WW 595 SEVERE TSTM IA IL MN WI 181950Z - 190300Z
URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 595
NWS Storm Prediction Center Norman OK
250 PM CDT Tue Aug 18 2026
The NWS Storm Prediction Center has issued a
* Severe Thunderstorm Watch for portions of
Northeast Iowa
Far Northwest Illinois
Southeast Minnesota
Southern Wisconsin
* Effective this Tuesday afternoon and evening from 250 PM until
1000 PM CDT.
* Primary threats include...
Scattered large hail and isolated very large hail events to 2
inches in diameter possible
Scattered damaging wind gusts to 70 mph possible
SUMMARY...Storms will continue to develop and intensify in multiple
areas across the region, with large hail and damaging winds possible
as storms organize and spread east-southeastward through early
evening.
The severe thunderstorm watch area is approximately along and 55
statute miles north and south of a line from 45 miles south
southwest of Rochester MN to 45 miles south southeast of Oshkosh WI.
For a complete depiction of the watch see the associated watch
outline update (WOUS64 KWNS WOU5).
PRECAUTIONARY/PREPAREDNESS ACTIONS...
REMEMBER...A Severe Thunderstorm Watch means conditions are
favorable for severe thunderstorms in and close to the watch area.
Persons in these areas should be on the lookout for threatening
weather conditions and listen for later statements and possible
warnings. Severe thunderstorms can and occasionally do produce
tornadoes.
&&
AVIATION...A few severe thunderstorms with hail surface and aloft to
2 inches. Extreme turbulence and surface wind gusts to 60 knots. A
few cumulonimbi with maximum tops to 550. Mean storm motion vector
30025.
...Guyer
WW 0595 Status Updates
STATUS FOR WATCH 0595 HAS NOT BEEN ISSUED YET
MD 2026 CONCERNING SEVERE POTENTIAL...WATCH POSSIBLE FOR SOUTHERN MONTANA AND FAR NORTHERN WYOMING.
Mesoscale Discussion 2026
NWS Storm Prediction Center Norman OK
0251 PM CDT Tue Aug 18 2026
Areas affected...southern Montana and far northern Wyoming.
Concerning...Severe potential...Watch possible
Valid 181951Z - 182115Z
Probability of Watch Issuance...60 percent
SUMMARY...Isolated strong to severe storms are possible this
afternoon/evening across southern Montana and far northern Wyoming.
DISCUSSION...Storm coverage has increased across central and
southern Montana over the last hour ahead of a mid-level shortwave
trough. Relatively weak instability is in place amid mostly 40sF
dewpoints. However, strong heating (mid to upper 80s) has yielded
steep lapse rates across the region. Moderate mid-upper level flow
(40-55 kts) will support storm organization including the potential
for supercells. The weak instability should limit the hail threat
somewhat, but the steep lapse rates and dry sub-cloud layer should
support some severe wind threat, including the potential for a few
75+ mph wind gusts.
Expect storms to remain mostly cellular which may limit a more
widespread severe wind threat. However, the stronger cores which
develop may be efficient wind producers. The downstream threat
across northern Wyoming remains uncertain due to extensive cloud
cover and limited heating.
..Bentley/Guyer.. 08/18/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...UNR...BYZ...GGW...RIW...TFX...PIH...
LAT...LON 47280983 47230752 47090704 46760586 46080555 45370552
44790570 44520692 44401010 44791160 46081135 47280983
MOST PROBABLE PEAK WIND GUST...65-80 MPH
MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN
MD 2025 CONCERNING SEVERE POTENTIAL...WATCH POSSIBLE FOR FAR SOUTHEAST SOUTH DAKOTA INTO SOUTHERN MINNESOTA AND NORTHERN IOWA
Mesoscale Discussion 2025
NWS Storm Prediction Center Norman OK
0247 PM CDT Tue Aug 18 2026
Areas affected...Far southeast South Dakota into southern Minnesota
and northern Iowa
Concerning...Severe potential...Watch possible
Valid 181947Z - 182145Z
Probability of Watch Issuance...40 percent
SUMMARY...While uncertainty in storm coverage remains, large hail
and damaging winds would be possible with storms that may develop
along the cold front. Convective trends will be monitored through
the afternoon for a possible watch.
