SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1227 PM CDT Mon Aug 28 2023
Valid 291200Z - 301200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
NORTHWEST/WEST-CENTRAL FLORIDA PENINSULA...
...SUMMARY...
The potential for a few tornadoes should gradually increase
along/near parts of the Florida Gulf Coast and into north Florida
through Tuesday night as Tropical Cyclone Idalia approaches.
...Florida into Southeast Georgia...
Latest forecast for TC Idalia centers the system northwest of
western Cuba early Tuesday morning, with
northeastward/north-northeastward motion taking the storm to just
off northwestern FL Peninsula by 12Z Wednesday morning. Strong
low/mid-level flow associated with this system will gradually spread
northward across the FL Peninsula throughout the day, with the
strongest winds expected along the western coast after 00Z. Rain
bands will likely begin moving across the peninsula during the early
afternoon, with a generally northeastward storm motion anticipated.
Lapse rates will be poor, but the moist airmass across the region
will still support moderate buoyancy and the potential for a few
strong updrafts. The most significant increases in low-level shear
are not expected under after 00Z, so the severe-gust and tornado
potential with these multicellular bands will be low, but not zero.
After 00Z through the remainder of the period, strengthening low to
mid-level flow will result in a gradually increasing tornado
potential, particular along the west-central and northwest portions
of the FL Peninsula. TC tornado climatology shows a notable
preference for tornadoes between 200-300 km northeast of the center
for northeastward progressing major hurricanes. This matches well
with the most favorable environmental conditions for tornadogenesis
in this case, which are along the northwest/west-central FL coast
from 06Z-12Z.
...Interior Pacific Northwest into the Northern Rockies...
A negatively tilted shortwave trough is forecast to progress across
the Pacific Northwest on Tuesday. Moderate mid-level flow and
moisture will spread eastward ahead of this wave across ID and into
western MT. Resulting combination of a deeply mixed boundary layer,
increasing mid-level moisture, and strengthening ascent is expected
to result in afternoon/evening thunderstorm development. 20 to 30 kt
of effective shear will help organize some updrafts, with high cloud
bases and steep low-level lapse rates supporting the potential for
strong outflow. An instance or two of hail is possible as well.
...Great Lakes/OH Valley...
A cold front is forecast move southeastward across the Great Lakes
and parts of the Midwest/OH Valley, in tandem with an
eastward-moving upper trough. Dewpoints will likely be in the upper
50s and low 60s from IL into IN and MI ahead of this front, but
mid-level temperatures will be relatively warm, limiting buoyancy
and updraft strength/duration. Damaging gusts would be possible with
any deep, sustained updrafts, but the overall probability of
occurrence currently appears low.
...Appalachians...
Scattered thunderstorms should develop across parts of the
southern/central Appalachians Tuesday afternoon, as modest ascent
associated with an upper trough moving Quebec and the Upper Great
Lakes/OH Valley glances the region. Modest deep-layer vertical shear
is anticipated amid the southwesterly mid-level flow stretching
across the region, supporting potential updraft organization. Even
so, poor lapse rates should limit instability and overall updraft
strength. A generally multicellular, outflow-dominant storm mode is
anticipated, and the potential for a damaging gust or two exists
within any bowing segments. However, overall severe coverage is
expected to remain too low to include severe probabilities.
..Mosier.. 08/28/2023
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