209
FXUS64 KJAN 051529
AFDJAN

Area Forecast Discussion
National Weather Service Jackson MS
1029 AM CDT Fri Jul 5 2024

...New MESOSCALE UPDATE...

.MESOSCALE UPDATE...
Issued at 1021 AM CDT Fri Jul 5 2024

A frontal boundary is evident on radar and on satellite this
morning and should continue to push southward towards the I-20
corridor and later on the Pine Belt and southwestern areas in the
vicinity of HWY 84 this afternoon. This will serve as the focus
for numerous showers and thunderstorms. There is growing concern
for the potential for flash flooding given a daily record of 2.43
inch PWAT airmass, very high freezing level of nearly 17k ft, and
deep moisture. Have opted to add a limited risk for flooding to
capture this potential. Short term guidance has indicated a 30-50%
probability of 3 inches or greater, with a primary focus south
and east of the Natchez Trace. Will continue to monitor ongoing
conditions for flash flooding. Storms should begin to taper off
later this evening with the loss of daytime heating./SAS/

&&

.DISCUSSION...
Issued at 425 AM CDT Fri Jul 5 2024

Today through tonight: Not much has changed concerning our
forecast thinking with considerable heat stress and convective
rainfall expected today. With temperatures struggling to fall
below 80 early this morning over portions of the forecast area, it
will not take much heating to reach heat advisory criteria, and it
appears the greater convective emphasis will be later this
afternoon as previous guidance may have been a little too
aggressive with convective outflow, so have gone ahead and issued
a heat advisory for the entire area.

In terms of today`s storm potential, the scenario remains the same
with a cold front forecast to push southeast into northwest
portions of the forecast area by this afternoon. The air over our
region is tropical-like with precipitable water values well over
two inches and H850 dewpoint temperatures around 18 deg C. Pool
lapse rates will limit the convective intensity, and so locally
heavy rainfall may be the primary concern given the anomalous
moisture parameters. Expect mostly disorganized shower/storm
coverage to peak during the mid/late afternoon hours, but there
should be enough mid level flow to support a few multicell storm
clusters. Expect convective rainfall to diminish this evening with
rain chances diminishing this evening behind the cold front. /EC/

Tomorrow night through midweek: For anyone unaware of what the
past stretch of heat has been like, there may be some
consternation in calling the weekend airmass "post frontal" as it
will certainly not be "cool", never mind "cold". Nevertheless, a
drier, "less-hot" airmass will reside across the area resulting in
a reduction in the degree of oppressive heat. Three cheers for
returning to "normal hot summer"!

No? Fair enough.

It WILL be slightly better, though as highs Saturday and Sunday bump
up "only" into the low to mid 90s F and heat indices "only" in the
100-105 F range, about 10 degrees cooler in the apparent temperature
category. Perhaps more noticeable will be the overnight lows which
will be 5-8 F cooler in the 72-75 F range.

While widespread heat products will be less likely, there is still a
possibility that we will need a lower-end outlook for heat stress
particularly along and south of the highway 84 corridor. Given the
marginal conditions (max apparent temps 104-105), will wait until
the frontal airmass is sampled/modeled better later today as it is
possible that convective reinforcement could push the boundary just
south of our area allowing those areas to remain just under heat
criteria over the weekend.

The lowered upper heights and glancing influence of the upper trough
responsible for the frontal intrusion will linger into midweek and
temperatures along with afternoon, mostly diurnal, showers and
storms will continue into midweek. Highs will remain lower 90s F,
lows low-mid 70s F.

One fly in the ointment by the middle of next week will be what
exactly happens with the weak disturbance associated with the
remnants of Hurricane Beryl. With the weak upper trough around, this
could allow for the pocket of cloudiness and somewhat higher PWAT
environment to advect across our area. This would serve to increase
scattered shower/storm activity and give us another day or two of
seasonable temperatures. On the other hand, should the cyclone fully
dissipate or become tucked underneath a strengthening ridge aloft
across the Southwest and into Texas, our upper heights could rise
more expediently. In short, the mid week forecast is a bit more
challenging with at least two most likely possibilities:
Showers/storms and only "normal" July hot, or fewer showers/storms
and a return to excessive heat conditions. We will be monitoring
this closely.

As of now, neither of these two solutions appear to be particularly
impressive in terms of hazard-production outside of the heat risk.
If we do see some additional aid in terms of deep layer tropical
moisture, locally heavy rains appear possible. For that reason we
can`t fully rule out an isolated flash flooding risk for mid
week. /86/

&&

.AVIATION...
(12Z TAFS)
Issued at 649 AM CDT Fri Jul 5 2024

IFR/LIFR category low stratus over southeast portions of the area
will be the primary concern until mid morning, and likely again
late tonight into early Saturday morning along with some reduced
vsby due to IFR category br/fg possible as well. Thereafter,
attention will turn to convective rainfall potential through much
of today with emphasis on the aftn ahead of the approaching front.
Expect rain chances to diminish early this evening. /EC/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       92  74  90  73 /  80  50  50  10
Meridian      94  74  92  71 /  80  50  60  20
Vicksburg     93  74  91  72 /  80  60  40  10
Hattiesburg   93  76  93  76 /  70  50  80  20
Natchez       92  73  89  73 /  70  50  60  10
Greenville    93  72  91  71 /  70  30  10   0
Greenwood     93  72  92  71 /  70  20  10   0

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Heat Advisory until 7 PM CDT this evening for MSZ018-019-025>066-
     072>074.

LA...Heat Advisory until 7 PM CDT this evening for LAZ007>009-015-016-
     023>026.

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

&&

$$

EC/LP/EC