DISCUSSION...Cumulus have been deepening near a weak mesoscale low
in southeast South Dakota. Additional cumulus towers have been
observed along the cold front farther east, though convergence is
much weaker and agitated cumulus have not been long lived. With
around 50 kt of shear and destabilization occurring south of the
front, large hail (potentially near 2 in.) and damaging winds would
be possible. The main question will be how many storms will be able
to form this afternoon. The weak surface convergence across much of
the front and upper-level clouds moving in from the west limit
confidence in this regard. Some CAM guidance has suggested storm
development along the front may be delayed until late
afternoon/early evening when a stronger southerly surge of the front
is expected. Convective trends will need to be monitored for a
possible watch.
..Wendt/Guyer.. 08/18/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MPX...DMX...FSD...
LAT...LON 44159704 44409669 44019512 43939408 43669375 43429368
42739352 42499362 42499396 42569417 42629467 43159654
43899706 44159704
MOST PROBABLE PEAK WIND GUST...UP TO 60 MPH
MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN
MD 2024 CONCERNING SEVERE POTENTIAL...WATCH LIKELY FOR NORTHERN IOWA INTO SOUTHEAST MINNESOTA AND SOUTHWESTERN WISCONSIN
Mesoscale Discussion 2024
NWS Storm Prediction Center Norman OK
0152 PM CDT Tue Aug 18 2026
Areas affected...Northern Iowa into southeast Minnesota and
southwestern Wisconsin
Concerning...Severe potential...Watch likely
Valid 181852Z - 182045Z
Probability of Watch Issuance...80 percent
SUMMARY...Large hail (some around 2 in.) and damaging winds will be
possible with scattered storms in the Upper Midwest. A watch is
likely this afternoon.
DISCUSSION...A weak MCV and associated cloud cover is present within
much of central/southern Wisconsin this afternoon. That said, strong
heating is occurring near a surface trough in northeast Iowa.
Thunderstorms have recently developed but have thus far not been
able to mature. Continued destabilization into southwestern
Wisconsin may allow this activity to pose an increasing severe
threat over the next couple of hours. Convective coverage is also
expected to increase along the cold front, though this may be
delayed until later this afternoon given the cloud cover. Moderately
strong mid-level winds on the southern flank of the upper-level low
is supporting around 40-45 kt of effective shear. Hodographs are
long and straight which suggests splitting supercells. Large hail
(with hail to around 2 inches possible, particularly in the
westernmost areas where mid-level lapse rates are steeper) and
damaging winds will be possible this afternoon.
..Wendt/Guyer.. 08/18/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...GRB...MKX...DVN...ARX...MPX...DMX...
LAT...LON 42579070 42349238 42389302 42499334 43029352 43669364
44319313 44689080 44338997 43978961 42968992 42579070
MOST PROBABLE PEAK WIND GUST...UP TO 60 MPH
MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1151 AM CDT Tue Aug 18 2026
Valid 181300Z - 191200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE CENTRAL
PLAINS/LOWER MISSOURI VALLEY AND UPPER MIDWEST...
...SUMMARY...
Thunderstorms with severe wind gusts and isolated large hail will be
possible this afternoon and evening from the central Plains into the
lower Missouri Valley, as well as the Upper Midwest. Other storms
capable of severe wind gusts and hail will also be possible from the
Northern Rockies into the central High Plains this afternoon into
tonight.
...Central Plains into Lower Missouri Valley...
Scattered weakening thunderstorms continue across northeast
Kansas/southeast Nebraska into northern Missouri, reinforcing a
convective boundary that extends across the region. Thunderstorm
redevelopment/intensification is conditionally possible through the
diurnal heating cycle near the boundary, which would carry with it
the potential for at least isolated hail/damaging winds.
A more certain scenario is expected this evening, when thunderstorm
development/re-invigoration is more probable as the low-level jet
increases. Steep lapse rates and moderate vertical shear support the
potential for thunderstorms capable of large hail during the
initially more cellular mode. These storms will likely cluster
quickly, with a trend towards upscale growth into a
forward-propagating MCS with an increasing damaging wind potential
as it spreads toward/across Missouri.
