Severe Storm Outlook Narrative (AC)
Issued by NWS
ACUS02 KWNS 261730
SPC AC 261728
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1228 PM CDT Wed Apr 26 2017
Valid 271200Z - 281200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM A PORTION
OF THE SOUTHEAST INTO THE OH VALLEY AND GREAT LAKES...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF WESTERN KS AND NORTHWEST OK...
At least a marginal risk for a few severe storms capable of isolated
damaging wind gusts and hail is expected from the Southeast States
into the Ohio Valley and Great Lakes and across portions of western
Kansas and northwest Oklahoma on Thursday.
Broad troughing will cover the majority of the CONUS throughout the
period as one embedded shortwave trough progresses northward through
the OH Valley and upper Great Lakes into Ontario and another series
of smaller shortwave troughs moves across the Great Basin and
southern/central Rockies towards the Plains. Surface low initially
centered over upper MI will occlude as it tracks northward into
Ontario, just ahead of its parent shortwave trough. Northern portion
of the cold front attendant to this low will move eastward across
the OH and TN valleys into the Northeast and mid-Atlantic while the
southern portion slowly moves eastward as a composite outflow
boundary/cold front across Southeast. This southern portion of the
front will become increasingly displaced from the shortwave trough
over time and its eastward progress is expected to gradually slow
throughout the day. Farther west, a deepening lee trough is
anticipated across the High Plains with cyclogenesis likely
occurring across the central High Plains during the afternoon.
Composite outflow boundary/cold front will likely extend from
eastern TN southward/southwestward into southwest AL at the
beginning of the period. Thunderstorms will likely be ongoing along
this boundary with the expectation for this activity to persist
throughout the day as the front continues eastward. Mid-level flow
will remain sufficient for occasionally organized updrafts capable
of isolated hail and/or damaging wind gusts but the lack of stronger
synoptic forcing for ascent and only weak convergence along the
frontal boundary is expected to keep overall severe coverage too low
to merit slight-risk-equivalent probabilities.
The best combination of low-level moisture and vertical shear will
likely exist across portions of the Carolina Piedmont where surface
dewpoints are expected to be in the mid 60s and 0-6 km bulk shear
around 50 kt. However, warm temperatures aloft are expected to
temper instability and suppress potential storm development. Hail
and damaging winds would be possible if any storm was able to
The better low-level moisture is expected to remain south of the
region but surface dewpoints could still reach the upper 50s to low
60s ahead of the line of storms moving through the area. This
limited low-level moisture coupled with cool temperatures aloft will
support enough instability for storm persistence, and, given the
strength of the shear, some isolated damaging wind gusts and hail.
...Western KS...Northwest OK...
A conditional severe threat exists across portions of western KS
into Northwest OK where a few storms may develop as a result of
strong isentropic ascent northeast of the deepening surface low.
Meager low-level moisture is anticipated but cold temperatures aloft
(i.e. -20 deg C at 500 mb) and a deeply mixed boundary-layer may
still support enough instability for a few storm strong enough to
produce isolated hail. Additionally, given the deeply mixed
boundary-layer, any persistent storms that develop during the
afternoon may produce gusty winds.