406
FXUS64 KJAN 191723 AAC
AFDJAN

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
1223 PM CDT Fri Jul 19 2024

...New AVIATION...

.MESOSCALE UPDATE...
Issued at 947 AM CDT Fri Jul 19 2024

Rest of Today...A broad mid/upper level trough will remain over the
region today.  This, as a stationary frontal boundary remains draped
across the forecast area along a line extended from near the Golden
Triangle area, southwest to near the Jackson metro area, to near
Natchez, MS/Vidalia, LA.  Despite this boundary over the area, a
very deeply moist airmass encompasses the CWA with precipitable H2O
values hovering around 2 inches per the KJAN 12Z RAOB.  2.02 inches
to me exact.  With the addition of daytime heating, along with some
weak ascent moving over the area, showers will become more widespread
across the CWA this afternoon, along with a few thunderstorms.
Again, given the high moisture content over the forecast area,
heavy downpours will be biggest concern with today`s activity.
This could result in some localized flash flooding across much of
the area, particularly in low-lying and poor drainage areas.

As far a temperatures are concerned, with both cloud cover and
convection around, highs will be noticeably lower today compared to
previous days.  However, it`ll still feel very muggy as dew points
generally reside in the 70s areawide.  Look for highs today to only
top out in the 80s.

The ongoing forecast is in pretty good shape.  I did make some minor
adjustments to hourly elements of the forecast based on current
trends.  Otherwise, no major changes will be made on this morning`s
forecast update. /19/

&&

.DISCUSSION...
Issued at 453 AM CDT Fri Jul 19 2024

Today through Tonight...

Early morning water vapor/RAP & evening hand analysis indicate the
region remaining in perturbed flow/trough axis. The main corridor
of the vertically stacked low resides over eastern Canada. Deep
ridging persists in two areas: over the Four Corners, northern
Rockies to west-northwestern Canada & southwestern Atlantic
subtropical ridging extending into the FL Peninsula to southeast
Gulf of Mexico. This Rex Block type will keep an active pattern
expected through this afternoon through evening. Water vapor
analysis indicates a stronger spoke of the jet over the Gulf Coast
region, with some increased vorticity/ascent driving the early
morning shower development. There is some ongoing convection for
areas along & west of the MS River corridor & also into the Golden
Triangle, but expected a gradual uptick in more scattered to
numerous showers & some storms into the aftn. The highest coverage
will be along & southeast of the Natchez Trace corridor while more
more scattered to the northwest. Light upwind propagation
vectors, soupy tropical airmass of 2-2.25 inches (>90th
percentile) precipitable water (PWs) & HREF localized prob match
mean / maximum of the ensemble envelope that could support some
3-4", with localized 5-7" rainfall amounts. HREF prob match mean
indicate 30% probs of >3 inches along & southeast of the Natchez
Trace. Even though some of these central areas have not seen as
much rain recently, slow-moving, tropical downpours with warm
rain processes (i.e. freezing levels >15kft) support localized
heavy downpours & flash flooding potential in low-lying & urban
areas. Introduced a "Limited" graphic for areas southeast of the
Natchez Trace, mainly along & south of a line from along the I-55
corridor in Grenada to Issaquena in MS & westward along the I-20
corridor in West-East Carroll & Morehouse parishes in LA. This
seems to be the most focused corridor of potential that could
persist into the weekend, so we continued mention of this into
Saturday. Temperatures will be seasonably cool today in the low-
mid 80s, with seasonable lows in the upper 60s-low 70s through the
weekend. Heat stress will be held in check today. Some patchy fog
is possible in the Pine Belt this morning & again into tonight,
especially in areas that receive sufficient rainfall. There are
some HREF probs for dense fog but confidence is low with broad
cloud shield/stratus expected across the area. While some strong
storms can`t be ruled out due to some light westerly bulk shear in
the 0-6km layer, severe storms will be hard pressed in the low
lapse rate environment. /DC/

Saturday through Friday...

The long term period will remain stuck in this stagnant pattern of
rain as tropical moisture and multiple rounds of shortwave energy
flow into the southeastern states.

Upper level troughing will remain centered over the mid/lower MS
Valley throughout the longterm period often being influenced by the
shortwave energy of a low pressure system as it makes its way
through the mid-west. With this current weather regime pops will
continue to be scattered to numerous in coverage with some areas of
heavy precip but generally much of the same day to day throughout
the period. It is worth noting that SE Ark/MS Delta will see
lower storm coverage this weekend as PWs drop into the 1.5in range
before building back into the 2-2.5in range at the beginning of
next week. With the consistent nature of this pattern and areas
already seeing rainfall totals upwards of 2in, a limited flash
flooding threat was introduced in the graphical HWO for a
majority of the CWA through this weekend as some areas could see
upwards of 2-4in of rain with locally higher amounts. At least for
this weekend portions of SE Ark/MS Delta with lower PW values
show indications that they will be left out of the higher bands of
rain thus were excluded from the limited threat. As for heat,
consistent cloud cover and rain chances will keep the heat in
check, keeping max temps well below climo for this time of the
year. /KP/

&&

.AVIATION...
(18Z TAFS)
Issued at 1223 PM CDT Fri Jul 19 2024

With a frontal boundary stalled across the area, a mix of VFR to
IFR flight categories will be observed at area TAF sites during
the 18Z forecast period. This will predominately be as a result on
low ceilings, but it`ll be further aided by reduced visibilities
from scattered to numerous convection across the area this
afternoon into this evening. As far as winds are concerned,
they`ll be from the south and southwest between 5-8 knots ahead of
the front, and from the north around 5-8 knots in the wake of the
boundary. Winds will overall subside to calm to light this
evening and overnight. /19/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       71  88  72  88 /  50  80  50  80
Meridian      69  88  71  88 /  70  90  60  90
Vicksburg     71  88  72  89 /  30  50  30  60
Hattiesburg   72  90  73  89 /  70  90  50  90
Natchez       70  88  72  87 /  30  60  40  70
Greenville    69  88  71  89 /  10  20  10  30
Greenwood     69  88  71  89 /  30  40  20  50

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...None.
LA...None.
AR...None.
&&

$$

19