...Northern Rockies through the Central High Plains...
A shortwave trough will progress southeastward from British
Columbia/Alberta into the northern Rockies. Thunderstorm development
is anticipated across the northern Rockies as this wave interacts
with the destabilized and buoyant airmass across the region.
Moderate westerly flow aloft with support the potential for more
organized storm structures and the development of several line
segments. These widely scattered thunderstorms are forecast to
progress east-southeastward this afternoon/evening, with additional
development possible from Wyoming into the central High Plains. The
moderate westerly flow aloft, high storm bases, and steep low-level
lapse rates support the potential for strong to severe wind gusts
and possibly some increased hail potential through evening/early
overnight as these storms progress east-southeastward toward the
richer reservoir of moisture/buoyancy across the central High
Plains, including western Nebraska/northeast Colorado/northwest
Kansas.
...Upper Midwest including portions of Iowa/Wisconsin/Michigan...
Low-level moisture is expected to increase across the Midwest ahead
of an approaching cold front, resulting in moderate buoyancy by late
afternoon. Near-frontal convergence will influence convective
initiation, with the combination of moderate buoyancy and seasonally
strong westerly flow aloft supporting strong to severe storms
including some initial/semi-discrete supercells, which could yield
large hail. A transition into linear segments is expected by
evening, with damaging wind gusts becoming the more prevalent severe
risk as storms spread generally southeastward.
...Mississippi/Alabama to northern Florida...
Scattered thunderstorm development is expected this afternoon,
particularly across portions of Mississippi into western/southern
Alabama and northern Florida. These storms will develop amidst a
very moist and unstable environment. Vertical shear will be weak,
with an outflow-dominant/multicellular mode expected. Some
clustering into one or more line segments appears probable,
resulting in scattered thunderstorm coverage. Steep low-level lapse
rates and relatively high cloud bases support the potential for
strong downdrafts capable of locally damaging winds.
..Guyer/Wendt.. 08/18/2026
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1212 PM CDT Tue Aug 18 2026
Valid 181630Z - 191200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE CENTRAL
PLAINS/LOWER MISSOURI VALLEY AND UPPER MIDWEST...
...SUMMARY...
Thunderstorms with severe wind gusts and isolated large hail will be
possible this afternoon and evening from the central Plains into the
lower Missouri Valley, as well as the Upper Midwest. Other storms
capable of severe wind gusts and hail will also be possible from the
Northern Rockies into the central High Plains this afternoon into
tonight.
...Central Plains into Lower Missouri Valley...
Scattered weakening thunderstorms continue across northeast
Kansas/southeast Nebraska into northern Missouri, reinforcing a
convective boundary that extends across the region. Thunderstorm
redevelopment/intensification is conditionally possible through the
diurnal heating cycle near the boundary, which would carry with it
the potential for at least isolated hail/damaging winds.
A more certain scenario is expected this evening, when thunderstorm
development/re-invigoration is more probable as the low-level jet
increases. Steep lapse rates and moderate vertical shear support the
potential for thunderstorms capable of large hail during the
initially more cellular mode. These storms will likely cluster
quickly, with a trend towards upscale growth into a
forward-propagating MCS with an increasing damaging wind potential
as it spreads toward/across Missouri.
...Northern Rockies through the Central High Plains...
A shortwave trough will progress southeastward from British
Columbia/Alberta into the northern Rockies. Thunderstorm development
is anticipated across the northern Rockies as this wave interacts
with the destabilized and buoyant airmass across the region.
Moderate westerly flow aloft with support the potential for more
organized storm structures and the development of several line
segments. These widely scattered thunderstorms are forecast to
progress east-southeastward this afternoon/evening, with additional
development possible from Wyoming into the central High Plains. The
moderate westerly flow aloft, high storm bases, and steep low-level
lapse rates support the potential for strong to severe wind gusts
and possibly some increased hail potential through evening/early
overnight as these storms progress east-southeastward toward the
richer reservoir of moisture/buoyancy across the central High
Plains, including western Nebraska/northeast Colorado/northwest
Kansas.
...Upper Midwest including portions of Iowa/Wisconsin/Michigan...
