Mesoscale Discussion 136

Issued

Feb 28, 2021, 1:01 PM CST (19:01 UTC)

Expired

Feb 28, 2021, 3:00 PM CST

In force

119 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch likely

Chance of a watch

80%

The Little Rock radar (KLZK), 106 km from the middle of the area, began a volume at 19:03 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

• Tornado Watch 13Feb 28, 2:20 PM CST

526 
ACUS11 KWNS 281901
SWOMCD
SPC MCD 281901 
TNZ000-KYZ000-MSZ000-MOZ000-ARZ000-282100-

Mesoscale Discussion 0136
NWS Storm Prediction Center Norman OK
0101 PM CST Sun Feb 28 2021

Areas affected...Central/eastern Arkansas...northern
Mississippi...western/Middle Tennessee

Concerning...Severe potential...Watch likely 

Valid 281901Z - 282100Z

Probability of Watch Issuance...80 percent

SUMMARY...Storm coverage and intensity will increase this afternoon
across parts of Arkansas, northern Mississippi, and western/Middle
Tennessee. Damaging wind gusts will likely be the primary threat
with this activity, but a few tornadoes are also possible. A WW will
likely be issued within the next 2 hours.

DISCUSSION...Visible satellite imagery shows boundary-layer cumulus
with increased convective character as temperatures have rising into
the low 70s F with mid to upper 60s F dewpoints. Recent surface
observations also indicate pressure falls increasing across the
area. With time, the cold front should begin to move southeast and
interact with an increasingly unstable airmass across Arkansas,
northern Mississippi, and western Tennessee.

Deep-layer wind fields are still quite strong with KLZK and KNQA
showing around 60 kts of 0-6 km shear. While 850 mb winds have
weakened from this morning, low-level hodographs are still
sufficiently large to support a risk for tornadoes. The 18Z observed
LZK sounding showed 1000 MLCAPE with little inhibition. Even with
veered surface winds and 850-700 mb flow weakness, effective SRH was
still over 100 m2/s2. 850 mb winds are expected to increase later
this afternoon across southeast Arkansas, northern Mississippi, and
into Middle Tennessee. With primarily a linear storm mode, the exact
level of tornado threat is uncertain. Cellular activity moving
northeast out of WW 12 or developing ahead of the front would pose
the greatest risk with lesser risk posed by QLCS activity. Flow of
40-50 kts in the lowest 3 km will bring a threat for damaging wind
gusts. Damaging gusts will increase as the front moves southeastward
this evening. Mid-level lapse rates and long hodographs are
sufficient for large hail, though this risk decreases with eastward
extent.

A WW is likely within the next 2 hours.

..Wendt/Hart.. 02/28/2021

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

ATTN...WFO...OHX...PAH...MEG...JAN...LZK...

LAT...LON   34739403 35709278 36598993 36658840 36328791 35398783
            34628880 34258985 34029024 33899149 33809259 34149354
            34509404 34739403

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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.