SPC AC 061259

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0759 AM CDT Sat Jun 06 2020

   Valid 061300Z - 071200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS THE
   NORTHERN PLAINS...

   ...SUMMARY...
   Severe thunderstorms are likely across parts of the northern Great
   Plains this afternoon into tonight. Severe wind gusts, large to very
   large hail, and a couple of tornadoes are possible. Severe
   thunderstorms are also expected across the central/northern Rockies
   today.

   ...Northern Plains including the Dakotas/western Nebraska...
   A developing surface low is expected over the northern High Plains
   with a well-developed lee trough extending through the central High
   Plains. A warm front will advance north across the north-central
   Great Plains and extend across South Dakota during the
   afternoon/evening.

   Strengthening low-level flow will usher increasingly moist air from
   the central Great Plains northward into South Dakota with an arc of
   66-74 deg F dewpoints extending from southeast South Dakota
   west-northwestward into west-central South Dakota by mid-afternoon.
   Strong heating will contribute to steepening low-level lapse rates
   beneath 7-8 deg C/km 700-500mb lapse rates. Widely scattered storm
   development will likely ensue in the more deeply mixed/hotter air
   across far eastern Wyoming/Nebraska Panhandle and adjacent South
   Dakota. A mixed mode of organizing bands growing upscale and
   discrete supercell activity are expected. Large hail, severe gusts,
   and a few tornadoes are possible  Farther east in southeast South
   Dakota, lower storm coverage along the warm frontal zone is expected
   towards early evening. Despite weaker mid- to high-level flow, large
   hodographs within a boundary layer characterized by 17-18 g/kg
   lowest 100mb mean mixing ratios, suggests the potential for a few
   tornadoes. As the mid-level wave approaches during the evening, more
   widespread storm coverage is expected and upscale growth will favor
   a transition to primarily a severe wind gust threat spreading
   northeastward during the evening and overnight as a low-level jet
   strengthens.

   ...Central Rockies...
   Considerable forcing for ascent and appreciably strengthening
   deep-layer shear will overspread the region, with storms expected to
   increase/intensify relatively early today, initially across eastern
   Utah into western Colorado. Even with modest destabilization, very
   long hodographs will support some supercells over the higher terrain
   in addition to an evolution of fast northeastward-moving bands of
   storms. Some hail could occur, but severe-caliber thunderstorm gusts
   of 60-85 mph can be expected through the afternoon. Additionally, a
   tornado risk cannot be ruled out given supercell-favorable wind
   profiles with ample low-level shear/SRH.

   ...New England...
   Isolated to scattered thunderstorms are forecast to increase
   generally near a southeastward-moving cold front. Moderate
   pre-frontal heating and steepening low/mid-level lapse rates will
   support intensifying thunderstorms by afternoon in the presence of
   strengthening deep-layer winds. Strong to severe multicells capable
   of marginally severe hail and damaging gusts in the 50-60 mph range
   are expected. This activity will push east of the coast by the early
   evening.

   ...Mid-Atlantic States...
   A zone of moderate heating/destabilization will occur today with the
   expected development of isolated/widely scattered thunderstorms as
   the air mass destabilizes and a southeastward-moving cold front
   overtakes a pre-frontal trough. Steepening low-level lapse rates and
   25-35 kt effective shear could allow for stronger downdrafts capable
   of localized wind damage.

   ...Middle Gulf Coast to Florida/Tropical Storm Cristobal...
   Reference NHC forecasts for the latest forecast details regarding
   Cristobal. A mini-supercell related tornado risk could approach the
   middle Gulf Coast region late tonight/early Sunday, although the
   low/mid-level winds will more appreciably strengthen into inland
   areas after 12Z Sunday.

   Well to the east of Cristobal, a couple of weakly rotating storms
   have been noted early today just off the western Florida Peninsula.
   While the strongest low/mid-level winds will remain over the Gulf of
   Mexico, adequate low-level wind speeds/SRH could allow for some
   weak/transient supercells today into tonight with gusty winds and/or
   a low tornado risk possible, mainly across the central/southwest
   Florida Peninsula.

   ..Guyer/Leitman.. 06/06/2020

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