SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0756 AM CDT Wed Mar 13 2024
Valid 131300Z - 141200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
NORTHEASTERN KANSAS AND NORTHWESTERN MISSOURI...
...SUMMARY...
Large to very large hail, severe thunderstorm gusts and a few
tornadoes are expected this afternoon into evening across parts of
the central Plains and lower Missouri Valley. Isolated severe
storms may occur late this afternoon across parts of the southern
Plains.
...Synopsis...
The mid/upper-level synoptic pattern will amplify through the period
and into day 2, as a shortwave trough now over the interior
Northwest digs mostly southward and strengthens. The main vorticity
max, then over the Great Basin, and the associated/developing closed
500-mb circulation, will make their closest approach to the outlook
area during the afternoon into early evening. Meanwhile, smaller
perturbations -- evident in moisture-channel imagery over
southwestern and eastern CO -- will move northeastward toward
positions over northern NE and western KS by 00Z. This will occur
in a regime of broadly difluent flow aloft, leftward of the
500-300-mb jet maxima. By 12Z, the 500-mb low that will anchor a
multi-day, cutoff Southwestern cyclone should be located near LAS.
A series of vorticity lobes/maxima will extend from the southeastern
quadrant of the cyclone, over AZ, northeastward across the central
Plains to near southern Lake Michigan.
At the surface, 11Z analysis showed weak lows near MCI and between
SPD-LBL, connected by a quasistationary frontal zone that arched
across southeastern KS and northwestern OK. The western low should
deepen and migrate eastward then northeastward across western/
central KS into this evening, prompting the boundary to move
northward across central/eastern KS and central/northern MO as a
warm front. A dryline -- initially analyzed from a frontal
intersection over northern OK to west-central TX then southward into
Coahuila -- should mix eastward today. The dryline should arch from
central to southeastern KS, northeastern to south-central OK, and
north-central TX into the Edwards Plateau by late afternoon, before
retreating westward.
...Central Plains/Lower MO Valley...
Isolated to scattered thunderstorms are expected to develop this
afternoon, in an arc extending from near the western KS low eastward
to east-northeastward over northern KS, then east-southeastward
across central/eastern MO and perhaps south-central IL. Supercells
with all severe hazards are possible, including at least a few
tornadoes and significant (2+ inch) hail. The greatest
concentration of severe threat appears to be in northeastern KS and
northwestern MO, in and near the "enhanced" area.
Activity should develop preferentially along/near the frontal zone
and shift northward to northeastward only a little faster than the
boundary, thereby remaining in a narrow sector of favorable
buoyancy, low-level shear and boundary-layer vorticity for some time
before moving into cooler air and weakening. Nearby parts of the
dryline also might form a storm or two. In the frontal corridor
near I-70 in northern KS to northwestern MO, modified model
soundings depict strong veering of flow with height (contributing to
locally favorable hodographs and SRH), steep midlevel lapse rates,
and adequate low-level moisture, with dewpoints commonly reaching
the low/mid 50s F. MLCAPE should range from around 500-1000 J/kg
over a very narrow, northward-moving sliver of west-central/
north-central KS to a broader area of 1500-2500 J/kg developing to
between MHK-COU, then weaker (but still sufficient for strong-severe
storms) eastward into IL. Deep shear should be favorable in I-70
corridor as well, though it will be maximized farther south ahead of
the dryline where initiation is more uncertain.
Many models (including most HREF members) have been depicting
earliest convection initiation near or after 00Z, which seems
somewhat late given:
1. Their known biases (e.g., excess RAP/HRRR mixing/drying,
too-cool NAM surface conditions, poor resolution of very narrow warm
sectors, etc.),
2. The overall pattern and history of similar scenarios, with
sufficient frontal convergence/lift for convection typically earlier
in the afternoon and closer to the low, and
3. Expected diurnal destabilization (from both warm advection and
surface heating) around the dryline, frontal zone and leading edge
of the dry slot aloft.
Notably, experimental MPAS members are sooner to initiate and
farther south, more in line with conceptual models.
During late afternoon and early evening, a window of tornado
opportunity may be maximized with discrete cells in LLJ-enlarged
hodographs, before the near-surface layer nocturnally stabilizes too
much. Coverage is expected to increase for a few hours after 00Z,
maximizing hail/wind threat density, though at least isolated severe
potential may persist into the following morning over eastern parts
of the outlook area.
...Southern Plains...
Isolated thunderstorm(s) may form late this afternoon along a
roughly 300-nm long segment of the dryline over portions of
south-central/southeastern KS, into east-central OK and adjoining
parts of north TX. While development and maintenance of any cells
forming in this regime is in question due to EML-related capping,
any sustained storms can become supercells with all hazards possible
-- including very large hail. Except for the strong CINH, the
parameter space will be favorable, with stronger surface heating,
greater low-level moisture (dewpoints mid 50s to low 60s F) and
faster mid/upper winds (contributing to 50-60 kt effective-shear
magnitudes) than farther north. However, uncertainty is too great
to focus larger unconditional probabilities on any particular part
of this corridor.
..Edwards/Dean.. 03/13/2024
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