaries collide.

Temperatures during this period will settle closer to normal due
to increasing coverage of clouds/storms, with warm and humid
conditions prevailing.

&&

.Aviation...
VFR conditions will prevail at the regional terminals through at
least 08Z. The Atlantic sea breeze will move across the JAX
terminals by 21Z and VQQ towards 22Z, with surface winds becoming
southeasterly around 10 knots through sunset. Patchy fog will
develop inland tonight, with MVFR visibilities possibly developing
after 08Z at GNV and VQQ.

&&

.Marine...
High pressure extending from the western Atlantic into the
southeast Gulf of Mexico will slowly lift northward during the
next few days, but will remain centered south of our waters. This
will create light offshore flow during the overnight and morning
hours, with the Atlantic sea breeze developing around noon over
the near shore waters and pushing inland each afternoon.
Meanwhile, a weak frontal boundary will approach the southeast
Georgia waters from the northwest on Tuesday afternoon. Showers
and thunderstorms will gradually increase in coverage each
afternoon and evening, with activity most likely impacting the
near shore waters during the late afternoon and evening hours,
progressing into the offshore waters during the late evening and
overnight hours. Strong to isolated severe thunderstorms will be
possible, with damaging wind gusts and frequent lightning strikes
being the primary threats. Outside of thunderstorm activity, a
weak local pressure gradient will remain in place and will
result in mostly light wind speeds into next weekend.

Rip Currents: Low risk expected to continue through at least
Thursday due to low surf heights. Sea breezes will develop each
afternoon with breezy conditions developing at area beaches, but
low wave heights will not create a large-scale elevated risk.

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  69  91  69  90 /  10  20  10  30
SSI  76  89  73  86 /  10  40  30  40
JAX  71  93  72  90 /  10  40  30  50
SGJ  73  91  74  88 /   0  40  40  40
GNV  69  94  70  92 /   0  30  20  40
OCF  69  94  70  92 /   0  20  20  40

&&

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

$$

Nelson/Shuler/Corless



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