LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0125 AM CDT Thu Jul 13 2023
Valid 131200Z - 141200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
OHIO VALLEY INTO THE NORTHEAST AND PARTS OF THE CENTRAL/SOUTHERN
HIGH PLAINS...
...SUMMARY...
Scattered severe thunderstorms capable of producing damaging winds,
large hail, and perhaps a couple of tornadoes are possible Thursday
across parts of the Ohio Valley into the Northeast, and portions of
the southern/central Plains. Isolated very large hail may occur
across parts of the central Plains.
...Synopsis...
A shortwave trough continues through the Lower Great Lakes region.
This feature will reach the Northeast by early afternoon. Moderate
mid-level winds will exist across parts of the northern Mid-Atlantic
into New England. Stronger northwesterly flow aloft will be present
across much of the northern and central Plains. At the surface, a
low pressure system will deepen along the Canadian border in the
Northeast through the day. A cold front will extend southwestward to
near the Mid-South. Convective outflow is likely to be situated from
northern Arkansas into parts of northern Oklahoma.
...Northeast...
While some cloud cover may be present during early portions of the
day ahead of the approaching shortwave, these clouds should not be
overly prohibitive with regard to surface heating by the afternoon.
Ahead of the trough and surface front, 850 mb winds are forecast to
reach around 35 kts. Shear will be sufficient for some storm
organization, but a majority of that shear will exist in the lowest
3 km or so. Wind profiles above that level are unidirectional and
fairly uniform in speed as well. The very moist airmass in place
(likely upper 60s F dewpoints) will support 1500-2000 J/kg MLCAPE. A
line of storms is expected to form along the cold front in central
New York and progress eastward during mid/late afternoon. Wind
damage is expected to be the primary threat. Given the low-level
shear, a few tornadoes occur could as circulations develop within
the line or a discrete storm or two forms ahead of the line. The
most intense updrafts may also produce large hail. Given
line-parallel upper level winds, the eastward progress of the line
may only be modest. This decreases confidence in higher potential
for wind damage.
...Parts of Ohio Valley...
Stronger mid-level flow will extend southwestward into the Ohio
Valley. The airmass will be similarly moist in this region as well.
With the upper-level jet moving into the region, deep-layer shear
will approach 40-50 kts. Scattered storms will be capable of
damaging winds and large hail. Low-level shear will be relatively
weak, though a brief tornado could occur with the strongest
supercell structures.
...Central/southern Plains...
Moderate mid-level flow across the Divide will allow storms
initiating within the higher terrain to organize into supercells. As
storms move into the moist airmass to the east, large to very large
hail and severe/damaging winds will be possible. Some clustering may
occur with time and lead to corridors of greater wind damage
potential. With an outflow boundary expected to be situated in
northern/central Oklahoma, it is possible that some activity from
the High Plains will track eastward during the evening. The Slight
risk has been extended east to account for this possibility, but may
need adjustment as observations and newer guidance warrants.
...Northern Plains into parts of Upper Midwest..
At least isolated to widely scattered storms are expected from
north-central Montana into the Dakotas and Minnesota. Northwest flow
aloft will be strong enough to promote 25-35 kts of effective shear
to the west with values increasing to 35-45 kts farther east. Lack
of greater surface moisture should limit the overall severe threat.
Greater moisture is possible near the Nebraska/South Dakota border
into southern Minnesota, but model guidance may be too high with
dewpoints. Large hail and damaging winds are the expected hazards.
If an area of higher storm concentration becomes apparent, an
increase in wind/hail probabilities may be warranted.
..Wendt/Thornton.. 07/13/2023
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