SPC Jul 11, 2020 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0100 AM CDT Sat Jul 11 2020

Valid 111200Z - 121200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF
THE CENTRAL/SOUTHERN PLAINS INTO THE OZARK PLATEAU AND MID MS
VALLEY...

...SUMMARY...
Severe thunderstorms with damaging wind and hail are possible on
Saturday from parts of Kansas and Oklahoma into the lower and mid
Mississippi Valley. A few strong storms are also possible during the
afternoon from the coastal Mid-Atlantic into New England with
isolated damaging wind the main threat.

...Synopsis...
An upper ridge will remain in place across the Southwest into the
southern Plains today. Around the periphery of the ridge, a
shortwave trough is forecast to move southeastward from the northern
Plains into portions of the Midwest and mid-MS Valley. An upper
trough will remain in place across the East. The remnant circulation
of T.C. Fay will move quickly into Canada this morning, in advance
of a shortwave trough moving from the OH Valley into New England. 

...Central/southern Plains into the Ozark Plateau...
Uncertainty remains quite high regarding the evolution of the severe
threat today into tonight. The key factor will be the potential
development (or lack thereof) of a southeastward-propagating MCS
this morning across the central Plains/MO Valley. Most 00Z guidance
has trended away from developing an extensive early-day MCS, which
may be due to the stabilizing effects of extensive convection on
Friday across parts of KS/OK. If this scenario verifies, then the
primary severe threat will likely be delayed until late afternoon or
evening across eastern parts of KS/OK into the Ozark Plateau, and
the magnitude of the severe threat will be greater due to the
potential for more substantial destabilization prior to the onset of
the primary threat. Strong instability and effective shear in excess
of 40 kt would favor the potential for organized convection under
this scenario, with initial supercells likely growing upscale into
one or more organized clusters. Significant hail and perhaps a
tornado would be possible early in the convective evolution, with
potential for upscale growth and more widespread damaging wind with
time. 

Meanwhile, if a more extensive early-day MCS evolves, then the
primary threat for much of the area may be damaging wind and
isolated hail associated with the early storms, and a more
conditional threat late this afternoon or evening along any remnant
outflow boundaries. 

Given the uncertainties, a broad Slight Risk has been included with
this outlook. Some refinement to this area, and possibly an increase
in probabilities, will be possible in subsequent outlooks as details
become clearer. 

Further west into western OK and the TX Panhandle, widely scattered
thunderstorm development is possible this afternoon within a hot,
well-mixed environment. Effective shear will be sufficient for some
updraft organization with any storms in this area. Coverage remains
uncertain, but a conditional threat for severe wind gusts will be
present, with steep low-level lapse rates and large DCAPE developing
by afternoon. 

...Midwest/Mid MS Valley...
The magnitude of destabilization across the Midwest/Mid MS Valley
will depend to some extent on the evolution of morning convection
coming out of the central Plains, but at least moderate buoyancy is
likely to develop by afternoon. Foci for initiation will likely be
subtle given the nebulous surface pattern, but weak capping and
large-scale ascent attendant to the shortwave will favor scattered
thunderstorm development. Unidirectional wind profiles with
effective shear of 30-40 kt will favor the potential for discrete
supercells, with an attendant risk of large hail and locally
damaging wind. 

...Northern Mid Atlantic into New England...
The remnant of T.C. Fay is forecast to move quickly into Canada
later this morning, but rich low-level moisture and modestly
enhanced low/midlevel flow should remain in place ahead of the
shortwave trough moving out of the OH Valley. Scattered thunderstorm
development is expected by late morning/early afternoon along and
ahead of a weak surface boundary. The strongest storms will be
capable of producing locally damaging wind, especially in areas
where stronger heating and steepening of low-level lapse rates can
occur.

..Dean/Lyons.. 07/11/2020

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from SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_1200.html