ACUS02 KWNS 150530
SWODY2
SPC AC 150529
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1229 AM CDT Thu May 15 2025
Valid 161200Z - 171200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FRIDAY
AFTERNOON INTO FRIDAY NIGHT ACROSS PARTS OF NORTHEASTERN
ARKANSAS...EAST CENTRAL AND SOUTHEASTERN MISSOURI...SOUTHERN ILLINOIS...SOUTHERN INDIANA...SOUTHWESTERN OHIO...MUCH OF WESTERN
AND CENTRAL KY...WESTERN AND MIDDLE TENNESSEE...
...SUMMARY...
Severe thunderstorms appear likely to develop across parts of the
middle Mississippi through lower and middle Ohio Valleys Friday
afternoon into Friday night. During the late afternoon into
evening, this may include a few intense supercells posing a risk for
large hail and tornadoes. During the evening into the overnight
hours, this probably will include an upscale growing and organizing
cluster posing a risk for strong, damaging winds and perhaps a
continuing risk for tornadoes.
...Discussion...
Downstream of a prominent mid-level high over the southern mid- to
subtropical latitudes of the eastern Pacific, split flow will
persist across much of North America through this period. Within
this regime an initially deep and occluded surface cyclone, centered
over northern Minnesota at the outset of the period, is forecast to
weaken Friday through Friday night, as it migrates into the Upper
Great Lakes region in response to a short wave perturbation pivoting
around the southern periphery of the mid-level circulation center.
It appears that this perturbation will come in phase with another
short wave perturbation forecast to accelerate east-northeast of the
central Great Plains through much of the Ohio Valley by early
Saturday. Another vigorous short wave trough digging around the
northeastern periphery of the Pacific ridge may reach the northern
California coast by the end of the period, preceded by at least one
more modest perturbation migrating northeastward across the northern
Baja vicinity.
In lower levels, associated with the occluding cyclone, a
weak/weakening Pacific cold front/dry line appears likely to stall
across the lower Great Lakes through Ohio River vicinity, and across
the Ark-La-Tex into Rio Grande River by 12Z Friday. This may be
trailed by another weak front across the Upper Midwest through the
central Great Plains and Texas South Plains, which is forecast to be
overtaken by the primary cold front surging southeastward from the
upper Mississippi Valley/northern Great Plains. By late Friday
night, this cold front may reach the lower Ohio Valley and central
Great Plains.
Preceding the consolidating fronts, low-level moisture return and
moderate to strong destabilization is forecast across the middle
Mississippi and lower Ohio Valleys on strengthening south to
southwesterly flow. The potential northern extent of the moisture
return remains unclear, based on model output, and this could be
impacted by outflow associated with possible early period convective development across the lower Ohio Valley into portions of the
Allegheny and Cumberland Plateaus. Depending on how these
uncertainties play out, it might not be out of the question that a
more substantive outbreak of severe thunderstorms could evolve than
currently depicted. It is possible areal coverage and probabilities
could be increased further in later outlooks for this period.
...Lower Great Lakes into northern Mid Atlantic...
Uncertainty lingers concerning the potential for severe weather.
However, the intersection of the initial weak surface cold
front/dryline and warm front could still be providing a focus for
strong to severe thunderstorm development at the outset of the
period across the lower Great Lakes/upper Ohio Valley vicinity.
Aided by continuing inflow from better potential instability across
the Ohio Valley, in the presence of moderate to strong vertical
shear, it is possible that this could continue into the day Friday,
perhaps evolving into an organizing cluster which should tend to
propagate southeastward and perhaps pose potential for strong to
severe surface gusts.
...Middle Mississippi into Ohio Valley...
There remains at least some signal that a modest short wave
perturbation, within the belt of westerlies emanating from the
subtropical eastern Pacific, may be contributing to vigorous
convective development at the outset of the period, or shortly
thereafter, across parts of the lower Ohio Valley. If this occurs,
it might not be out of the question that the boundary-layer
downstream, into the western slopes of the Appalachians, might
destabilize in time to support an upscale growing cluster with
potential to produce to produce severe wind and hail.
The impact of this possible early period convection might be the
primary contributor to at least some continuing model disparity
concerning upstream boundary-layer moistening and destabilization
(particularly the northern extent) across the middle Mississippi
into lower Ohio Valleys. However, it still appears most probable
that destabilization, as far north as the I-44 corridor of
central/eastern Missouri, will support the initiation of storms by
early afternoon, in response to forcing for ascent associated with
the mid-level perturbation emerging from the central Great Plains.
This is generally forecast to shift east-northeastward into the
lower Ohio Valley through late Friday afternoon, in an environment
that may support at least a window of opportunity for
sustained/long-lived supercells with potential to produce large to
giant hail and a couple of strong tornadoes. Into Friday evening
and overnight, there remains a considerable signal in model output
that large-scale forcing for ascent will support a notable upscale
growing and organizing cluster, in the presence of seasonably strong
(and increasingly convectively augmented) westerly deep-layer mean
flow. This may support widespread severe surface gusts,
occasionally in excess of 65 kt, across a swath from southern
Indiana/western Kentucky and northern Tennessee toward the Allegheny
and Cumberland Plateaus.
..Kerr.. 05/15/2025
$$
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