Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 221751

Area Forecast Discussion
National Weather Service Jackson MS
1251 PM CDT Sat Jul 22 2017


Updated for 18Z aviation discussion


18Z TAF discussion:
VFR conditions are expected to prevail for the TAF period with the
exception of VCSH/VCTS during the afternoon and early evening
hours (21z/22 - 2z/23) which will bring tempo MVFR/IFR conditions.
Greatest thunderstorm coverage will be along and south of I-20
with only isolated activity further north at GLH/GWO/GTR. Winds
will be light out of the south/southwest through the period. /TW/


As of 14z, the main synoptic scale features influencing the
weather over the ArkLaMiss are a 593dam ridge currently centered
over northeast Oklahoma and extending east through the lower
Mississippi River Valley, and a cold core closed mid/upper-level
low and associated inverted trough drifting west over the northern
Gulf of Mexico beneath the aforementioned ridge. Convective
activity has gotten an early start this morning across the Hwy 82
corridor with area radars showing a cluster of showers and
thunderstorms moving west towards I-55 and the Delta. While there
hasn`t been much lightning activity these showers and storms have
been efficient rain makers so locally heavy rainfall can be
expected. For the remainder of today, the main headline will
continue to be the heat stress concerns with a heat advisory
ongoing for most of the Delta and the Hwy 82 corridor where heat
index values are expected to peak between 105-108 degrees. One
limiting factor will be the ongoing showers and storms that could
cut back on high temperatures in some locations, however coverage
is not great enough to warrant canceling the heat advisory or
adding any other counties, so will let it ride as is for the rest
of the day. Elsewhere outside of the heat advisory, heat index
values are expected to remain between 100-105 degrees with greater
afternoon convective coverage as the upper low/inverted trough
continue to slide west. Adjusted 12z JAN sounding indicated a low
end potential for an isolated microburst or two with any deeper
convection this afternoon, but organized severe weather is not
expected. Storms should start to weaken with loss of daytime
heating tonight and expect most activity to be gone by midnight.

Prior discussion below:

Today and Tonight:

The upper ridge will continue weaken across the area today, and
this combined PWATS ranging from 1.8 to 2.0 inches and afternoon
heating, will allow for another round of thunderstorms. High
temperatures will be a little cooler across most of the area, with
highs in the low/mid 90s. Although the temperatures will be a
touch cooler than yesterday, dewpoints in the mid 70s will cause
heat indices to exceed 105 degrees for areas generally along and
north of I-20. A heat advisory is in affect for later this morning
through the afternoon hours.

The convection will diminish after sunset this evening with skies
becoming partly cloudy overnight. Expect warm overnight lows once
again in the mid 70s./15/

Sunday through the end of the coming work week:

Still looking like our region will get a bit of relief from the
hot and humid conditions through the first portion of the coming
week as the eastern extent of the heat ridge yields to a very weak
cut-off upper level disturbance over the Lower MS Valley vicinity.
It is important to emphasize that overall heat and humidity
levels will not be drastically lower over this period and the
main relief will come from a good deal of afternoon shower and
thunderstorm activity. On Sunday some northern and western
locations still may peak near 105 heat index values midday through
early afternoon, but at this point we do not anticipate needing
an advisory for tomorrow. The very slight cooling trend will
continue into Monday and Tuesday when peak heat index values
should remain closer to 100 degrees for most areas. Overall rain
chances Sunday through Tuesday will be highest over the eastern
half of zones although all locations should be fairly confident of
getting at least a bit of rain over this span. Certainly not out
of the question that some (luckier?) spots in eastern MS may get a
few inches of precipitation Sunday through Tuesday considering
thunderstorms will be producing locally torrential downpours. We
are relatively confident any flooding issues that arise should be
minor and extremely localized. There are no great signals for
particularly robust afternoon storms worthy of more than marginal
microburst threats.

Of course the re-wetting of the region through the early portion
of the coming week may have some negative impact by the time we
get to mid through late in the coming work week. By that time
model consensus is now pretty good that the very "dirty" eastern
extent of the heat ridge over us in the short term will
restrengthen over at least the northwest half of our region. This
evolution should gradually decrease rain chances and confine them
to mainly the southeast half of zones with peak afternoon
temperatures and heat index values responding upwards
(particularly over the Arklamiss Delta). So, once we get past
Tuesday it is quite possible will may be dealing with some
additional heat advisories being necessary, especially by Thursday
or Friday. This will be briefly mentioned in the HWO although
graphics will focus on short term heat implications for now.

Model consensus shows potential for a cold (more like "cool")
front sliding south into the region sometime next weekend. If this
boundary can come through with gusto our region has some hope of
getting more than marginal relief from the heat. However, at this
point it is too early to have much confidence in details this far
out in the forecast. /BB/


Jackson       92  74  92  75 /  45  34  48  22
Meridian      92  74  92  74 /  40  23  44  23
Vicksburg     92  75  92  75 /  37  20  47  23
Hattiesburg   92  74  91  74 /  50  25  54  23
Natchez       91  74  90  74 /  50  30  59  24
Greenville    94  76  93  75 /  47  10  36  23
Greenwood     93  75  92  76 /  47  11  42  22


MS...Heat Advisory until 7 PM CDT this evening for MSZ018-019-025>042-

LA...Heat Advisory until 7 PM CDT this evening for LAZ007>009-015-016-

AR...Heat Advisory until 7 PM CDT this evening for ARZ074-075.



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