spc ac 211721
day 2 convective outlook
nws storm prediction center norman ok
1221 pm cdt sun jun 21 2026
valid 221200z - 231200z
...there is a slight risk of severe thunderstorms across portions of
the mid-atlantic into southern appalachians...and over parts of the
northern and central high plains...
...summary...
scattered severe storms appear possible across portions of the
mid-atlantic into the southern appalachians monday afternoon and
evening. widely scattered severe storms are expected across the
northern and central high plains, with more isolated severe weather
possible from the southern plains into the lower mississippi valley.
...synopsis...
a series of perturbations, embedded within broadly cyclonic
mid-level flow, will progress eastward to the atlantic coast, to the
south of an upper low tracking from eastern ontario into southern
quebec. farther west, separate vorticity maxima will overspread the
northern and central high plains, in tandem with a belt of
strengthening mid-level winds.
in the lower levels, a 40-50 kt low-level jet (llj) is forecast to
migrate from the allegheny plateau into the lower hudson and de
river valleys monday afternoon, ahead of a surface low developing
toward those same areas. meanwhile, a trailing cold front will
advance south through the central appalachians, tn valley, and ozark
plateau, with the western extension of the boundary linking with a
secondary low over western tx. elsewhere, a lee cyclone is expected
to deepen over eastern wy, along a weak front settling southeast
through the northern high plains.
...mid-atlantic into the southern appalachians...
12z cam guidance is in relatively good agreement in depicting the
remnants of an overnight (sunday night/early monday morning) mcs
overspreading ny and pa, within a zone of warm air and moisture
advection occurring with the terminus of the llj. to the
south/southeast of that convection across the lower hudson and de
river valleys, modest air mass destabilization is expected, with
comparably stronger instability with southward extent into the
central/southern appalachians and piedmont. deep-layer shear is
forecast to strengthen through the day as a belt of 40-50 kt winds
at 500 mb overspreads the region from the west.
thunderstorms are expected to increase in areal coverage and
intensity during the afternoon from the vicinity of the outflow or
differential heating boundary in eastern pa south/southwest into the
southern appalachians and piedmont. damaging winds will be the
primary hazard owing to steepening low-level lapse rates and high
moisture content, which will enhance wet-microburst processes. a
relatively narrow corridor of potentially greater tornado potential
may materialize from the delmarva into the de river valley, where
stronger low-level shear is forecast. however, given uncertainties
in the degree of air mass destabilization in the northern extent of
that area, the 2% unconditional tornado probability will be
maintained. a separate area of tornado potential may materialize
monday afternoon across parts of the southern appalachians within
the southwest extension of the llj, where a number of the 12z cams
indicate updraft-helicity swaths embedded within a linear complex of
storms.
...northern and central high plains...
the deepening lee cyclone will enhance the flux of an increasingly
moist low-level air mass into the high terrain, beneath a plume of
steep mid-level lapse rates, supporting moderate afternoon
instability. greatest storm coverage is expected across portions of
eastern mt and western nd monday afternoon within the northern
extent of the instability axis, where the strongest forcing for
ascent is expected. weaker forcing with southward extent is expected
to lead to more widely spaced storms in eastern wy and co. here,
comparatively stronger instability and vertical shear will support
supercells capable of large to very large hail and perhaps a brief
tornado or two during the afternoon and evening hours.
...southern plains...
areas of storms ongoing monday morning across parts of the red river
valley into the arklatex region are expected to gradually weaken by
midday, owing to rising mid-level heights across the region. in the
wake of that activity, moderate to strong instability is forecast by
afternoon in the vicinity of the stalled synoptic front and any
remnant outflow boundaries. however, considerable uncertainty
remains in surface-based storm development given the absence of
appreciable forcing for ascent. as such, the low unconditional
probabilities will be maintained with this forecast update. on the
condition surface-based storms develop and are sustained, the
parameter space would support intense supercells capable of large to
very large hail and some tornado threat.
..mead.. 06/21/2026
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note: the next day 2 outlook is scheduled by 0600z