Low-level moisture is expected to increase across the Midwest ahead
of an approaching cold front, resulting in moderate buoyancy by late
afternoon. Near-frontal convergence will influence convective
initiation, with the combination of moderate buoyancy and seasonally
strong westerly flow aloft supporting strong to severe storms
including some initial/semi-discrete supercells, which could yield
large hail. A transition into linear segments is expected by
evening, with damaging wind gusts becoming the more prevalent severe
risk as storms spread generally southeastward.
...Mississippi/Alabama to northern Florida...
Scattered thunderstorm development is expected this afternoon,
particularly across portions of Mississippi into western/southern
Alabama and northern Florida. These storms will develop amidst a
very moist and unstable environment. Vertical shear will be weak,
with an outflow-dominant/multicellular mode expected. Some
clustering into one or more line segments appears probable,
resulting in scattered thunderstorm coverage. Steep low-level lapse
rates and relatively high cloud bases support the potential for
strong downdrafts capable of locally damaging winds.
..Guyer/Wendt.. 08/18/2026
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0252 PM CDT Tue Aug 18 2026
Valid 182000Z - 191200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PORTIONS OF THE
UPPER MISSISSIPPI VALLEY INTO THE GREAT LAKES...ACROSS PORTIONS OF
THE PLAINS...AND ACROSS PARTS OF THE NORTHERN AND CENTRAL HIGH
PLAINS...
...SUMMARY...
Thunderstorms with severe wind gusts and isolated large hail will be
possible this afternoon and evening from the central Plains into the
lower Missouri Valley, as well as the Upper Midwest. Other storms
capable of severe wind gusts and hail will also be possible from the
Northern Rockies into the central High Plains this afternoon into
tonight.
...20z Update...
The primary adjustment for this update was the introduction of
additional 15% wind probabilities across southern Montana into
northern Wyoming and far western South Dakota. Latest GOES imagery
and lightning trends show deepening convection within the higher
terrain of southern to central MT. An approaching shortwave trough
will promote additional ascent and east/southeastward propagation
off the terrain through late afternoon and early evening. As this
occurs, thunderstorms will spread into a warm and deeply-mixed
environment featuring 0-3 km lapse rates on the order of 8-9 C/km
and sufficient buoyancy to sustain convection. Given this favorable
thermodynamic profile and ample shear across the region (sampled by
18 UTC RAOBs from RIW and UNR), the potential for severe winds
appears higher than previously anticipated. Recent HRRR/RRFS
time-lagged ensemble guidance appears to be capturing this trend and
depicts higher severe wind potential than earlier solutions.
...Southeast Wyoming into Colorado and Nebraska...
The early stages of deepening convection is noted near the Casper,
WY area ahead of a weak mid-level disturbance and where daytime
heating has resulted in surface temperatures climbing into the low
80s. While this initial activity will likely remain sub-severe, the
potential for intensification should steadily increase as it spreads
southeast into a more moist air mass. Similarly, cumulus is noted
across north-central CO on the western fringe of the higher-quality
moisture. Guidance continues to show considerable spread regarding
convective coverage and evolution across both regions, but given
these observed trends and a fairly supportive environment downstream
of emerging convection, expanding hail and wind risk probabilities
appeared prudent.
...Northeast Kansas/western Missouri...
Latest guidance continues to show additional thunderstorm
development later tonight within a warm advection regime across
northeast KS into west/northwest MO. However, there has been a
notable northward trend in recent HRRR/RRFS solutions compared to
12z guidance. 15% hail and wind probabilities have been adjusted
northward to account for this trend.
..Moore.. 08/18/2026
.PREV DISCUSSION... /ISSUED 1212 PM CDT Tue Aug 18 2026/
...Central Plains into Lower Missouri Valley...
Scattered weakening thunderstorms continue across northeast
Kansas/southeast Nebraska into northern Missouri, reinforcing a
convective boundary that extends across the region. Thunderstorm
redevelopment/intensification is conditionally possible through the
diurnal heating cycle near the boundary, which would carry with it
the potential for at least isolated hail/damaging winds.
A more certain scenario is expected this evening, when thunderstorm
development/re-invigoration is more probable as the low-level jet
increases. Steep lapse rates and moderate vertical shear support the
potential for thunderstorms capable of large hail during the
initially more cellular mode. These storms will likely cluster
quickly, with a trend towards upscale growth into a
forward-propagating MCS with an increasing damaging wind potential
as it spreads toward/across Missouri.
