Mesoscale Discussion 424

Issued

Apr 24, 2021, 1:22 PM CDT (18:22 UTC)

Expired

Apr 24, 2021, 3:15 PM CDT

In force

113 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

40%

The Northeast Alabama radar (KHTX), 73 km from the middle of the area, began a volume at 18:25 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

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• Severe Thunderstorm Watch 110Apr 24, 4:55 PM CDT

678 
ACUS11 KWNS 241823
SWOMCD
SPC MCD 241822 
GAZ000-TNZ000-ALZ000-MSZ000-242015-

Mesoscale Discussion 0424
NWS Storm Prediction Center Norman OK
0122 PM CDT Sat Apr 24 2021

Areas affected...portions of central and northern Alabama into far
southern Middle Tennessee and extreme northwest Georgia

Concerning...Severe potential...Watch possible 

Valid 241822Z - 242015Z

Probability of Watch Issuance...40 percent

SUMMARY...A gradual increase in storm coverage is expected over the
next few hours. A couple of the stronger storms may produce
marginally severe hail and perhaps a damaging gust or two. Severe
coverage however, is expected to be somewhat limited by relatively
marginal instability, though convective coverage will be monitored
for the need of a Severe Thunderstorm Watch.

DISCUSSION...The eastward progression of a surface low, along with
continued heating, are expected to contribute enough low-level lift
to support increasing convective coverage over the next few hours
across portions of central and northern AL into far southern middle
TN. Clearing skies are allowing for some modification of the
boundary-layer, while the westward approach of a 7-7.5 C/km
mid-level lapse rate plume will encourage some airmass
destabilization while overspreading the modifying boundary layer.
However, given the amount of overturning from earlier convection,
the atmosphere is expected to only become marginally unstable, with
500-1000 J/kg MLCAPE being common (with perhaps localized areas of
1000-1500 J/kg possible). Nonetheless, 50-70 kts of effective bulk
shear and the near 7.5 C/km mid-level lapse rates will promote at
least marginally severe hail with the more intense storms. A couple
damaging gusts may also occur with the stronger downdrafts.

While convective coverage is expected to increase through the
afternoon, severe coverage may be on the more sparse end, though a
localized cluster of hail/damaging gust instances cannot be
completely ruled out. As such, conditions will be monitored for the
need of a Severe Thunderstorm Watch should a localized swath of
severe hail/winds become evident in future observations/guidance
trends.

..Squitieri/Hart.. 04/24/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...MRX...FFC...OHX...BMX...HUN...MEG...JAN...

LAT...LON   33248565 33028705 33208819 33528833 34438821 34688806
            35288760 35498711 35528656 35478613 35368569 35118542
            34758513 34408508 34028520 33618543 33248565

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The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.