SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0243 PM CDT Tue Jul 12 2022
Valid 122000Z - 131200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM EASTERN
PENNSYLVANIA SOUTHWESTWARD TO NORTHERN VIRGINIA...
...SUMMARY...
Thunderstorms capable of producing locally damaging winds are
expected to continue from New England through the Mid-Atlantic
States into the central Appalachian region and Tennessee Valley,
this afternoon and early evening. A few strong storms may also be
noted across the Upper Midwest and over the central High Plains.
...Discussion...
Convection continues to evolve as expected/forecast per prior
outlooks, with the only appreciable changes that appear necessary at
this time are to adjust western portions of the thunder/severe risk
areas to account for eastward advance of the cold front/convective
initiation zone.
Otherwise, severe risk remains greatest from New England across the
central Appalachians, where a zone of storms continues to evolve at
this time. Lesser risks persist across the Upper Mississippi
Valley/western Upper Great Lakes area, and over parts of the central
High Plains.
..Goss.. 07/12/2022
.PREV DISCUSSION... /ISSUED 1117 AM CDT Tue Jul 12 2022/
...Appalachians/Mid-Atlantic/Northeast this afternoon/evening...
No changes to the previous outlook. Within a broad midlevel trough
over the Great Lakes, an embedded speed maximum will eject
eastward/northeastward from the central Appalachians/lower Great
Lakes to the Mid-Atlantic and New England this afternoon/evening, as
an associated surface cold front likewise moves
eastward/southeastward from the upper OH Valley and western PA/NY.
Destabilization will proceed from west-to-east through the afternoon
in advance of the front in conjunction with low-level moisture
advection and surface heating, and visible satellite imagery
suggests that multiple cells/small clusters will form along and
ahead of the cold front by early-mid afternoon from central PA/NY
eastward.
MLCAPE of 1000-2000 J/kg and relatively long/straight hodographs
with effective bulk shear of 35-50 kt is expected from the
Mid-Atlantic northward, along with DCAPE near 1000 J/kg. The
near-storm environment and expected convective mode will favor
clusters and supercells capable of producing damaging winds, though
isolated large hail and an isolated tornado or two may also occur
with the strongest storms. Some upscale growth into line segments
will be possible, which would favor damaging winds as the primary
threat.
...Ozarks to TN Valley this afternoon through late evening...
Vertical shear will weaken with southwestward extent along a cold
front moving slowly southward into TN/AR. Surface temperatures will
warm into the 95-100 F range by late afternoon, with steep low-level
lapse rates and moderate buoyancy immediately ahead of the front.
Widely scattered thunderstorm development is expected by late
afternoon/evening along the front, and the strongest storms will be
capable of producing isolated strong/damaging downburst winds from
late afternoon into this evening.
...Central High Plains this evening...
Boundary-layer dewpoints in the mid-upper 50s reside across eastern
CO as of mid morning, though some vertical mixing is expected this
afternoon along with strong surface heating. A few high-based
storms are expected to form late this afternoon/evening immediately
east of the higher terrain, along a developing surface lee trough
from southeast WY into northeast CO. Deep-layer northwesterly shear
will be sufficient for some storm organization/supercell structures,
while the steep lapse rates and modest buoyancy support the threat
for isolated strong-severe outflow winds and marginally severe hail
for a few hours late this afternoon/evening.
...MN/WI this afternoon/evening...
An embedded shortwave trough will move southeastward from southern
MB/far western ON across northern MN and WI through this evening.
Surface heating and residual low-level moisture, beneath cool
midlevel temperatures (near -15 C at 500 mb), will result in MLCAPE
of 500-1000 J/kg this afternoon with minimal convective inhibition.
Thus, scattered thunderstorm development is expected from northeast
MN into northern WI, where the modest buoyancy and deep-layer
west-northwesterly shear will be sufficient for clusters and low-end
supercells capable of producing marginally severe hail and outflow
gusts for a few hours later this afternoon/evening.
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