Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0221 AM CDT Mon May 12 2025

Valid 141200Z - 151200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS PARTS OF THE
CENTRAL AND NORTHERN PLAINS...

...SUMMARY...
Isolated severe thunderstorms are possible across parts of the
central to northern Plains Wednesday afternoon and evening.

...Synopsis...
A progressive upper trough is forecast to pivot from the
Intermountain West into the northern Plains through the day
Wednesday. Ahead of this wave, an elongated surface trough draped
across the Plains will undergo consolidation as a surface cyclone
begins to organize over the Dakotas through the forecast period. The
arrival of a cold front coincident with the ejection of the upper
trough will provide an impetus for thunderstorm development across
the central to northern Plains during the afternoon and evening
hours. Further east, a weakening upper wave over the Mid-Atlantic
will continue to slowly lift to the northeast. A combination of cold
temperatures aloft, moist low-level conditions, and modest
broad-scale ascent will promote widespread showers and weak
thunderstorms across the upper OH River Valley and Mid-Atlantic
region. 

...Central/Northern Plains...
A somewhat expansive warm sector will become established across much
of the Plains through the day Wednesday; however, the eastward
advection of a strong EML will hinder convective development for
much of the southern and central Plains. Although moisture return
into the northern Plains will be somewhat modest compared to
locations further south (dewpoints only reaching the mid to upper
50s), strong deep-layer ascent ahead of the approaching wave and
within the left-exit region of the attendant mid-level jet will
sufficiently erode residual capping by late afternoon to promote
thunderstorm initiation along the cold front within an unstable air
mass. The favorable thermodynamic and kinematic environment should
promote a few strong/severe storms capable of severe hail/wind,
though deep-layer shear vectors and initial storm motions largely
parallel to the front will promote quick upscale growth into one or
more convective clusters/line segments that may limit the overall
duration and coverage of the severe threat. A more prolonged, but
isolated, severe threat may materialize late evening into the
overnight hours within the MO River Valley as isentropic ascent at
the terminus of the nocturnal jet increases and promotes additional
thunderstorm development - though model consensus regarding this
potential is limited at this range.

..Moore.. 05/12/2025

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.

Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
0152 AM CDT Mon May 12 2025

Valid 121200Z - 131200Z

...CRITICAL FIRE WEATHER AREA FOR MUCH OF THE NORTHERN PLAINS AND
UPPER MIDWEST...

...Synopsis...
As the blocking within the upper-air pattern begins to breakdown a
trough will deepens over the western US. Strong mid-level flow will
gradually move into the Plains, as upper ridging moves eastward.
Strong lee troughing/cyclogenesis will support gusty south/westerly
winds over the High Plains. Fire-weather conditions are expected
across the Northern Great Plains and Southwest this afternoon and
evening.

...Northern Plains and Midwest...
Another day of strong southerly winds are likely across the northern
Plains and Midwest as ascent from the western US trough overspreads
the region. A lee cyclone will support southerly gusts of 20-30 mph
over a A broad area amid fuels with ERC values above the 97th
percentile. While afternoon RH minimums may not be as low as prior
days, record-setting temperatures in the lower to upper 90s are
again expected across the region supporting dry surface conditions
with RH below 30%. This will support widespread critical
fire-weather concerns given the state of drought and recent fire
activity.

...Southwest...
As the western US trough begins to eject, strong westerly flow aloft
will overspread parts of the Southwest from southern AZ into NM.
Downslope winds of 15-25 mph along with low RH below 15% will
support several hours of elevated to locally critical fire-weather
conditions within dry fuels, that have supported recent fire
activity.

..Lyons.. 05/12/2025

...Please see www.spc.noaa.gov/fire for graphic product...