Jun 1, 2020 2000 UTC Day 1 Convective Outlook

Categorical Graphic 20200601 2000 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
MARGINAL 63,708 494,602 Billings, MT…Bismarck, ND…Bozeman, MT…Mandan, ND…Dickinson, ND…
Probabilistic Tornado Graphic 20200601 2000 UTC Day 1 Tornado Probabilities Graphic Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 – EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Probabilistic Damaging Wind Graphic 20200601 2000 UTC Day 1 Damaging Wind Probabilities Graphic Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Day 1 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
5 % 45,873 356,157 Billings, MT…Bozeman, MT…Dickinson, ND…Belgrade, MT…Livingston, MT…
Probabilistic Large Hail Graphic 20200601 2000 UTC Day 1 Large Hail Probabilities Graphic Probability of hail 1″ or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2″ or larger within 25 miles of a point.
Day 1 Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
5 % 48,938 227,079 Bismarck, ND…Mandan, ND…Dickinson, ND…Miles City, MT…Lewistown, MT…
   SPC AC 011950

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0250 PM CDT Mon Jun 01 2020

   Valid 012000Z - 021200Z


   Isolated, marginally severe wind and hail are possible over parts of
   central Montana between 4 to 8 PM MDT. A separate area of isolated
   severe hail and wind may develop farther east along the North
   Dakota/South Dakota border region after 2 AM MDT.

   ...20z Update...

   The only changes to the ongoing Day 1 outlook were to remove the
   Marginal risk (wind/hail probs) from portions of MN/WI. Storms that
   had earlier been strong to severe have since weakened and mostly
   dissipated and severe storms are not expected the rest of the period
   across that region. 

   Elsewhere, the outlook remains on track with locally strong gusts
   and hail possible across parts of central MT through this evening.
   Overnight into early Tuesday morning, additional storms may develop
   across parts of southwest ND and northwest SD. These storms will be
   capable of large hail and locally strong gusts.

   ..Leitman.. 06/01/2020

   .PREV DISCUSSION... /ISSUED 1130 AM CDT Mon Jun 01 2020/

   ...Central MT...
   A couple of marginally severe storms may develop east-northeast off
   the higher terrain of southwest MT within a weak low-level upslope
   regime ahead of a developing surface trough. Surface dew points in
   the current post-frontal air mass were generally holding in the low
   to mid 40s. Some increase in moisture is anticipated this afternoon
   as surface winds veer to easterly. Nearly cloud-free insolation will
   support steep low-level lapse rates at peak heating. Scant buoyancy
   appears to be the primary limiting factor to a greater severe
   threat. However, effective shear around 50 kt should support small
   to perhaps marginally severe hail and fairly efficient momentum
   translation into downdrafts capable of marginally severe wind gusts.

   ...MT/ND/SD border area...
   Weak mid-level height falls owing to a shortwave trough progressing
   east over the Prairie Provinces and strengthening warm/moist
   advection between 850-700 mb may yield elevated convection
   developing overnight near the MT/ND/SD border area. Guidance does
   differ with how far south convection would develop, which will be
   critical to severe potential given a plume of moderately large
   buoyancy becoming established over SD. While some guidance fails to
   sustain convection, the potential exists for a few cells that might
   evolve into an eastward-moving cluster. Given around 40-kt effective
   shear magnitudes and a dry sub-cloud layer to the surface, isolated
   severe hail and wind are possible.

   ...East-central MN/northwest WI...
   A risk for isolated marginally severe hail may persist through early
   afternoon with elevated convection supported by 700-mb warm/moist
   advection. This forcing for ascent should weaken during the
   afternoon as flow slowly veers. Until that occurs, ample speed shear
   in the cloud-bearing layer will favor modest mid-level updraft
   rotation for small to marginally severe hail.