SPC 2000Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0247 PM CDT Tue Apr 21 2026

Valid 212000Z - 221200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
THE OHIO VALLEY AND THE CALIFORNIA CENTRAL VALLEY...

...SUMMARY...
Isolated strong thunderstorms are possible in the California Central
Valley, capable of gusty winds and perhaps a tornado or two. Other
strong storms are possible over parts of the Great Lakes region.

...20Z Update...
The primary changes to the outlook were to extend Category
1/Marginal Risk probabilities in CA farther north into the
Sacramento Valley, and expand severe probabilities in the Great
Lakes area to include far southwestern Lower MI. In CA, MRMS mosaic
radar imagery shows convection deepening farther north into the
Sacramento Valley, and where 19Z mesoanalysis shows well over 100
J/kg 0-3 km CAPE in place with a focused corridor of low-level
vertically oriented vorticity. As such, a low-topped supercell could
develop this afternoon or evening, which may be capable of producing
hail/wind and perhaps a brief tornado. Thunderstorms, with a history
of producing marginally severe hail over extreme southeastern WI,
are currently traversing far southern Lake MI, and have been slow to
diminish. A corridor of MUCAPE is developing over far southwestern
Lower MI as 8+ C/km mid-level lapse rates, coinciding with a
southwesterly WAA regime, overspreads the Great Lakes. Therefore,
Category 1/Marginal risk wind/hail probabilities were extended
northeastward into far southwestern Lower MI to account for
potential strong thunderstorms in this region.

..Squitieri.. 04/21/2026

.PREV DISCUSSION... /ISSUED 1051 AM CDT Tue Apr 21 2026/

...Central CA...
Morning water vapor loop shows a well-defined shortwave trough
approaching the coast of central CA.  An associated mid/upper level
jet will nose into CA, with forcing for ascent in the left-front
quadrant of the jet aiding in the development of afternoon/evening
thunderstorms over parts of the Central Valley.  Forecast soundings
show steep low and mid level lapse rates and sufficient CAPE for a
few robust updrafts.  Vertical shear will be strong enough for
supercell structures, including a risk of a tornado or two, small
hail, and gusty winds.

...Northern IN/IL...
A fast-moving shortwave trough currently over IA/MN will track
quickly southeastward into WI/IL/IN this afternoon.  Visible
satellite and radar imagery show a line of high-based thunderstorms
developing ahead of the trough over southern WI.  As these storms
track into northern IL/IN, continued heating/weak destabilization
will increase the risk of gusty/locally damaging wind gusts and
small hail in the strongest cores this afternoon.

SPC Day 2 Fire Weather Outlook

Day 2 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
0243 PM CDT Tue Apr 21 2026

Valid 221200Z - 231200Z

...CRITICAL FIRE WEATHER AREA FOR EAST-CENTRAL NEW MEXICO INTO THE
NORTHERN HIGH PLAINS...

...Portions of the High Plains...
An expansive fire weather threat is expected to impact a large
portion of the High Plains into areas west of the Rockies and
Southwest. Broad west-southwesterly flow aloft and a strengthening
associated mid-level shortwave will result in a moderately strong
lee surface trough and a deepening surface low over eastern MT.
Southeast of the surface low, large scale ascent is expected to
promote high based convection along an emerging dryline. Forecast
soundings depict a prominent dry sub-cloud layer and precipitable
water between 0.5"-0.75", allowing for some threat of dry
thunderstorms to evolve where fuels remain receptive. IsoDryT
highlights have been introduced from southwestern SD into far
northwest KS to account for this threat. 

