SPC Aug 21, 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
1256 AM CDT Fri Aug 21 2026

Valid 211200Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
THE CENTRAL PLAINS...THE MIDWEST AND THE CAROLINAS...

...SUMMARY...
Scattered damaging hail (some greater than 2 inch diameter) and
severe wind gusts may occur over parts of the central Plains this
afternoon and evening. Scattered storms, some with severe wind gusts
and hail, also are possible across parts of the Midwest. Scattered
to numerous storms with damaging wind guts are possible over the
Carolinas and Southeast.

...Central Plains...
Mid-level ridging over the western US is forecast to intensify,
strengthening northwesterly flow aloft over much of the central US.
Several embedded disturbances will pass overhead with the enhanced
northwesterlies through the day. A surface low will move
southeastward through the Great Lakes as a weak trailing cold front
moves southward through the central Plains and Midwest.

Ahead of the front, a plume of steep mid-level lapse rates will
shift eastward across the central Plains toward the Mid-MO Valley
atop a corridor of rich low-level moisture. Diurnal destabilization
should result in 3000-4000 J/kg of MLCAPE from SD to NE. Isolated to
widely scattered thunderstorm development is expected from the Black
Hills southeastward along the cold front. Elongated/straight
hodographs and 45+ kt effective shear will favor initial supercells.
Large to very large hail (some greater than 2 inches diameter) will
be possible. With time, a forward propagating cluster or two may
develop and move southeast across parts of NE and KS with the
potential for severe gusts (a few near 70-80 mph). It is unclear
exactly how far southeast any storms will persist overnight, but any
more substantial clustering could allow at least an isolated severe
threat to continue into early Saturday.

A much drier and hotter environment over the High Plains to the west
could also support isolated to widely scattered high-based storms
from eastern CO into western KS. Very steep lapse rates in the
lowest 2-3 km with modest buoyancy aloft could allow a few severe
gusts.

...Midwest...
Beneath the upper trough over the western Great Lakes, cool
mid-level temperatures and robust surface moisture should result in
moderate destabilization from WI into eastern IA and northwest IL.
Scattered thunderstorms by mid afternoon ahead of the cold front
spreading southeastward. Enhanced northwesterly flow with deep-layer
shear of 30-40 kt will promote a mix of organized clusters and
supercells. The large buoyancy will support a risk for damaging
gusts and some hail.

...Southeast and Gulf Coast...
A broad upper trough will move across the central US into parts of
the southern Appalachians while a weak cold front moves southward
from the mid Atlantic today and tonight. Weak ascent from the upper
trough and near the front should focus diurnal thunderstorm activity
across the Carolians and southern Appalachians. Warm surface
temperatures and plentiful boundary-layer moisture will support
large buoyancy (3000+ J/kg MLCAPE) through the afternoon and evening
despite modest mid-level lapse rates. With scattered to numerous
storms expected, a few organized clusters may emerge with a risk
primarily for damaging wind gusts. Slight enhancement of the
westerly flow aloft could also support some isolated hail with the
stronger updrafts.

Farther south and west, a very humid and warm air mass is forecast
to become strongly unstable by early afternoon across the lower MS
Valley and Gulf Coast. Scattered to numerous thunderstorms are
expected along prior outflows and a weak, southward moving cold
front from East TX into LA/MS. The very strong buoyancy and high
PWAT content will support clustering and strong downdrafts with
sporadic damaging gust potential. Otherwise, weak vertical shear
will limit overall organization.

..Lyons/Weinman.. 08/21/2026


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SPC Aug 20, 2026 2000 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 2000Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0255 PM CDT Thu Aug 20 2026

Valid 202000Z - 211200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE MID-ATLANTIC...PARTS OF THE SOUTHEAST...AND FROM THE CENTRAL
PLAINS INTO THE UPPER MISSISSIPPI VALLEY...

...SUMMARY...
Scattered severe storms are possible this afternoon into this
evening across parts of the Mid Atlantic, posing a risk for a couple
of tornadoes and damaging wind gusts. Large hail and isolated wind
damage will be possible late today into tonight with severe storms
from Nebraska into northwest Wisconsin. Scattered damaging gusts
are possible over parts of the Deep South this afternoon into the
early evening.

