SPC Aug 29, 2020 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1256 AM CDT Sat Aug 29 2020

Valid 291200Z - 301200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE MID
ATLANTIC INTO PORTIONS OF NEW ENGLAND AND FOR EASTERN OK...AR...AND
ADJACENT PORTIONS OF SOUTHEAST KS/SOUTHERN MO...

...SUMMARY...
Severe storms are possible for parts of eastern Oklahoma into
Arkansas this afternoon and evening, with damaging winds and large
hail the main threats. A few strong to severe storms will also be
possible from portions of the Carolinas into the Mid Atlantic and
New England during the day, with damaging winds and perhaps a couple
of tornadoes possible.

...Synopsis...
An upper trough over the upper Great Lakes this morning will amplify
and move into the Northeast by tonight, as a surface cyclone deepens
and moves across northern New England. In advance of the large-scale
trough, the surface-to-midlevel trough associated with the remnant
of Laura will continue to weaken and move quickly offshore by early
afternoon. Further west, an MCV is forecast to move from Kansas into
the Ozark Plateau, while another upper trough begins to amplify over
the Northwest. 

...Carolinas into New England...
Clouds and precipitation will likely be widespread at the start of
the period this morning from the Carolinas into New England.
However, there will be some potential for modest
heating/destabilization for near-coastal regions of the Mid Atlantic
into the Carolinas, to the east of the more widespread morning
convection. Enhanced low/midlevel flow associated with the 
combination of Laura's remnant and the larger-scale upper trough to
the northwest will favor a risk of locally damaging wind and perhaps
a tornado or two from late morning into the afternoon, should any
appreciable destabilization occur prior to convection moving into
the region.

Further north, in the wake of early convection, scattered
thunderstorm development along the advancing front will be possible
from central NY eastward into New England. Increasing midlevel flow
and deep-layer shear will support organized convection, with a
threat of locally damaging wind and perhaps some marginally severe
hail with the strongest cells. 

...Oklahoma into Arkansas/southern MO...
A cold front is expected to advance southward today across southern
MO into portions of OK/AR. An MCV is forecast to move eastward to
the north of the front across southern KS into MO, as a weak surface
low develops along the boundary in the vicinity of the Red River.
Substantial heating and rich low-level moisture will contribute to
strong destabilization, with MLCAPE of 2500+ J/kg expected by
afternoon near/south of the boundary and east of the surface low.
This instability combined with effective shear of 25-35 kt will
support a conditional threat of organized severe thunderstorms. 

Evolution of convection remains somewhat uncertain across this
region. Overnight convection may persist and intensify this morning
into early afternoon just north of the boundary, with additional
more discrete development possible late this afternoon near/east of
the surface low and in the vicinity of the front and/or any outflow
boundaries across the area. Storm coverage will likely increase this
evening within a warm-advection regime as a southwesterly low-level
jet develops, with eventual evolution into one or more
upscale-growing clusters. Hail and locally damaging wind will be a
threat with any semi-discrete storms. A somewhat greater coverage of
damaging wind will be possible with any organized cluster. 

...High Plains...
Widely scattered strong thunderstorms are possible this
afternoon/evening across portions of the central/southern High
Plains, within a post-frontal upslope-flow regime. Moderate
instability and sufficient deep-layer shear will support a few
organized storms with a corresponding risk of hail and locally
severe wind gusts. 

Further north, modest low-level moisture will advect northward into
portions of WY/western SD and the NE Panhandle, to the east of a
developing lee trough. A few strong storms may develop over the
higher terrain and spread eastward, with a corresponding risk of
isolated severe hail/wind.

..Dean/Jirak.. 08/29/2020

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