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000
ACUS01 KWNS 150558
SWODY1
SPC AC 150557

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1257 AM CDT Mon Apr 15 2024

Valid 151200Z - 161200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF SOUTH DAKOTA...NEBRASKA...AND KANSAS...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PORTIONS OF THE
MID ATLANTIC...

...SUMMARY...
Scattered severe thunderstorms are likely across the southern to
central Great Plains, mainly this evening and into tonight. Large to
very large hail, damaging wind gusts, and a few tornadoes are
possible. More isolated severe storms are also possible over parts
of the Ohio Valley and Mid Atlantic with a risk for mainly damaging
winds and hail.

...Synopsis...
An upper low over the western Great Basin is forecast to amplify
considerably as it begins to phase with an increasingly strong
mid-level subtropical jet located over the Southwestern US. Early
morning WV imagery and RAOBS show this jet is currently moving out
of northern MEX into southern AZ and NM. As the upper low and jet
amplify, they will move eastward and spread broad-scale ascent over
much of the southern and central High Plains late in the diurnal
cycle. At the same time, a subtle mid-level perturbation east of the
building central US ridge will move south overspreading a modestly
warm air mass near a slowly sagging cold front in the Mid Atlantic.
An initially diffuse lee trough/weak cyclone is forecast to quickly
consolidate and deepen below 1000 mb over eastern CO and western NE
by late afternoon. Large-scale mass response from the approaching
trough and deepening low will aid in advecting a fairly broad and
increasingly moist (mid 60s F surface dewpoints) modified Gulf air
mass northward, east of a sharp dryline. While some uncertainty
exists regarding convective initiation owing to the late arrival of
large-scale ascent, mid and high-level cloud cover and capping,
scattered severe thunderstorms capable of all hazards are possible
over much of the Plains. Isolated storms are also possible over
parts of the OH Valley and Mid Atlantic with a risk for damaging
gusts.

...Central Plains Triple Point/Warm Front...
A well defined warm front is expected to mark the northern edge of
the ongoing moisture return near the KS/NE border at 12z. As the
surface cyclone to the west begins to deepen, the warm front should
lift northward into central NE and southern SD by mid afternoon.
Strong low-level moisture advection and sheltering by mid and
high-level clouds should allow for upper 50s to low 60s F dewpoints
to pool near the front ahead of a subtle shortwave trough on the
eastern periphery of the approaching upper low. Diurnal heating and
forcing for ascent from the approaching shortwave should allow for
removal of remaining inhibition by mid to late afternoon near and
along the warm front and closer to the triple point. Mid-level lapse
rates near 8-8.5 C/km and cool mid-level temps will support moderate
buoyancy with large clockwise curved hodographs. Initial supercells
are likely with the potential for large to very large hail. A few
tornadoes are also possible given large low-level buoyancy and
enhanced low-level SRH along the warm front.

...Central and southern Plains Dryline...
Considerable uncertainty exists regarding diurnal convective
development east of the dryline. Mid and high-level cloud cover from
the active subtropical jet may stunt daytime heating/mixing while
the later arrival of the main upper-low will limit large-scale
ascent. With a stout EML in place, it is unclear if subtle ascent
from embedded perturbations within the subtropical jet and the
dryline circulation will support convective development from western
KS and OK into the TX Panhandle during the day. CAM guidance
suggests a few storms may develop farther south in west/western
North TX within the deeply mixed air mass. With increasingly strong
wind fields in place these storms would likely be supercellular with
large to very large hail and the potential for a couple tornadoes.

Additional development appears likely later in the evening and into
the overnight hours as a Pacific front moves east and intersects
with the retreating dryline. Uncertainty remains high with various
model solutions, but higher probabilities of convective development
appear likely across western and central KS with mid-level height
falls and strong tropospheric flow fields increasing overnight.
Large hail and damaging winds would be possible with this second
round of storms, along with potential for a couple of tornadoes.

...Ohio Valley into VA and NC...
Weak height falls from the subtle trough are expected to move over
Mid Atlantic by early to mid afternoon timed with peak heating and
modest boundary-layer moisture return. Weak surface convergence
along a sagging cold front and surrounding terrain should be
sufficient to support isolated to scattered thunderstorm development
through the afternoon across the central OH Valley into eastern WV
and northern VA. Ahead of the front, potentially low 50s F surface
dewpoints and mid-level lapse rates of 7-8 C/km will support
1000-1500 J/kg of MLCAPE with moderately strong mid and upper-level
flow. Several bands or clusters of storms are expected to develop
and may pose a risk for isolated severe hail and damaging wind gusts
as they track east/southeast into the evening hours. The threat
should gradually diminish after sunset with the loss of diurnal
heating.

..Lyons/Kerr.. 04/15/2024

$$