SPC Jun 12, 2025 0100 UTC Day 1 Convective Outlook

SPC 0100Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0800 PM CDT Wed Jun 11 2025

Valid 120100Z - 121200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS EVENING
ACROSS PARTS OF NORTHEASTERN IOWA INTO ADJACENT SOUTHWESTERN
WISCONSIN AND NORTHWESTERN ILLINOIS...

...SUMMARY...
Thunderstorm activity may still increase across parts of central
Texas, toward the upper Texas coastal plain, tonight accompanied by
at least some risk for severe weather.  Otherwise, ongoing
thunderstorm development elsewhere is expected to generally wane by
mid to late evening.

...01Z Update...

...Midwest...
Convection with small cluster which has evolved along a stalled
frontal zone across northeastern Iowa remains strong.  However, it
appears that forcing associated with a supporting mid-level
perturbation is beginning to shift east of the Upper Midwest into
Great Lakes, where the environment along the frontal zone becomes
less unstable and will trend more stable with the loss of daytime
heating.  As this occurs, storms are expected to generally diminish
in intensity this evening across northeastern Iowa through southern
Wisconsin/northern Illinois.

...Northern Intermountain Region and Rockies...
Downstream of a weak mid-level trough progressing eastward into the
northern Rockies, stronger convection is now spreading in a swath
across south central Montana and northern Wyoming.  Instability is
weak due to limited low-level moisture, but steep
lower/mid-tropospheric lapse rates, including a modestly heated and
deeply mixed boundary layer, are contributing to the generation of
strong to severe gusts with the most vigorous storms.  This should
begin to wane as low-level lapse rates stabilize with the onset of
boundary-layer cooling.

...Texas...
Within slow moving, weak mid-level troughing, a digging
smaller-scale perturbation is supporting increasing thunderstorm
development  near/west of the I-35 corridor of central Texas.  In
the presence of  10-20 kt westerly to southwesterly deep-layer mean
flow, it appears that instability and large-scale forcing for ascent
will be sufficient to support a further increase in convection
through 04-06Z, which probably will tend to slowly advect across and
east of the I-35 corridor.  

It appears that low-level warm advection/convergence focused along a
remnant frontal zone near/north of the San Antonio/Austin area could
support an upscale growing cluster, perhaps aided by inflow of
seasonably moist air becoming characterized by CAPE in excess of
2000 J/kg.  This may be accompanied by at least some increase in
potential for strong to severe gusts associated with a developing
cold pool while spreading toward the upper Texas coast overnight. 
However, given the initial weakness of the ambient mean flow/shear
and lack of steeper lower/mid-tropospheric lapse rates, the severe
threat appears conditioned on strong convective augmentation of the
wind fields, which seems relatively low in probability.

..Kerr.. 06/12/2025

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