...20z Update...
The previous forecast largely remains on track with only minor
adjustments made based on recent convective trends and recent
guidance. Regional radar mosaics show the development of discrete
and semi-discrete supercells across the northern MD into southern PA
ahead of a mid-level perturbation and weak cold front. The recent 18
UTC IAD sounding sampled modest buoyancy (around 1000 J/kg MLCAPE),
which seems to be more marginal compared to recent RAP mesoanalysis
MLCAPE depictions. Nonetheless, strong shear was sampled by this
RAOB, including just under 200 m2/s2 effective SRH. This environment
likely exists downstream into far southeast PA and western NJ and
warranted a slight northward expansion of the CIG1 tornado contour.
Confidence in convective coverage with southwestward extent into
southern VA and NC remains limited based on trends in
radar/satellite trends and latest high-res guidance. Other forecast
thoughts outlined in the previous discussion below remain on track.

...Northern MS/AL...
Convection is developing along/ahead of a weak surface front and
mid-level wave across southeast AR into northern MS. This aligns
well with recent guidance, especially RRFS solutions, which depict
increasing thunderstorm coverage through early evening. Wind and
hail probabilities have been adjusted slightly across northern
AL/southern TN to reflect these solutions and capture areas where
air mass recovery continues.

...Northern MN...
A surface low is becoming apparent in surface observations and GOES
visible imagery across northern MN with early stages of convection
noted over the past 45 minutes. With 64-66 F dewpoints spreading
north towards north-central MN, some potential exists for more
robust convection than previously depicted by guidance. Recent
RRFS/HRRR time-lagged ensembles have also trended slightly north
with the strongest UH signals, which matches these recent
observations and warranted a northward expansion of probabilities.

Elsewhere, the forecast outlined below remains on track. See MCD
#2053 for additional short-term details regarding the near-term
severe threat across north-central NE.

..Moore.. 08/20/2026

.PREV DISCUSSION... /ISSUED 1133 AM CDT Thu Aug 20 2026/

...Central Appalachians into the Mid-Atlantic...
Radar mosaic late this morning showed a couple of weak convectively
related vorticity maxima moving east across the central and southern
Appalachians (i.e., southwest PA, eastern KY). One of these lead
disturbances was sampled by the WSR-88D VAD at Jackson, KY, with an
upstream shortwave trough over the OH Valley moving towards the
Mid-Atlantic states.

The airmass across the Mid-Atlantic into the Carolinas will continue
to heat amid patchy but thinning cloud cover. Model guidance shows
moderate buoyancy developing by early to mid afternoon from the
southern Appalachians northward into the northern Mid-Atlantic
region. A belt of stronger 700-500 mb westerly flow (30-45 kt) will
overspread the northern half of VA northward into PA/NJ. Beneath
this stronger flow, southerly low-level flow veering and
strengthening with height will support hodographs favorable for
organized severe storms, including supercells and organized line
segments. The latest model guidance shows a few simulated
supercells developing in the area centered over MD and the upper
Chesapeake Bay vicinity during the 20-00z timeframe. This scenario
seems plausible given some low-level enlargement to the hodograph
and effective shear around 40 kt. A tendency for upscale growth
into a line segment is expected as this activity moves east towards
the coast during the evening. A couple of supercell tornadoes are
possible with this activity, in addition to a line-embedded
mesovortex and scattered damaging gusts.

...Carolinas into the TN Valley and lower MS Valley...
Ample low-level moisture and strong heating will result in an
unstable airmass from the Carolinas into much of the Southeast.
Low-level convergence along a cold front that will extend from the
western Carolinas into AR this afternoon will result in scattered
thunderstorm coverage as 2500-4000 J/kg MLCAPE develops by mid
afternoon. High PW (in excess of 2 inches) and steep 0-3 km lapse
rates and modest westerly to west-northwesterly flow will favor
damaging downbursts with the stronger southeast-moving clusters.

...Central Plains into the Upper MS Valley...
A tongue of relatively rich low-level moisture (mainly 60s F surface
dewpoints) will extend from the central Great Plains northward ahead
of a cold front, which is forecast to be draped from western MN into
western NE this afternoon. Thunderstorm initiation is anticipated
first across the Upper MS Valley before expanding southwestward.

Moderate northwesterly flow aloft will support supercell wind
profiles, with elongated/straight hodographs, and the threat for all
severe hazards. Large to very large hail (i.e. greater than 2 inch
diameter) will be the primary severe hazard, particularly during the
early evening as the storms move into greater instability. Isolated
strong to severe gusts (i.e. 55 to 75 mph) are possible as well.
Given the supercellular storm mode and low-level southerly flow, a
low-probability tornado risk also exists. Some risk for isolated
damaging gusts may persist into the early overnight across southern
NE and northern KS if clustering can
occur.

