Mesoscale Discussion 0445
NWS Storm Prediction Center Norman OK
1022 AM CDT Wed Apr 15 2026

Areas affected...Eastern Nebraska into much of Iowa

Concerning...Severe potential...Watch possible 

Valid 151522Z - 151745Z

Probability of Watch Issuance...40 percent

SUMMARY...The severe risk will gradually increase and spread
eastward into this afternoon. A few instances of severe hail is the
main concern for the next few hours. While timing is uncertain, a
watch may eventually be needed for parts of the area.

DISCUSSION...Water-vapor imagery indicates a midlevel trough moving
eastward across the central Plains, preceded by around 50 kt of
southwesterly midlevel flow (per regional VWP data). An accompanying
surface low, currently analyzed over southeast NE, will track
eastward along a composite outflow/stationary front draped across
southern IA into this afternoon. Isolated elevated thunderstorms are
already evolving to the northeast of the surface low and to the
north of the boundary in eastern NE, which will pose a risk of
isolated severe hail in the near term. This activity will generally
spread/develop eastward along/north of the surface boundary in
tandem with the surface low and deep-layer ascent accompanying the
midlevel trough into this afternoon. Despite the expected elevated
nature of these storms for the next several hours,
elongated/straight hodographs (40-50 kt of effective shear) and
steep midlevel lapse rates/modest buoyancy atop the boundary layer
will support transient elevated supercell structures capable of
producing severe hail.

With time, the low-level mass response accompanying the midlevel
trough and surface low will draw lower/middle 60s dewpoints
northward into central IA in the wake of ongoing convection.
Depending on the degree of diurnal heating in cloud breaks, this may
support a transition to surface-based storms into the afternoon,
with an associated risk for damaging wind gusts and large hail with
organized clusters and supercells. It is unclear if the
ongoing/morning and early-afternoon elevated storms will warrant a
watch, though current thinking is that a watch may eventually be
needed for parts of the area.

..Weinman/Gleason.. 04/15/2026

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...DVN...ARX...DMX...FSD...OAX...

LAT...LON   40829616 41109669 41539692 42079675 42439631 42739541
            43059318 43079208 42849135 42369096 41799105 41349153
            41089232 40909421 40829616 

MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 95 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0746 AM CDT Wed Apr 15 2026

Valid 151300Z - 161200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN
PLAINS INTO THE MIDWEST AND SOUTHERN GREAT LAKES...

...SUMMARY...
Severe thunderstorms posing a risk for large hail to very large
hail, severe gusts, and a couple of tornadoes will be possible
across portions of the southern Plains toward the Great Lakes this
afternoon and evening.

...Synopsis...
Water-vapor imagery this morning shows an upper trough from the
eastern Dakotas south-southwestward into the southern Rockies.  A
few disturbances will migrate eastward coincident with the trough
with the most notable being over the central High Plains this
morning.  The aforementioned disturbance will move east reaching the
mid-upper MS Valley with the trailing southern extent of the wave
moving into the MO Ozarks and OK by daybreak Thursday.  A weak
diffuse low will move from northern KS to the southwest Great Lakes
by late tonight.  Farther east, an MCV near MO-IL will translate
east and become perhaps a focus for storm activity later this
afternoon across OH-PA.  A rather complex forecast is apparent due
in large part to considerable convection and related outflow
permeating the warm sector overnight across much of the Slight-Risk
area.  

...Iowa into the mid MS Valley...
In the wake of showers/storms this morning from IA southward into
MO, a moist and weakly capped airmass will destabilize through early
afternoon.  The eastward approach of the mid-level disturbance will
likely contribute towards scattered thunderstorms developing 19-21z
from near the weak low eastward along the composite outflow/frontal
zone into IL-WI and southward into MO within a weakly capped warm
sector.  Forecast soundings show straight-line hodographs over IA
with sizable CAPE in the hail growth zone.  The potential for
splitting supercells appears evident with the stronger storms
capable of very large hail and perhaps some tornado risk across IA
and northern MO.  

