Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1144 PM CST Sat Feb 27 2021
Valid 281200Z - 011200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE ARKLATEX
TO MIDDLE TENNESSEE...
Strong to severe thunderstorms are likely from parts of Texas into
Middle Tennessee on Sunday. Damaging wind gusts and a few tornadoes
should be the main hazards, but some large hail may also occur.
Several mid-level shortwave troughs are embedded within a larger
trough across the central CONUS. A stronger shortwave will move
through the Upper Midwest/Great Lakes through the day. A compact
shortwave will develop into a closed low across the Southwest
throughout the day while several weaker perturbations will move
through moderate southwesterly flow extending from the Southern
Plains to the Ohio Valley. At the surface, an area of low pressure
will begin the day in Iowa before deepening as it moves
northeastward into the Great Lakes. As this surface low strengthens,
a cold front will sharpen and advance southeastward from the Midwest
to the southern Plains. Numerous thunderstorms, some severe, are
expected along and ahead of this cold front.
...Southern Plains to the Ohio Valley...
A shortwave trough seen on Water Vapor across northern Mexico early
this morning will move quickly northeastward through the morning.
Weak ascent associated with this mid-level shortwave is expected to
overspread a moist and unstable warm sector across
north-central/northeast Texas and southeast Oklahoma this morning
which will likely initiate scattered convection. Supercells are
possible given moderate instability (1000-1500 J/kg), steep
mid-level lapse rates (~7.5 C/km) and effective shear around 65 kts.
All severe weather hazards will be possible with these early storms.
This includes the potential for a tornado or two given the moderate
Temperatures ahead of the cold front are expected to increase into
the low 70s with dewpoints in the low to mid 60s from the southern
Plains as far northeast as southwest Kentucky by mid afternoon. This
should yield MLCAPE around 1000 to 1500 J/kg from the southern
Plains northeastward to far southern Kentucky. This destabilization
of the air mass, combined with the tightening low-level frontal
circulation should support widespread storm development along the
front by early to mid afternoon. Storms may initially struggle to
become severe due to some warmer temperatures near 700mb and the
propensity for storms to initially move to the cool side of the
boundary and become elevated. However, through time, storms are
expected to grow upscale into a forward propagating MCS.
This line of storms will likely pose a threat for damaging winds
given the strong low-level flow and a broad region of weak to
moderate instability downstream. 00Z CAM guidance suggests the most
robust linear segments may occur from northeast Arkansas into
western Tennessee where height falls and cooling temperatures aloft
may assist in stronger updraft development. Low level flow is
expected to increase above 40 knots at 0.5 km in this region which
will support a greater threat for severe wind and a favorable
low-level shear profile for potentially a few tornadoes embedded
within the line. By late evening, instability is expected to weaken
substantially which will likely support the line weakening by the
early overnight hours.
A few storms are expected to form late in the period (after 07Z)
near the Edwards Plateau and move eastward. Moderate instability
(1500 to 2000 J/kg) is expected in this region with steep mid-level
lapse rates around 8 C/km. Supercells will be the likely storm mode
given effective shear around 60 to 65 knots. Low level flow will
remain quite weak and thus large hail will be the primary threat
with this activity.