SPC May 18, 2025 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0753 AM CDT Sun May 18 2025

Valid 181300Z - 191200Z

...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FOR SOUTHWEST
AND CENTRAL KANSAS INTO FAR NORTHWEST OKLAHOMA...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE
LOWER MISSISSIPPI VALLEY AND PARTS OF ALABAMA AND GEORGIA...

...SUMMARY...
Severe thunderstorms capable of all severe hazards are expected
later today across portions of the central and southern Plains. 
Several strong to intense tornadoes are possible.

...Central/Southern Plains...
Water-vapor imagery this morning shows a potent mid- to upper-level
trough over the Four Corners with a couple of downstream MCVs moving
east-southeast over AR and AL this morning.  A 500-mb speed max (60+
kt) is forecast to move through the base of this trough and eject
into the TX Panhandle/southwestern KS late this afternoon and
evening as the trough evolves into a negative tilt.  Rich low-level
moisture was observed at both surface sites and raob sites over the
southern Great Plains this morning.  Increasing moisture at 850 mb
was sampled beneath very steep 700-500 mb lapse rates on the Dodge
City raob.  

Southerly low-level flow is forecast to increase today across the
southern-central Great Plains as a composite frontal zone/outflow
over OK advances northward as a warm front into southern KS later
this afternoon.  Models show surface dewpoints rising into the 60s
across western KS with lower 70s farther south near the OK/KS border
and locales southward along/east of the dryline later this
afternoon.  Model guidance shows the strongest signal for scattered
storm development from parts of the central High Plains southeast
into southwest KS later this afternoon/evening as large-scale ascent
overspreads the destabilizing moist/unstable sector.  

Confidence is greatest in scattered supercells developing across
western/southwest KS later this afternoon as CINH erodes amidst
strong boundary layer heating.  A very to extremely unstable airmass
with long hodographs will rapidly promote supercell evolution with
any sustained/maturing updraft.  The LLJ is forecast to intensify
during the late afternoon/evening and enlarge the hodographs,
supporting tornado potential.  The combination of shear/buoyancy
will become very favorable for intense supercells capable of large
to giant hail (potentially 3-4+ inches in diameter) and strong to
intense tornadoes, especially from western OK northward into
south-central and western KS.  It is within a focused corridor on
the northern periphery of the richer moisture over parts of
south-central and southwest KS where a potent environment and
expected higher storm coverage prompted an upgrade to Moderate Risk.
Lower storm coverage is expected farther south across western OK,
but a similar environment will exist.  

Similar to previous forecast thinking, it remains uncertain how much
convection will develop along the dry line south of I40, especially
across TX. However, minimal inhibition warrants concern, as any
updrafts that evolve within a strongly sheared and buoyant air mass
should produce at least large hail.

Farther north, left-exit region of mid-level jet will encourage a
secondary corridor of strong/severe thunderstorms from northeast CO
into western NE. Surface low is expected to track across eastern CO
into western KS which will maintain a moist/upslope component to
boundary layer across this portion of the High Plains.  Strong
low-level warm advection will assist organized convection as it
spreads northeast during the overnight hours.

...AR eastward into GA...
A pair of MCVs this morning are aiding in a couple of severe
thunderstorm clusters being sustained along a residual frontal zone
that serves as the northern periphery of richer low-level moisture. 
Short-term model guidance has varied considerably in the depiction
of these MCS.  Nonetheless, the 11 UTC BMX raob showed an very
unstable airmass (3300 J/kg MUCAPE) and 65-kt 500 mb flow.  Current
thinking is both MCSs will pose a risk for mainly damaging gusts
through this morning.

..Smith/Marsh.. 05/18/2025

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