095 
FXUS62 KJAX 220647
AFDJAX

Area Forecast Discussion
National Weather Service Jacksonville FL
247 AM EDT Sat Jun 22 2019

...OPPRESSIVE HEAT REMAINS, SEVERE THUNDERSTORMS POSSIBLE THIS 
WEEKEND...

.Currently (12am)...

Surface temperatures have been slow to decrease this evening with many
locations still in the 80s and heat indices in the low to mid 
90s...at midnight. Surface dewpoint temperatures in the mid to 
upper 70s keep low temperatures elevated until morning with rich
moisture continuing to stream in from the Gulf Coast. This will
set the stage for another day of elevated heat indices near
heat advisory levels. 

Additionally, a slowly decaying mesoscale convective system (MCS)
which originated across central Kansas Thursday evening is now
moving through northern Georgia/Alabama/Mississippi. While this
feature continues to decay overnight, the outflow boundary left
behind may be a vital piece to figuring out the puzzle for 
Today's slight risk for severe weather. 


.NEAR TERM...Today and Tonight...

Complicated scenario to start the weekend as a very moisture rich
environment sets the stage for a potentially busy weather day
across the area. Overnight, a slowly decaying MCS has pushed into
the Southeast with an outflow boundary moving south ahead of the
convection. This could assist convective development during the
afternoon hours as temperatures rise into the mid to upper 90s
and dewpoint temperatures persist in the low to mid 70s. An
elevated mixed layer originating well to the west continues to
supply steep mid- level lapse rates for the weekend, increasing 
CAPE values and increasing the chance for strong updrafts. SPC
Sounding Climatology shows that the average mid-level lapse
(700-500 mb) are near 5.8 C/km this time of year. Forecast 
soundings suggest mid-level lapse rates near 7-7.5 C/km. Hail and
strong wind gusts will be the favored severe threats with any 
strong storms that develop in this environment. Relatively weak 
shear and warm temperatures below 850 mb (weak capping) could be 
limiting factors during the early afternoon hours. 

Convective development and mode are rather uncertain and could
vary across the area. With steering flow primarily out of the west
to northwest, it's hard to see how any MCS would make it into the
area late Saturday. Extreme northeast zones and Atlantic waters
could see the western periphery of a southeastward moving MCS late
Saturday. With the lack of strong mid-level flow from the north, 
cold pool propagation on the western edge of the MCS would likely
lead to undercutting of any storms that were to develop, limiting
there chances of being severe. Nevertheless, given the
environment, scattered storms developing late in the afternoon
north of I-10 will pose the best threat for severe weather.
Further south, coverage is expected to remain isolated.

Regarding temperatures, the message remains the same as yesterday.
Mostly sunny skies allow temperatures to quickly warm across the
area with the highest temperatures across Georgia/Jax Metro. There
is still a concern of near criteria heat indices with dewpoint
temperatures in the mid 70s and temperatures in the mid 90s. The
area of highest concern is across SE Georgia where indices reach
105-109. With only a small area forecast to reach criteria for 
1-2 hours decided to hold off on a heat advisory for now. Special
caution should be taken with any outdoor activities this weekend.

.SHORT TERM...Sunday through Monday...

Slightly different scenario for Sunday as steering flow becomes 
more northerly east of the ridge axis over the Gulf Coast. With
Saturday's convective events likely playing a role in Sunday's
convective initiation, there is some uncertainty as to how events
play out on Sunday. An upper level trough moves through the
Southeast with thunderstorms developing across central Georgia and
South Carolina. These thunderstorms should then congeal into a
line and move south/southeast during the afternoon and evening
hours. A more favorable steering pattern should aid thunderstorm
movement down the coast. Global models favor an MCS type feature
moving through the I-95 corridor on Sunday, but there isn't much
high-resolution support yet given the various possible scenarios
on Saturday conflicting the model output. For now, it is known
that the environment will continue to be unstable and therefore
supportive of severe weather. A Day 2 marginal risk has been added
for Sunday's potential. Most likely severe weather type will be
gusty winds. 

On Monday, the trough and deeper moisture finally pushes south 
ushering in less favorable chances for convection, however,
temperatures remain very warm with much of the area still seeing
mid to upper 90s for daytime highs. Best chance for isolated
showers/thunderstorms will be south of a line from Gainesville to
St. Augustine. 


.LONG TERM...Tuesday through Friday...

By Tuesday, steep mid-level lapse rates originating from the cooler
elevated mixed layer air finally begin to increase (warm) as the 
upper level ridge is replaced by a weak shortwave trough moving 
through west to east zonal flow. Weak, stagnant flow continues
through the rest of the long term period as an upper level trough
axis slowly retrogrades from east to west along the Gulf Coast.
Moisture content is not incredibly rich with 1.6-1.8 inch PWATs
available throughout the week. The driest day appears to be on
Tuesday as a corridor of 1.5 inch PWATs move in over the region.
Days will consist of diurnally driven convection originating from
sea-breeze boundaries with mostly scattered coverage. 

With the ridge axis overhead to start the period, Tuesday will be
the warmest day of the long term with widespread mid-upper 90s.
The rest of the period features high temperatures in the low to
mid 90s with decreasing heat indices as surface dewpoints
decrease by a few critical degrees.

&&

.AVIATION...

Prevailing VFR conditions with VCTS for Duval/SSI TAF sites this
afternoon as scattered thunderstorms are expected. 

&&

.MARINE...

High pressure to the southwest and low pressure to the northeast
promote westerly flow over area waters. Northwesterly flow in the
mid-levels provides the opportunity for severe storms over area
waters this weekend. For next week, typical afternoon showers and
thunderstorms are expected with sea-breeze boundaries moving
inland. 

Rip Currents: Low risk of rip currents with westerly flow this
weekend. 


&&

.PRELIMINARY POINT TEMPS/POPS...
AMG  94  75  95  73 /  10  10  40  20 
SSI  91  78  90  76 /  20  10  40  30 
JAX  94  75  95  75 /  30  20  20  20 
SGJ  92  75  92  74 /  30  10   0  20 
GNV  91  74  93  74 /  20  10   0  10 
OCF  90  74  92  74 /  10  10   0  10 

&&

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

$$

McGinnis/Wolf