SPC Jul 18, 2026 1630 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1630Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1120 AM CDT Sat Jul 18 2026

Valid 181630Z - 191200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
THROUGH LATE EVENING FROM THE LOWER GREAT LAKES INTO THE
MID-ATLANTIC...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON EVENING FOR PARTS OF WESTERN MONTANA...

...SUMMARY...
Severe thunderstorms are expected across portions of the Ohio Valley
and Lower Great Lakes into the Mid-Atlantic and Northeast this
afternoon and evening. Damaging gusts will be the primary threat,
but a few tornadoes are possible, including perhaps a strong
tornado.

...Mid-Atlantic to the lower Great Lakes this afternoon/evening...
Ongoing convection across central PA/NY will continue to spread
eastward through early afternoon within a warm advection zone along
and north of a surface warm front. The warm front will move
northward today in advance of a surface cyclone and associated
midlevel trough now in the vicinity of Lake Huron. In the wake of
the ongoing convection, destabilization will occur as boundary-layer
dewpoints rise to near 70 F and surface temperatures into the 80s,
resulting in moderate buoyancy in the warm sector. Destabilization
will occur earlier immediately south-through-west of the ongoing
storms across eastern PA/NJ, and a little later this afternoon into
central NY.

Additional thunderstorm development is beginning in southwest PA and
vicinity as of 16z and a continued increase in storms is expected
into early-mid afternoon along a cold front and along pre-frontal
confluence zones/lake-enhanced boundaries. A mixed convective mode
(line segments and clusters) is expected, with embedded bowing
segments and a chance for pre-frontal supercells in PA/NY/NJ where
vertical shear and hodograph curvature will be larger along the warm
front. Wind damage will be the primary severe threat with both the
frontal convection and pre-frontal storms, with a few tornadoes
possible with supercell structures and/or embedded mesovortices.

...Northern Rockies late this afternoon/evening...
Scattered thunderstorm development is expected later this
afternoon/evening across western MT and vicinity, within the
northwest fringe of the midlevel ridge and monsoonal moisture plume.
Midlevel flow will be somewhat enhanced to the immediate southeast
of a midlevel trough moving over southeast BC, thus some organized
storm structures will be possible with faster storm motions compared
to yesterday. Occasional severe outflow gusts and large hail up to
1.5 inches in diameter will be the main threats.

..Thompson/Bunting.. 07/18/2026


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SPC Jul 18, 2026 1300 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1300Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0719 AM CDT Sat Jul 18 2026

Valid 181300Z - 191200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PORTIONS
OF THE NORTHEAST...MID ATLANTIC AND LOWER GREAT LAKES...

...SUMMARY...
Severe thunderstorms are expected across portions of the Ohio Valley
and Lower Great Lakes into the Mid-Atlantic and Northeast this
afternoon and evening. Damaging gusts will be the primary threat,
but a few tornadoes are possible, including perhaps a strong
tornado.

...OH Valley and Great Lakes to the Mid Atlantic and Northeast...
Water-vapor imagery this morning shows a potent mid-level shortwave
trough moving southeast over the Upper Great Lakes towards the
Northeast during the period. The primary upper vorticity max will
rotate through the base of the larger-scale trough and through the
St. Lawrence Valley, before an upstream disturbance west of James
Bay this morning pivots southeast and reaches Maine/eastern Quebec
by early Sunday. Surface analysis this morning places a 1004-mb low
north of Georgian Bay and a cold front extending west-southwestward
into northern IA. An attendant warm front arching southeastward
through the Lower Great Lakes and draped over the Mid-Atlantic
states will advance northward as the cyclone develops east towards
northern Maine by late evening. Concurrently, the cold front will
push southeast across much of Great Lakes into the OH Valley.

South of the boundary, a very moist air mass was sampled this
morning by 12 UTC raobs and surface observations (i.e., upper 60s to
lower 70s F dewpoints). A few thunderstorm clusters this morning
have developed near the warm frontal zone from the Lower Great Lakes
into the Mid-Atlantic states. The early day storm activity will
likely be limited in storm vigor, due in part to initially
widespread cloud cover inhibiting strong heating in the areas
downstream over parts of PA/NY. Gradual dissipation of clouds and
heating coupled with the northeastward advancement of the warm
sector will promote a broad area to become moderately to strongly
unstable later today (1000-3000 J/kg MLCAPE) from the OH Valley
eastward into the Mid-Atlantic and parts of the Northeast.

