spc ac 181720
day 2 convective outlook
nws storm prediction center norman ok
1220 pm cdt mon may 18 2026
valid 191200z - 201200z
...there is a slight risk of severe thunderstorms from the great
lakes into southern plains...
...summary...
widely scattered severe thunderstorms will be possible along a cold
front extending from the great lakes into the ohio valley and the
southern plains on tuesday. damaging winds and large hail will be
the primary threats.
...synopsis...
a short-wave trough over the northern plains into upper ms valley
tuesday morning will translate northeast into ontario with an
associated belt of strong mid-level flow overspreading the great
lakes. the stronger mid-level winds will extend southwest into the
central high plains, downstream from a positively tilted trough
moving through the great basin and lower co valley.
at the surface, low pressure associated with northern plains
disturbance will develop from the upper great lakes through
southeast ontario into quebec. meanwhile, a trailing cold front will
move through the great lakes and oh valley, with the trailing
extension of the boundary advancing through the mid ms valley and
southern plains. the cold front and any preceding outflow boundaries
associated with early-day convection will serve as the main foci for
diurnally enhanced strong to severe storm development.
...ohio valley into the great lakes and new england...
a southwesterly low-level jet will sustain a moist boundary layer
across the pre-frontal warm sector with dewpoints in the 60s to
perhaps low 70s in the oh valley. the moisture will combine with
daytime heating to support mlcape ranging from 1000-1500 j/kg across
the mid/lower great lakes into new england, with as high as
2000-3000 j/kg forecast in the oh valley. a broad zone of low-level
warm advection coupled with the glancing influence of the ontario
short-wave trough are expected to support a gradual increase in
thunderstorm coverage and intensity through the afternoon along and
ahead of the synoptic cold front.
the strongest low/mid-level flow and resultant deep-layer shear is
forecast to reside across the great lakes and northern new england,
where transient bowing and/or supercell structures appear possible.
weaker shear with southward extent into the oh valley will be
supportive of multicell clusters. damaging wind gusts appear to be
the primary hazard in both regimes, though isolated occurrences of
marginally severe hail are also possible.
...mid mississippi valley into the southern plains...
thunderstorms are expected to be ongoing tuesday morning along or
ahead of the cold front from the ozarks into ok. daytime heating of
the downstream air mass coupled with boundary-layer dewpoints in the
60s to low 70s and steepening mid-level lapse rates with
southwestward extent will support moderate to strong afternoon
instability with mlcape of 2000-3000+ j/kg. the 12z models suggest
that a subset of the early-day storms will intensify by afternoon
across the ozark plateau with additional thunderstorm development
anticipated along the synoptic cold front and preceding convective
outflow boundaries from the mid ms valley into the southern plains.
there is some model signal that one or multiple, weak disturbances
will translate from the southern plains into ozark plateau during
the day, which will aid in the diurnally enhanced storm development.
as alluded to in the synopsis, the strongest mid-level flow and
associated vertical shear is expected remain confined to the
post-frontal air mass. the exception will be across parts of the tx
permian basin into the big bend and edwards plateau, where easterly
low-level winds ahead of front will augment modest mid-level flow to
support 30-40 kt of effective bulk shear. as such, predominant
convective modes will be multicell clusters and line segments
capable of damaging winds and marginally severe hail. large hail
potential (some hailstones in excess of 2") increases with
southwestward extent into tx owing to steeper mid-level lapse rates
and the potential for supercell storm modes, given the stronger
vertical shear.
..mead.. 05/18/2026
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note: the next day 2 outlook is scheduled by 0600z