...Northern Rockies through the Central High Plains...
A shortwave trough will progress southeastward from British
Columbia/Alberta into the northern Rockies. Thunderstorm development
is anticipated across the northern Rockies as this wave interacts
with the destabilized and buoyant airmass across the region.
Moderate westerly flow aloft with support the potential for more
organized storm structures and the development of several line
segments. These widely scattered thunderstorms are forecast to
progress east-southeastward this afternoon/evening, with additional
development possible from Wyoming into the central High Plains. The
moderate westerly flow aloft, high storm bases, and steep low-level
lapse rates support the potential for strong to severe wind gusts
and possibly some increased hail potential through evening/early
overnight as these storms progress east-southeastward toward the
richer reservoir of moisture/buoyancy across the central High
Plains, including western Nebraska/northeast Colorado/northwest
Kansas.
...Upper Midwest including portions of Iowa/Wisconsin/Michigan...
Low-level moisture is expected to increase across the Midwest ahead
of an approaching cold front, resulting in moderate buoyancy by late
afternoon. Near-frontal convergence will influence convective
initiation, with the combination of moderate buoyancy and seasonally
strong westerly flow aloft supporting strong to severe storms
including some initial/semi-discrete supercells, which could yield
large hail. A transition into linear segments is expected by
evening, with damaging wind gusts becoming the more prevalent severe
risk as storms spread generally southeastward.
...Mississippi/Alabama to northern Florida...
Scattered thunderstorm development is expected this afternoon,
particularly across portions of Mississippi into western/southern
Alabama and northern Florida. These storms will develop amidst a
very moist and unstable environment. Vertical shear will be weak,
with an outflow-dominant/multicellular mode expected. Some
clustering into one or more line segments appears probable,
resulting in scattered thunderstorm coverage. Steep low-level lapse
rates and relatively high cloud bases support the potential for
strong downdrafts capable of locally damaging winds.
SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1230 PM CDT Tue Aug 18 2026
Valid 191200Z - 201200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS WEDNESDAY INTO
WEDNESDAY NIGHT ACROSS MUCH OF SOUTHERN MISSOURI...PARTS OF SOUTHERN
ILLINOIS...WESTERN KENTUCKY AND TENNESSEE AND NORTHERN ARKANSAS...
...SUMMARY...
One or two organized clusters of thunderstorms with potential to
produce swaths of damaging surface gusts appear possible across
parts of the Ozark Plateau into Mid South, and perhaps central and
southeastern Arizona, Wednesday through Wednesday night.
...Discussion...
An initially notable cyclone to the southwest of Hudson Bay is
forecast to weaken, with its broadening mid-level circulation
redeveloping across and east of southern Hudson/James Bays through
this period. To the south of this feature, broad cyclonic mid-level
flow will overspread much of the Upper Midwest/Great Lakes and Ohio
Valley through Northeast, downstream of initially building mid-level
ridging across the Pacific Northwest through northern Rockies, to
the north of a prominent mid-level high slowly shifting
northeastward toward the Four Corners region.
Beneath a plume of elevated mixed-layer now advecting along the
southern fringe of the westerlies, across the central Great Plains,
toward the Mid South, a lower-level baroclinic zone, likely
reinforced by convective outflow, may be in the process of advancing
southward across the Mid South/Ozark Plateau and south central Great
Plains (Kansas/Oklahoma border vicinity) at the outset of the
period. In the wake of one possible MCV initially migrating
east-southeastward into the Mid South, and ahead of a possible
trailing MCV, and trailing digging short wave impulse, it appears
that the southward progression of the front may slow or stall across
the Ozark Plateau/Mid South, while continuing more steadily, but
slowly, across Oklahoma and the Texas Panhandle. There is
substantive spread evident in the model output concerning these
developments, however.
...Ozark Plateau/Mid South...
