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ms discuss

Office: JAN

FXUS64 KJAN 170942

Area Forecast Discussion
National Weather Service Jackson MS
442 AM CDT Wed Aug 17 2022

Today and tonight...

With the upper ridge having pushed further west, the region remains
under the influence of East Coast troughing. A front is stalled and
draped across the forecast area. It generally is located from
southeast Arkansas down to the south and east toward Meridian. North
of this front, slightly drier air is in place with dewpoints in the
upper 60s and temperatures are in the upper 60s to low 70s, with a
slight north wind. South of this front, conditions continue to be
rather muggy with dewpoints in the lower 70s and temperatures to
match and either calm or southerly winds. Showers and thunderstorms
have been moving through northern Mississippi overnight and some are
just now beginning to move into the northern parts of my forecast
area. However, the expectation is, per CAM guidance, that these
storms will take more of an eastward push toward Alabama rather than
a southward push. With some early convection and clouds, this will
allow for a temperature gradient in place across the forecast area.
Highs today will be in the lower to mid 80s across the northern tier
of the forecast area, generally north of the Highway 82 corridor.
Highs will be much warm farther south, where clouds and convection
will be slower to develop until this afternoon. Readings are
forecast to reach the lower 90s that see rain first, but otherwise
mid to upper 90s for the remainder of the area. Those locations
along and south of the boundary will also remain rather muggy as
moisture should pool near the boundary. Heat indices will reach 105
to 110 degrees in an area roughly from Hamburg, AR to Laurel, MS. A
Heat Advisory has been issued for this region with the thinking that
additional storms that develop this afternoon would not occur until
after 18Z and potentially closer to 21Z, leaving enough time for
conditions to become uncomfortable.

As the front slowly slides south this afternoon, it will interact
with daytime heating and sufficient instability to generate
additional showers and storms. Some storms will have the potential
to become severe with wind gusts being the primary concern. A
marginal risk is in place to highlight this risk and area with best
timing coming around 2pm until 7pm, perhaps an hour or two later.
Much of this activity should diminish through the evening, though
there remains potential for additional showers and embedded
thunderstorms to continue to affect the region overnight, especially
in western portions of the area. /28/

Thursday Through Tuesday Night...

Relief is spelled "T-R-O-U-G-H" through this forecast period. The
unrelenting upper high that has resulted in a summer of hot and very
humid conditions is now seeing signs of taking a hiatus out west at
least for a while. Upper troughing will be very slow to move away
from the eastern CONUS through the upcoming week and will be
reinforced by late weekend by an additional upstream shortwave.
Models differ on how they handle the eventual evolution of that
wave, with the 12Z ECMWF suggesting only lingering troughing and the
GFS with a significantly stronger solution. Ensemble solutions as
well as the more recent 00Z cycle of the ECMWF indicate that the
previous 12z run of the ECMWF may be a bit too weak and as such it
is likely that the troughing will be sufficient to send a
reinforcing cold front into our area heading into next week.

In terms of weather impacts, this evolution will result in continued
enhanced rain and storm chances with continued diurnal increases in
storm activity in the afternoons and early evenings. Temperatures
will generally be below to near climate normals and as such we can
now more confidently say we will be taking a break from the
excessive heat for at least a while. We won't be "cool" by any
stretch of the word, but most places will see daily highs rising
into the 80s F with highs approaching 90 F confined to the northern
Delta areas. Overnight lows will range from the upper 60s F to the
lower 70s F each night.

The trough and the associated frontal boundary will likely fail to
fully clear our area through the weekend, getting hung up due to a
lack of upper level support. This will likely result in a continued
chance for scattered showers and storms through the weekend and
perhaps even into next week though confidence beyond Saturday/Sunday
is low. The best chances for showers and storms each day are
expected during the afternoons and early evenings during the best
diurnal heating and mixing periods.

While storms and rain chances will remain, with little upper level
support and only weakly veering winds with height along and south of
the boundary that will remain closer by through the period,
substantially organized severe weather is not expected. Precipitable
water will remain high (> 1.75") near the boundary and daily maximum
instability could climb to 2,500 J/KG which could allow for a
damaging wind gust or two. The current best chance for a damaging
gust or two appears to be across far southern portions of the area
on Thursday, near and south of the boundary. This area has been
delineated with a Marginal Risk (1/5) for severe weather to account
for that possibility. This deep moisture and enhanced convergence
near the boundary with deep layer flow largely parallel may favor
some risk for locally heavy rains to train over the same areas with
some risk for mostly urban ponding on non-porous surfaces and poor
drainage areas. /86/


06Z TAF discussion:
VFR conditions are occurring overnight and expected to mostly
prevail. There could be some MVFR vis restrictions where patchy
fog develops overnight. Additional showers and storms will impact
the region later this morning through the day. All sites are
likely to be impacted through this time period with reduced vis
and ceiling restrictions possible. Gusty winds will also be
possible. /28/


Jackson       93  71  84  70 /  72  71  79  49
Meridian      90  70  85  70 /  71  70  74  52
Vicksburg     95  71  83  70 /  63  70  68  41
Hattiesburg   95  72  88  72 /  57  65  87  67
Natchez       95  71  85  70 /  40  58  78  58
Greenville    87  69  84  68 /  69  49  33  14
Greenwood     85  67  86  68 /  80  52  33  17


MS...Heat Advisory from 10 AM this morning to 6 PM CDT this evening
     for MSZ040-041-047>049-053>055-059>065-072>074.

LA...Heat Advisory from 10 AM this morning to 6 PM CDT this evening
     for LAZ007>009-015-016-023>026.