Mesoscale Discussion 435

Issued

Apr 27, 2021, 1:17 PM CDT (18:17 UTC)

Expired

Apr 27, 2021, 3:15 PM CDT

In force

118 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch likely

Chance of a watch

80%

The Altus AFB radar (KFDR), 67 km from the middle of the area, began a volume at 18:19 UTC, the scan nearest the moment this went out.

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

• Severe Thunderstorm Watch 113Apr 27, 1:55 PM CDT

486 
ACUS11 KWNS 271817
SWOMCD
SPC MCD 271817 
OKZ000-TXZ000-272015-

Mesoscale Discussion 0435
NWS Storm Prediction Center Norman OK
0117 PM CDT Tue Apr 27 2021

Areas affected...Portions of west/northwest TX and western/central
OK

Concerning...Severe potential...Watch likely 

Valid 271817Z - 272015Z

Probability of Watch Issuance...80 percent

SUMMARY...The threat for large hail, damaging wind gusts, and
perhaps a couple tornadoes is expected to increase this afternoon.
Some of the hail may be very large (2+ inches in diameter). Watch
issuance is likely.

DISCUSSION...Towering cumulus has begun to form early this afternoon
along a dryline across parts of west TX to the south of Lubbock,
with lightning recently noted with a recent attempt at initiation in
Lynn County TX. Current expectations are for additional convective
development to occur in the next couple of hours across portions of
west TX along/near the dryline as weak ascent associated with
multiple small-scale mid-level perturbations overspreads the
southern High Plains and continues to erode the cap. Rather steep
(8-8.5 C/km) mid-level lapse rates are present across much of
west/northwest TX into central OK per area 12Z soundings. These
steep lapse rates aloft combined with strong mid/upper-level flow
suggest supercells capable of producing large hail will be the main
threat initially. The boundary-layer still appears capped farther
east into western north TX and western OK per latest mesoanalysis
estimates. Still, visible satellite imagery is showing some breaks
in the cloud deck, with temperatures warming into the mid/upper 70s
as of 18Z. As diurnal heating continues, the development of
1500-2000 J/kg of MLCAPE appears likely by mid afternoon across much
of the warm sector along and east of the dryline.

Some convection-allowing guidance suggests that substantial
mixing/drying of the boundary layer will occur this afternoon across
parts of west/northwest TX where the depth of the low-level moisture
return remains shallow. Some evidence of this may already be
occurring near San Angelo TX per recent surface observations. If
this trend continues, then a relatively narrow corridor may exist
for severe storms to develop, roughly from the vicinity of Lubbock
towards Childress TX. Still, as storms move northeastward into
western/central OK, they should encounter increasing low-level
moisture, greater instability, and strong deep-layer shear. This
favorable environment will likely support storm organization, with
large to isolated very large hail possible with any supercells.
Although low-level flow is not forecast to be overly strong through
the afternoon, a modest increase in a south-southwesterly low-level
jet may occur by early this evening across parts of western OK and
vicinity. If this occurs and convection can remain at least
semi-discrete, then a couple of tornadoes appear possible given the
expected increase in low-level shear. Some increase in the damaging
wind threat may also develop with time if storms congeal into one or
two small bowing clusters. Regardless of eventual convective
evolution, an increasing severe threat across this region will
likely warrant watch issuance.

..Gleason/Hart.. 04/27/2021

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

ATTN...WFO...OUN...LUB...AMA...MAF...

LAT...LON   33120085 32840165 32770197 33220188 33510170 33850133
            34420094 35559994 36169918 36579840 36719777 36529719
            36149694 35509705 34829780 34189865 33459984 33120085

Mesoscale Discussions in Oklahoma, 2021Mesoscale Discussions in Texas, 2021Every mesoscale discussion in 2021

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.