RSS Mesoscale Discussions from Storm Prediction Center
No watches are valid as of Fri Jul 17 08:01:02 UTC 2026.
No Mesoscale Discussions are in effect as of Fri Jul 17 08:01:02 UTC 2026.
SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1258 AM CDT Fri Jul 17 2026
Valid 171200Z - 181200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
THE NORTHERN ROCKIES...GREAT LAKES AND OHIO VALLEY TO THE SOUTHERN
APPALACHIANS....
...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 gusts are possible over parts of the
Ohio Valley and southern Appalachians.
...Northern Rockies and Adjacent Plains...
An upper low over the Pacific Northwest is forecast to lift slowly
northward as an expansive upper ridge continues to build across the
western US. East of the low, a broad area of monsoon moisture will
persist over much of the Rocky Mountains. Weak ascent on the
periphery of the upper low and diurnal heating across the higher
terrain should allow for scattered thunderstorm development through
the afternoon. While displaced from the core of the stronger flow
aloft as the upper low drifts to the north, sufficient effective
shear of 25-35 kt will exist for occasional storm organization.
Isolated hail and severe gusts could accompany the strongest storms
into the evening across ID and western MT.
...Upper Midwest and northern Great Lakes...
An upper trough initially over AB/SK will move southward into the
northern Great Lakes by early Saturday. A belt of stronger mid-level
flow accompanying the upper trough will aid in deepening a surface
low as it moves into western ON. A warm front will lift north with
the deepening low over the Upper Midwest. A cold front trailing the
surface low will provide a focus for thunderstorm development over
northern MN, WI and the UP of MI this afternoon and evening.
A cluster of elevated thunderstorms is likely to be ongoing early in
the period near or just across the international border. These
storms could reinvigorate with a risk for some damaging gusts and
hail, though confidence in the convective evolution is low. Later in
the day ahead of the cold front, moderate buoyancy and sufficient
deep-layer shear will conditionally support a threat for isolated
supercells or organized multicell clusters, with a threat of hail
and damaging winds. Any persistent supercell may also pose at least
a brief tornado threat, especially in closer proximity to the
surface low and warm front where low-level shear will be maximized.
As the main upper trough continues to southeast one or more clusters
of strong to severe storms may persist into the overnight along the
warm front. However, confidence in this scenario is lower owing to
the prior convection and uncertainties of diurnal development along
the cold front. Still, a strengthening wind field and ample moisture
could support a risk for damaging winds into northern Lower MI
overnight.
...OH Valley to the southern Appalachians...
A warm and seasonably moist air mass will support moderate to
locally strong buoyancy beneath the upper ridge from the OH valley
toward the Southeast and southern Appalachians. A weak, convectively
enhanced sub-tropical disturbance moving northward and the higher
terrain should focus more widespread diurnal thunderstorm activity
from portions of IN/OH, into eastern KY/TN, the western Carolinas
and northern GA. Despite weak deep-layer shear below 20 kt, moderate
to strong MLCAPE (2000-3000 J/kg) and PWATS exceeding 2 inches may
allow for sporadic damaging gusts with any stronger multicell
clusters.
...FL...
CAM guidance shows vigorous storm development just offshore of the
FL Gulf Coast Friday morning, in association with a weak midlevel
trough/low. Additional storm development is expected by afternoon
across much of the peninsula. Large buoyancy and high PWATs suggest
localized strong to severe gusts cannot be ruled out near the coast
and inland this afternoon.
..Lyons/Weinman.. 07/17/2026
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SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1232 AM CDT Fri Jul 17 2026
Valid 181200Z - 191200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE OHIO
VALLEY INTO THE MID-ATLANTIC AND SOUTHERN NEW ENGLAND...
...SUMMARY...
Severe thunderstorms are expected across portions of the Ohio Valley
and Lower Great Lakes into the Mid-Atlantic, mainly Saturday
afternoon into the evening. Some threat may linger into late
Saturday night.
...Ohio Valley/Great Lakes to Mid-Atlantic...
An upper shortwave trough over the Great Lakes is expected to
amplify as it pivots east across the Ohio Valley and into the
Mid-Atlantic/Northeast region on Saturday. As this occurs,
deep-layer flow will increase, with guidance suggesting 850-500 mb
flow in the 40-50 kt range will be common. At the surface, low
pressure will deepen as it shifts east across Ontario and Quebec. A
trailing cold front will develop south/southeast across the region
during the late afternoon into nighttime hours. Ahead of the front,
a quasi-warm front is expect to be oriented across the Mid-Atlantic
and will lift northward through the day within a strong warm
advection regime. Initially modest boundary layer moisture across
PA, northward through the Hudson Valley will rapidly moisten ahead
of the approaching cold front. A corridor of moderate to strong
destabilization is expected from the Mid-MS and OH Valleys into the
Mid-Atlantic.
Convection may be ongoing across parts of PA/NY into the
Mid-Atlantic Saturday morning within the strong warm advection
regime. Some potential for an initial round of severe storms could
accompany this activity, especially near the surface warm front.
Additional thunderstorms will develop during the afternoon near a
prefrontal trough and along higher terrain in VA/NC. Vertical shear
will be somewhat less with southward extent, but scattered cells and
clusters will develop east through early evening posing a risk for
damaging wind gusts. Supercell wind profiles are apparent in
forecast soundings and a tornado risk is also possible, especially
near the surface warm front and prefrontal trough where 0-1 km SRH
will be maximized.
