SPC AC 141630

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1130 AM CDT Thu Jun 14 2018

   Valid 141630Z - 151200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FAR NORTHERN
   ND...

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS PARTS OF THE
   DAKOTAS...

   ...SUMMARY...
   Scattered to numerous severe storms are expected during the late
   afternoon and evening across parts of the Dakotas into northwest
   Minnesota. A couple tornadic storms, very large hail, and intense
   wind gusts are possible.

   ...Dakotas to MN/WI...
   A shortwave trough over the northern Rockies will eject northeast
   into the southern Prairie Provinces through early Friday. A surface
   cyclone over southeast MT should develop into separate lows with one
   tracking northeast into southwest Manitoba by evening and a
   thermal-induced circulation near the Black Hills, along a cold front
   that progresses east across the Dakotas tonight. Rich boundary-layer
   moisture sampled by the 12Z OAX sounding and characterized by mid
   60s to low 70s surface dew points will spread north from the Mid-MO
   Valley beneath a stout elevated mixed layer as sampled by the 12Z
   UNR sounding. With robust surface heating underway, this setup will
   result in a plume of strong to extreme buoyancy across the Dakotas
   by early evening with MLCAPE commonly reaching 2500-5000 J/kg.

   Ongoing elevated storms across far northeast MT into northwest ND
   may continue to produce isolated severe hail over the next few
   hours. In the wake of this activity, two corridors of surface-based
   storm development are anticipated during the late afternoon. One is
   expected to be over far northwest ND into southeast Saskatchewan and
   southwest Manitoba, in the zone of stronger large-scale forcing for
   ascent along the northwest edge of the warm sector. These storms
   will be supercells, a couple of which may be long-tracked. These
   will be capable of producing very large hail and tornadoes given the
   steep mid-level lapse rates/buoyancy and sufficient low-level
   moisture with strong low-level shear/hodograph curvature. The areal
   extent of this risk in northern ND should be rather confined as the
   cap will probably inhibit storm development to its immediate south.
   The second corridor of storm development is anticipated across
   western SD in the zone of strongest surface heating and deep mixing.
   Here, surface temperatures around 100 should weaken the cap
   sufficiently for high-based storm development near the lee
   trough/cyclone in vicinity of the Black Hills. Outflow generated by
   this convection could help it persist as an MCS spreading northeast
   through the evening. The very large MLCAPE plume and steep
   low/mid-level lapse rates should result in severe wind being the
   primary hazard, with isolated significant severe gusts possible.
   Morning guidance does suggest that in spite of a strengthening
   southwesterly low-level jet tonight, negative theta-e advection will
   become increasingly common across the eastern Dakotas into
   central/southern MN. This indicates a stout capping inversion will
   overspread this region and likely result in weakening intensity of
   this MCS overnight. However, a separate MCS should form as elevated
   storms become widespread from northern MN southeast into WI in
   association with strengthening low-level warm advection, on the
   northeast edge of the elevated mixed-layer. While heavy rain should
   be a comparatively greater hazard, the strongest cores could produce
   isolated severe hail overnight.

   ..Grams/Nauslar.. 06/14/2018

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