Potential convective evolution Wednesday through Wednesday night
remains uncertain. However, it appears that a notable belt of
convectively augmented mid-level flow, including 30-50+ kt around
700 mb, will gradually nose from the lower Missouri through lower
Ohio Valley during the day. Depending on how the near-surface
boundary becomes oriented as this occurs, aided by a corridor of
seasonably high moisture content along it, there appears potential
for destabilization and shear to become conducive to organized
severe thunderstorm development. This may include supercells and/or
one or two evolving clusters accompanied by developing swaths of
strong to severe wind gusts through the period.
...Southern Rockies into Great Plains...
In the wake of the primary front, it appears that the boundary-layer
will remain sufficiently moist to support modest instability in the
presence of relatively weak mid-level inhibition across the middle
into lower Missouri Valley. Aided by forcing for ascent associated
with one lead digging short wave impulse, and a trailing one digging
into/across the international border, at least widely scattered
strong to severe storm development appears possible through the
period, in the presence of favorable strong deep-layer shear.
A drier, but more strongly heated and deeply mixed boundary-layer by
late Wednesday afternoon, near and to the lee of the Front Range
through Sangre de Cristo Mountains, may also become conducive to
widely scattered to scattered strong storms with potential to
produce severe wind and hail, aided by a weak short wave impulse
migrating around the Four Corners ridge.
...Arizona...
With the evolution/progression of the mid-level ridge, potential
steering flow for convective development is forecast to take on a
prominent easterly component with weak to modest strength by late
Wednesday afternoon across much of the Mogollon Rim through lower
deserts. Coupled with a preceding Gulf moisture surge, forecast
soundings indicate profiles supportive of at least weak to moderate
CAPE, even as the boundary-layer becomes hot and deeply mixed with
40-50F+ surface temperature/dew point spreads by peak afternoon
heating.
Initially more modest late afternoon instability in the lower
deserts around Phoenix may gradually destabilize with boundary-layer
moistening after sunset, eventually supporting the propagation of
convection into/across the Greater Phoenix area by late evening.
Details of the potential convective evolution remain uncertain, but
at least some model output suggest the evolution of a substantive
convective cluster is possible, which could become accompanied by
more widespread strong to severe gusts.
..Kerr.. 08/18/2026
SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0230 PM CDT Tue Aug 18 2026
Valid 201200Z - 211200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THURSDAY ACROSS
PARTS OF THE MID ATLANTIC AND PARTS OF CENTRAL GREAT PLAINS INTO
UPPER MIDWEST...
...SUMMARY...
A few strong to severe storms are possible Thursday across parts of
the Mid Atlantic and north central Great Plains into Upper Midwest.
...Discussion...
In advance of weak, large-scale mid-level troughing slowly
approaching the Pacific coast, mid-level ridging may continue to
amplify northward through the northern U.S. and Canadian Rockies, to
the north of a prominent mid-level high slowly shifting northeast of
the Four Corners through this period. Downstream, broad mid-level
troughing is forecast to begin to gradually shift to the north and
east of the Great Lakes and Northeast, but weak lingering troughing
upstream may continue dig southeast of the middle Mississippi/lower
Ohio valley toward the southern Appalachians. One or two,
convective generated or augmented, perturbations may accelerate
northeastward out of the Ohio Valley through the northern Mid
Atlantic after emerging from the latter regime. In their wake, it
appears that a surface frontal zone will continue a southward
progression, reaching the southern Mid Atlantic, northern Gulf
States and southern Great Plains Red River Valley by 12Z Friday.
Based on latest model output, convective potential through this
period still appears relatively limited, or at least uncertain due
to its dependence on sub-synoptic developments with low
predictability at this time frame. As a result, the prior outlook
for this period has largely remained unchanged.
...Mid Atlantic/Southeast...
Latest model output suggests that stronger pre-frontal
destabilization to the east of the Appalachians may be confined to
the coastal plain, from northern North Carolina through the Delmarva
Peninsula. Coupled with strengthening lower/mid-tropospheric flow
and forcing for ascent downstream of the approaching convectively
augmented perturbation, the environment may become conducive to
thunderstorms capable of producing damaging wind gusts.
...North central Great Plains into Upper Midwest...
A narrow corridor of stronger destabilization appears at least
possible ahead of a short wave perturbation digging within modest
northwesterly mid-level flow. It is possible that this could become
sufficient to promote a risk for widely scattered strong storms with
potential to produce severe hail and wind late Thursday afternoon
into evening.
