SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0252 PM CDT Sun Jun 15 2025
Valid 152000Z - 161200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS LATER THIS
AFTERNOON INTO EARLY TONIGHT FROM CENTRAL/EASTERN MONTANA INTO
ADJACENT AREAS OF NORTH DAKOTA...SOUTH DAKOTA AND WYOMING...
...SUMMARY...
Scattered severe thunderstorms capable of producing large to very
large hail and swaths of severe/damaging gusts (some 75+ mph) are
likely across portions of central/eastern Montana into northeast
Wyoming and the western Dakotas this afternoon through tonight.
Additional strong to severe thunderstorms may occur across the
central/southern Plains, and over parts of Virginia and North
Carolina.
...20z Update...
5% hail/wind risk probabilities were reduced across portions of
central TX in the wake of a decaying MCS. Surface observations over
the past 1-2 hours have largely been sampling 30-55 mph winds with
the convective band with further weakening expected as it becomes
increasingly displaced from stronger mid-level flow. However, a few
strong/severe storms remain possible as the MCS collides with a
northward-propagating sea breeze boundary across eastern TX this
afternoon and migrates into a very buoyant (3000-3500 J/kg MLCAPE)
air mass in place across south-central TX.
A slight expansion of 2% tornado probabilities was made across
south-central SD where shallow cumulus is beginning to develop
within a diffuse warm frontal zone where temperatures are quickly
warming into the upper 80s and low 90s. A few recent CAM solutions
(most notably the RRFS) suggest a supercell or two may develop
within this weakly forced regime between 22-02 UTC. If this occurs,
the environment will support organized supercells with some tornado
risk (in addition to the potential for large hail/severe wind).
Given the recent observed trends, and the HRRR's tendency to
struggle to initiate convection in such weakly forced regimes, some
expansion of tornado risk probabilities appears warranted.
Elsewhere, the forecast remains on track as outlined in the previous
discussion (below). See MCD #1302 for additional short-term details
pertaining to the Enhanced risk across MT.
..Moore.. 06/15/2025
.PREV DISCUSSION... /ISSUED 1128 AM CDT Sun Jun 15 2025/
...MT to SD/NE through tonight...
Moderate buoyancy is expected again this afternoon along and south
of a an outflow-reinforced baroclinic zone, in advance of a midlevel
shortwave trough (now over WA/OR) that will crest the ridge over MT
this evening. Scattered thunderstorm development is expected in the
zone of ascent along the baroclinic zone and in advance of the
midlevel trough, in concert with the diurnal heating cycle in cloud
breaks. MLCAPE of 2000-3000 J/kg, steep midlevel lapse rates and
long hodographs will favor supercells with very large hail (2-3
inches in diameter). Clustering of storms through the evening will
contribute to an increasing threat for severe outflow winds of 60-80
mph as convection spreads eastward toward the SD/ND/MT border region
through tonight.
Farther south into the High Plains, the scenario will be similar to
the previous two days, with a few storm clusters expected to form
east of the higher terrain and spread eastward through late evening.
Buoyancy/vertical shear will be sufficient for a couple of
supercells with some hail threat, though relatively deep mixing
supports upscale growth on outflow interactions, with an attendant
threat for severe outflow gusts.
...Southeast SD/northwest IA/southwest MN this afternoon/evening...
An MCV from overnight convection will continue to move
east-southeastward across southeast SD and northwest IA/southwest MN
through this evening. Morning convection across northwest IA has
weakened, but residual clouds linger. Some flow enhancement in the
low-midlevels on the south side of the MCV, in combination with
diurnal destabilization in cloud breaks/steep midlevel lapse rates,
could support a cluster of storms with some hail/wind threat later
this afternoon/evening. Will re-evaluate this corridor this
afternoon, but will maintain MRGL risk given lingering clouds and
some uncertainty regarding the magnitude of destabilization.
...NW/central TX today...
Merged cold pools with overnight convection in OK continue to spread
southward across western north TX, with a history of occasional
measured gusts near 60 mph. Daytime heating/destabilization ahead
of the cold pool will result in sufficient destabilization for
storms to continue to develop southward with the cold pool.
However, vertical shear is weakening with time with the loss of the
nocturnal low-level jet, so convection organization is expected to
slowly diminish over time. Still, the thermodynamic environment and
the established cold pool (per surface observations and KDYX radar
data) will support the continued potential for occasional
strong-severe outflow gusts toward central TX/parts of the Edwards
Plateau through the afternoon.
...Mid-Atlantic this afternoon/evening...
A front, reinforced by differential heating across southern VA,
appears to be mixing slowly northward and could serve as a focus for
thunderstorm development this afternoon. Weak enhancement to
low-level shear/hodograph curvature along the boundary could support
weakly rotating storms with the potential to produce a brief tornado
or two. Otherwise, the main concern will be isolated wind damage
with largely sub-severe winds where low-level lapse rates steepen
this afternoon along and south of the front.
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