023
FXUS64 KMEG 161058
AFDMEG

Area Forecast Discussion
National Weather Service Memphis TN
558 AM CDT Tue Jul 16 2024

...New AVIATION...

.SYNOPSIS...
Issued at 329 AM CDT Tue Jul 16 2024

Dangerous heat and humidity will continue across the Mid-South
this afternoon. Isolated afternoon thunderstorms are possible,
mainly across northeast Mississippi, but most areas will remain
rain-free through sunset. Thunderstorm chances increase tonight
through Wednesday night as a cold front moves into the region.
Cooler conditions are anticipated for the end of the week with
highs in the 80s. Unsettled weather is expected this weekend with
below normal temperatures and rain chances each day.

&&

.DISCUSSION...
(Today through Monday)
Issued at 329 AM CDT Tue Jul 16 2024

Oppressive heat and humidity will affect the Mid-South again
today. Temperatures are poised to climb into the mid/upper 90s
with dewpoints in the mid 70s, resulting in maximum heat indices
from 105-112F across most of the CWA. We may experience sufficient
vertical mixing this afternoon to keep heat indices just below
110F across portions of the Excessive Heat Warning, but it`s going
to be hot regardless. Thus, no changes were made to the going
heat headlines. A few pop-up storms this afternoon may provide a
brief respite from the heat for a few, but coverage should be
quite limited. The area more favored for diurnal convection is
northeast MS with a secondary area near the MO Bootheel. Moisture
pooling in the vicinity of a cold front over the Mid MS Valley
will enhance instability near the KY/MO border with MLCAPE near
2500 J/kg this afternoon. Generally modest deep-layer shear (0-6
and 0-8 km bulk shear of 20-25 kts) will support ordinary and
multicell convection. The overall severe weather threat is low but
favors damaging wind as the primary hazard.

Storms over north MS are expected to dissipate around sunset with
the loss of diurnal heating, but storms closer to the front may
persist/increase during the evening and overnight periods as a
shortwave trough moves out of the Central Plains increasing low-
level convergence. Most of this looks to stay north of the CWA in
the Mid MS Valley through early evening, but a favorable steering
flow, mid-level dry air, and steep low-level lapse rates a
favorable for an MCS moving into the region from the northwest
overnight. Most of the CAMs are indicating this possibility though
the HRRR is the least aggressive of the suite. This certainly
bears watching and PoPs were ramped up above the generally low NBM
values.

Confidence in Wednesday`s surface pattern is relatively low.
Outflow from nocturnal convection may contaminate the area and a
cold front will arrive later in the day. Otherwise, slightly
cooler temperatures are expected given lower heights (cooling
aloft) and more cloud cover. Areas south of I-40, especially
across north MS, will have to deal with another day of heat
indices near or above 105F. Another Heat Advisory may be required
for some areas, but we`ll let the current headlines run for now
given the spatial uncertainty. The other fly in the ointment is
the potential for more convection Wednesday afternoon, especially
over the southern half of the CWA. This would be favored near the
surface front and any residual outflow boundaries from evening and
overnight convection. The greatest opportunity for organized,
widespread precipitation will be Wednesday night as a more
organized shortwave trough traverses the region. Precipitable
water near 2.0" (90th percentile of climatology) will be in place
along with a slow-moving cold front to support the potential for
localized heavy rainfall.

The CAM suite doesn`t go out quite far enough to capture this
period but the HREF does indicate about a 50-60% chance of 1.0"
of rainfall across northeast AR through 7 PM Wednesday. The LREF
(grand ensemble including all 100 members of the EPS, GEFS, and
GEPS members) is much less aggressive with only a 30% chance of
1.0" of rain in the same area through 7 AM Thursday. This
discrepancy is likely due to the coarser resolution and
convective parameterization of the global ensembles. The current
thinking is that rainfall amounts will average 0.50-0.75 inches
with localized amounts up to 2-3 inches possible.

Cooler conditions are anticipated across the Mid-South Thursday
with high temperatures only expected to reach the low/mid 80s.
Coupled with dewpoints in the upper 60s and lower 70s, heat
indices won`t be much of an issue. We still expect scattered
thunderstorms south of I-40, but coverage/intensity should be
limited.

An unsettled pattern will persist Friday into early next week as a
strong ridge builds over the western CONUS and a broad trough
lingers over the east. There isn`t much disagreement in the global
ensembles until this weekend. By this time, the primary source of
uncertainty is the position and amplitude of the synoptic trough.
Despite these differences, there isn`t a lot of variability in
the sensible weather across the Mid-South, so conditions are
fairly high in below normal temperatures and scattered convection
each day.

MJ

&&

.AVIATION...
(12Z TAFS)
Issued at 550 AM CDT Tue Jul 16 2024

VFR conditions continue. SW winds today and most of the night,
shifting northwest early tomorrow. Winds should gust to 15-20kts
today. A few showers associated with a weakening MCS may approach
the MEM and JBR terminals early tomorrow while CIGs begin to
lower. Steadier rain and thunderstorms should approach MEM before
18z as a cold front approaches from the north.


&&

.MEG WATCHES/WARNINGS/ADVISORIES...
AR...Excessive Heat Warning from 10 AM this morning to 9 PM CDT this
     evening for ARZ009-018-026>028-035-036-048-049-058.

MO...Excessive Heat Warning from 10 AM this morning to 9 PM CDT this
     evening for MOZ113-115.

MS...Excessive Heat Warning from 10 AM this morning to 9 PM CDT this
     evening for MSZ001-007-008-010>012-020.

     Heat Advisory from 10 AM this morning to 9 PM CDT this evening
     for MSZ002>006-009-013>017-021>024.

TN...Excessive Heat Warning from 10 AM this morning to 9 PM CDT this
     evening for TNZ001>003-019-020-048>051-088-089.

     Heat Advisory from 10 AM this morning to 9 PM CDT this evening
     for TNZ004-021-022-052>055-090>092.

&&

$$

PUBLIC FORECAST...MJ
AVIATION...JDS