388
FXUS64 KJAN 051807
AFDJAN

Area Forecast Discussion
National Weather Service Jackson MS
107 PM CDT Fri Jul 5 2024

...New AVIATION...

.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...
(18Z TAFS)
Issued at 107 PM CDT Fri Jul 5 2024

Main aviation concerns this aftn again will be SHRA & TSRA
coverage, with more scattered to numerous ongoing across a large
portion of sites, outside of GLH & GWO. Some of these could
contain gusty/variable wind, upwards of 40-50mph & drops to IFR
flight categories at worst. Most thunder should wind down by
06/02-04Z & SHRA before 06/06Z. MVFR-IFR ceilings/stratus, with
some LIFR psbl, is psbl at east-southeast TAF sites of MEI, PIB &
HBG & can`t be ruled out on the fringes at JAN, HKS, & HEZ. Flight
restrictions should improve by 06/14-16Z, with some increase in
SHRA for central to southern TAF sites. Light northerly winds, at
times variable, will prevail through most of the period through
midday Saturday. More SHRA & TSRA are psbl into Saturday aftn at
most TAF sites. /DC/

&&

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

&&

.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.

&&

$$

SAS20/LP/DC