963 
ACUS02 KWNS 121700
SWODY2
SPC AC 121658

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1158 AM CDT Sat Sep 12 2026

Valid 131200Z - 141200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE OHIO
VALLEY TO THE NORTHEAST...

...SUMMARY...
Scattered strong storms accompanied by small to marginally severe
hail and potential for locally damaging wind gusts may impact parts
of the Northeast through upper Ohio Valley Sunday afternoon and
evening.

...Ohio Valley to the Northeast...
A mid-level shortwave trough will amplify as it moves from the Upper
Midwest to the eastern Great Lakes on Sunday. A primary surface low
will move across Quebec with a cold front extending into the eastern
Great Lakes. In addition, a lee trough will develop east of the
Appalachians with weak surface low development along the coast.

A large area of showers and embedded thunderstorms will likely be
ongoing at the beginning of the period across the Mid-Atlantic to
the Northeast. West of this activity, modest heating and mid 60s
dewpoints will support weak to potentially moderate instability.
This instability, combined with moderate to strong deep-layer shear
will support the potential for strong to severe storms. However,
storm coverage remains uncertain. A warm nose around 2km should
limit storm development away from the front. Even along the front,
storm coverage/intensity remains uncertain. Convergence will not be
that strong as the surface low-develops along the coast. Therefore,
a conditional severe weather environment remains from the Ohio
Valley to the Northeast, but concerns with storm coverage preclude
anything more than a Marginal Risk at this time. 

...Central High Plains...
Lee troughing will strengthen across the central Plains Sunday
afternoon. As this occurs, upslope flow will strengthen across
eastern Wyoming and vicinity. A cluster of storms will likely
develop during the evening and move across South Dakota during the
overnight period. Marginal instability will likely preclude any
severe weather potential with this activity. 

...North-central Montana...
A mid-level jet streak will eject northeast from the base of a
mid-level trough across the Northwest and overspread western
Montana. Showers and a few thunderstorms will develop across western
Montana during the afternoon and evening amid modest surface
heating. Strong flow above 3km may occasionally mix to the surface
with some gusty winds. If greater heating/instability can develop,
an isolated severe wind threat may be possible with the strongest
storms.

..Bentley.. 09/12/2026

$$


File: /home/ldm/var/data/BY_SOURCE/KWNS/ACUS02/20260912T1700.txt



823 
ACUS02 KWNS 120510
SWODY2
SPC AC 120509

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1209 AM CDT Sat Sep 12 2026

Valid 131200Z - 141200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SUNDAY AFTERNOON
AND EVENING IN A CORRIDOR FROM WESTERN NEW ENGLAND THROUGH THE UPPER
OHIO VALLEY...

...SUMMARY...
Scattered strong storms accompanied by small to marginally severe
hail and potential for locally damaging wind gusts may impact parts
of the Northeast through upper Ohio Valley Sunday afternoon and
evening.

...Discussion...
Latest model output suggests that the initially notable mid-level
low inland of the Pacific Northwest coast by 12Z Sunday may be
slower to devolve into an open short wave trough.  However, it still
is forecast to remain progressive, slowly accelerating northeastward
across the northern U.S. Rockies, in advance of a short wave impulse
digging toward the northwestern Canadian Prairies.  Within the
downstream westerlies, models indicate that short wave ridging will
build across much of the northern U.S. Great Plains through Upper
Midwest, and adjacent portions of the southeastern Canadian Prairies
through northwestern Ontario, while downstream troughing digs across
Quebec and the lower Great Lakes region into Northeast.

It appears that the primary surface cyclone associated with eastern
troughing may migrate from northern Quebec into the Labrador Sea by
late Sunday night.  However, another surface low may begin to
form/consolidate near/northeast of coastal northern New England,
with a trailing cold advancing southeast of the lower Great Lakes
region into the northern Atlantic Seaboard through Allegheny Plateau
by the end of the period.  Westward through the Ohio and middle
Mississippi Valleys into the central Great Plains, it appears that
this front may stall south of the stronger westerlies, with a cool
surface high maintaining influence across much of the northern into
central Great Plains until it centers shifts east of the upper
Mississippi Valley late Sunday night.

...Parts of western New England into the Ohio Valley...
In the wake of a sheared mid-level perturbation shifting across and
east of the northern and middle Atlantic Seaboard during the day,
low-level convergence and destabilization ahead of the main cold
front advancing to the southeast of the lower Great Lakes region
remains unclear.  However, both HREF and REFS calibrated
thunderstorm guidance suggest at least widely scattered thunderstorm
development is probable by or shortly after peak heating Sunday,
from the lee of the lower Great Lakes through the upper Ohio Valley.
It is possible that this may coincide with sufficient strengthening
of westerly flow in the 700-500 mb layer to support modestly
organizing thunderstorm activity with potential to produce
marginally severe hail and localized damaging wind gusts, before
weakening Sunday evening.

...North central Great Plains/Middle Missouri Valley vicinity...
Latest model output continues to exhibit substantive spread
concerning convective potential across the region through this
period.  It now appears probable that at least a shallow relatively
cool/stable boundary layer will remain entrenched as far south and
west as Kansas into the northern high plains, beneath warming
elevated mixed-layer air advecting north-northeast of the higher
terrain.  Forcing for ascent downstream of the approaching mid-level
low/trough may support increasing thunderstorm development across
the Dakotas Sunday night.  However, based on forecast soundings,
this may be rooted within/above the elevated mixed-layer, with weak
CAPE limiting potential for severe hail.

..Kerr.. 09/12/2026

$$


File: /home/ldm/var/data/BY_SOURCE/KWNS/ACUS02/20260912T0510.txt