355
FXUS64 KJAN 041800
AFDJAN

Area Forecast Discussion
National Weather Service Jackson MS
100 PM CDT Thu Jul 4 2024

...New AVIATION...

.MESOSCALE UPDATE...
Issued at 1042 AM CDT Thu Jul 4 2024

Rest of today...

Morning analysis this July 4th holiday indicates 595DM mean 500mb
ridge axis centered across the Gulf Coast states, with continued
anomalous & moist tropical southerly return flow situated across
the region (i.e. PWs >=90th percentile to near climatological
maximum around 2.25 inches). Moisture profiles observed this
morning along the northern Gulf Coast were at record values. With
moist boundary layer in the low-mid levels, mixing will be at a
minimum & dewpoints will remain near 77-80 degrees. This soupy
airmass will feel quite awful, but such high boundary layer
moisture has kept persistent ceilings/stratocumulus & earlier
convective initiation (CI) this morning. This early CI will aid
in hindering some of the worst dangerous heat potential southeast
of the Natchez Trace corridor, where the more scattered to
numerous rain & storms will be focused. Widespread clouds could
hamper heating somewhat, but with limited mixing of sfc dewpoints,
aftn heat indices/heat stress will remain quite awful, with areas
along & northwest of the Natchez Trace likely peaking >110 degree
F & upwards around 115-120 degree F range. Observations currently
this morning are indicating the low 100s while less cloudy areas
already peaking above Heat Advisory or even Excessive Heat Warning
criteria. Heat headlines/graphics look on track & no changes are
needed. With further heating & high sfc dewpoints, SBCAPE will
peak in the 90th percentile range in the 4000-4500 J/kg, with some
microburst potential possible per 12Z modified soundings. Gusty
winds & hail would be the main concern with any stronger storms &
isolated severe storm can`t be ruled out. Storms should wind down
into the evening, which would alleviate concerns for any upcoming
outdoor activities. Due to deep, tropical moisture & light
southwesterly upwind propagation, storms will be slow moving.
There is some support, in the Hwy 98 to I-59 corridors, in HREF
prob match mean >3 inches & convective allowing models of some
locally heavy rain in spots. This is localized enough to not
mention in the HWO graphics. Updates are out. /DC/

&&

.DISCUSSION...
Issued at 322 AM CDT Thu Jul 4 2024

Today and Tonight:

Happy Independence Day, ArkLaMiss!

Today won`t be very independent of the week it resides in, however,
with hot and humid conditions continuing. One silver lining to that
grey cloud, however, is... well, grey clouds. As increasing depth of
the low level moisture continues amid consistent southerly flow and
500 mb heights falling from around 594-596 dam to the 592-594 dam
range, we should see a bit more shower and storm coverage with
the best chances across southern Mississippi where some afternoon
seabreeze influence could offer additional lift. The rain chances
are unlikely to cool the area off too much though and the only
noticeable difference may be from southeast, where the best rain
chances reside, to the northwest where lowest chances are
expected. This will likely mean that southern Mississippi is
slightly less oppressively hot compared to the north where heat
indices are likely to reach 110-120 F compared to "only" 106-110 F
further south.

Excessive heat warnings and heat advisories delineate these areas
and the lack of overnight relief as lows this morning (and yesterday
morning..) hang out around 80 F will mean that the heat is
especially dangerous. Greenville, for example, recorded max heat
indices around 109 F Tuesday, 120 F Wednesday, and will likely see
>110 F again today. For that reason, and especially for the Delta
but area wide too, extra caution should be taken when outdoors
particularly from mid morning into the early evening as heat stroke
will be likely with prolonged activity.

Temperatures will be slow to fall tonight with overnight lows again
in the upper 70s F to near 80 F. Exceptions will be in those lucky
cooler spots that see evening rain showers where temperatures likely
settle into the middle 70s. In those areas, however, patchy fog will
be likely late tomorrow night amid weak winds and dewpoints in the
middle 70s F alongside those temperatures. /86/

Friday through next Wednesday: Most guidance indicate a small
shift in the upper level pattern as westerlies are forecast to dip
farther south and suppress the subtropical ridge. Overall, this
should help to reduce heat stress and increase convective
rainfall coverage over the forecast area.

A cold front is expected to move into northern portions of the
area Friday. As the front interacts with tropical-like moisture
during peak heating, we should see considerable shower/storm
coverage, especially over central/eastern MS. With mid level flow
up to about 20kt, multicell storm line segments seem plausible,
which may help to increase storm organization and wind gust
potential. It appears the very humid boundary layer will heat up
significantly ahead of the front, and have therefore expanded the
elevated threat to include the entire area.

Going through the weekend, greater moisture convergence and
associated rain chances will be suppressed and confined mainly to
southern portions of the forecast. Likewise, reduced boundary
layer humidity will help to limit heat stress to more tolerable
levels.

Looking ahead to early/mid next week, while Hurricane Beryl is not
expected to have a direct impact on the Lower Mississippi Valley
region, there is a good bit of uncertainty on how the system will
interact with the upper level pattern. It is possible that
tropical moisture will help to enhance rainfall coverage, and
we`ll be monitoring that potential. Otherwise, fairly typical
summertime weather is forecast with diurnally driven convective
rainfall. /EC/

&&

.AVIATION...
(18Z TAFS)
Issued at 100 PM CDT Thu Jul 4 2024

Main aviation concerns this aftn will be focused on aftn SHRA &
TSRA coverage, with more scattered to numerous for central to
southeastern TAF sites, especially at JAN, HKS, MEI, PIB & HEZ.
This will wind down by early evening, by 05/01-02Z at the latest.
MVFR ceilings will redevelop ahead of a frontal boundary dropping
south Friday, with some potentially lower at east-southeast TAF
sites of MEI, PIB & HBG. Any lowered flight categories should
improve by 05/14-16Z, with an early morning through midday increase
in SHRA & VCTS from north to south from approaching fronth. Light
southerly winds will prevail through most of the period before
switching more northwesterly through midday Friday. /DC/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       77  92  74  91 /  20  80  70  50
Meridian      76  93  73  92 /  20  80  70  60
Vicksburg     78  92  73  91 /  20  70  60  40
Hattiesburg   77  94  76  92 /  30  80  70  80
Natchez       77  92  73  90 /  10  70  60  60
Greenville    78  92  73  92 /  40  60  50  20
Greenwood     77  91  71  92 /  40  70  60  20

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Excessive Heat Warning until 8 PM CDT this evening for MSZ018-
     019-025>030-032-034>037-040>043-047-048-053-054-059-060.

     Heat Advisory until 8 PM CDT this evening for MSZ031-033-038-039-
     044>046-049>052-055>058-061>066-072>074.

LA...Excessive Heat Warning until 8 PM CDT this evening for
     LAZ007>009-015-016-023>026.

AR...Excessive Heat Warning until 8 PM CDT this evening for ARZ074-
     075.

&&

$$

DC/EC/DC