Mesoscale Discussion 1798

Issued

Oct 5, 2021, 12:45 PM CDT (17:45 UTC)

Expired

Oct 5, 2021, 2:45 PM CDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch unlikely

Chance of a watch

20%

The Columbus AFB radar (KGWX), 90 km from the middle of the area, began a volume at 17:45 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

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657 
ACUS11 KWNS 051746
SWOMCD
SPC MCD 051745 
ALZ000-MSZ000-TNZ000-ARZ000-051945-

Mesoscale Discussion 1798
NWS Storm Prediction Center Norman OK
1245 PM CDT Tue Oct 05 2021

Areas affected...portions of Alabama...Mississippi and Tennessee

Concerning...Severe potential...Watch unlikely 

Valid 051745Z - 051945Z

Probability of Watch Issuance...20 percent

SUMMARY...Scattered thunderstorms are expected this afternoon in
proximity to a weak upper low and stationary front across the
Southeast. Cool temperatures aloft will favor the potential for
small hail with the strongest storms. A weather watch is unlikely
though conditions will be monitored.

DISCUSSION...Afternoon WV imagery showed a weak upper low centered
near the AR, MS, LA border. Within a zone of broad ascent to the
east of the low and a diffuse surface front, visible imagery and
radar showed a cu field and a few weak thunderstorms developing
across MS and AL. Continued weak ascent and diurnal warming will
remove the already limited inhibition in place and support scattered
thunderstorm development in the next couple of hours. Seasonably
warm and moist conditions along with steep mid-level lapse rates
near the cold core aloft will support 1500-2000 J/kg of MLCAPE this
afternoon. Lingering mid-level flow wrapped around the eastern half
of the upper low will provide adequate deep-layer shear(25-30 kt)
for organized multicells/clusters.

Latest hi-res guidance depicts scattered storms, with several storm
clusters, moving west/northwest around the upper low across far
western AL, southern TN and much of MS into this evening.  Given the
favorable thermodynamics (500 mb temps near -15C), strong updrafts
will likely be capable of marginally severe hail and perhaps a
strong wind gust given the potential for storm clusters and merging
outflow. Some uncertainty remains on the expected severe coverage
given lower-end deep-layer shear and subtle forcing. This suggests
severe potential will remain mostly isolated and outside the need of
a weather watch.

..Lyons/Guyer.. 10/05/2021

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

ATTN...WFO...BMX...MOB...MEG...JAN...

LAT...LON   31698933 32279033 33049082 33879092 34429061 35029008
            35408960 35498927 35388882 35158859 34788847 34018817
            33458820 32788820 32418824 32098840 31728887 31698933

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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.