A strong upper jet will push into the Rocky Mountain region on
Wednesday supportive of downslope enhanced winds as lee surface
pressure gradients tighten. Critical highlights were expanded west
to encompass the San Luis Valley where single digit RH and strong
gusts of up to 45 mph are likely. Critical conditions are expected
to last up to 12 hours for portions of central-eastern CO and
southeastern WY. Locally extremely critical conditions are possible
where mountain wave influence could enhance downslope drying to
single digits and sustained winds up to 30 mph with terrain-driven
gusts up to 70 mph. Elevated highlights were expanded into eastern
MT through central MN where 20-30 percent RH and 15-20 mph
west-southerly winds will overlap drying fuels. Additionally,
elevated highlights were expanded farther west to cover eastern UT,
western CO, and portions of central WY for westerly sustained winds
up to 30 mph amid 10-15 percent RH and drying fuels. A cold front
will push through WY during the afternoon and evening, and likely
through much of CO and the central High Plains overnight. Cooler
temperatures, higher RH, and scattered showers are likely behind the
front in WY into northern CO, west of the Divide/Front Range.
However, strong winds will continue across southeast WY into western
NE and northeast CO overnight with RH increasing to 30-50 percent
after midnight. These conditions will likely persist through nearly
the entire overnight period, further exacerbating the fire
environment.

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

..Elizalde-Garcia.. 04/21/2026

.PREV DISCUSSION... /ISSUED 0100 AM CDT Tue Apr 21 2026/

...Synopsis...
A pronounced, eastward progressing upper-level trough, accompanying
55-65 knot mid-level jet and deepening lee surface troughing over
the High Plains will promote a broad fire weather threat across the
central/southern High Plains and portions of the Southwest
Wednesday. A surface trough and associated frontal boundary will
traverse the Southern Great Lakes and Mid Atlantic regions.
Increased southwesterly flow south of the trough will contribute to
fire weather concerns across the Mid Atlantic.

...Southwest into the Southern and North-Central Plains...
A lee surface low will deepen across the northern High Plains as the
robust mid-level trough advances into Intermountain West, with the
associated mid-level jet moving over the Upper CO River Basin. An
expansive fire weather concern will emerge across portions of the
Southwest into the central and southern Plains as southwest winds
accelerate beginning late Wednesday morning. Downslope enhanced
southwest winds of 20-25 mph with higher gusts aligning with
critically low relative humidity below 10% should be most pronounced
across eastern WY/CO and into portions of northeastern NM and
adjacent TX/OK Panhandle areas, where Critical Highlights were
introduced. Locally extremely critical fire weather conditions
including southwest winds of 30-35 mph and single digit RH are
possible in favored terrain gaps along and east of the Sangre De
Cristo Mountains and the CO Front Range where fuels remain receptive
to wildfire spread.

...Piedmont and portions of Mid Atlantic...
Dry and breezy conditions ahead of an approaching trough and
associated cold front will bring a fire weather threat to portions
of the Carolinas and southern VA Wednesday. Persistent northwest
flow aloft and tighter surface pressure gradients will support
increasing winds and downslope drying in the lee of the
Appalachians. West to southwest winds of 10-20 mph along with RH 
falling to 20-30% during peak heating will align with a receptive
fuelscape to promote several hours of elevated fire weather
conditions. Elevated Highlights were expanded slightly northward and
eastward based on latest forecast guidance.

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

SPC 1930Z Day 3 Outlook

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0237 PM CDT Tue Apr 21 2026

Valid 231200Z - 241200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PORTIONS OF THE
MID-MISSOURI VALLEY VICINITY INTO SOUTHERN KANSAS AND NORTHERN
OKLAHOMA...

...SUMMARY...
Severe thunderstorms will be possible from northern Oklahoma into
southern Minnesota on Thursday. Large hail to very large hail,
damaging winds, and a few tornadoes are possible.

...Synopsis...
Two shortwave troughs within a larger-scale trough over much of the
Rockies will pivot northeast on Thursday. The initial shortwave will
impact parts of the central Plains and mid-Missouri Valley. A
second, compact shortwave will pivot into parts of Oklahoma and
Kansas. At the surface, moisture return will continue ahead of a
Pacific cold front in the central Plains. A weak surface low is
expected to develop along the Oklahoma/Kansas border and track
eastward. Attendant to this low, a dryline will drape southward into
the Permian Basin.