...AZ...
Not much change from prior forecast thinking in that isolated to
widely scattered storms are forecast but a generally lower risk for
severe gusts is anticipated later today into this evening. Steep
lapse rates and inverted-V profiles will support an isolated risk
for severe gusts with the more intense downdrafts.


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SPC Aug 20, 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
1133 AM CDT Thu Aug 20 2026

Valid 201630Z - 211200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE MID-ATLANTIC...PARTS OF THE SOUTHEAST...AND FROM THE CENTRAL
PLAINS INTO THE UPPER MISSISSIPPI VALLEY...

...SUMMARY...
Scattered severe storms are possible this afternoon into this
evening across parts of the Mid Atlantic, posing a risk for a couple
of tornadoes and damaging wind gusts. Large hail and isolated wind
damage will be possible late today into tonight with severe storms
from Nebraska into northwest Wisconsin. Scattered damaging gusts
are possible over parts of the Deep South this afternoon into the
early evening.

...Central Appalachians into the Mid-Atlantic...
Radar mosaic late this morning showed a couple of weak convectively
related vorticity maxima moving east across the central and southern
Appalachians (i.e., southwest PA, eastern KY). One of these lead
disturbances was sampled by the WSR-88D VAD at Jackson, KY, with an
upstream shortwave trough over the OH Valley moving towards the
Mid-Atlantic states.

The airmass across the Mid-Atlantic into the Carolinas will continue
to heat amid patchy but thinning cloud cover. Model guidance shows
moderate buoyancy developing by early to mid afternoon from the
southern Appalachians northward into the northern Mid-Atlantic
region. A belt of stronger 700-500 mb westerly flow (30-45 kt) will
overspread the northern half of VA northward into PA/NJ. Beneath
this stronger flow, southerly low-level flow veering and
strengthening with height will support hodographs favorable for
organized severe storms, including supercells and organized line
segments. The latest model guidance shows a few simulated
supercells developing in the area centered over MD and the upper
Chesapeake Bay vicinity during the 20-00z timeframe. This scenario
seems plausible given some low-level enlargement to the hodograph
and effective shear around 40 kt. A tendency for upscale growth
into a line segment is expected as this activity moves east towards
the coast during the evening. A couple of supercell tornadoes are
possible with this activity, in addition to a line-embedded
mesovortex and scattered damaging gusts.

...Carolinas into the TN Valley and lower MS Valley...
Ample low-level moisture and strong heating will result in an
unstable airmass from the Carolinas into much of the Southeast.
Low-level convergence along a cold front that will extend from the
western Carolinas into AR this afternoon will result in scattered
thunderstorm coverage as 2500-4000 J/kg MLCAPE develops by mid
afternoon. High PW (in excess of 2 inches) and steep 0-3 km lapse
rates and modest westerly to west-northwesterly flow will favor
damaging downbursts with the stronger southeast-moving clusters.

...Central Plains into the Upper MS Valley...
A tongue of relatively rich low-level moisture (mainly 60s F surface
dewpoints) will extend from the central Great Plains northward ahead
of a cold front, which is forecast to be draped from western MN into
western NE this afternoon. Thunderstorm initiation is anticipated
first across the Upper MS Valley before expanding southwestward.

Moderate northwesterly flow aloft will support supercell wind
profiles, with elongated/straight hodographs, and the threat for all
severe hazards. Large to very large hail (i.e. greater than 2 inch
diameter) will be the primary severe hazard, particularly during the
early evening as the storms move into greater instability. Isolated
strong to severe gusts (i.e. 55 to 75 mph) are possible as well.
Given the supercellular storm mode and low-level southerly flow, a
low-probability tornado risk also exists. Some risk for isolated
damaging gusts may persist into the early overnight across southern
NE and northern KS if clustering can
occur.

...AZ...
Not much change from prior forecast thinking in that isolated to
widely scattered storms are forecast but a generally lower risk for
severe gusts is anticipated later today into this evening. Steep
lapse rates and inverted-V profiles will support an isolated risk
for severe gusts with the more intense downdrafts.

