998
FXUS64 KJAN 180244 AAB
AFDJAN

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
944 PM CDT Sat Aug 17 2024

...New MESOSCALE UPDATE...

.MESOSCALE UPDATE...
Issued at 943 PM CDT Sat Aug 17 2024

Convective activity has shifted out of the forecast area and just
some remnant convective debris is left across the south half.
Several updates were made earlier to capture temps that were
impacted by precip/cooler outflow so things are pretty much on
track. Will updated to capture temp tweaks shortly.

Focus will shift to Sunday, it will be HOT as we will reside in the
lower level thermal axis. It sure looks like it will be the hottest
day of the year for most locations with Highs peaking in the 98-102
range with some 100-105 very possible. As for storms, it`s not a
slam dunk as the atmosphere, as often the case with volatile
situations, will be right up to a point that could go either way. In
the "either way" I`m referring to is just enough to convect and we
get very windy storms which in-turn establish deep enough cold
pools to develop additional cells and we ultimately get an organized
cluster. The other way would be there`s too much dry air and limited
lower level convergence that doesn`t overcome any capping resulting
in few to no convective cells. While each scenario remains on the
table, the latest 00z CAMs are favoring convection. While
instability is not anticipated to be extreme, there`s other elements
of the likely environment that are very rare for us. First will be
storms developing in 98-104 degree temps. From this, there will be
very steep lapse rates in the 0-3 and 0-4 km layers that will allow
for efficient momentum transfer to the surface. Also between 700-
400mb there will be strong flow of 30-40kts. I`ll add in dry air in
the mid levels as well which will all for more evaporative cooling
as we should see Dcape values in the 1200-1600 j/kg range. So, with
all that, the signal we see from the HRRR and NAM3km with strong
downdraft wind signatures are very telling. Compiling all of this
offers the potential for a more widespread wind event along with
some potential for sig type wind gusts as well. Still more details
to cover, but wanted to offer the potential and some background as
to why. Lastly, timing looks to be later and main time window for
this appears to be 4p to midnight.  /CME/

&&

.DISCUSSION...
Issued at 231 PM CDT Sat Aug 17 2024

Tonight through Monday...

Tonight: Convection should persist through early evening, but wind
down before midnight. In the wake, a quiet night will be in store,
with some potential patchy fog in low-lying areas or locations that
receive rainfall. With increased boundary layer moisture,
persistence forecast, with seasonably warm lows in the mid-upper 70s
(74-78F) are expected.

Sunday-Monday: An active period of excessive heat & severe storms is
expected Sunday, before a frontal zone moves through, finally
breaking the grip of the heat & more seasonable & dry conditions
move in next week. Synoptic & sfc pattern will consist of deep mid-
level ridge centered over west TX to the southwest states while mean
longwave trough persist east of the MS River Valley. This will keep
perturbed northwest flow & a frontal zone is expected to sink
southward into Sunday. Moisture & deep mixing is anticipated in
advance of the frontal zone moving in. Guidance indicates efficient
mixing up to 850-700mb layer. There are indications combined with
this deep mixing, favorable thermo profiles (i.e. 28-30C vertical
totals & DCAPE nearly 1800-2000 J/kg) & 25-40kt bulk shear in the
mean 0-2 to 0-6km layer, southward moving organized convective
clusters could contain some higher end gusts near 70mph at times &
quarter size hail. Convective allowing models (CAMs) indicate some
potential of gusts in excess of 50-60kts, so strong to severe storms
remain a low-medium chance, where advertised "Slight" risk looks on
track. The convective outlook area has been brought further
southwards towards I-20, which seems to be in agreement with most
guidance. With convective storm onset in the mid-late aftn
timeframe, mainly between 2-4PM, high boundary layer moisture ahead
of the boundary will lead to continued dangerous heat stress again
into the aftn to early evening hours. With seasonably warm highs in
the 98-102F range & excessive heat potential more expansive, the
"Significant" area was expanded east along I-20 & southeast, with
the "Extreme" taken out of the Delta, with less oppressive
conditions today, while pulled eastward near east MS due to ongoing
persistent dangerous heat & expected conditions Sunday. Heat
headlines were maintained from mid-morning to early evening , with a
heat advisory in east-northeast MS & a Excessive Heat Warning areal
configuration with similar but slightly larger coverage. The
Excessive Heat Warning may be able to be adjusted to the northeast
but some earlier convective coverage makes this potential a low
confidence forecast. Will led later shifts decide on any further
adjustments. Expect storms to persist into the evening hours but
could linger a little later closer to midnight. For now, timing
looks mostly intact but may be able to be refined as confidence
increases. Timing looks to be mid-late aftn & persist into the
evening, with rain & storm chances in the isolated to scattered
range (15-40%).

As heights in the ridge to the west begins to fall, there will be
continued surges of drier & less oppressive airmass beginning to
move in the region into next week. This will help highs become more
seasonable in the low-mid 90s & lows in the mid-upper 60s north of I-
20 to upper 60s to near 70F in the south into Tuesday morning. Some
storms are possible but become more focused into the Hwy 84 corridor
into Monday aftn to early evening. Can`t rule out an isolated strong
storm in southwest MS & portions of northeast LA on Monday. /DC/

Tuesday through Friday...

Post frontal passage will bring relief from the oppressive
heat/humidity of the previous week. Upper/mid-lvl ridge will
primarily encompass the Southern Plains/CO/NM area, placing the
ArkLaMiss region on the periphery of the ridge. As a result,
northwest to northerly flow allows for dewpoints to fall into the
upper 50-mid 60s range across the area, lowering humidity for the
area. Afternoon high won`t be as hot either, as upper 80s/lower 90s
temps are expected. Low temperatures will more likely resemble early
fall than summer, as low temperatures are expected to range in the
60s midweek to near 70 degrees by late week. /SW/

&&

.AVIATION...
(00Z TAFS)
Issued at 635 PM CDT Sat Aug 17 2024

Precip/storms have moved to our south and TAF sites will remain
VFR for the period. By Sunday afternoon, the northern half of the
area will see WNW winds with some gusts as we heat up. Storm
chances will increase late, but that looks to be mainly after 21z
and will hold off on including in the TAFs until timing/location
fit better. /CE/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       76 100  74  92 /   0  20  40  20
Meridian      74 101  71  93 /   0  30  30  10
Vicksburg     76 101  74  92 /   0  20  30  20
Hattiesburg   76 100  75  95 /  10  10  30  20
Natchez       76 100  75  92 /  10  10  30  30
Greenville    75 100  72  90 /   0  20  30  20
Greenwood     75 100  72  92 /   0  10  20  10

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Excessive Heat Warning from 10 AM to 8 PM CDT Sunday for MSZ018-
     019-025>029-032-034>037-040>044-047>066-072>074.

     Heat Advisory from 10 AM to 8 PM CDT Sunday for MSZ030-031-033-
     038-039-045-046.

LA...Excessive Heat Warning from 10 AM to 8 PM CDT Sunday for
     LAZ007>009-015-016-023>026.

AR...Excessive Heat Warning from 10 AM to 8 PM CDT Sunday for ARZ074-
     075.

&&

$$

CME/DC/SW