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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SPC Aug 20, 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
0100 AM CDT Thu Aug 20 2026

Valid 201200Z - 211200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE MID ATLANTIC...THE MIDWEST AND CENTRAL PLAINS....

...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.

...Mid Atlantic and central Appalachians...
A shortwave trough embedded within broader northwesterly flow aloft
is forecast to move eastward from the OH valley into the Mid
Atlantic through today. Embedded within a broader upper trough over
the eastern Great Lakes, this shortwave perturbation will serve as a
focus for convective development across the Mid Atlantic and central
Appalachians this afternoon. As ascent overspreads the area, a warm
front is forecast to lift northward across southern PA, northern MD
into NJ and southern NY.

South of the front, a very moist air mass (dewpoints in the 70s F)
will lift northward. Despite poor low and mid-level lapse rates,
moderate buoyancy is expected south of the front and ahead of a
trailing lee trough into southern VA. Ongoing storms from a remnant
morning cluster may reintensify as they cross the Appalachians late
morning and early afternoon. Additional, possibly discrete,
development may occur east of the Blue Ridge and across the higher
terrain of southern PA and northern MD near the front by late
morning. 40-50 kt of deep-layer shear ahead of the front is forecast
to support a mix of supercells and line segments. Damaging winds and
isolated severe gusts appear probable. Enlarged low-level hodographs
near the front may also support a couple of tornadoes and marginally
severe hail with any more robust QLCS segments or supercells.

...Central Plains...
Strong northwesterly flow aloft will overspread a cold front moving
southward from the western Great Lakes into the central Plains.
Ahead of the front, warm temperatures and dewpoints in the mid to
upper 60s F will support moderate to large buoyancy by mid
afternoon. A shortwave impulse within the broader trough should
overspread the destabilizing air mass and aide in convective
development along the front across MN and SD, and farther south near
the front and surface trough intersection in central NE.

Forecast soundings show supercell wind profiles, with
elongated/straight hodographs aloft. Isolated to widely scattered
storms will develop by late afternoon/early evening, posing a risk
for large hail, severe wind gusts and perhaps a tornado. Some
significant hail (greater than 2 inch diameter) is possible across
the southern risk area given steeper mid-level lapse rates/cool
temperatures aloft and somewhat deeper low-level moisture. Some risk
for isolated damaging gusts may persist into the early overnight
across southern NE and northern KS if clustering can occur.

...Southeast...
South of the primary upper wave over parts of the Western Carolinas
and TN Valley, a surface trough in the lee of the Appalachians may
focus convective development during the afternoon. A few stronger
clusters with damaging gusts are possible, though weaker flow aloft
suggests more limited storm organization.

Additional scattered thunderstorms are expected again this afternoon
within a seasonably hot and humid air mass across the southeast and
lower MS Valley. Convective coverage is likely to focus along a
weakening cold front sagging southward across parts of AR/LA and
western MS and near a weak MCV across the central Gulf Coast. With
PWATs upwards of 2 inches, some potential for wet microbursts are
possible with the stronger storm clusters through early evening.

...AZ...
Strong heating beneath a prominent upper ridge will support another
round of scattered thunderstorms this afternoon and evening.
Seasonably rich monsoon moisture (dewpoints in the upper 50s to 60s
F) will support moderate destabilization amid modest easterly
mid-level flow. A few high-based clusters are possible, initially
over the higher terrain, before expanding west and south into the
lower elevations. This could support a few severe gusts given steep
lapse rates.

..Lyons/Thornton.. 08/20/2026


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SPC Aug 19, 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
0257 PM CDT Wed Aug 19 2026

Valid 192000Z - 201200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
THE LOWER MISSOURI VALLEY...THE MID MISSISSIPPI VALLEY...AND
SOUTHERN ARIZONA...

...SUMMARY...
Thunderstorms capable of severe wind gusts and hail will be possible
this afternoon across the lower Missouri Valley, the mid Mississippi
Valley, and southern Arizona.

...20z Update...
A compact, but severe, MCS has begun tracking eastward along a
residual/diffuse frontal zone into southeast NE. Based on the recent
18 UTC OAX RAOB, the MCS is beginning to orient more orthogonal to
the deep-layer bulk shear vector, which should continue to promote
storm organization and intensity. The potential for severe winds,
including winds near 75 mph, should continue through late afternoon
and early evening hours before moving into more stable air mass
across north-central MO. See MCD #2041 for additional short-term
details.

