SPC AC 220600

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0100 AM CDT Fri May 22 2020

   Valid 231200Z - 241200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS WESTERN
   ND...WESTERN/CENTRAL SD...AND MUCH OF NE...

   ...SUMMARY...
   An organized cluster of thunderstorms may develop to the east and
   southeast of the Black Hills Saturday afternoon, before spreading
   into adjacent portions of the Plains and middle Missouri Valley,
   accompanied by a risk for large hail and strong wind gusts through
   Saturday evening.

   ...Synopsis...
   Broad upper troughing is forecast to be in place over much of the
   western CONUS early Saturday. An upper low within this upper
   troughing, initially centered near the NV/UT/ID border intersection,
   is expected to gradually shift northeastward through western WY
   throughout the day. A pair of shortwave troughs are also forecast to
   rotate trough the upper trough. The southernmost shortwave will
   likely reach northern Mexico by early Sunday morning while the more
   northerly shortwave will likely be near the Four Corners. Evolution
   of each of these systems will contribute to a slightly eastward
   shift, but overall maintenance, of the western CONUS upper
   troughing.

   Most prominent surface feature early in the period will be the
   expansive lee troughing along the length of the High Plains. This
   troughing is expected to deepen throughout the day with eventual
   cyclogenesis anticipated across eastern CO Saturday evening. The
   resulting surface low is then expected to move northeastward towards
   central NE. 

   Sufficient low-level moisture and instability for thunderstorms will
   be in place across much of the central and eastern CONUS. Highest
   storm coverage and severe potential is anticipated over the northern
   High Plains into SD/NE. Some severe threat will also exist across
   the southern High Plains and at least scattered thunderstorm
   coverage is forecast near a weak surface low moving into the
   Midwest.

   ...Northern/Central High Plains into the Mid MO Valley...
   Lee troughing is expected to sharpen throughout the day,
   contributing to increase surface convergence amidst a diurnally
   destabilizing air mass. A modest increase in large-scale forcing for
   ascent is also expected from the approaching upper low. These
   conditions are forecast to result in convective initiation from far
   eastern MT/western ND southward into eastern WY/western NE
   Panhandle. Strong instability in place will favor robust updrafts
   capable of both severe hail and damaging downbursts, particularly
   across southwest SD and the NE Panhandle where the
   instability/vertical shear supports the potential for some very
   large hail.

   The severe threat is then forecast to shift eastward into the Mid MO
   Valley overnight. This threat could result from an organized
   convective line moving into the region and/or new development north
   of the warm front supported by a strengthening low-level jet.

   ...Midwest into Lower MI...
   A weakening surface low is expected to move across Iowa and into the
   Upper Midwest. Warm sector associated with this cyclone will spread
   into the Midwest, bringing mid 60s dewpoints through much of IL/IN
   and perhaps into Lower MI. Instability is not expected to be overly
   strong but southerly (perhaps southeasterly) surface winds and
   enhanced mid-level flow will result in enough vertical shear to
   support organized storms. Uncertainty exists regarding true warm
   sector development, limiting severe probabilities with this
   forecast. However, increased probabilities may be needed in later
   forecasts if sufficient warm-sector storm coverage looks probable.

   ...Southern High Plains...
   Guidance varies on overall coverage, but dryline storms appear
   likely across the southern High Plains. Any storms that do form
   would likely be severe, at least initially. Given the conditionality
   of the risk, a rather broad 5% wind/hail is in place. Refinements
   will likely be needed in subsequent outlooks as the mesoscale
   details become better resolved.

   ..Mosier.. 05/22/2020

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