Post by Will - Ascension Parish on Apr 13, 2020 14:00:48 GMT -6
Day 1 Convective Outlook CORR 1
NWS Storm Prediction Center Norman OK
0110 AM CDT Sun Apr 19 2020
Valid 191200Z - 201200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
FAR EAST TEXAS EASTWARD ACROSS THE SOUTHEAST TO SOUTH-CENTRAL
GEORGIA...
CORRECTED FOR REGIONAL DESCRIPTORS
...SUMMARY...
An outbreak of tornadoes and severe thunderstorms is expected today
from parts of the lower Mississippi Valley across much of the the
Southeast. In addition to tornadoes, many of the storms will have
very large hail and wind damage. The severe threat will be greatest
from north-central Louisiana eastward to southern and central
Mississippi, southern and central Alabama into south-central
Georgia. Additional severe storms with a threat for tornadoes, wind
damage and hail will be possible in parts of east Texas this morning
and in the Carolinas tonight.
...Regional Outbreak of Tornadoes and Damaging Winds Expected Across
Parts of the Lower Mississippi Valley and Southeast Today...
...Lower Mississippi Valley/Southeast...
A potent upper-level trough will move quickly eastward across the
southern Plains today as a 60 to 75 kt mid-level jet moves eastward
across the Southeast. Ahead of the system, a corridor of moderate to
strong instability is forecast to develop from parts of the lower
Mississippi Valley eastward across much of the Southeast. This
combined with steep mid-level lapse rates and strong low-level shear
will be very favorable for severe storms. As the mid-level jet moves
eastward into the Southeast, a regional outbreak of severe weather
including tornadoes appears likely from parts of the lower
Mississippi Valley eastward across parts of Mississippi, Alabama and
Georgia. The greatest threat for tornadoes is expected to last from
late morning through the afternoon and evening into the overnight
period.
At the start of the period, a moist and unstable warm sector will be
in place from southeast Texas eastward across much of the Gulf
Coast. The northern edge of the moist sector will gradually move
northward as moisture advection occurs. A severe convective cluster
appears likely to be ongoing this morning from east Texas into the
Arklatex where large hail and wind damage will be possible. As
surface temperatures warm this morning, a threat for hailstones
greater than 2 inches in diameter will be possible. If some of the
storms become surface-based, a tornado threat could also develop.
Eastward from this complex, an undisturbed moist sector will exist
from south-central Louisiana eastward across the southern half of
Mississippi, the southern half of Alabama into southern Georgia. RAP
forecast soundings by early to mid afternoon along this corridor
have MLCAPE of 2000 to 3000 J/kg with 0-6 km shear in the 50 to 60
kt range. This environment will likely be very favorable for
supercells and tornadoes. 0-3 storm-relative helicities are forecast
to be favorable being maintained in the 300 to 400 m2/s2 range in
the late afternoon as a low-level jet becomes focused ahead of the
approaching system.
The first round of severe storms is expected to move eastward out of
east Texas into western Louisiana late this morning. Large hail and
wind damage should be the main threat initially. But as the storms
mature, tornadoes will be possible along the southern edge of the
complex with supercells that become surface-based. This convective
complex is expected to move eastward along a warm front across
central Mississippi into west-central Alabama during the mid to late
afternoon. The stronger and more dominant supercells that interact
with the warm front may produce tornadoes, some potentially strong,
along with wind damage and large hail.
Further south across southern Mississippi and southwestern Alabama,
the airmass is expected to remain undisturbed through mid afternoon
with a corridor of strong instability setting up from southern
Mississippi eastward into south-central Alabama. Supercells are
possible ahead of the main complex along this corridor in the late
afternoon as large-scale ascent increases ahead of the upper-level
trough. At this time, the mid-level jet will become coupled with the
low-level jet, creating a favorable combination of lift and shear
for potentially strong tornadoes. The greatest chance for a regional
cluster of tornadoes is forecast from just southeast of Jackson,
Mississippi and Hattiesburg, Mississippi eastward across southwest
and south-central Alabama.
In addition to the tornado threat, large hail and wind damage will
be likely across a large part of the Southeast this afternoon and
evening. The wind-damage threat is expected to increase as an MCS
moves eastward across southeastern Alabama and into south-central
Georgia by early this evening. Squall-line development will be
possible ahead of the cold front tonight from central Georgia into
the Carolinas, where a wind damage, large hail and a tornado threat
will be possible.