LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1249 AM CDT Fri Jul 21 2023
Valid 211200Z - 221200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHEAST...
...SUMMARY...
Severe thunderstorms with wind damage and hail will be possible
today across parts of the Southeast. Marginally severe storms will
also be possible in parts of the Northeast and High Plains.
...Southeast...
Mid-level flow will be west-northwesterly today across much of the
central and eastern U.S. At the surface, a moist airmass will be in
place across much of the Southeast with surface dewpoints in the
lower to mid 70s F. Moderate instability will quickly develop this
morning, with a gradient of instability extending east-southeastward
across the Gulf Coast States. A shortwave trough will approach the
unstable airmass this morning. Large-scale ascent associated with
this feature will support a morning MCS located in the southern
Plains at the start of the period. The MCS is forecast to gradually
intensify during the day, moving east-southeastward along a gradient
of moderate instability.
RAP forecast soundings around midday along the track of the MCS from
eastern Arkansas into north-central Alabama have MLCAPE increasing
to around 3000 J/kg. The soundings have veered winds in the low to
mid-levels, and increasing winds with height to about 40 knots at
500 mb. This wind profile will likely support the development of a
linear MCS with a wind-damage threat. The potential for wind damage
is expected to increase as low-level lapse rates steepen in the
afternoon. The MCS is expected to remain organized as it tracks
across the central Gulf Coast states this afternoon, reaching the
southern Atlantic Seaboard by early evening.
...Northeast...
An upper-level trough will move eastward across the lower Great
Lakes and Mid-Atlantic today. At the surface, an associated cold
front will advance eastward into the region. Ahead of the front,
surface dewpoints in the lower to mid 70s F, will contribute to the
development of a pocket of moderate instability. Storms are expected
to form near and ahead of the front, moving eastward into the
instability during the afternoon. Forecast soundings along the axis
of instability from eastern Maryland northward into New Jersey have
0-6 km shear around 30 knots, along with 0-3 km lapse rates
approaching 7.5 C/km. This should support marginally severe
multicells with an isolated wind-damage threat. Although the
greatest potential for isolated wind damage may be in the
Mid-Atlantic, a marginal wind-damage threat could develop as far
north as western New England this afternoon.
...High Plains...
Northwesterly mid-level flow will be in place today across the High
Plains. At the surface, flow will be upslope across the southern and
central High Plains. In response, a moist airmass will be in place
across eastern Colorado. As surface temperatures warm, scattered
thunderstorms will develop in the higher terrain of central Colorado
and move southeastward into the central High Plains. MLCAPE across
the central High Plains is forecast peak in the 1000 to 1200 J/kg
range this afternoon. 0-6 km shear is expected to range between 25
and 35 knots, suggesting that an isolated severe threat could
develop. Hail and strong gusty winds will be possible with the
stronger multicells.
..Broyles/Wendt.. 07/21/2023
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