...Southwest...
Mid-level flow may transition to at least a bit more of a component
to the south of east during this period, but still potentially
conducive to propagation of convection off the higher terrain of
central and southeastern Arizona, given sufficient destabilization
in lower elevations. This remains uncertain due to potential
impacts of convection Wednesday through Wednesday night, so will
hold off on adding low severe probabilities for wind at this time.
..Kerr.. 08/18/2026
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1029 AM CDT Tue Aug 18 2026
Valid 181700Z - 191200Z
Minor changes were made to the Elevated area over the Columbia
Basin. In agreement with the latest forecast guidance, portions of
the nearby Snake River over southeastern WA were added into the
Elevated area. During peak heating with temperatures near to just
above normal, afternoon RHs will fall to near 15% with sustained
westerly winds of 10-15 mph within and adjacent to the Snake River
valley through WA. Elsewhere, over the southern Plains, the forecast
remains on track as previously described. Occasionally gusty diurnal
winds may promote brief near-elevated conditions over portions of
the Snake River Plain in ID and across the lower elevations of the
southern Great Basin this afternoon as well.
..Stearns.. 08/18/2026
.PREV DISCUSSION... /ISSUED 1227 AM CDT Tue Aug 18 2026/
...Synopsis...
Heights with the western ridge will rise again today, with warming
temperatures and dry conditions across much of the Pacific
Northwest. Along the northern periphery of the ridge, a shortwave
passage will bring breezy conditions to areas east of the Cascades.
Dry and breezy conditions will also be possible south of a frontal
boundary across western Oklahoma into the Texas Panhandle.
...Portions of the Columbia Basin...
A split flow regime aloft will induce west-northwesterly flow over
Washington, and southwest-westerly flow over Oregon. Combined with
lee surface troughing, wind speeds will increase across the Cascade
Gaps. West-northwesterly surface winds of around 10-15 mph will
encompass a broad area of the Columbia Basin, with stronger winds of
20-30 mph within the gaps. At peak heating, relative humidity values
will decline to around 15-20 percent. Broadly elevated fire weather
conditions are expected in the lee of the Cascades, with locally
critical conditions possible.
...Southern Plains...
Drought conditions are prominent across much of the region,
expanding from the Texas Panhandle into western/central Oklahoma to
produce a stressed fuel environment. Breezy and dry conditions are
expected near the surface trough across the Texas Panhandle into
western Oklahoma. Profiles will be deeply mixed, with temperatures
approaching the 100s F again this afternoon. This will support
afternoon relative humidity values of 10-15% amid southwest winds of
15-20 mph, maintaining an Elevated risk area.
...Please see www.spc.noaa.gov/fire for graphic product...
SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0203 PM CDT Tue Aug 18 2026
Valid 191200Z - 201200Z
...NO CRITICAL AREAS...
No changes were made to the previous outlook. While thunderstorms
are anticipated over dry fuels across portions of south Florida
during the afternoon of Day 2/Wednesday and portions of the southern
Plains (in particular, northern OK and the TX Panhandle) after
sunset, relatively high precipitable water values will preclude any
drawn areas.
..Stearns.. 08/18/2026
.PREV DISCUSSION... /ISSUED 1228 AM CDT Tue Aug 18 2026/
...Synopsis...
Upper ridging will expand farther into the Intermountain West on Day
2/Wednesday, supporting hot and dry conditions amid generally
lighter winds. Deeper monsoonal moisture will remain embedded within
the Desert Southwest, but residual mid-level moisture in the Great
Basin could support a few isolated showers in the higher terrain. In
the southern Plains, a weak frontal boundary will sag into the Texas
Panhandle and Oklahoma throughout the day. Models vary on the timing
of the front, and progression will largely depend upon thunderstorm
outflow across southwestern Kansas on Day 1/Tuesday
evening/overnight. Nevertheless, a deeply mixed profile will lead to
another day of high temperatures in the 100s F and RH values of
15-20% ahead of the front, promoting locally elevated fire weather
concerns amid a drought stressed fuelscape.
...Please see www.spc.noaa.gov/fire for graphic product...
|
