013
ACUS48 KWNS 120901
SWOD48
SPC AC 120859

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CDT Mon May 12 2025

Valid 151200Z - 201200Z

...DISCUSSION...
An active period of severe weather is anticipated through early next
week based on recent trends in long-range guidance. A transition to
a progressive upper-level regime is expected over the next seven
days as a series of upper waves traverse the CONUS with favorable
wavelengths for air mass/moisture recovery into central portions of
the CONUS. Although both the GFS and ECMWF (and their respective
ensemble families) show similar synoptic evolutions through the
extended period, predictability in any severe threat currently
appears greatest on D4/Thursday and D5/Friday.

...D4/Thursday...
The upper-level trough currently over the Pacific Northwest is
forecast to eject into the upper MS River Valley through the day
Thursday with an attendant surface low deepening across the upper MS
Valley. A Pacific front is forecast to push east into an expanding
warm sector that should span from the MS River into the upper Great
Lakes and OH River Valley. Strong mid-level flow orthogonal to the
front should generally promote discrete/semi-discrete convection by
late afternoon on the eastern fringe of a stout EML. The consistent
signal for QPF within the warm sector coincident with 50-60 knot
mid-level flow and the intensifying nature of the synoptic low
suggests that a widespread severe weather event is possible and may
expand further east than depicted in previous forecasts. Despite
these trends, regional discrepancies among guidance limit confidence
in where the more robust severe corridors will become established.
Notable factors limiting confidence are the potential for strong
capping across much of the OH Valley and a faster progression of the
surface low/front in recent GFS/GEFS solutions (which typically
exhibit a fast bias at this range).

...D5/Friday...
The Pacific front/outflow associated with D4/Thursday`s convection
is expected to stall across the lower OH Valley/mid-MS Valley before
gradually returning north as an effective warm front on Friday.
Ensemble guidance shows a reasonably strong signal for dewpoints in
the mid/upper 60s (potentially into the low 70s) along and south of
this boundary by peak heating. A mid-level impulse propagating over
the region should maintain elongated hodographs and provide
sufficient lift for thunderstorm development along the boundary.
This synoptic regime suggests that one or more organized
clusters/linear segments may propagate along the boundary and into
parts of the mid-MS Valley, lower OH Valley, and potentially into
the TN Valley. Given the thermodynamic and kinematic environment
forecast by ensemble guidance, such a cluster/line will likely pose
a severe threat. A 15% risk area has been introduced where the QPF
signal associated with this regime has been most consistent over
recent model runs, but further forecast refinements are expected.

..Moore.. 05/12/2025