RSS Mesoscale Discussions from Storm Prediction Center
No watches are valid as of Fri Jul 17 20:15:02 UTC 2026.
MD 1642 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR WEST AND SOUTHWEST MONTANA AND EXTREME NORTHEAST IDAHO
Mesoscale Discussion 1642
NWS Storm Prediction Center Norman OK
0312 PM CDT Fri Jul 17 2026
Areas affected...West and southwest Montana and extreme northeast
Idaho
Concerning...Severe potential...Watch unlikely
Valid 172012Z - 172215Z
Probability of Watch Issuance...20 percent
SUMMARY...Scattered thunderstorms are expected to form through
mid-late afternoon with a gradual increase in the threat for
isolated severe outflow gusts and large hail.
DISCUSSION...Visible satellite imagery reveals deepening convection
over the high terrain across southwest and western MT where surface
temperatures have warmed well into the 80s with dewpoints in the
mid-upper 50s. The 18z soundings from TFX and BOI suggest that
surface temperatures need to warm to 90+ F to eliminate convective
inhibition for the lower elevations, though inhibition has
diminished over the higher terrain. Though forcing for ascent will
remain subtle, there are embedded perturbations rotating northward
over ID/western MT around the northwest periphery of the midlevel
ridge. These perturbations, in combination with additional surface
heating, will support scattered thunderstorm development the next
few hours. Steepening low-level lapse rates will favor
strong-severe outflow gusts as the main threat in an environment
with moderate buoyancy. Isolated large hail may also occur with any
more organized/supercell storms, given effective bulk shear of 30-35
kt.
..Thompson/Guyer.. 07/17/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...BYZ...TFX...MSO...OTX...
LAT...LON 46011013 45580943 45210931 45080955 45271109 45631269
45671368 46071469 47121509 48091510 48921488 48951402
48931310 47981257 47041194 46431126 46011013
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN
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MD 1641 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR THE WESTERN LAKE SUPERIOR VICINITY...INCLUDING PARTS OF NORTHEASTERN MINNESOTA...NORTHWESTERN WISCONSIN AND ADJACENT PORTIONS OF UPPER MICHIGAN
Mesoscale Discussion 1641
NWS Storm Prediction Center Norman OK
0246 PM CDT Fri Jul 17 2026
Areas affected...the western Lake Superior vicinity...including
parts of northeastern Minnesota...northwestern Wisconsin and
adjacent portions of Upper Michigan
Concerning...Severe potential...Watch unlikely
Valid 171946Z - 172145Z
Probability of Watch Issuance...20 percent
SUMMARY...Initiating thunderstorm activity is likely to intensify
late this afternoon across the western Lake Superior vicinity.
Coverage of stronger storm development remains unclear due to the
stabilizing lake boundary layer, but a few supercell structures
posing a risk for severe hail and wind are possible. It is not
clear that this will require a severe weather watch, but trends will
be monitored.
DISCUSSION...A short wave trough within the westerlies is beginning
to dig southeast of the the Canadian Prairies, with the southern
fringe of modest mid-level height falls overspreading the Minnesota
international border vicinity. An associated developing frontal
wave is slowly beginning to deepen across Ontario, to the northwest
of Lake Superior, and is forecast to gradually migrate
east-southeastward into early evening. A trailing surface front is
already advancing through the northern U.S. Great Plains and
becoming better defined with differential surface heating, now near
or northwest of the Hibbing, Brainerd and Alexandria MN vicinities.
Perhaps preceded by a pocket of mid/lower level subsidence drying,
the deeper moist boundary layer appears largely focused along the
cold frontal zone, based on latest Rapid Refresh output and
supported by surface analysis. However, this is advancing
southeastward beneath a plume of warm elevated mixed-layer air (as
roughly depicted by 10-12C temperatures around 700 mb) overspreading
the Red River Valley toward upper Great Lakes late this afternoon.
Deepening convective development is underway within the moist
environment beneath this regime, which may be characterized by mixed
layer CAPE on the order of 2000-3000 J/jg. As this spreads toward
the western Lake Superior vicinity through 22-00Z, guidance suggests
that some combination of weaker inhibition and strengthening
large-scale forcing for ascent may allow for continued thunderstorm
initiation and intensification. Beneath moderate northwesterly
mid-level shear this may include a few evolving supercell structures
posing a risk for severe hail and wind.
..Kerr/Guyer.. 07/17/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...DLH...
LAT...LON 47919211 48218994 47408907 46399081 46189173 46429262
47249315 47919211
MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH
MOST PROBABLE PEAK WIND GUST...UP TO 60 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN
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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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SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0251 PM CDT Fri Jul 17 2026
Valid 172000Z - 181200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM CENTRAL
IDAHO INTO MONTANA...THE GREAT LAKES...AND THE OHIO VALLEY INTO 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.
...20z Update...
The previous forecast remains largely on track based on latest
trends in ensemble guidance. Recent runs of the RRFS/HRRR
time-lagged ensemble continue to show some potential for organized
convection across northern WI and into the U.P. of Michigan later
this evening, and latest trends in GOES imagery show building
cumulus that seem to support these solutions. However, the overall
ensemble signal for widespread severe convection on the U.S. side of
the international border remains limited. Similarly, a corridor of
more focused wind potential may emerge across west-central MT this
evening, but given low ensemble probabilities for severe winds,
coupled with modest low-level lapse rates in latest RAP mesoanalyses
and forecast soundings, limits confidence in a widespread severe
wind threat. See the previous discussion below and MCD #1641 for
additional details.
