SPC AC 101955

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0255 PM CDT Thu Jun 10 2021

   Valid 102000Z - 111200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS THE
   WESTERN DAKOTAS INTO FAR NORTH-CENTRAL NEBRASKA...

   ...SUMMARY...
   Scattered severe thunderstorms are likely late this afternoon and
   tonight across much of the northern and central Plains, especially
   across eastern Montana, the Dakotas, and Nebraska. All severe
   hazards are possible, including very large hail, wind gusts above 70
   mph, and a few tornadoes.

   ...20Z Update...

   ..Northern/Central Plains...
   Overall forecast outlined in the previous outlook remains valid,
   with a very strong instability across the northern and central
   Plains supporting severe thunderstorms late this afternoon through
   tonight. Recent 18Z LBF sounding sampled an impressive thermodynamic
   environment with a 100-mb mean mixing ratio of 17 g/kg and over 3500
   J/kg of MLCAPE. An initially discrete supercell mode is still
   anticipated, with all severe hazards possible. Upscale growth into
   one or more convective line is then expected, with the resulting
   convective lines pushing eastward/southeastward across the northern
   and central Plains. Strong wind gusts, some possibly over 70 mph,
   will be the primary severe threat overnight. Only change to the
   previous outlook was to extend the 45% wind probability/Moderate
   Risk southward into far north-central NE. This change was made based
   on trends within the most recent guidance.

   ...Northern Wisconsin/Upper Michigan...
   Recent issued MCD #906 discussed the short-term severe potential
   across northern WI and the western Upper MI. In this area, widely
   scattered to scattered thunderstorms are possible. The strongest
   storms are most likely near the WI/MI border, where shear is
   maximized, and a few isolated instances of marginally severe hail
   and/or damaging wind gusts may occur.

   ..Mosier.. 06/10/2021

   .PREV DISCUSSION... /ISSUED 1149 AM CDT Thu Jun 10 2021/

   ...Northern/central Plains including Dakotas/Nebraska/E Montana...
   An active severe-weather day is expected across the region late this
   afternoon and tonight and have upgraded parts of the western Dakotas
   to a categorical Moderate Risk, with much of this regional risk
   expected to persist well through the late-night hours.

   12Z upper-air analysis/soundings essentially sampled near-record
   moisture content by early/mid-June standards across the High Plains
   in terms of mean mixing ratios/850mb dewpoints, including locations
   such as Dodge City/North Platte/Rapid City/Bismarck/Glasgow Montana,
   although mid-level/700 mb temperatures were notably warm
   (near-record values) at these locations as well.

   Thunderstorms should develop initially this afternoon into early
   evening near the surface low and adjoining frontal segments over
   eastern Montana and the western Dakotas. Supercells capable of all
   hazards (tornado, large to giant hail, severe wind gusts) are
   expected in the first few hours of the convective cycle. This should
   be followed by a transition to one or more organized convective
   complexes with a dominant destructive-wind hazard, with isolated
   severe hail and possibly some tornado threat. During and after that
   transition, very damaging gusts to hurricane force may be observed
   through the evening and possibly the early overnight hours.

   Very steep mid-level lapse rates will overlie a corridor of
   moist/theta-e advection and diurnal heating south of the warm front
   and east of the low/cold front. This will contribute to MLCAPE
   strengthening into the 2000-3000 J/kg range (locally higher), amidst
   intensifying deep shear (effective-shear magnitudes reaching 35-50
   kt). Low-level shear should be maximized along the warm front and
   east of the surface low across eastern Montana and western North
   Dakota.

   Farther south across portions of South Dakota/Nebraska and perhaps
   northeast Colorado, high-based supercells should form late this
   afternoon/early evening near the dryline/lee trough, offering
   significant hail and severe gusts. However, this activity may evolve
   upscale more quickly to a QLCS configuration with a dominant wind
   threat. Deep, well-mixed sub-cloud layers will support maintenance
   of both severe hail and gusts to the surface during earlier,
   relatively discrete stages, but also, foster quick cold-pool
   aggregations and rapid expansion. Forced ascent of a foregoing
   boundary layer containing 60s to near 70 F surface dew points, with
   MLCAPE commonly remaining above 2000 J/kg even well after sunset,
   will help to drive the severe-wind threat southeastward over much of
   Nebraska tonight.

   ...Northern Wisconsin/Upper Michigan...
   Widely scattered thunderstorms -- some in clusters -- are expected
   to develop by late afternoon/early evening within a weakly capped
   air mass characterized by favorably rich moisture, but modest
   deep-layer shear. The lake breeze, localized convergence zones and
   outflow boundaries will also be influences. The combination of
   large-scale lift ahead of the Ontario shortwave trough with boundary
   layer heating will steepen low/middle-level lapse rates favorably,
   contributing to MLCAPE in the 1500-2500 J/kg range south of the
   Superior lake-breeze front. Isolated instances of severe hail/wind
   will be possible as storms develop south-southeastward.

   ...Arkansas/ArkLaMiss...
   Scattered thunderstorms should redevelop through the afternoon into
   evening particularly on the western/southern periphery of the
   lingering convective complex over the ArkLaMiss vicinity at late
   morning. Locally damaging downbursts of water-loaded cores will be
   the main concern from a severe-weather perspective. An
   outflow/differential-heating zone related to the decaying overnight
   convection -- and oriented with a substantial component parallel to
   the northwesterly midlevel flow vectors, should provide most of the
   early focus for this redevelopment. Diurnal heating of a very moist
   boundary layer -- with surface dew points in the 70s F and PW near 2
   inches -- will foster peak MLCAPE in the 2500-3500 J/kg range, in a
   very deep troposphere. Weak vertical shear will tend to limit
   organization to pulse characteristics with multicell modes, although
   a few transient supercells could occur with storms interacting with
   the outflow/differential heating boundary.

   ...West/southwest Texas...
   A few late-afternoon thunderstorms again are possible over higher
   terrain of the Davis Mountains/Big Bend area, and more
   conditionally, the adjoining segment of the dryline, offering
   locally strong-severe gusts and hail. Strong capping will make
   convective development more improbable with northward and eastward
   extent. The lack of more-robust deep-layer winds (and of stronger
   vertical shear) should keep convection multicellular in character
   and slow-moving, remaining close to its genesis area. Hot, deep,
   well-mixed boundary layers will contribute to strong wind gust
   potential aside from some hail risk.

   ...Carolinas...
   A weak mid-level wave and somewhat stronger mid-level westerlies
   should influence storm development and organization to a degree this
   afternoon within a moist/unstable air mass. Some of the stronger
   storms may produce wet microbursts capable of locally damaging
   winds.

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z