SPC AC 021248

   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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