...Mid-Mississippi Valley/lower Ohio Valley...
Recent GOES visible imagery and surface observations show
temperatures rebounding into the low to mid 80s as skies clear ahead
of an approaching mid-level wave. This destabilization appears to be
on track with recent guidance, which suggests that initially
discrete/semi-discrete storm development should begin by around
22-00 UTC across south-central MO on the western fringe of the
residual cold pool. Forecast soundings from this region depict
elongated hodographs conducive for large hail, including the
potential for hail up to 2 inches in diameter (based on sounding
analogs and hodograph structure). Given a favorable kinematic
environment, adequate buoyancy, and a signal in recent high-res
ensemble guidance for strong convection, a CIG 1 hail contour has
been introduced to portions of southern Missouri.

Elsewhere, only minor modifications were made based on recent
convective trends. See the discussion below and MCD #2040 for
additional details.

..Moore.. 08/19/2026

.PREV DISCUSSION... /ISSUED 1134 AM CDT Wed Aug 19 2026/

...Mid MO Valley...
Radar/visible satellite mosaic imagery depicts a small cluster of
severe thunderstorms immediately ahead of a migratory shortwave
trough moving southeast over the mid MO Valley. Some heating
downstream of this activity will result in temperatures warming and
the airmass gradually destabilizing amid filtered sunshine. Gradual
upscale growth is underway and should continue into the early
afternoon. Large hail and severe gusts 60-70 mph will be the
primary severe hazards as this cluster moves into adjacent portions
of NE/MO/IA later this afternoon.

...Ozarks into the Mid MS Valley...
Residual showers/thunderstorms from an overnight MCS over the
southeast MO into western KY vicinity will slowly dissipate this
afternoon with greater heating ensuing in the wake of these storms.
Models continue to show moderate destabilization by late this
afternoon ahead of the MO Valley upper vort. Weak low-level
convergence along an upstream cold front will support thunderstorm
development within this destabilized airmass this evening.
Strengthening mid-level flow will result in moderate to strong
deep-layer vertical shear supportive of supercells. Models vary
regarding the propensity for cellular mode to be maintained beyond
the initial storm development phase, casting doubt on supercell
longevity and tornado potential. Nonetheless, some strengthening of
850-mb flow during the evening may enable some mesocyclone potential
to persist, and an accompanying isolated risk for a tornado or two.
Otherwise, storms will tend to cluster with eastward extent, with
the threat for damaging gusts persisting within these bowing line
segments.

...Ohio Valley...
A somewhat secondary area of late afternoon/early evening
thunderstorm development is anticipated from central IL into central
IN and central OH. Moderate buoyancy and strong westerly flow aloft
supports the potential for isolated supercells capable of large hail
and isolated damaging gusts.

...Central/Southern High Plains...
A seasonably moist airmass will undergo strong heating/mixing and
result in moderate buoyancy by mid-late afternoon. Thunderstorm
development is expected across the higher terrain before then
progressing eastward into the lower elevations. Moderate
northwesterly flow aloft will support organized storms
structures, and large hail is possible along the Foothills.
Steep lapse rates and large temperature-dewpoint depressions will
lead to outflow-dominant storms capable of severe gusts with the
more intense cores/outflow.

...AZ...
The presence of monsoon moisture will support moderate buoyancy
across the lower elevations of south-central AZ during the late
afternoon. Scattered storms are expected to eventually develop
towards the early evening. Trends in model guidance showing a
cluster potentially evolving within an adequately moist/inverted-V
environment lend confidence in introducing a level 1 intensity
highlight for peak gusts in the 70-80 mph range.

...Southeast into northern FL...
A very moist airmass analyzed late this morning (mid to upper 70s F
surface dewpoints) will remain in place along the Gulf Coast. Strong
heating is anticipated, with high temperatures in the upper 90s
across much of the region. As surface temperatures warm, moderate
instability will develop, with scattered thunderstorms expected amid
modest low-level convergence from MS into western/southern AL and
across the FL Panhandle into northern FL. The deep low-level
moisture combined with steep low-level lapse rates will support an
isolated wind-damage threat during the mid to late afternoon.


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