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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SPC Jul 17, 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
1130 AM CDT Fri Jul 17 2026

Valid 171630Z - 181200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
THE NORTHERN ROCKIES AND HIGH PLAINS...UPPER GREAT LAKES...AND OHIO
VALLEY TO THE SOUTHEAST...

...SUMMARY...
Strong to potentially severe storms are possible today across parts
of western Montana and northern Idaho, and also across parts of the
Upper Midwest and northern Great Lakes. More isolated strong to
severe storms with damaging wind gusts are possible over parts of
the Ohio Valley and Southeast.

...Northern Rockies and northern High Plains...
The region will be influenced by an increasingly progressive
shortwave trough moving northeastward from off the Washington coast
and over southern British Columbia. The preceding upper ridge will
flatten/shift eastward particularly near the international border,
with a plume of rich monsoonal moisture extending into the region,
highlighted by prevalent middle 50s to lower 60s F dewpoints along
the Continental Divide. Orographic lift and heating will promote the
development of scattered thunderstorms this afternoon, especially
across eastern/northern Idaho and western Montana. Steepened
low-level lapse rates will potentially yield storms capable of
isolated severe wind gusts beginning this afternoon and continuing
into mid-late evening. Isolated large hail may occur with the
stronger thunderstorm cores, especially over northwest Montana where
deep-layer shear may exceed 30 kt.

...Upper Midwest and northern Great Lakes...
A decaying cluster of storms continues to spread southeastward
across northern Michigan, and smoke will continue to be a factor
regionally, albeit with some west-to-east abatement later today. A
cold front associated with the upper wave will push southeastward
across the Upper Midwest and provide a focus for thunderstorm
redevelopment late this afternoon, and more so into this evening.
Forecast model guidance shows moderate buoyancy developing today
within a belt of 25-40 kt west-northwesterly 500-mb flow as upstream
shortwave trough amplification occurs.

A few of the stronger thunderstorms could evolve into supercells and
organized multicell clusters, although uncertainty persists
regarding the overall magnitude/extent of today's severe potential.
Isolated large hail and damaging gusts are the primary hazards,
although a brief tornado risk may also develop in the areas
surrounding Lake Superior. One or more clusters of strong to severe
storms may persist into the overnight along the warm front.

...Ohio Valley to the southern Appalachians and Florida...
A moist and diurnally destabilizing airmass will support scattered
to numerous storms developing by the mid afternoon. Some of the
stronger water-loaded downdrafts will potentially be capable of
50-60 mph gusts and isolated wind damage.

...West-central Texas...
A weak mid- to upper-level low over west Texas will move little
during the day while a warm/moist conveyor persists across southern
into central parts of Texas. Despite very moist low levels and some
enlargement of the low-level hodograph, weak flow in the mid levels
should limit storm organization and meaningful supercell potential,
more so favoring a heavy rain threat.

..Guyer/Thompson.. 07/17/2026


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