SPC AC 291727

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1227 PM CDT Mon Jun 29 2020

   Valid 301200Z - 011200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS MAINLY TUESDAY
   EVENING ACROSS PARTS OF THE CENTRAL AND EASTERN DAKOTAS INTO CENTRAL
   AND NORTHEASTERN NEBRASKA...

   ...SUMMARY...
   Intense thunderstorms posing a risk for severe wind gusts and hail
   are possible across the central and eastern Dakotas and parts of
   central and northeastern Nebraska late Tuesday afternoon through
   Tuesday evening.

   ...Synopsis...
   Models suggest that mid/upper flow over North America may become
   characterized by increased blocking during this period.  It appears
   that a mid-level high centered near/northeast of the upper Great
   Lakes region may become more prominent Tuesday through Tuesday
   night.  Downstream of this feature, a mid-level low may remain
   nearly stationary along the New England coast, while perhaps
   elongating along an axis roughly from northern New England into
   middle portions of the Ohio Valley, central/southern Appalachians,
   and southern Mid Atlantic region.  This may suppress ridging
   initially present across the Tennessee Valley.

   Meanwhile, as subtropical ridging builds west-northwestward across
   parts of the lower Rio Grande Valley, Texas Gulf coast and southern
   Plains, and another short wave impulse digs along the British
   Columbia coast into the Pacific Northwest, the increasingly deformed
   remnants of a significant mid-level low are forecast to pivot across
   and northeast of the Rockies.  As this occurs, models indicate that
   an associated surface cold front will surge east of the Rockies,
   into initially deep surface troughing across much of the northern
   and central plains.

   Ahead of the impulse emerging from the intermountain region, a
   fairly broad plume of very warm and capping elevated mixed-layer air
   is currently overspreading much of the plains, into portions of the
   Mississippi Valley.  At the same time, the boundary layer continues
   to moisten.  By Tuesday, mid 60s to lower 70s surface dew points
   likely will be common across most areas east of the Rockies, with
   the exception of parts of the high plains and lower Great Lakes into
   Northeast.  This seasonably high moisture content will contribute to
   areas of moderate to large CAPE, particularly beneath the steep
   mid-level lapse rates across the plains.

   ...Dakotas/Nebraska...
   It appears that an eastward surge of the surface cold front may
   precede the main lingering mid-level impulse emerging from the
   intermountain region, overspreading much of the western Dakotas and
   Nebraska by midday.  However, within the pre-frontal troughing,
   insolation beneath the very warm and capping elevated mixed-layer
   air is expected to allow for strong destabilization, including
   mixed-layer CAPE in excess of 3000-4000+ J/kg by late Tuesday
   afternoon.

   Deep-layer southerly wind fields and shear may be initially weak,
   but moderate low-level flow (on the order of 30 kt at 850 mb),
   coupled with modest strengthening of mid-level wind fields (perhaps
   30-40 kt at 500 mb) Tuesday evening, may contribute to an
   environment conducive to severe storms, including supercells and
   organizing clusters.  Timing of the onset of primary convective
   development remains somewhat unclear, as strong mid-level cooling
   and weakening of inhibition may not occur until after 01/00Z, but
   there still should be a window of opportunity for storms to pose a
   risk for severe wind and hail.

   ...Tennessee Valley into southern Mid Atlantic...
   Deep-layer west-northwesterly flow on the order of 10-20+ kt,
   coupled with the development of moderately large CAPE (up to 2000+
   J/kg), may be sufficient to contribute to scattered clusters of
   storms capable of producing potentially damaging wind gusts Tuesday
   afternoon and evening.

   ..Kerr.. 06/29/2020

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