SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook CORR 1
NWS Storm Prediction Center Norman OK
0812 AM CDT Sun Jul 14 2024
Valid 141300Z - 151200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
CORRIDOR FROM THE NORTHERN PLAINS TO THE UPPER MIDWEST AND OHIO
VALLEY...
CORRECTED FOR GRAPHICAL LABEL POSITION
...SUMMARY...
Strong to severe thunderstorms are expected from the northern Plains
into the Upper Midwest and Ohio Valley.
...Synopsis...
The mid/upper-level pattern will remain dominated by mean troughing
from the Great Lakes southwestward across TX, and an anticyclone
over the Four Corners States, though each should deamplify through
the period. A belt of relatively maximized, west-northwesterly to
northwesterly flow will persist from the northern Rockies to the
Great Lakes, with strong difluence on its southern and southeastern
fringes from the central Plains to parts of the mid-Mississippi and
Ohio Valleys. Convectively generated/enhanced perturbations now
over Lower MI, southern WI and southeastern SD will traverse the
flow belt across the southern Great Lakes region through the period.
Upstream, a strong shortwave trough was evident in moisture-channel
imagery over parts of northern/western AB. This feature should move
southeastward to southeastern AB and southern SK by 00Z, then reach
the Red River (of the North) Valley near the end of the period.
At the surface, features relevant to today's convective potential
mostly were outflow-related at 11Z, south of what had been a
synoptic warm to stationary front. These will be discussed in
greater detail below. As the outlook areas are predicated on
multiple interactions between existing and future boundaries and MCS
activity, the outlook lines may shift considerably through the day
as mesoscale trends and newer guidance focus potential better.
...Northern Plains...
One or more clusters of severe thunderstorms may develop over the
region this afternoon or tonight, with potential for severe gusts.
This includes the possibility of significant (65+ kt) gusts.
However, confidence has decreased in placement or timing of any
specific significant-gust area. The airmass in and around the one
from the previous outlook has been directly and substantially
overturned by a large and significantly severe overnight MCS.
Convectively parameterized ("synoptic") guidance and
convection-allowing progs are widely dispersed in location, size,
and to lesser extent timing of MCS upscale development over this
area. The general consensus appears to be for MCS potential over
ND, north of the main corridor disrupted by the major complex of
last night. This may be the most reasonable solution synoptically,
given the increasing large-scale ascent likely tonight from the
approaching Canadian shortwave trough, and potential for residual
moisture not directly affected by the prior MCS to suffice in its
inflow region. Still, questions remain regarding how much
associated convectively processed air will affect inflow
trajectories of activity farther north. The outflow boundary from
that complex -- which generated intense pressure perturbations and a
broad rear-inflow jet -- has surged all the way into central IA,
southeastern NE and northern KS -- well south of substantial flow
aloft and south of supportive upper-air features. Given these
intervening developments, the unconditional "slight" area has been
trimmed northward more in line with potential for an overnight
complex in ND, whose severity and longevity itself is uncertain.
...Upper Mississippi Valley region to Lower Great Lakes States...
This outlook area covers two potential MCS/severe episodes, though
considerable uncertainty remains as to which may be more dominant in
terms of total report distribution. Skeletal remnants of an earlier
MCS, with remaining convection non-severe in nature, was apparent
over portions of northwestern OH, northern IN and southern Lower MI.
The outflow boundary from this activity was drawn across IN/IL/IA
near a LAF-MLI-CID line, where it was being overtaken on the west by
outflow from a complex over southern WI and northern IL, that was
penetrating an airmass stabilized by the earlier activity, but
undergoing modification from low-level warm/moist advection. As
this complex or its associated outflow arc moves southeastward into
less-modified, more strongly diurnally heated boundary layer near
and north of the oldest outflow boundary, additional strengthening
appears increasingly probable, with damaging to severe gusts the
main concern.
Regardless of how severe it becomes later, the ongoing complex, in
turn, should continue to deposit outflow across northern IL and
eastern IA, reinforcing the baroclinic zone in that region, with
some northeastward shift possible through the day amid modest but
steady low-level warm advection. When the remnant pressure/theta
perturbation from the old SD complex interacts with this boundary
this afternoon, during a period of peak diurnal heating and weakest
MLCINH, additional thunderstorms should develop -- with fairly quick
upscale evolution into yet another MCS possible. As with its
predecessors, any such complex should move parallel to, mainly along
and north of the residual outflow boundary and generally with the
mid/upper-level flow, offering damaging gusts and isolated large
hail. The upstream boundary layer that will source inflow for these
potential complexes is characterized by rich moisture, with surface
dewpoints remaining commonly in the upper 60s to low 70s F (locally
higher) along and south of the outflow boundaries, supporting a
corridor of MLCAPE ranging from near 4000 J/kg in the IA/northern IL
area to 2000-3000 J/kg over parts of OH/IN.
...AZ...
Widely scattered thunderstorms are expected to develop this
afternoon -- initially over higher terrain where diurnal heating
preferentially erodes MLCINH fastest -- then move generally westward
or west-southwestward to lower terrain and deeper boundary layers.
Isolated severe gusts are possible from the most vigorous cells,
atop a deep subcloud layer characterized by nearly dry adiabatic
lapse rates from surface to LFC. This motion should be supported by
a layer of substantial easterly component roughly from 700-300 mb.
Enough low-level moisture should remain over the desert floors
through the heating/mixing cycle to support 500-1500 J/kg MLCAPE,
and 1000-1500 J/kg DCAPE.
..Edwards/Broyles.. 07/14/2024
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