SPC AC 120559

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1259 AM CDT Sun Jul 12 2020

   Valid 131200Z - 141200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PORTIONS OF THE
   CENTRAL PLAINS INTO THE EASTERN DAKOTAS AND WESTERN MN...

   ...SUMMARY...
   Severe storms are possible across portions of the central Plains
   into the eastern Dakotas, western Minnesota and Iowa on Monday
   afternoon into Monday night. Additional isolated strong storms are
   possible from the eastern Carolinas into Southern New England Monday
   afternoon.

   ...Synopsis...

   A strong upper trough will develop eastward from the northern
   Rockies to the northern Plains on Monday. This will result in
   substantial height falls from the central Rockies and central Plains
   northward across the northern Plains and into the Upper Midwest.
   This will result in a band of strong west/southwest flow spreading
   across the region. At the surface, low pressure over the central
   Dakotas during the morning will develop east/northeast toward
   southeast Manitoba and Ontario with a trailing cold front advancing
   east/southeast across the northern/central Plains during the
   afternoon into early Tuesday morning. Thunderstorms are expected to
   develop along the front during the afternoon across the eastern
   Dakotas. Additional storms are expected further southwest during the
   evening as convection moves off the higher terrain of CO/northeast
   NM.

   Further east, an upper trough will be oriented from the lower Great
   Lakes to the southeastern U.S. A shortwave trough embedded within
   the northern portion of the trough near Lake Huron will pivot
   eastward across the Northeast. A surface low and trailing front will
   shift east across the mid-Atlantic and southern New England through
   the afternoon, and scattered strong storms are possible.

   ...Eastern Dakotas into western MN/IA...

   Most guidance shows strong moisture return will occur ahead of the
   surface front on strong southerly low level flow. Surface dewpoints
   as high as the mid/upper 60s are forecast with strong heating
   occurring ahead of the boundary across the eastern Dakotas into
   western MN. This will result in a corridor of moderate to strong
   MLCAPE amid strong effective shear and steep midlevel lapse rates.
   With increasing upper forcing and lower level frontal forcing,
   capping should erode and initially discrete cells are possible.
   Backed low level winds ahead of the surface boundary, and 0-3 km
   shear near 35 kt will result in enlarged, curved hodographs,
   suggesting a few tornadoes will be possible should convection remain
   discrete. However, LCLs will be on the high side and mean mixing
   ratio values near 14 g/kg suggest this may temper the tornado threat
   somewhat. Large to very large hail also will be possible with any
   more discrete convection. A low level jet is expected to increase
   during the evening, and upscale development into a bowing line
   segment/QLCS is possible as convection spread eastward across MN and
   parts of IA into the nighttime hours. 

   ...Central/Southern High Plains into the Central Plains...

   Further south, a surface trough will extend southward through the
   High Plains of CO/NM with a weak lee cyclone developing near the
   intersection of this surface trough and the cold front associated
   with the northern Plains surface low. Southeasterly low level winds
   along the boundary will transport low to mid 60s dewpoints as far
   east as parts of western KS into central NE, with values quickly
   falling into the mid 40s to mid 50s across eastern CO southward into
   northwest NM and the OK/TX Panhandle. Falling heights with the
   approaching of the trough and strong heating amid steep midlevel
   lapse rates will support thunderstorm development over the mountains
   during the afternoon. As this convection spreads eastward, adequate
   effective shear should maintain organized cells through a corridor
   of weak to moderate MLCAPE. A deeply-mixed boundary layer will aid
   in strong downdrafts and isolated severe gusts are possible.
   Convection could become better organized along the surface boundary
   across NE later in the evening as the low level jet increases and
   storms encounter a more unstable air mass, with some guidance
   suggesting a second MCS south of the northern plains MCS could move
   eastward across parts of the central Plains overnight. 

   ...Eastern Carolinas to the Mid-Atlantic and southern New England...


   A belt of moderate midlevel southwesterly flow will overspread
   portions of Atlantic coast from the eastern Carolinas into New
   England as one shortwave impulse ejects eastward offshore during the
   afternoon, and another pivots eastward from the Great Lakes during
   the evening. A surface low will track northeast across New England
   with a front extending southward through the Mid-Atlantic, and a
   surface trough extending southward through the Piedmont vicinity. A
   seasonally warm/moist air mass will be in place, with weak to
   moderate instability occurring by late morning. Scattered strong
   storms are possible with locally damaging winds through the
   afternoon.

   ..Leitman.. 07/12/2020

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