Valid 192000Z – 201200Z
…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE OZARKS
INTO THE OHIO VALLEY AND FROM EASTERN NEBRASKA…SOUTHERN IOWA AND
Severe thunderstorms appear possible through tonight over a broad
part of the central U.S., with the greatest threats over parts of
southeastern Nebraska/southern Iowa/northern Missouri, and from
parts of the Ozarks to the lower Ohio Valley.
Recent surface analysis places a low over east-central CO with a
cold front extending northeastward to another low centered very near
OMA. A warm front then extends eastward from this second low
eastward/east-southeastward across southern IA, central IL, and
central IN. A dryline also extends southwestward from the OMA low
through central OK and into southwest TX.
Strongest storms are currently ongoing along and ahead of the
dryline from east-central OK southwestward into western portions of
north-central TX. MCD 204 was recently issued discussing the
expected storm evolution for the next few hours. Tornado Watch 56
was also recently issued over this area to cover the anticipated
severe threat. The ongoing storms looks to move into a progressive
more favorable environment downstream over the next several hours.
This is expected to result in increased storm coverage and
intensity. Based on recent radar and environmental trends as well as
recent HRRR guidance, the Enhanced risk was expanded back westward
to cover more of northwest AR.
Farther north, the air mass continues to destabilize near the OMA
surface low, evidenced by the strengthening elevated storms across
south-central/southeast NE and deepening CU downstream across
northwest MO/southwest IA. Strong low-level shear is still expected
to result in supercells capable of all severe hazards.
Lastly, increasing storm coverage is still anticipated later this
afternoon and evening across the Lower OH Valley. Primary severe
threat is damaging wind gusts but a few tornadoes are also possible.
.PREV DISCUSSION… /ISSUED 1130 AM CDT Thu Mar 19 2020/
…Ozarks to lower Ohio Valley…
An ejecting low-amplitude shortwave trough and its broad, strong
low-level jet is resulting in a favorable kinematic environment for
organized severe storms over a broad region today. However,
widespread areas of rain and clouds are slowing destabilization over
a large part of the warm sector. Pockets of heating will eventually
promote gradual destabilization over a portion of this region with
additional storms expected to intensify along warm conveyor belt
from eastern portions of the southern Plains into the lower MS
Valley and OH Valley region. Large 0-1 km hodographs and 50 kt
effective bulk shear within a modestly unstable environment
(1000-1500 J/kg MLCAPE) will support potential for supercells and
bowing line segments capable of damaging wind, tornadoes and hail.
..Northern MO/NE/IA and vicinity…
Scattered thunderstorms, including several supercells should develop
in one or two arcs today, near the southern NE/IA warm front and
across parts of northeastern KS/northwestern MO, near the nose of a
low/middle-level dry slot forced by the ejecting shortwave trough.
Deep-layer forcing for ascent will strengthen through the day as the
mid/upper perturbation approaches. The related mass response will
lead to increasing low-level lift and backing of surface flow along
and very near the warm front, though veered surface winds are
probable southward into the warm sector. The frontal zone will act
as a localized low-level SRH/lift maximum, supporting tornado
potential with any storms that can maintain enough residence time in
it before encountering too much poleward stable air.
Thermodynamic support will arise from steepening midlevel lapse
rates, diurnal surface heating behind early cloud cover/precip, and
a ribbon of favorable low-level moisture advection into the
corridor. Forecast soundings suggest dew points ranging from low
50s west to low/mid 60s east can support a ribbon of 1500-2500 J/kg
peak MLCAPE over parts of southeastern NE, northwestern MO,
northeastern KS and southwestern IA. Buoyancy should decrease
eastward amidst weaker lapse rates, and westward amidst less
moisture. Deep shear will be highly variable under strongly
difluent mid/upper-level flow, with contribution from near-frontal
backing, but generally stronger near the Missouri Valley and over
IA. The convective regime and associated severe potential should
spread eastward across the outlook area into early evening.