..Smith/Wendt.. 08/20/2026


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SPC Aug 20, 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
0746 AM CDT Thu Aug 20 2026

Valid 201300Z - 211200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE MID-ATLANTIC...AND FROM THE CENTRAL PLAINS INTO THE UPPER
MISSISSIPPI VALLEY...

...SUMMARY...
Scattered severe storms are possible today and tonight across parts
of the Mid Atlantic, posing a risk for damaging wind gusts. Large
hail and isolated wind damage will be possible with severe storms
from Nebraska into northwest Wisconsin.

...Central Appalachians into the Mid-Atlantic...
Broad upper troughing currently extends from the northern Plains
through New England, with an embedded shortwave trough progressing
across the Mid MS Valley into the Lower OH Valley. Showers and
thunderstorms are ongoing ahead of this shortwave, and the
expectation is that these showers and thunderstorms will continue
weakening this morning. A moist airmass is in place downstream of
this wave (i.e. from the central Appalachians and upper OH Valley
into the Mid-Atlantic), and reintensification and/or new development
is expected ahead of this wave as it continues northeastward into
this diurnally destabilized region.

Surface low associated with this wave is currently over the IN/OH/KY
border vicinity. This low is forecast to deepen slightly as it moves
northeastward just ahead of the parent shortwave trough. Modest
low-level moisture advection will precede this low, and a warm front
is forecast to lift northward across southern PA, northern MD, and
most of NJ. Despite poor lapse rates, ample low-level moisture south
of the front will support moderate buoyancy. Reintensification
and/or new thunderstorm development is expected first near the Blue
Ridge and across the higher terrain of southern PA and northern MD
before increasing in coverage and intensity with eastward extent. A
belt of slightly stronger mid-level flow will precede the shortwave,
resulting 40 to 50 kt of effective bulk shear. This is more than
sufficient to support a mix of supercells and organized line
segments. Damaging wind gusts will be the primary risk, but
southerly winds will enlarge low-level hodographs from the Delmarva
into central NJ, supporting the potential for a couple of tornadoes.

...Carolinas into the Southeast...
Ample low-level moisture and strong heating will result in an
unstable airmass from the Carolinas into much of the Southeast.
Low-level convergence along a cold front that will extend from the
western Carolinas into AR this afternoon will result in scattered
thunderstorm coverage. Vertical shear will be weak, and an
outflow-dominant storm structure is anticipated. Even so, moderate
to strong buoyancy and ample moisture (PW around 2") will support
occasionally strong water-loaded downbursts, particularly from
western TN into AL and MS where high temperatures in the upper 90s
are anticipated.

...Central Plains into the Upper MS Valley...
A reservoir of greater low-level moisture (i.e. dewpoints in the
upper 60s) currently extends from AR/eastern OK northwestward across
much of KS and into NE. Modest low-level moisture advection is
anticipated throughout this corridor today, as a tightening surface
pressure gradient results in stronger southerly surface winds. Mid
60s dewpoints could reach as far north as southwest MN. Moderate to
strong buoyancy will develop within this corridor, with the greatest
buoyancy likely from the CO/KS/NE border vicinity northeastward into
southeast SD. At the same time, a cold front will progress
southeastward across western MN, central SD and western NE,
interacting with this buoyancy to support thunderstorm development.
Thunderstorm initiation is anticipated first across the Upper MS
Valley before expanding southwestward.

Moderate northwesterly flow aloft will support supercell wind
profiles, with elongated/straight hodographs, and the threat for all
severe hazards. Large to very large hail (i.e. greater than 2 inch
diameter) will be the primary severe hazard, particularly during the
early evening as the storms move into greater instability. Isolated
strong to severe gusts (i.e. 55 to 75 mph) are possible as well.
Given the supercellular storm mode and low-level southerly flow, a
low-probability tornado risk also exists.
Some risk for isolated damaging gusts may persist into the early
overnight across southern NE and northern KS if clustering can
occur.

...AZ...
Another round of scattered thunderstorms this afternoon and evening
amid seasonably rich monsoon moisture (dewpoints in the upper 50s to
60s F) and moderate buoyancy. The lower elevations will be
characterized by greater convective inhibition than yesterday, with
the overall buoyancy slightly lower as well. Consequently, despite a
similar upper pattern, the overall potential for strong gusts is
expected to be lower than yesterday. Even so, isolated gusts are
still possible as storms move off the high terrain into the deeply
mixed airmass over the lower elevations.

..Mosier/Bunting.. 08/20/2026


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