...Ozarks into Oklahoma and north Texas...
Morning raobs showed steep 700-500 mb lapse rates (7.5-8 deg C/km)
atop a seasonably very moist return-flow airmass.  Models generally
show storm development near the dryline by mid afternoon with
initial development becoming supercellular.  Large to very large
hail will be possible with the stronger updrafts.  Residual outflow
from overnight convection moving into the Ozarks may play a role in
enhancing low-level shear later today.  Forecast soundings show
somewhat limited low-level hodographs with a tendency for a
veer-back-veer signature.  Additional storms will favor some
clustering and upscale growth with time due in part to the forecast
hodographs.  Nonetheless, all hazards will be possible at least
through the early convective life cycle before the possibility for
wind damage and linear structures perhaps evolve during the evening.
 
...Southern Great Lakes into the Northeast...
The remnants of an overnight squall line are moving east across
NY-PA this morning with a trailing outflow boundary extending
westward into OH and northeast IN.  Moist low levels and the
eastward advection of steeper mid-level lapse rates will act to
destabilize the southern Great Lakes into western PA through midday
and into the afternoon.  Forcing for ascent and enhancement of flow
associated with the MCV will potentially focus thunderstorms and aid
in their organization potential beginning this afternoon. 
Considerable uncertainty remains regarding this scenario and whether
a mesoscale corridor of higher tornado probabilities is needed
(i.e., northeast OH).  Will defer to later outlooks to where perhaps
mesoscale corridors of greater wind/hail threat and an isolated risk
for a couple of tornadoes could develop.

..Smith/Dean.. 04/15/2026

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1130 AM CDT Wed Apr 15 2026

Valid 151630Z - 161200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN/CENTRAL PLAINS INTO THE MIDWEST/OHIO VALLEY AND
SOUTHERN GREAT LAKES...

...SUMMARY...
Severe thunderstorms posing a risk for large to very large hail,
damaging winds, and perhaps a few tornadoes will be possible across
parts of the southern/central Plains into the Midwest/Ohio Valley
and southern Great Lakes this afternoon and evening.

...Synopsis...
Severe potential across the broad warm sector will be complicated by
ongoing thunderstorms/MCVs and associated cloud cover. A neutral to
positively tilted upper trough will eject northeastward across the
southern/central Plains today, with a broad zone of enhanced
mid-level southwesterly winds extending over much of TX/OK into the
Midwest/OH Valley and Great Lakes. At the surface, a weak low over
southeast NE late this morning is forecast to develop slowly
northeastward across IA through the afternoon and evening, with a
quasi-stationary front extending northeastward from this low towards
southern WI/Lower MI. A dryline extends southward across KS/OK into
west TX. Multiple MCVs related to ongoing/earlier convection are
also noted in recent visible satellite/radar imagery, and these
features may aid additional convective development this afternoon.

...Iowa into Missouri...
Forcing for ascent associated with the ejecting upper trough will
overspread the front draped across IA this afternoon. Ongoing
supercell in western IA and cloudiness near the front late this
morning cast some uncertainty on the degree of destabilization that
will occur this afternoon, and the overall intensity of convection.
Still, expectations are for additional robust thunderstorms to
eventually develop by 19-21Z along/near the front in IA, with steep
mid-level lapse rates noted on the observed 12Z TOP sounding
supporting moderate to locally strong MLCAPE even if
clouds/precipitation hinder daytime heating to some extent. Various
NAM/RAP forecast soundings show elongated/nearly straight hodographs
at mid/upper levels and 50+ kt of deep-layer shear, which will be
favorable for upper-level/anvil venting and hail production with any
supercells that form. Large to very large hail will be a concern
with initially discrete convection. But, some tendency for
clustering and movement north of the surface front casts
considerable uncertainty on the wind/tornado potential. Even so,
some chance for a few tornadoes and scattered damaging winds may
exist along/south of the front across IA into MO with any convection
that can develop east of the dryline.

