SPC Day 1 Outlook

   SPC AC 101629

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1029 AM CST Wed Mar 10 2021

   Valid 101630Z - 111200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS
   AFTERNOON INTO TONIGHT ACROSS PARTS OF THE UPPER MIDWEST INTO THE
   LOWER MISSOURI VALLEY AND ADJACENT PORTIONS OF THE CENTRAL GREAT
   PLAINS...

   ...SUMMARY...
   A few severe thunderstorms are possible late this afternoon into
   this evening across parts of central Iowa into southeastern
   Minnesota and adjacent portions of western Wisconsin, and perhaps
   this evening into the overnight hours across parts of eastern Kansas
   into northwestern Missouri.

   ...Synopsis...
   Models suggest that broad, positively-tilted mid-level troughing, 
   within a southern branch of split mid-latitude westerlies, will be
   reinforced across the western U.S., as the southwestern portion of a
   splitting vigorous short wave trough emerging from the Arctic
   latitudes digs southward along the northern Pacific coast.  Within
   the northern branch, consolidating short wave troughing is forecast
   to gradually turn eastward across eastern portions of the Canadian
   Prairies.  As it does, one significant short wave emerging from the
   southern branch troughing is expected to accelerate northeastward
   across the middle Missouri Valley through the upper Great Lakes
   region by late tonight.

   Model spread concerning the lead short wave perturbation and related
   developments has been sizable.  In general, though, guidance appears
   to have trended toward stronger associated surface frontal wave
   development northeast of the middle Missouri Valley through the
   Upper Midwest late this afternoon and evening, along with
   intensification of the perturbation through mid-levels.  This likely
   will be accompanied by considerable intensification of lower/mid
   tropospheric wind fields (including 90-100+ kt at 500 mb and 50-70+
   kt at 850) within the evolving warm sector of the surface cyclone. 
   However, low-level moisture return from the western Gulf of Mexico
   remains modest to weak, even across the southern Great Plains, and
   this will tend to limit destabilization.

   ...Central Great Plains into Upper Midwest...
   Severe weather potential is supported by synoptic forcing and strong
   wind fields associated with the developing system, but remains
   largely conditioned on sufficient boundary-layer destabilization,
   which remains unclear.

   Stronger mid/upper support for convective development seems likely
   to be largely focused ahead of the short wave impulse, in closer
   proximity to the developing surface cyclone across the Upper Midwest
   late this afternoon into tonight.  However, at least somewhat better
   low-level moisture return and associated destabilization will be
   focused in the immediate wake of the short wave impulse, as strong
   southerly low-level flow persists ahead of the large-scale
   Southwestern mid-level troughing.

   Severe probabilities across the Upper Midwest have been adjusted a
   bit to focus where models now appear in better agreement with the
   narrow corridor of stronger pre-frontal boundary-layer warming
   across western/central Iowa into southeastern Minnesota (roughly
   based on late afternoon model positioning of the 925-850 mb thermal
   ridge axis).  It appears that surface dew points may increase into
   the mid 50s+ F within a narrow corridor near/just east of this axis,
   and contribute to at least weak boundary-layer destabilization when
   coupled with mid-level cooling.  Given the strengthening of the
   low-level and deep-layer shear, thermodynamic profiles may become
   marginally conducive to supercells, including a risk for tornadoes,
   for at least a couple hour period late this afternoon and evening. 
   Thereafter, a narrow, broken squall line could evolve ahead of the
   eastward surging cold front, and continue to pose a risk for strong
   wind gusts into this evening, before activity weakens in diminishing
   instability.

   Thunderstorms may develop southward along the front into the central
   Great Plains through this evening, as far southwest as the leading
   edge of stronger mid-level height rises/capping in the wake of the
   short wave impulse.  This may be aided by an area of enhanced
   lower/mid tropospheric warm advection along/above the surface
   frontal zone, across parts of southeastern Kansas into western
   Missouri, where a number of stronger storms may pose at least some
   risk for severe hail.

   ..Kerr/Wendt.. 03/10/2021

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