A belt of westerly 30-45 kt 700-mb flow from northern VA into the
Northeast will aid in storm organization and severe potential this
afternoon and evening. Models differ substantially regarding
evolution/timing of possible bands of storms and clusters with
embedded cells. Regardless of specific details, it seems plausible
several multicellular bands of storms will develop during peak
heating and organize as these bands move east. Some of the more
intense cells will potentially become supercellular posing an
all-hazards severe risk. Have largely unchanged the previous
outlook given the inherent thunderstorm evolution-based
uncertainties. Potentially widespread damaging gusts [50-60 mph,
locally stronger (55-70 mph) perhaps paralleling the I-95 corridor
from Chesapeake Bay into southern New England]. A few tornadoes are
possible both from linear and cellular storm structures given some
low-level hodograph enlargement and moist low levels.

Farther west, veered low-level flow ahead of the cold front will
promote upscale growth into a few bands of cells and line segments
across the southern Great Lakes into the OH Valley. Damaging gusts
appear to be the primary hazard but a localized risk for hail and
perhaps a couple of tornadoes may accompany this activity.

...Northern Rockies...
The mid/upper-level low that has lingered over the Pacific Northwest
this week is forecast to move northeastward and weaken to an open
wave as it lifts across far northern ID/MT into southern Canada.
While only glancing over the northern Rockies, modestly enhanced
southwesterly flow aloft will be maintained across the region
through the day/evening. Monsoon moisture and strong diurnal
heating will support widely scattered storm development during the
afternoon, with MLCAPE increasing to near 1000 J/kg and effective
shear of 30+ kt. This could support a threat of isolated hail and
localized strong to severe gusts with the more robust storms.

..Smith/Broyles.. 07/18/2026


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SPC Jul 18, 2026 0600 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1257 AM CDT Sat Jul 18 2026

Valid 181200Z - 191200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PORTIONS
OF THE NORTHEAST...MID ATLANTIC AND LOWER GREAT LAKES....

...SUMMARY...
Severe thunderstorms are expected across portions of the Ohio Valley
and Lower Great Lakes into the Mid-Atlantic and Northeast, this
afternoon into the evening. Some threat may linger into late
tonight.

...OH valley and Great Lakes to the Mid Atlantic and Northeast...
An unseasonably strong upper trough is forecast to move from
southern ON into the northeast US through early Sunday. As the
trough intensifies, a 60+ kt mid-level jet will overspread portions
of eastern Canada and the Northeast, aiding in deepening a surface
low across the eastern St Lawrence Valley. Strong surface mass
response will lift a warm front northward across eastern NY and
southern New England. South of the boundary, a very moist air mass
will be in place ahead of a cold front over the OH Valley and Great
Lakes. A rather broad area, is expected to be conducive for numerous
strong to severe storms with the potential for widespread damaging
winds over the Northeastern US today and tonight.

One or more clusters of showers/thunderstorms appears likely to be
ongoing at the start of the period from central PA and southern NY
into eastern ON as isentropic ascent increases along the advancing
warm front. The impact of this overnight/early morning convection is
somewhat uncertain, but most guidance shows substantial air mass
recovery in its wake by midday with dewpoints in the mid 70s across
much of the Mid Atlantic. Given the degree of moisture and minimal
inhibition present, even modest diurnal heating should support rapid
destabilization with MLCAPE of 2000-3000 J/kg common by early
afternoon.

Several different forcing regimes are expected to be active which
makes the convective evolution highly uncertain. The early morning
storms near the advancing warm front in PA could re-intensify as the
air mass to their south and east gradually destabilizes. This would
favor an increasing risk for damaging gusts. 35-45 kt of deep-layer
shear could also support some supercell structures. A couple of
tornadoes (some possibly strong) may occur, given favorable backed
low-level flow and ESRH of 200-300 m2/s2 near the front from
southeastern PA, into NJ and southern NY.

Additional storms are likely to develop along a pre-frontal
confluence axis/lee trough east of the higher terrain from southern
PA into eastern MD and northern VA to northern NC. Large buoyancy
and deep-layer shear of 30-40 kt would favor a mixed mode of line
segments and supercells. These storms should move eastward toward
DelMarVa and the I-95 Corridor by early afternoon. RAP/HRRR
soundings show 40-50 kt of flow aloft as the upper trough and jet
streak move overhead. Regardless of storm mode, the high PWAT
content (2-2.5 inches) should foster strong downdrafts and momentum
transfer to the surface. Widespread damaging gusts are likely from
northeast VA, eastern MD, into southeast PA and NJ. Higher wind
probabilities (60%) may be needed if confidence in a more
linear/cluster storm mode develops.

