SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0749 AM CDT Tue Mar 26 2024
Valid 261300Z - 271200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
MICHIANA REGION TO EASTERN INDIANA...WESTERN OHIO AND CENTRAL LOWER
MICHIGAN...
...SUMMARY...
Damaging to severe thunderstorm gusts are possible today over parts
of the Lower Michigan/southern Great Lakes region, and the eastern
Gulf Coastal Plain.
...Synopsis...
In mid/upper levels, mean troughing will shift eastward into the
central CONUS, as northern- and southern-stream perturbations move
into phase. The northern-stream system -- now manifest as a
complex, closed cyclone over central Canada -- should remain nearly
in place, but with intensification of its southern part into a
distinct, closed 500-mb low over the southern MB/SK line by 18Z
today. The low then should dig southeastward and eastward over the
northern international border region, reaching northern MN and
adjoining northwestern ON by 12Z tomorrow.
To its southeast, a mid/upper-level cyclone over IA is devolving
into an open-wave trough, and will pivot across the upper
Mississippi Valley today. By 00Z, that trough should extend from
western Lake Superior across WI to northwestern IN. By 12Z, a
weakened version will have ejected to northern ON. In the southern
stream, a series of mostly low-amplitude shortwave troughs and
vorticity maxima will pivot from the Desert Southwest across TX to
the lower Mississippi and Tennessee Valley regions, shifting that
part of the larger-scale trough to Coahuila and west-central TX by
the end of the period.
The 11Z surface analysis showed a strong/sub-989-mb low over west-
central WI, with polar cold front across western IL, to near MEM,
then southwestward over southwestern LA and the northwestern Gulf.
The low should occlude and move northeastward to near MQT by 00Z,
with polar front overtaking a leading/Pacific boundary across
eastern Lower MI and western OH, then extending across middle TN to
southeastern LA. The outflow-reinforced, Pacific front will shift
from its present position over parts of southern AL and northwestern
Fl Panhandle eastward across the Southeast, reaching western SC,
central GA and the AAF area by 00Z. The combined front should reach
central SC, southeastern GA and the FL coastal bend by 12Z.
...Southern Great Lakes, Lower MI...
Surface-based convection is expected to develop this afternoon over
western parts of the outlook area, in a zone of favorable low-level
convergence near the arctic front, into a corridor of diurnal
heating behind a plume of morning clouds/precip. Though buoyancy
will be modest (MLCAPE generally under 500 J/kg), and much of the
convection may not even deepen enough to produce lightning, fast
cell motions and downward momentum transport from intense flow aloft
may result in sporadic damaging to severe downdrafts. Even with
activity being low-topped, 50-60 kt cloud-layer shear vectors
aligned nearly parallel to the front will support an organized,
quasi-linear convective system (QLCS). Convection should race
northeastward across parts of IN, Lower MI and western OH while
backbuilding somewhat, spreading a threat for strong/locally severe
gusts over the region for a few hours. Activity should weaken this
evening as it encounters both weaker ambient theta-e and nocturnal
diabatic stabilization.
...Eastern Gulf Coastal Plain...
A swath of precip, with scattered embedded thunderstorms, will
continue to shift eastward across southern parts of AL/GA and the FL
Panhandle through the period. Most of this activity should remain
behind the outflow-reinforced front, keeping severe potential
marginal. Though the overall threat appears to have decreased for
this morning, isolated strong-severe gusts or a brief tornado still
are possible with the convection as it shifts eastward across the
outlook area through today and tonight.
The net vector motion of the boundary remains to the right of flow
aloft. Accordingly, anafrontal convective behavior has persisted
for several hours as cells form either on the boundary or just to
its east, then move to the cold side before deepening substantially.
Isolated/brief strengthening of any such cells to severe limits
remains possible, but conditional. Farther east, forecast soundings
reasonably suggest that elevated buoyancy developing this afternoon
and evening will transition to effectively surface-based late
overnight (after about 08Z), and spread inland across the eastern
Panhandle, coastal bend and southern GA region ahead of the
boundary. A wind shift near the surface, from southeasterly off the
relatively stable FL Peninsula to southerly and south-southwesterly
off the Gulf, appears responsible for that, and may increase
boundary-layer moisture/theta-e enough to yield 500-1000 J/kg
MLCAPE. Some reintensification of the convection therefore is
possible for a few hours before the start of the day-2 period.
...Central AZ...
Isolated to widely scattered thunderstorms are expected today,
particularly along and north of the Mogollon Rim. A few cells may
produce strong gusts or small hail. The last in a series of
shortwaves -- apparent in moisture-channel imagery over the Sierra
and western NV -- should shift southeastward across this region
today, contributing to cold air aloft (-25 deg C or less at 500 mb)
and steep midlevel lapse rates. Meanwhile, diurnal heating of
higher elevations on/above the rim will destabilize the boundary
later and remove CINH, contributing to a field of up to about 500
J/kg MLCAPE. While low/middle-level flow will be nearly
unidirectional and not very strong (generally less than 25 kt from
surface to 500 mb), with effective-shear magnitudes only around
20-30 kt, intense upper/anvil-level flow may aid with some storm
organization. Severe potential appears too low and conditional for
an outlook area at this time.
..Edwards/Leitman.. 03/26/2024
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