SPC AC 071244
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0644 AM CST Tue Nov 07 2017
Valid 071300Z - 081200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
Thunderstorms are possible from the coastal Carolinas/Delmarva to
parts of east Texas today.
In mid/upper levels, a broad belt of zonal flow will cover most of
the central and eastern U.S., downstream from a positively tilted
shortwave trough now located over the northern Plains, northern
Rockies and Great Basin. That trough is forecast to elongate and
shift east-southeastward, and by 00Z, should reach southern Lake
Michigan, northern IA, northern NE, southern WY, to an anchoring
vorticity lobe over eastern UT. The trough will continue to stretch
overnight, extending from the Mid-Atlantic across much of the Corn
Belt to the main vorticity max over CO by 12Z. Though lacking
substantial embedded shortwaves, the downstream/zonal pattern across
the Southeast will be characterized by height falls.
At the surface, a weak low was analyzed at 11Z over eastern Middle
TN, with cold front southwestward across northern MS, northern LA,
and central/southwest TX. The low should migrate across the
mountains and NC, along a slower-moving to stationary segment of the
front to its east. Meanwhile, by 00Z, the cold front should reach
northern GA, central MS, and southeast/south-central TX. By 12Z,
the front should be located from southern SC across southern parts
of MS/AL to the northwestern Gulf, and deep south Texas.
...Northern GA, southeastern TN, western/central Carolinas...
Isolated to widely scattered thunderstorms are possible today near
the surface cold front as the boundary crosses the region.
Destabilization for surface-based parcels becomes more uncertain
with northward extent across the southern Appalachians region, in
the wake of ongoing non-severe thunderstorms crossing the region.
To their south, a combination of diurnal/diabatic surface heating
and dew points in the 60s F may yield a southwest-northeast plume of
MLCAPE reaching 500-1000 J/kg from midday through late afternoon.
Weak lapse rates/instability aloft, and veered prefrontal winds in
the boundary layer, cast doubts on strength of lift needed to
sustain convection, and thus on convective coverage/strength, even
though forecast soundings suggest 40-50 kt effective-shear
magnitudes are possible. Isolated damaging gusts approaching severe
limits, or small hail, cannot be definitively ruled out from a
thunderstorm or two in this environment; however, the potential
still appears too conditional to warrant categorical-level
probabilities at this time.
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