...Central and southern Kansas...Oklahoma...
With mid-level ascent arriving mid/late afternoon, storms are likely
to initiate along the cold front as well as near the triple point
associated with the weak surface low along the KS/OK border.
Supercells are most likely near the triple point and could persist
so long as storm interactions remain minimal. 40-45 kts of shear and
2000-3000 J/kg MLCAPE will promote storms capable of all hazards,
including tornadoes and very-large hail. A strong low-level jet will
develop ahead of this activity during the evening. The tornado
threat could increase for storms that can remain discrete.

In Oklahoma, if and how many storms develop remains uncertain along
the dryline. Northern portions of Oklahoma are more likely to have
severe storms given the proximity to the surface low. A similar
environment will exist east of the dryline as does farther north
into southern Kansas. There is a conditional threat for all severe
hazards.

...Mid-Missouri Valley...
Storms are expected to develop along the cold front potentially as
early as mid afternoon. However, capping appears strong enough in
forecast soundings that initiation could delay until late afternoon.
Steep mid-level lapse rates will be in place along and ahead of the
front. Deep-layer shear will be 30-40 kts, but generally parallel to
the front. Initial storms could be supercellular and produce large
to very-large hail early in the convective cycle. Upscale growth
appears likely to occur rather quickly. Damaging/severe winds would
become the primary risk at that point. Tornadoes are also possible
given the low-level shear, both with initial supercells and perhaps
with QLCS circulations.

..Wendt.. 04/21/2026

SPC 1730Z Day 2 Outlook

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1224 PM CDT Tue Apr 21 2026

Valid 221200Z - 231200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE
HIGH PLAINS...

...SUMMARY...
Severe thunderstorms capable of hail and gusty winds may develop
during the late afternoon and evening on Wednesday across portions
of the High Plains.

...Synopsis...
A broad trough within parts of the Northwest and Great Basin will
progress eastward through the day Wednesday. The mid-level jet will
round the base of this trough and impact the northern High Plains
during the evening overnight. A secondary mid-level jet will dig
into the Southwest by early Thursday morning. The upper-level ridge
across the Plains will begin to break down and shift eastward. At
the surface, a deep surface low will track along the Montana/Canada
border. Strengthening flow across the Rockies will promote a
moderately strong lee trough. Surface moisture will continue to
advect north and west during the period. Richer moisture will
generally remain within the southern Plains and adjacent High Plains
with less certain moisture quality farther north.

...Western Nebraska...western South Dakota...
With greater large-scale ascent and closer proximity to the surface
low, confidence in storm development is higher in these areas. The
main question will be the degree of moisture return that can occur
through the day. Model guidance still varies widely in this regard.
Dewpoints near 50 F are possible into southwest Nebraska, but this
may occur towards 00Z or later. Farther north, dewpoints in the 40s
F may be the ceiling for late afternoon/early evening. A probable
scenario is that high-based convection develops within the terrain
of eastern Wyoming/western South Dakota and within the surface
trough. Some intensification is possible as this activity encounters
greater surface moisture to the east. Severe wind gusts will be the
main hazard given the steep low-level lapse rates and inverted-v
thermodynamic profiles. Linear structures would be favored in South
Dakota given the deep-layer flow orientation. A supercell or two
could occur in western Nebraska, should storms form.

...Southern High Plains into Western Kansas...
With the synoptic trough lagging to the west, mid-level height falls
will be very weak during the afternoon. The dryline/surface trough
will be the focus for storm development. Temperatures nearing 90 F
behind the dryline appear sufficient for an isolated storm or two to
develop. That said, some guidance does not develop any convection.
Deep-layer shear will be roughly perpendicular to the surface trough
and mid-level lapse rates will be steep. Storms that can develop
will be supercellular. Large hail would be the main concern with
this activity.

...Eastern Montana...
High-based convection is possible in association with the deepening
surface low. Dewpoints will not likely reach 40 F. Gusty outflow
winds are possible, but potential for severe gusts is low.

..Wendt.. 04/21/2026