SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0748 AM CDT Wed Apr 02 2025
Valid 021300Z - 031200Z
...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE
MID-SOUTH AND LOWER MISSISSIPPI VALLEY...
...SUMMARY...
A tornado outbreak is expected today and tonight from parts of the
lower Mississippi Valley into the Mid-South and lower Ohio Valley.
Numerous tornadoes, along with multiple EF3+ tornadoes, appear
likely. In addition, tornadoes, significant severe wind gusts, and
large hail to very large hail will be possible across a broad area
from north Texas northeastward to the southern Great Lakes.
...Synopsis...
A strong mid/upper-level trough with associated 100-120 kt mid-level
jet streak will advance quickly northeastward today across the Upper
Midwest and Great Lakes. A broader area of 50-70+ kt southwesterly
mid-level flow will persist over much of the southern Plains into
the lower/mid MS Valley and OH Valley. At the surface, the primary
low over far eastern NE/western IA this morning is forecast to
develop northeastward in tandem with the upper trough today,
eventually reaching the Upper Midwest by this evening. A trailing
cold front will continue east-southeastward across the southern
Plains and Ozarks today, before eventually stalling and lifting
northward as a warm front tonight. Weak secondary surface low
development is possible this afternoon and evening along or just
ahead of the front across AR into the Mid-South.
...Ozarks into the Lower/Mid Mississippi Valley, Mid-South, Ohio
Valley, and Southern Great Lakes...
Robust convection is ongoing this morning from northern MO
southwestward to southern OK and north TX along/near the cold front.
Even with some capping concerns noted on area soundings ahead of
this activity, a very strong (60-70 kt) southerly low-level jet is
providing ample low-level moisture transport to support continued
convective intensity. Steep mid-level lapse rates and strong
deep-layer shear are also fostering some embedded supercell
structures, with associated large hail threat. Otherwise, given the
strength of the low-level flow and very strong effective SRH,
scattered severe/damaging winds and a few tornadoes will remain the
primary threats with this line of convection as it continues
eastward this morning across the remainder of OK into AR and MO. A
strong tornado may occur with any sustained surface-based supercell.
The effect that this morning convection has on downstream afternoon
severe potential across the lower/mid MS Valley may be substantial.
Most guidance shows either a gradual weakening trend with the line
by late morning/early afternoon, or a devolution into a broken line
of supercells. Mid/high-level cloud debris could inhibit daytime
heating to some extent across much of the warm sector, and the
northern extent of the weakening line over northern MO may serve as
a cutoff for surface-based thunderstorms across the Midwest and OH
Valley later today. Even with these continued uncertainties, it
appears likely that a corridor of moderate to strong instability
will develop this afternoon across the lower MS Valley into the
Mid-South and lower OH Valley, generally ahead of whatever remains
of the ongoing/morning convection. With more nebulous/weaker
large-scale ascent over these regions given their spatial
displacement from the ejecting upper trough, there may be a more
mixed/supercell mode this afternoon/evening, particularly with
southward extent.
Current expectations are for several intense supercells and clusters
to develop by 20-00Z from far northern LA into eastern AR, northwest
MS, western TN/KY, and southeast MO, and southern IL/IN. This region
appears to have the most favorable overlap of moderate to strong
instability, strong deep-layer shear, and ample low-level shear to
support multiple tornadic storms. With most guidance showing
enlarged, curved hodographs through the boundary layer, and
effective SRH forecast to generally range 250-400+ m2/s2, several
strong tornadoes are likely. Multiple EF-3+ tornadoes should also
occur given the very favorable parameter space forecast, but this
high-end tornado potential may be dependent on a relative lack of
supercell/cluster interactions, which are difficult to pinpoint.
Still, based on latest high-resolution guidance trends showing
multiple intense supercells developing, the High Risk has been
expanded a bit southward with this update to include more of eastern
and south-central AR. The tornado and severe/damaging wind threat
will likely continue after dark, with updraft interactions
suggesting a messy mode, with clusters/lines and embedded supercells
all possible.
In addition to the tornado threat, large to very large hail (up to
2-3 inches in diameter) and severe/damaging wind gusts may occur
with these supercells and bowing clusters. A linear mode appears
more likely with northward extent across the mid MS Valley into the
southern Great Lakes as the cold front continues eastward today.
But, this area will also have less time to destabilize ahead of the
ongoing convection, which casts some uncertainty on the northern
extent of the substantial severe threat. Have trimmed the
Marginal/Slight Risks some across the Upper Midwest, but the
Enhanced Risk remains unchanged for now. Some risk for supercells
ahead of the line/clusters will exist across the OH Valley/Midwest.
But, confidence in this scenario occurring was not great enough to
expand the Moderate Risk for tornadoes northward into more of IN and
western OH.
...Southern Plains...
With the cold front expected to stall and eventually begin lifting
northward tonight, additional supercells may develop late in tandem
with ascent preceding another shortwave trough and a strengthening
southerly low-level jet. With steep mid-level lapse rates present
and ample MUCAPE and deep-layer shear, this convection should pose a
threat for mainly large to very large hail.
..Gleason/Leitman.. 04/02/2025
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