Substantial thunderstorm development is also expected within a
second corridor near the surface cold front from southern Quebec
into MI/IN/IL by midday. Surface dewpoints in the mid 60s to low 70s
F will provide ample support for 2000+ J/kg MLCAPE from the Mid MS
Valley toward western PA. Organized cells and line segments will
pose a risk for damaging wind swaths across the region.
Some uncertainty still exists due to effects from morning convection
and possible impacts from persistent smoke across parts of the
Mid-Atlantic. However, the overall pattern supports a broad area of
severe potential, with several swaths of damaging winds and a few
tornadoes expected.
...MT/ID...
A plume of steep midlevel lapse rates will overspread the area on
the southern periphery of stronger southwesterly flow aloft as an
shortwave upper trough shifts east across the Canadian Rockies.
Ample midlevel moisture amid steep lapse rates will foster MLCAPE
near 1000 J/kg. Forecast soundings also indicate elongated/straight
hodographs amid 35 kt effective shear magnitudes. Isolated organized
cells will pose a risk for hail and strong wind gusts through early
evening.
..Leitman.. 07/17/2026
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SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0126 AM CDT Fri Jul 17 2026
Valid 191200Z - 201200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
SC/NC INTO SOUTHEAST VA...
...SUMMARY...
Isolated to widely scattered strong to severe thunderstorms may pose
a risk for damaging wind gusts across portions of the southern
Appalachians to the coastal Carolinas/southeast Virginia vicinity on
Sunday.
...Southern Appalachians to Coastal Carolinas/Southeast Virginia...
Upper troughing will persist across the eastern U.S. on Sunday. A
couple of embedded vorticity maxima within the base of the trough
will move across the southern Appalachians/southern Mid-Atlantic
region through early evening. Deep layer westerly flow will remain
modest, but a very moist and strongly unstable airmass will be in
place. Large instability coupled with PW values near 2 inches will
support isolated severe storms capable of damaging wind gusts. A
corridor of relative greater risk may develop from southeast VA into
eastern NC near a stalled frontal boundary and where vertical shear
may be modestly stronger (25 kt effective shear).
...Eastern ND into northern MN...
Northwesterly flow aloft will strengthen on Sunday/Sunday night as
upper ridging flattens a bit as an upper shortwave trough emerges
over the Canadian Prairies. Vertically veering wind profiles will
foster 30+ kt effective shear magnitudes and a few organized cells
could develop. Some potential for capping could limit storm
coverage, but any storm that develops could be a higher-based
supercell capable of severe hail and strong gusts.
..Leitman.. 07/17/2026
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Day 4-8 Outlook
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0255 AM CDT Fri Jul 17 2026
Valid 201200Z - 251200Z
...DISCUSSION...
...Days 4-6/Mon-Wed -- Great Lakes/Midwest to the
Mid-Atlantic/Northeast...
A shortwave upper trough initially over the Canadian Prairies and
northern Plains will develop east/southeast across the Upper
Midwest/Great Lakes on Monday, then the Ohio Valley and Mid-Atlantic
vicinity on Tuesday. Meanwhile, another upper shortwave trough will
develop across the Great Lakes to the Northeast/Mid-Atlantic on
Wednesday. These features will support enhancement of mid/upper
level flow as a surface low tracks across Ontario/Quebec and New
England during this time. A trailing cold front will likewise
progress east/southeast over this three day period, with a very
moist and unstable airmass present ahead of the front. This overall
pattern will likely bring multiple days of severe storm potential
from the Upper Midwest/Great Lakes to portions of the Ohio Valley,
Northeast and Mid-Atlantic vicinity Monday through Wednesday,
necessitating severe probabilities. While these areas may shift some
over the coming day as the timing of mesoscale features and
influence of prior days convection becomes more clear, these general
regions are most likely to see at least isolated to widely scattered
damaging wind potential as the upper trough and surface cold front
sweep across the area.
...Days 7-8/Thu-Fri...
Surface high pressure building behind the aforementioned surface
cold front will become centered over the Midwest late in the
forecast period. Upper troughing will persist across the East while
an amplified upper ridge remains oriented from TX to MT. Overall,
severe potential appears low late in the forecast period.
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SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0149 AM CDT Fri Jul 17 2026
Valid 171200Z - 181200Z
...Synopsis...
A midlevel low will move northward along the Pacific Northwest coast
today. Between this feature and an expansive upper ridge over the
Rockies and Great Basin, a belt of enhanced south-southwesterly
low/mid-level flow will overspread the northern Great Basin and
Northwest. Downslope-enhanced warming/drying in the lee of the
northern Cascades and Columbia Basin will result in deep
boundary-layer mixing (10-15 percent RH). These warm/dry conditions
combined with around 15 mph sustained southwesterly winds atop
receptive fuels will yield elevated fire-weather conditions during
the afternoon.
..Weinman.. 07/17/2026
...Please see www.spc.noaa.gov/fire for graphic product...
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SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0150 AM CDT Fri Jul 17 2026
Valid 181200Z - 191200Z
...Synopsis...
Between a midlevel trough moving across BC and an expansive
large-scale ridge over the central/western CONUS, enhanced
deep-layer south-southwesterly flow will overspread a deep/dry
boundary layer (around 10-15 percent RH) in the lee of the northern
Sierra and Cascades. These dry conditions combined with around 15
mph sustained west-southwesterly surface winds will favor elevated
fire-weather conditions during the afternoon, given dry/receptive
fuels.
..Weinman.. 07/17/2026
...Please see www.spc.noaa.gov/fire for graphic product...
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