SPC May 17, 2025 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0748 AM CDT Sat May 17 2025

Valid 171300Z - 181200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS NORTH
TEXAS AND SOUTHERN OKLAHOMA...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
UPSTATE NEW YORK AND WESTERN NEW ENGLAND...

...SUMMARY...
Severe thunderstorms producing large to very large hail, damaging
gusts and a couple of tornadoes are expected across the southern
Plains. Additional severe storms are possible across the Northeast.

...Southern Plains Region...
Water vapor imagery depicts a pronounced southern stream upper-level
trough over the Baja Peninsula this morning, with evidence of a lead
impulse approaching southwest TX. This leading impulse will
contribute to ascent in the vicinity of a sharpening dryline across
Western North Texas/Oklahoma by early afternoon. To the east of the
dryline, extreme instability (MLCAPE in excess of 4000 J/kg) is
expected to develop given the moist low-level air mass and
relatively cool mid-level thermal profiles. With negligible CINH by
early/mid afternoon, thunderstorms are expected to develop along the
dryline and move east/northeast into North Texas and southern
Oklahoma. Supercells will be the dominant mode initially, with a
risk for very large hail (in excess of 3.5 inches), and damaging
gusts. Although low-level shear is not especially strong, some
tornado risk will exist given the magnitude of instability and
potential for storm-scale interactions. Eventual upscale growth into
a severe MCS is expected as storms continue to move across North
TX/southern OK this evening. Severe wind probabilities have been
increased across the Enhanced Risk area for the expectation of a
more concentrated corridor of damaging wind potential.

Across central/northwest OK, a narrowing plume of instability will
be present east of the dryline and south of an east-west oriented
frontal boundary.  Within this moist sector, strong to extreme
instability and around 50 kts of deep-layer shear will support at
least isolated supercell storm development this afternoon over
central OK. Very large hail (3 inches or greater) will be possible,
in addition to damaging gusts. Tornado risk will be dependent on
storm interactions. Thunderstorm development over northwest OK is
more uncertain, however should a storm develop a supercell mode will
be favored with all hazards possible. 

...Northeast...
Strong mid-level height falls will spread across much of the
northeastern U.S. today in response to the approaching Great Lakes
upper low. Large-scale ascent will increase with as the left-exit
region of the 500mb jet translates across PA. Scattered
thunderstorms, including supercells, are expected to develop
along/ahead of the synoptic cold front across upstate NY, with
subsequent movement expected into western New England. Multiple
rounds of thunderstorms are likely, with severe hail and winds as
the primary risks. A tornado or two cannot be ruled out with any
stronger and semi-discrete supercell. Please refer to Mesoscale
Discussion 836 for additional details on short-term expectations.

...Northern Utah Vicinity...
A Marginal Risk has been introduced across northern UT and vicinity
given expected higher concentration of storms within a deeply-mixed
boundary layer. Strong/severe gusts will be the primary severe risk.

...Lower Mississippi Valley/Southeast...
Thunderstorms continue from central MS into the western Carolinas at
13z, with occasional pulses of strong/severe cells. Isolated
stronger storms will remain possible as diurnal
heating/destabilization takes place in the presence of ample shear
for organized storms. However, with the line of convection oriented
generally parallel to the shear vector, any severe risk should be
isolated. Strong gusts will be the primary hazard.

..Bunting/Marsh.. 05/17/2025

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