spc ac 241717
day 2 convective outlook
nws storm prediction center norman ok
1217 pm cdt sat aug 24 2019
valid 251200z - 261200z
...there is a slight risk of severe thunderstorms across portions of
north dakota and south dakota...
...summary...
a few severe thunderstorms are possible on sunday across portions of
the northern great plains. more isolated severe storm activity is
possible in the southern plains.
...synopsis...
a strong mid-level jet will emanate from the pacific northwest into
the rockies sunday and will make slow eastward progress into the
northern/central plains sunday night. downstream of this jet and
attendant trough, a more loosely phased and lower-amplitude trough
will be oriented from the mid-mississippi valley southward to
louisiana. mid/upper ridging will extend from california to west
texas.
at the surface, a lee trough will gradually sharpen from the far
western dakotas through western kansas and gradually move eastward
through the evening. another surface low will slowly organize
across west texas. multiple outflow boundaries may persist/meander
across the southern plains/ozarks as a convective complex migrates
southeastward out of kansas and weakens through the day. the
dakotas trough and ozarks surface boundaries will impact severe
potential throughout the forecast period. finally, pending
evolution of a tropical disturbance near the texas/louisiana
coastlines, a low-end tornado threat may materialize across southern
louisiana late in the forecast period.
...dakotas, western minnesota, and northern nebraska...
the combination of convergence along the sharpening lee trough
across the western dakotas and lift associated with the approaching
exit region of the northern rockies mid-level jet will foster
scattered thunderstorm development during the afternoon initially
across the western dakotas. these storms will develop in a steep
lapse-rate environment, with 60s to near 70 f dewpoints supporting
moderate to strong instability as deep shear values increase with
the approach of the mid-level jet. storms should be
outflow-dominant initially and pose a wind/hail risk, though an
isolated tornado cannot be completely ruled out. significant hail
may be a possibility with initial development given long, straight
hodographs and potential for marginal supercell development. this
risk will be re-evaluated in later updates for the possibility of a
10% significant hail risk area.
over time, as storms increase in coverage and grow upscale, a mix of
linear and cellular modes should evolve, including one or two strong
to severe mcss. these storms should encounter gradually increasing
low-level shear attendant to a strengthening low-level let across
the region, but should also encounter increasing low-level
inhibition. they should also approach eastern portions of the
outlook area overnight with some lingering hail/wind threat
especially if storms can remain surface-based.
...southern plains eastward into the ozarks...
an early morning mcs is expected to migrate southeastward through
kansas and oklahoma, though most models depict a weakening trend
with this activity. any severe threat beyond mid-morning will be
tied areas that can experience greater insolation/destabilization
and possibly near any differential heating zones that can evolve.
shear profiles improve with western extent across oklahoma late in
the day as northwesterly mid-level flow increases atop modest
southerly low-level flow, although this region will also reside just
west of a mid-level trough, with attendant subsidence keeping any
afternoon/early evening development isolated at best. the overall
uncertainty of the severe threat precludes any increase in severe
probabilities for this outlook, and ongoing probabilities will be
reconfigured as mesoscale details become clearer.
...southern louisiana...
a weak low has recently formed off the texas gulf coast (ref. nhc
tropical outlook) and a very low risk of strengthening will exist
with this system as it moves slowly east. any increase in low-level
wind fields will result in a modest tornado threat with convection
across the region, though this scenario is too uncertain to
introduce probabilities at this time.
...maximum risk by hazard...
tornado: 2% - marginal
wind: 15% - slight
hail: 15% - slight
..cook.. 08/24/2019
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note: the next day 2 outlook is scheduled by 0600z