...Southern Plains into the Ozarks and Mid Mississippi Valley...
A seasonably moist low-level airmass remains in place across the
southern Plains into the Ozarks and mid MS Valley, with observed 12Z
soundings from FWD/OUN/SGF indicating mean mixing ratios ranging
12-13.6 g/kg. However, even with steep mid-level lapse rates noted
across TX/OK, profiles are fairly saturated at mid/upper levels, and
plentiful cloud cover is present in recent visible satellite imagery
across these regions. It still appears likely that surface-based
thunderstorms will develop this afternoon (around 19-21Z) along/east
of the dryline as MLCIN gradually erodes ahead of the ejecting upper
trough. But, overall evolution remains somewhat unclear, with
potential for messy storm modes/interactions fairly early in the
convective life cycle given a large degree of boundary-parallel flow
in low/mid levels. Initial supercells should pose a threat for
mainly large to very large hail (isolated 2+ inches in diameter),
before clustering and an increase in damaging wind potential occurs.
The tornado threat is less clear, as stronger low-level flow will
tend to remain focused farther north into the Midwest. Still,
sufficient low-level shear should exist this afternoon and evening
to support a threat for a few tornadoes with both supercells and
embedded within clusters.

...Midwest/Ohio Valley into Western Pennsylvania...
An MCV evident over eastern IL/western IN will continue to track
eastward into northern IN and eventually OH this afternoon and
evening. Ongoing thunderstorms associated with this MCV have
remained sub-severe through much of the morning. But, gradual
destabilization of the already moist low-level airmass downstream
should support some uptick in convective coverage and intensity
across the OH Valley by mid to late afternoon. Localized enhancement
to the west-southwesterly low-level winds should focus across parts
of northern OH and vicinity, where somewhat greater low-level shear
and tornado potential may exist. Strong deep-layer shear will easily
support organized convection, including the potential for supercells
with a threat for large hail, damaging winds, and perhaps a couple
of tornadoes. Additional thunderstorms may eventually develop
eastward from the mid MS Valley into IL/IN in association with
another MCV. Large hail, damaging winds, and a tornado or two may
also occur with this activity, if it develops.

..Gleason/Squitieri.. 04/15/2026

Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
1132 AM CDT Wed Apr 15 2026

Valid 151700Z - 161200Z

...Southern High Plains...
The eastern extent of the Elevated risk area has been trimmed back
slightly across western OK and the TX Rolling Plains. This is to
account for recently observed precipitation, marginal fuels, and
lighter surface winds during peak heating. In the lee of the
southern Rockies, poor overnight humidity recoveries are expected to
further exacerbate the local fire environment. Morning observations
portray 30 mph wind gusts and less than 25 percent RH in gap flow
areas with clear skies overhead. As deeper mixing occurs this
afternoon, RH is expected to bottom out around 10 percent locally
atop very dry fuels.

...Eastern WY/NE Panhandle/southwestern SD...
Westerly winds of 10-20 mph combined with RH of 20-25 percent will
promote locally elevated fire weather conditions for a few hours
this afternoon in sporadic areas that did not see recent
precipitation. Increasing mid-level cloud cover this afternoon is
expected to maintain marginal RH values, precluding the introduction
of Elevated highlights. 

The rest of the forecast remains on track, see the previous
discussion for more information.

..Elizalde-Garcia/Williams.. 04/15/2026

.PREV DISCUSSION... /ISSUED 1252 AM CDT Wed Apr 15 2026/

...Synopsis...
The upper-level trough will depart the southern Plains through the
day today. A weak lee trough will develop in the High Plains. Dry
return flow will continue in the southern Appalachians/Mid-Atlantic.

...Southern High Plains...
Modest mid-level winds across the southern Rockies will promote a
weak lee trough to the east. Surface winds of 15 to locally 20 mph
are possible amid a dry airmass (10-20% RH by the afternoon).
Elevated fire weather is expected given continued lack of rainfall
and dry fuels.

...Southern Appalachians into the Mid-Atlantic...
Dry and breezy conditions are expected during the afternoon as
temperatures warm into the mid 80s to low 90s F. RH of 25-35% is
probable for most areas, but values closer to 20% may occur locally.
Very dry fuels will support an elevated fire weather threat.

...Please see www.spc.noaa.gov/fire for graphic product...