SPC 1730Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1125 AM CST Sat Feb 27 2021

Valid 281200Z - 011200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN PLAINS INTO THE LOWER MISSISSIPPI VALLEY AND OHIO
VALLEY...

...SUMMARY...
Isolated strong to severe thunderstorms appear possible from parts
of Texas into the Ohio Valley on Sunday. Damaging wind gusts should
be the main hazard, but some hail and a couple tornadoes may also
occur.

...Southern Plains into the Lower Mississippi and Ohio Valleys...
Multiple mid-level shortwave troughs will move eastward across the
CONUS on Sunday. One such shortwave trough is forecast to advance
from the northern Plains and Upper Midwest to the Great Lakes by
Sunday evening. Another shortwave trough should develop slowly
southeastward from the Great Basin to the Southwest, eventually
closing off over AZ/NM late Sunday night. The primary surface low is
expected to develop northeastward across the Upper Midwest/Great
Lakes and into southern Ontario by Sunday evening, in tandem with
the previously mentioned shortwave trough. A cold front extending
southward from this low should be located over parts of the lower OH
Valley into the Mid-South and southern Plains Sunday morning. This
cold front will shift slowly southeastward through the period across
these regions, and it will likely provide a focus for convection.

A fairly broad swath of enhanced mid-level southwesterly winds
should overlie the frontal zone, but stronger forcing associated
with both shortwave troughs is likely to remain north of the warm
sector. Still, forecast soundings from northeast TX into the lower
MS Valley/Mid-South and continuing into parts of KY indicate a
veering and strengthening wind profile with height through mid
levels. Upwards of 50-60+ kt of effective bulk shear appears likely,
which is clearly sufficient for organized storms, including
supercells. However, two potentially limiting factors remain
apparent. One is the orientation of the front nearly parallel with
the southwesterly mid-level flow. Tendency may be for storms to form
along the front and then get quickly undercut while becoming
elevated. The other limitation may be generally weak low/mid-level
lapse rates and related modest instability. Even so, the presence of
surface dewpoints generally in the 62-68 F range coupled with some
diurnal heating south of the front should support MLCAPE around
250-1000 J/kg by Sunday afternoon.

Current expectations are for mainly elevated storms to be ongoing
across parts of the lower OH Valley Sunday morning in a strong
low-level warm advection regime. Additional convective development
appears likely along much of the length of the cold front by late
Sunday morning or early afternoon. Short bowing line segments may
pose an isolated damaging wind threat as they move
east-northeastward. Even though low-level flow should tend to veer
to southwesterly across much of the warm sector through the day,
enough low-level shear may remain to pose a threat for a couple
tornadoes with either semi-discrete storms or circulations embedded
within the line segments. Eventually, this isolated severe threat
should wane across the lower MS Valley and TN Valley Sunday evening
as storms become mainly elevated behind the front. Finally, some
hail threat may exist with elevated storms both Sunday morning and
Sunday night across parts of TX into the ArkLaTex vicinity.
Mid-level lapse rates should be modestly steepened across this
region in advance of the shortwave trough over the Southwest, and
deep-layer shear will likely be rather strong and uni-directional,
potentially supporting elevated supercells.

..Gleason.. 02/27/2021

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