037
FXUS64 KJAN 171800 AAA
AFDJAN

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

...New AVIATION...

.MESOSCALE UPDATE...
Issued at 1155 AM CDT Sat Aug 17 2024

Rest of today...

Morning RAP/water vapor analysis indicates ridge centered over
west TX into NM, with our region on the southern periphery
of increased northwest flow. Anomalous, tropical PWs near the 2
inch mark & steep low-level lapse rates favor increased microburst
potential developing across the I-20 corridor & is being observed
in morning mesoanalysis. To the northwest, there have been
overnight remnant outflow boundaries & gravity waves that emanated
southeast from convective storm complex in south- central AR &
propagated to the southeast. This has somewhat convectively
overturned areas northwest of the Natchez Trace into the Delta,
with some potential for dewpoints to slightly mix down a touch
lower. With a shortwave diving southeast into the area & potential
for convective initiation in this favorable thermodynamic
environment (i.e. 26-28C vertical totals, DCAPE of +1000 J/kg
steep lapse rates & northerly flow in the 0-2 to 0-6km layers up
to 15-20kts), isolated to scattered diurnal storms, some strong-
severe, are a low-medium chance today. After coordination with
SPC, the ongoing "Marginal" risk area has been adjusted southward,
with the focus of convection along & south of a line from near
Bastrop in LA to Yazoo City to Macon in MS. Damaging wind gusts &
some hail up to quarter size remain the main concerns. Heat to
the northwest of where the most vigorous aftn convection & air is
overturned may not have as much Excessive Heat potential, but
will be very favorable to the southeast. Left the ongoing Heat
graphics & headlines as is. Adjusted rain & storm chances slightly
southeast, with only low chance northwest of the Trace (15-20%) &
low-medium chance along & southeast (25-45%). Updates are out. /DC/

&&

.DISCUSSION...
Issued at 403 AM CDT Sat Aug 17 2024

Today and Tonight:

A moist tropical air mass remains in place across the Lower
Mississippi River Valley today, with analyzed PW values of 1.8-2.0
inches this morning representing the 50-75th percentile range for
mid August. Northwest flow between a ridge over the Desert Southwest
and low pressure system over the Great Lakes is carrying waves in
the jet stream across the Great Plains and interacting with a
frontal boundary in the region. One such wave overnight steered an
MCS into the heart of Arkansas before it lost momentum. A breakaway
portion of the energy is continuing east with storms in the Memphis
area, while an MCV developed from the remnant MCS and is sustaining
training thunderstorms with heavy rain over western Arkansas. Warm
advection is ongoing south of the front, helping to bring the heat
from the Southwest ridge toward our forecast area. High temps again
today should be in the 97-101 range for most of the area. The moist
air mass in the region is capable of supporting shower and
thunderstorm development with daytime heating again today, and it
appears that the wave aloft and convergence along the remnant
outflow boundary might favor the eastern and southeastern portions
of our forecast area today. Storms will have 2500-3500 J/kg of
SBCAPE and 1000+ J/kg of DCAPE to work with, so localized damaging
winds are possible with any strong to severe storms. Deep layer wind
shear of 10-20 kts will add some organization to storms and favor
southeastward moving storms. There is a Marginal Risk for severe
thunderstorms tied specifically to this possibility this afternoon
and evening, but it is always worth noting some isolated microburst
potential exists elsewhere too just given the thermodynamic profile.
/NF/

Sunday through next Friday:

By Sunday, surface ridging is expected to maximize across the region
ahead of a "cold" frontal boundary. Sunday looks to be our hottest
day this week, with many areas along and west of I-20 reaching
triple digit highs and heat indices. Excessive Heat Warning/Heat
Advisory products will be likely on Sunday as dangerous heat stress
dominates the beginning of the extended period. In addition to heat,
conditions for a Slight Chance (2/5) of severe storms will be
possible, with the highest chance of storms along and north of
the I- 20 corridor. Enhanced westerly flow along with increased
instability will create the potential for damaging wind gusts with
with more mature updrafts. The main threat for severe storms
looks to exists mostly in the afternoon into the late evening,
with hires guidance hinting at a potential MCS moving into SE
AR/NW LA by the early evening hours.

By Monday into the remainder of the extended period, a much needed
break from dangerous heat will take place. High temperatures will
range in the upper 80s to lower 90s through Thursday, with lows in
the low 60s to low 70s. Rain chances will remain fairly minimal with
isolated (15-30%) chances in the far southeast on Thursday and
Friday. /AJ/

&&

.AVIATION...
(18Z TAFS)
Issued at 100 PM CDT Sat Aug 17 2024

VFR flight conditions are expected to prevail through the TAF
period. Scattered cumulus/cirrus cloud cover; however; ceilings
aren`t impacted. Between 19Z Saturday-02Z Sunday, VCTS/VCSH/-SHRA
will be possible for sites near and south of I-20. Local decreased
visibilities and gusty winds above 40 kts will be likely near
storms. After 02Z Saturday, quiet conditions will prevail.
Additional thunderstorms will be possible Sunday afternoon. /SW/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       76 100  75  93 /  20  20  40  20
Meridian      74 101  71  94 /  20  30  30  10
Vicksburg     76 101  75  93 /  20  20  40  20
Hattiesburg   76 100  76  95 /  30  20  30  20
Natchez       76 100  75  93 /  20  10  30  20
Greenville    75 100  73  91 /  20  20  40  20
Greenwood     75 100  73  92 /  20  20  30  10

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Excessive Heat Warning until 8 PM CDT this evening for MSZ018-
     019-025>029-032-034>037-040>044-047>050-053>057-059>066-
     072>074.

     Heat Advisory until 8 PM CDT this evening for MSZ030-031-033-038-
     039-045-046-051-052-058.

LA...Excessive Heat Warning until 8 PM CDT this evening for
     LAZ007>009-015-016-023>026.

AR...Excessive Heat Warning until 8 PM CDT this evening for ARZ074-
     075.

&&

$$

DC/AJ/SW