To the west, ahead of the cold front, a broken band of cells and
clusters is likely from NY/VT to the Lower Great Lakes. The
strongest vertical shear should reside across upstate NY into
northwest PA and northeast OH, where a few supercells are possible.
While farther west, strongly veered surface flow should result in
more linear storm modes. Multiple wind-damage swaths may accompany
these storms, along with some potential for isolated hail. 70s F
surface dewpoints and enhanced low-level SRH could also support a
tornado threat with any discrete or embedded supercells, especially
closer to the surface low and near the effective warm frontal zone
where low-level shear is more favorable.

...Northern Rockies...
The mid/upper-level low that has lingered over the Pacific Northwest
this week is forecast to move northeastward and weaken to an open
wave as it lifts across far northern ID/MT into southern Canada.
While only glancing over the northern Rockies, modestly enhanced
southwesterly flow aloft will be maintained across the region
through the day/evening. Monsoon moisture and strong diurnal heating
will support widely scattered storm development during the
afternoon, with MLCAPE increasing to near 1000 J/kg and effective
shear of 30+ kt. This could support a threat of isolated hail and
localized strong to severe gusts with the more robust storms.

...Gulf Coast...
A remnant MCV may serve as a focus for diurnal thunderstorm
development along the northern Gulf Coast today. While vertical
shear is limited, locally moderate to strong buoyancy and very high
PWAT values could support sporadic downbursts with damaging gusts.
However, confidence in how widespread or sustained the severe threat
is too low for wind probabilities.

..Lyons/Weinman.. 07/18/2026


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SPC Jul 18, 2026 0100 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 0100Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0800 PM CDT Fri Jul 17 2026

Valid 180100Z - 181200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
IDAHO AND MONTANA...HE UPPER MIDWEST...AND PORTIONS OF THE
SOUTHEAST...

...SUMMARY...
Strong to potentially severe storms remain possible this evening and
tonight across parts of the Upper Midwest and northern Great Lakes
and western Montana/northern Idaho. Sporadic strong to severe storms
with damaging wind gusts cannot be ruled out over parts of the
Southeast.

...Upper Midwest and Great Lakes...
Early evening water vapor imagery showed an upper trough and belt of
enhanced mid-level flow moving from southern Canada into the
northern Great Lakes. Ahead of the trough, a prominent warm front is
in place along the southern edge of Lake Superior, into the UP of
MI. Along the front, an associated surface cyclone was observed over
Lake Superior with a cold front trailing southwestward into eastern
MN and northwest WI.

Several strong to severe storms have developed and intensified
across far eastern MN, northern WI and the shelf waters of Lake
Superior this evening ahead of the cold front. High-res model
guidance and convective trends suggest these storms should generally
spread southeastward across northern WI this evening. Here in the
warm sector, mid to upper 80s F surface temperatures and seasonably
high dewpoints in the 60s and 70-s F are supporting a moderate to
strongly unstable air mass, more than sufficient for maintenance of
the ongoing severe storms. 40-50 kt of deep-layer shear are also
supporting organized clusters and some supercell structures. This
suggests hail and damaging winds are possible into early tonight.

Across the UP, convection has been slower to evolve owing to
lingering inhibition and weaker buoyancy. However, model guidance
and recent radar trends show a gradual increase in storm coverage
this evening. If some clustering can occur, a brief tornado risk may
also develop given enhanced low-level shear along the warm front and
near the lakes. An isolated risk for damaging winds could also
continue overnight across the UP and far northern Lower MI with any
longer-lived clusters along the front.

...ID and MT...
On the northern fringes of an expansive upper ridge, an upper low
over the Pacific Northwest was supporting a broad fetch of
seasonably high monsoon moisture and moderate destabilization.
Scattered thunderstorms are ongoing over parts of ID and MT this
evening and should continue into the early overnight period. While
displaced from stronger westerly flow aloft, effective shear near
25-30 kt could support a few organized storms with a risk for hail
and damaging winds over parts of ID and MT. Especially if any
clustering can occur.

...OH valley to the Southern Appalachians and Southeast...
Numerous storms ongoing this evening should slowly diminish in
coverage and intensity over the next couple of hours as the
boundary-layer stabilizes. The highest concentration of stronger
storms should remain across parts of the Southeast in FL and GA
where a larger reservoir of moderate to large buoyancy remains. An
isolated damaging gust will remain possible with the more persistent
thunderstorm clusters this evening. However, the weakening buoyancy
and increasing stabilization should gradually limit the damaging
wind risk into tonight.

..Lyons.. 07/18/2026


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