Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 220145

Area Forecast Discussion
National Weather Service Huntsville AL
845 PM CDT Sat May 21 2022

...New NEAR TERM...

Issued at 844 PM CDT Sat May 21 2022

Isolated to scattered showers/storms currently across the
Tennessee Valley this evening. These showers/storms developed
earlier this afternoon in the hot, humid, and unstable atmosphere.
These showers/storms were initiated along outflow and
differential heating boundaries. With the large instability in
place, a few of these storms became marginally severe earlier this
evening. These storms are having a more difficult time developing
over the last hour or so with the loss of daytime heating and
expect this will continue to be the trend over the next couple of

The focus then shifts to the MCS approaching from the northwest.
This line of showers/storms has developed ahead of an approaching
cold front. Portions of the line are currently warned as it
approaches Memphis, TN. The last few scans indicate a shift
southward in the motion of the MCS. The MCS looks to try to stay
in the area of higher instability. Still not certain how intense
the MCS will be as it moves into NW AL. So far, not seeing much
warming at all in the cloud tops. However, the latest HRRR has the
activity falling apart as soon as it enter NW AL. Would expect a
weakening trend with the loss of daytime heating but so far things
are holding somewhat steady state. For now, have the line
entering NW AL around 05z and fading quickly as it moves across
the area.


.SHORT TERM...(Sunday through Tuesday night)
Issued at 242 PM CDT Sat May 21 2022

Present indications are that the decaying MCS discussed in the near
term section will continue to translate southeastward between 12-18Z
Sunday, with abundant cloud cover and lingering light rain in the
wake of this system expected to limit instability. Nonetheless,
virtually all model guidance suggests that widespread convection will
redevelop once again by early afternoon, as a slow-moving cold front
drops southeastward into the region. There is still a good deal of
uncertainty regarding how far south the cold front will penetrate
into the region, but our best guess is that is will remain nearly
stationary and bisect the forecast area from Sunday night through
Monday morning. It still appears as if a stronger mid-level
disturbance in the southern stream will begin to lift northeastward
from the southern LA vicinity on Sunday evening, providing weak but
sufficient synoptic scale ascent for the development of widespread
showers and thunderstorms on both sides of the front. Weak shear and
only meager instability suggest that the main impact from this
activity will be locally heavy rainfall, especially as convection to
the north of the boundary will be slightly elevated.

Although the location and orientation of the front will likely not
change, this precipitation regime should spread slowly eastward on
Monday afternoon/evening as the mid-level wave lifts northeastward
and away from the region. The stalled boundary will begin to return
northward as a warm front on Tuesday morning, as an amplifying
shortwave trough digs east-southeastward across the central Rockies
and adjacent High Plains. This will place the local area within the
warm/moist sector of the trough`s developing surface cyclone, with an
increasing coverage of showers and thunderstorms expected both
periods. Highs through the short term will be in the u70s-l80s, with
lows in the l-m 60s.


.LONG TERM...(Wednesday through Friday)
Issued at 242 PM CDT Sat May 21 2022

The central High Plains shortwave trough discussed above will
continue to deepen as it tracks eastward across the Great Plains
during the mid-week period, perhaps evolving into a partially closed
low as it reaches eastern MO/western IL by 00Z Friday. Given the
dynamic nature of this system, flow throughout the lower troposphere
will strengthen considerably to levels more typical of an early
Spring system rather than one in late May. With this in mind, deep-
layer shear will quickly become favorable for organized/severe
convection during the day on Wednesday, when several clusters of
thunderstorms will begin to spread northeastward in rapidly
strengthening warm advection ahead of this system. This regime will
persist on Wednesday night and Thursday, and with the low-level jet
expected to reach the 40-50 knot range atop a very moist boundary
layer with dewpoints in the m-u 60s, all severe hazards including
tornadoes will be possible. At this point, it appears as if some form
of a QLCS preceding the cyclone`s cold front will end both the risk
for severe weather and thunderstorms as it crosses the region
Thursday afternoon. A drier and cooler airmass will spread into the
region in the wake of this system for the end of the work week.


(00Z TAFS)
Issued at 631 PM CDT Sat May 21 2022

VFR conditions currently across the terminals. There are a few
isolated storms across the area this afternoon/evening but they
are outside of the 10 mile radius of the airports. For now, think
they will stay far enough away from the airports to not include
VCTS over the next couple of hours. Will monitor radar trends and
make amendments as necessary. Another area of showers/storms will
approach from the northwest later this evening around 04z. These
showers/storms should be weakening as they move through but did
include VCTS at both terminals overnight. This precipitation will
come to an end after midnight. However, another round of
showers/storms is forecast after 15z. Additionally, MVFR ceilings
are forecast late in the TAF cycle.




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