Severe Thunderstorm Warning 80, NWS Jacksonville, FL

Area Forecast Discussion
National Weather Service Jacksonville FL
435 PM EDT Thu Jun 20 2019

...SEVERE THUNDERSTORM WATCH IN EFFECT FOR ALL OF SE GA
AND NASSAU COUNTY UNTIL 10 PM THIS EVENING...

.NEAR TERM [Through Friday night)...

A moist and unstable (sfc based capes 3000-3500J) Sw flow to the
north of a deep layer ridge and southeast of a trough under a
moderate amount of shear was producing rounds of fast moving
showers and storms producing heavy rains and strong and gusty
winds. This activity will continue with the final round of
showers and storms moving offshore by early this evening.
Depending upon the amount of heating some of these storms may
produce strong to possibly damaging winds in addition to heavy
rain and frequent lightning.

Next concern is that high-res models consistent on developing
a squall line out ahead of short wave trough which will be
moving across much of Se Ga this eve. This squall line will
traverse Se Ga during the early eve and then weaken as it
heads towards the I-10 corridor later in the evening due
to loss of heating and weakening of trough. Due to steep
lapse rates in combination to moderate amounts of deep shear
and forced ascent...main concerns will be for severe storms
capable of hail and damaging winds. SPC has all of Se Ga
and Nassau county of Ne Fl until 10 pm this evening.

As the short wave trough exits to the Ne on Friday...an upper
ridge begins to build in across the Fl peninsula. Slightly
drier air works into the Se Ga resulting in low coverage of
storms there. However...PWATs of 1.80 to 2.00 inches will
continue across Ne Fl and expecting a round of scattered
afternoon storms enhanced by the west coast seabreeze.
Shear values will not be as much as today but given heating
and steep lapse rates...strong storms still possible with
strong and gusty winds. Afternoon high temps in the mid 90s
combined with the humidity will produce heat indices close
to 105 degrees. Any storms that manage to get going will
fade in the evening after loss of heating.

.SHORT TERM (Saturday-Sunday night)

Deep layer ridging will be across S Fl on Saturday and
retrograde to the Gulf of Mexico Sunday providing a
westerly flow on Saturday and northwest flow on Sunday.
While the air mass will be somewhat drier...the low
levels will be hotter with PWATs will still be above
1.50 inches. In addition...there will be some induced
troughing over the area especially Sunday as the deep
layer ridge moves into the gulf. This results in hot
afternoons with scattered storms developing from
seabreezes and weak troughing. Best rain rain chances
will be across Se Ga and also east of the I-75 corridor
across Ne Fl where collisions of seabreezes and outflows
will occur. Given steep lapse rates and slightly drier
air aloft...the concern would be for pulse storms
capable of strong to possibly damaging winds. Hot afternoon
temps in the mid 90s will combine with the humidity to
produce afternoon heat indices of 105 to 108 degrees
which is close to heat advisory criteria.

.LONG TERM (Monday-Thursday)...

The deep layer ridge will continue to slowly retrograde
along the gulf coast while there is broad induced
troughing across the region. The air mass will continue
moist and unstable which will lead to scattered afternoon
and evening storms each day enhanced by seabreezes and
outflows. Temps to continue above climo.

&&

.AVIATION...Passing showers and tstorms will continue to impact
the terminals through this afternoon. Non-convective gusts of
25-30 kts are expected from the WSW with tstorms producing gusts
of 35-40 kts. After 22Z, expect mainly lingering showers with
another line of storms moving over SE GA this evening which could
impact SSI during the evening hours. Heavy rainfall will cause
restrictions to IFR/MVFR. Tonight, winds relax while remaining WSW
as showers and thunderstorms decrease in coverage and intensity as
they drift southward over NE FL. Low stratus could cause some
early morning restrictions and trended toward FEW-SCT 1-2 kft at
this time.

&&

.MARINE...The combination of a ridge to the south and weak
low passing to the north tonight will produce southwest
winds reaching exercise caution criteria across the waters.
The ridge to the south moves further north which decreases
the gradient somewhat resulting in somewhat lower Sw winds
and no headlines expected. Tail end of Squall Line may be
moving across offshore across portions of the Se Ga waters
this eve.

Rip Currents: Low risk is expected for Friday.

&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  73  94  74  96 /  70  10   0  40
SSI  77  95  78  93 /  50  10   0  50
JAX  76  95  76  95 /  20  40   0  40
SGJ  76  94  76  93 /  20  40  10  30
GNV  75  93  75  93 /  20  40  10  10
OCF  76  92  74  93 /  20  30   0  10

&&

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

&&

PP/AE/MZ/KB

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