..Moore.. 07/17/2026
.PREV DISCUSSION... /ISSUED 1130 AM CDT Fri Jul 17 2026/
...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.
Read more
SPC 1730Z Day 2 Outlook
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
Read more
SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0229 PM CDT Fri Jul 17 2026
Valid 191200Z - 201200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE CAROLINAS INTO SOUTHEAST VIRGINIA...
...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. Strong to severe storms may also develop across parts of
eastern Montana into North Dakota and Minnesota.
...Southern Appalachians into the Coastal Carolinas/southern VA...
A broad mid/upper-level trough will remain in place across much of
the eastern CONUS on Sunday. A weakening cold front may become
nearly stationary by afternoon somewhere across southern VA.
Scattered storm development is expected during the afternoon
along/ahead of the remnant frontal zone, and also near the higher
terrain of the southern Appalachians.
Deep-layer flow/shear will generally be weak to modest, but large
PW, steepening low-level lapse rates, and moderate to locally strong
buoyancy will support vigorous updrafts and localized downbursts. In
addition, low/midlevel flow may be sufficient for one or two
outflow-driven clusters to evolve with time and move southeastward
into the early evening, with wind-damage potential.
...Parts of eastern MT into ND/MN...
A vigorous shortwave trough may evolve into a mid/upper-level low as
it moves eastward across the Canadian Prairies on Sunday. An
attendant surface low is forecast to gradually intensify as it moves
toward Lake Winnipeg. A surface trough/weak cold front will move
into northeast MT during the day and across parts of the Dakotas
during the evening.
A conditionally favorable environment is expected to evolve across
parts of far eastern MT into ND and northwest MN during the
afternoon/evening, as a 40-50 kt midlevel jet and steep lapse rates
overspread a warm and relatively moist boundary layer. However, with
the strongest height falls and ascent expected to remain north of
the international border, capping may inhibit diurnal storm
development. Any storms that are able to develop and mature during
the afternoon and early evening could evolve into organized cells or
clusters with severe wind and hail potential.
Even if surface-based diurnal development is suppressed, there will
be some potential for elevated convection to develop Sunday evening
into the overnight. Steep lapse rates, moderate elevated buoyancy,
and sufficient effective shear could support a hail threat with the
strongest elevated storms, and severe-wind potential with any
forward-propagating clusters that can develop Sunday night.
The Level-1/Marginal Risk has been expanded westward across ND and
far eastern MT to account for the conditional threat in these areas,
though confidence in the details of storm coverage and evolution
remains low at this time.
..Dean.. 07/17/2026
Read more
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1138 AM CDT Fri Jul 17 2026
Valid 171700Z - 181200Z
No significant changes to existing elevated highlights were needed.
Dry and breezy surface conditions bolstered by a mid-level low and
associated stronger flow aloft are expected across the Columbia
Basin and northeastern CA, southern OR and northwestern NV. RH as
low as 10% percent can be expected, particularly in the lee of the
Cascades where downslope drying effects will be more pronounced.
West to southwesterly winds of 10-15 mph will evolve this afternoon
as a well-mixed and dry boundary layer develops in the wake of
exiting monsoon moisture. The elevated fire weather conditions could
impact nascent wildfires in OR.
..Williams.. 07/17/2026
.PREV DISCUSSION... /ISSUED 0149 AM CDT Fri Jul 17 2026/
...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.
...Please see www.spc.noaa.gov/fire for graphic product...
Read more
SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0245 PM CDT Fri Jul 17 2026
Valid 181200Z - 191200Z
...Southeastern Wyoming...
Elevated highlights have been added to portions of southeastern WY
for Saturday. A large scale upper ridge over the central U.S. and
Intermountain West will promote unseasonably warm temperatures and
dry surface conditions to portions of the central and northern
Plains. A surface low developing in southwestern WY will aid in
stronger easterly low-level flow of 10-15 mph across eastern WY.
These winds along with minimum RH of 15-20% will support elevated
fire weather conditions over exceptionally dry fuels (ERC values
around the 95-98th percentile) Saturday afternoon.
...Columbia Basin, Idaho Panhandle, interior Oregon and adjacent
areas of California and Nevada...
Stronger mid-level southwest flow will linger over the Pacific
Northwest as an upper trough moves northeastward into British
Columbia. Dry, downslope flow in the lee of the Cascades and
northern Sierra Nevada will support RH of 15-20 percent by
mid-afternoon Saturday. These dry conditions along with receptive
fuels will support an elevated fire weather concern for the region
with impacts to active wildfires in the Pacific Northwest expected.
Latest model guidance suggests stronger surface winds across the ID
Panhandle Saturday under the 50-55 knot mid-level jet. This should
promote sustained winds of around 15 mph (locally higher favorable
terrain gaps) across the ID Panhandle Saturday. Due to potential for
impact from lightning ignitions from Day 1/Friday, extended elevated
highlights into ID Panhandle to cover this fire weather threat.
..Williams.. 07/17/2026
.PREV DISCUSSION... /ISSUED 0150 AM CDT Fri Jul 17 2026/
...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.
...Please see www.spc.noaa.gov/fire for graphic product...
Read more
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