spc ac 171729
day 2 convective outlook
nws storm prediction center norman ok
1229 pm cdt fri jul 17 2026
valid 181200z - 191200z
...there is an enhanced risk of severe thunderstorms for parts of
the lower great lakes into the mid-atlantic...
...summary...
severe thunderstorms are expected across portions of the ohio valley
and lower great lakes into the mid-atlantic and northeast, mainly
saturday afternoon into the evening. some threat may linger into
late saturday night.
...ohio valley/lower great lakes into the mid-atlantic/northeast...
an active severe-weather day is expected saturday from parts of the
ohio valley and lower great lakes into the mid-atlantic, as
scattered to widespread storms move through an increasingly
favorable environment. a 45% wind area has been added, resulting in
a categorical upgrade to level-3/enhanced risk. the enhanced risk
area is a combination of multiple regimes which may eventually
overlap, with some areas potentially seeing multiple rounds of
strong to severe storms.
a mid/upper-level shortwave trough is forecast to move across the
northern great lakes vicinity through the day, before approaching
new england by evening. in conjunction with this shortwave trough, a
deepening surface low is expected to move across southern quebec
toward northern maine, as a trailing cold front moves through the
great lakes and eventually parts of the mid atlantic and northeast.
a remnant surface front initially draped from southern nj into
western pa will lift northeastward as an effective warm front, in
advance of the surface low and cold front.
as strengthening deep-layer wind fields overspread increasingly rich
moisture, a broad region from the ohio valley and lower great lakes
into the mid-atlantic and parts of the northeast will become
supportive of organized convection and severe-thunderstorm
potential. hrrr-based forecasts suggest that smoke will become less
prominent from west to east by afternoon, which should allow for
relatively strong diurnal heating and moderate destabilization in
areas not affected by early-day convection. effective shear of 35-45
kt will support organized clusters and possibly occasional
supercells from the lower great lakes into the northern mid-atlantic
and northeast, while strong heating and steep low-level lapse rates
will result in a favorable wind-damage environment within the
somewhat weaker flow regime across the southern mid-atlantic and
parts of the carolinas.
elevated convection may be ongoing or else develop during the
morning across parts of pa/ny, within a warm-advection regime
associated with the returning warm front. depending on the timing of
this convection and downstream heating/destabilization, some
intensification of ongoing convection may occur by early afternoon.
additional development may occur along the southwest flank of
early-day convection and related outflow, which may intensify and
move across the northern mid-atlantic during the afternoon. in
addition to a wind-damage threat, some hail and tornado potential
may also evolve with any supercell development, given the presence
of favorable effective srh.
farther north, a broken band of storms is expected to develop along
the cold front and move across the lower great lakes region,
eventually reaching a larger part of oh/pa/ny by late afternoon or
early evening. additional storms may develop ahead of the frontal
convection, depending on the extent of heating in the wake of
early-day storms. multiple wind-damage swaths may accompany this
convection, along with some potential for isolated hail. rich
moisture and some enhancement to low-level srh may also support a
tornado threat with any discrete or embedded supercells, especially
near the effective warm frontal zone or any remnant outflow
boundaries from morning convection.
an initially separate regime of storm development and severe
potential is expected to develop along/east of a surface trough
across parts of the southern mid-atlantic into nc. while deep-layer
flow will tend to weaken with somewhat southward extent, strong
heating and steepening of low-level lapse rates will provide a
favorable thermodynamic environment for downbursts and damaging
outflow winds.
depending on the extent of outflow from prefrontal storms, frontal
convection may continue to pose at least an isolated severe threat
through the evening as it spreads southeastward.
...parts of id/mt...
a mid/upper-level low initially near vancouver island is forecast to
move east-northeastward as a shortwave trough across southern bc/ab
on saturday. this shortwave will only have a glancing influence on
parts of the northwest and northern rockies, but modestly enhanced
midlevel southwesterlies will be maintained across the region
through the day/evening. widely scattered storm development is again
expected during the afternoon, with mlcape increasing to near 1000
j/kg and effective shear of 30+ kt supporting a threat of isolated
hail and localized strong to severe gusts.
..dean.. 07/17/2026
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note: the next day 2 outlook is scheduled by 0600z