Special Weather Statement, NWS Jackson, MS

Area Forecast Discussion
National Weather Service Jackson MS
1241 PM CDT Sat Jul 8 2017

.UPDATE...
Updated for 18Z aviation discussion

&&

.AVIATION...
18Z TAF discussion:
A front currently draped across the ArkLaMiss, stretching from the
Golden Triangle to the Central LA, will serve as a focus for
convective storms as it continues to push slowly south. Chances
for storms will be be greater in locations south of the front
which has already pushed through the Jackson Metro. Expect -TSRA
to impact KGTR, KMEI, and KHBG over the next few hours as the
front slowly meanders. Flight conditions will lower to MVFR/IFR
levels at sites impacted by storms. Coverage of storms will begin
to decrease after 00Z however some scattered showers and isolated
storms will remain a possibility through the early hours of
nightfall.

&&

.DISCUSSION...
Active morning already across portions of the ArkLaMiss, in
particular the Delta region. A complex of storms that originated
across the Ozarks(or even further north) overnight continued to
move into the Delta early this morning. Some of these storms were
strong to severe with damaging winds and hail being the main
concern. This activity continues to dive south into the central
portion of the forecast area, but numerous outflow boundaries look
to precede these storms and the complex has finally been showing
signs of weakening as it moves south. However, as daytime heating
progresses, some additional storms have developed along this
outflow boundary further south closer to the I-20 corridor.
Another cluster of storms has been lingering across portions of
the Pine Belt this morning but these looks to remain sub-severe.

How this morning convection will impact the remainder of the
forecast today is still the challenge. The front that is expected
to move through today remains further to our north and our region
is situated under northwest flow aloft. Hi-res models indicate
varying solutions as the HRRR shows this current convection
decreasing in severity as it moves south and then not developing
much else through the remainder of the day. However, others show
some development in the south later this afternoon perhaps in
association with any lingering boundaries. Taking all of this into
account, I tried to make some adjustments to the POPs and weather
to account for latest trends. I feel that this activity will
continue its push south, bringing some kind of showers and/or
storms to the central and southern parts of the forecast area but
the earlier activity may very well wipe us out for much for the
rest of the day.

As for severe potential, still cannot rule out an isolated severe
storm as this activity pushes south. However, current mesoanalysis
indicates this will move into an area of poorer lapse rates, weak
shear. Will continue with the marginal risk for an isolated storm,
especially as any boundaries interact with daytime heating.

Temperatures this afternoon will also be tricky as plenty of cloud
cover will limit heating, particularly in areas that have seen
rain and convection this morning. I have gone ahead and lowered
highs some in the Delta and trimmed back highs elsewhere as clouds
look to encroach on the region quickly. /28/

Prior discussion below:

Today and Tonight...Right out of the gate this morning, convection,
ahead of a cold front currently draped across the Mid-South region,
has dropped south into the Delta region.  Latest radar trends show
an outflow boundary associated with this activity has raced well
ahead of it, which has caused the activity to lose a bit of its
punch and dissipate on its southward trek.  This trend is expected
to continue through sunrise, with sporadic activity popping up along
the outflow.  Another area of convection dropping southeast out of
the Ozarks into Central Arkansas, could yet again affect the Delta
region, if it holds together and remains on its current trajectory,
by 13-14Z this morning.  Thus, as we begin the today period, the
better POPs will reside over the Delta region through the morning
hours, with only isolated showers and storms possible elsewhere.

As the day progresses, the forecast area will become better fixed
under northwest flow aloft as a trough axis swings further east of
the CWA.  This will force the aforementioned cold front to sink
south and into the ArkLaMiss.  This front, in addition to any
residing outflow boundaries or disturbances aloft propagating over
the region, where a hot, moist, and unstable airmass will reside
today, will result in scattered to numerous showers and storms
developing across the CWA, primarily during the afternoon hours.

Some isolated severe storms will be possible today as well,
especially during the afternoon and early evening hours.  Damaging
wind gusts will be the primary hazard with the most intense storms
during this time.  However, a few storms could perhaps become
capable of producing some hail.  Frequent lightning and heavy
downpours, as precipitable H2O values sit near 2 inches, will
accompany all of today's storms as well.

Currently, it looks like much of the convection will gradually
subside during the evening hours.  However, some activity could
continue off and on overnight across southern portions of the CWA
where the boundary is progged to reside.  Also, with the forecast
area under northwest flow aloft, attention will need to be paid
upstream for any disturbances aloft that might try to spark
convection and propagate towards and possibly into the CWA.

As far as temperatures are concerned, highs this afternoon will
range from the upper 80s to lower 90s.  Of course, these forecasted
highs could be lower if affected by convection or clouds over the
area as peak heating rolls around.  With dew points in the 70s,
afternoon heat indices could climb to around 100 in a some locales.
Some drier air will begin to seep into mainly northern portions
of the forecast area tonight. Lows early Sunday morning will range
from the upper 60s north to lower 70s south. /19/

Sunday through next Friday:

Global models are in general agreement on the upcoming weather
pattern with an amplified western CONUS ridge and eastern CONUS
trough expected to slowly shift eastward resulting in building
heights and hotter temperatures as we go later into the week. In the
shorter term, a much drier airmass with precipitable water values
dropping below an inch will surge southward over the ArkLaMiss
Sunday behind the previously mentioned frontal passage, and this
will bring at least a couple of days of mostly rain-free weather
with maximum heat indices below 100. But as would be expected in
mid-July, the deeper moisture will not waste much time returning,
so we expect precipitable water to rise back to near two inches
Tuesday afternoon and Wednesday resulting in greater diurnal
pulse-type storm coverage.

With the building ridge, would also expect hotter temperatures and
heat indices beginning to approach 105 as we go into Thursday and
Friday. At first glance, the mid level ridge looks like a favorable
pattern for above normal temperatures, but the low-level thermal
ridge in the GFS/ECMWF output is not overly extreme, and the 08/00z
NAEFS actually shows little if any H850 temperature anomaly, so am
hesitant to go much above guidance for now, and will hold off on any
mention of heat threats in the HWO/graphics. /EC/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       91  71  91  71 /  58  24  17   5
Meridian      91  71  90  69 /  58  31  15   6
Vicksburg     91  72  91  71 /  56  23  13   5
Hattiesburg   92  72  89  71 /  60  50  36  13
Natchez       91  72  89  72 /  58  38  29  11
Greenville    84  69  91  71 /  66   5   5   4
Greenwood     87  69  91  70 /  45   6   5   3

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...None.
LA...None.
AR...None.

&&

JPM3

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