SPC Jun 30, 2020 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook
Day 1 Outlook Image

Day 1 Convective Outlook NWS Storm Prediction Center Norman OK
0256 PM CDT Tue Jun 30 2020 Valid 302000Z - 011200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON INTO THIS EVENING ACROSS PARTS OF THE NORTHERN PLAINS... ...SUMMARY...
A few severe thunderstorms are possible late this afternoon and
evening, mainly across parts of central and eastern South Dakota and
Nebraska, into eastern North Dakota, posing a risk for large hail
and strong wind gusts. ...20Z Outlook Update...
Categorical and probabilistic lines have been adjusted in an attempt
to better account for gradual progression of synoptic and
sub-synoptic features, and latest trends concerning destabilization
which will impact convective potential late this afternoon through
tonight. The surface cold front has advanced eastward/southeastward into
central South Dakota and Nebraska, to the south of an area of low
pressure migrating north-northwest of Pierre SD, toward the Mobridge
SD area, within deep surface troughing. The front is approaching
Pierre, but has advanced east/southeast of the Valentine and North
Platte NE vicinities. Outflow from prior convection has impacted
the boundary layer across much of central North Dakota, but its
leading edge appears to have stalled east of the Devils Lake into
the Jamestown vicinity and areas south of Bismarck. A narrow corridor of strong daytime heating, just ahead of the front
across central Nebraska and South Dakota, seems to provide the focus
for the most substantive convective potential late this afternoon
and evening. Beneath steep mid-level lapse rates associated with a
lingering plume of very warm elevated mixed-layer air, mixed-layer
CAPE appears in excess of 4000 J/kg. This appears to be occurring
just ahead of the stronger south-southeasterly mid-level flow in
advance of the approaching negatively tilted troughing. However,
deep-layer shear may still be sufficiently strong where storms
initiate to support isolated supercells initially, then organizing
clusters as activity gradually grows upscale this evening. ..Kerr.. 06/30/2020 .PREV DISCUSSION... /ISSUED 1103 AM CDT Tue Jun 30 2020/ ...Northern Plains...
A persistent upper low remains centered over ID today, with
moderately strong and deep southerly flow across the
central/northern Rockies and northern Plains. A large cluster of
thunderstorms has been affecting western ND this morning, providing
abundant clouds/precipitation, and limiting heating/destabilization
across the region. There is limited confidence whether this area
can recover from morning storms and pose an afternoon/evening threat
of severe storms. Will maintain the ongoing SLGT risk, but portions
of western/central ND may be removed in later outlooks. Farther south, strong heating will lead to a very unstable air mass
across portions of southeast ND/SD/NE, with forecast soundings
showing MLCAPE values of 3500-5000 J/kg. A shortwave trough
currently rotating around the base of the low across WY/CO will
approach the corridor of strong CAPE by late afternoon, resulting in
rather widespread thunderstorm development. Initial storms may be
supercellular, but it appears activity will rapidly evolve into
multiple linear structures capable of damaging winds and some hail. These storms will likely persist through much of the night as they
spread eastward into parts of western MN/IA. ...TX...
Similar to yesterday, hot surface temperatures exceeding 100F are
expected along the dryline that will extend from the San Angelo area
into southwest OK. East of the dryline, near dry-adiabatic low/mid
level lapse rates and dewpoints near 70F will yield extreme CAPE
values. Forcing is weak. But thermal circulations along the
dryline may result in isolated thunderstorms for a few hours late
this afternoon and early evening. Those storms that form may
produce locally damaging wind gusts and hail. ...Mid MS Valley...
Water vapor imagery shows a remnant MCV north of St Louis. There is
a corridor to the south of the MCV from southeast MO into western
KY/TN where strong heating and significant destabilization is
occurring. This area is likely to see scattered thunderstorm
development this afternoon. Vertical shear is weak, suggesting
activity will be chaotic and weakly organized. But large CAPE
values and steep low-level lapse rates will support a risk of
locally gusty/damaging winds. 

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