RSS Mesoscale Discussions from Storm Prediction Center
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1021 AM CST Thu Nov 13 2025
Valid 131630Z - 141200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Minimal thunderstorm chances are evident today over parts of central
California. Severe weather is not forecast.
...Synopsis...
A deep upper-level trough will gradually move eastward over the
Pacific Coast region today. An embedded deep-layer cyclone is
forecast to gradually weaken as it moves east-southeastward off of
the northern CA coast. The low/midlevel moisture plume associated
with this system will continue to overspread parts of CA through the
period. Weak buoyancy (MUCAPE of 100-200 J/kg) within this moist
plume will support isolated/sporadic lightning potential with
embedded convective elements, especially where orographic lift is
maximized in the vicinity of the Sierra Nevada. While low-level
flow/shear will remain rather strong into this afternoon, negligible
surface-based instability should limit potential for convectively
augmented gusts.
Elsewhere, cold midlevel temperatures will support weak convection
over parts of the Northeast, though the greatest relative lightning
potential is expected to remain offshore of southern New England.
Some elevated buoyancy may develop late tonight across parts of
MO/IL, along the northern periphery of modest 850 mb moisture
return, but there is minimal signal for development of deep
convection in this region prior to the end of the period.
..Dean.. 11/13/2025
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SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1034 AM CST Thu Nov 13 2025
Valid 141200Z - 151200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
The risk for thunderstorms appears negligible across the U.S. Friday
through Friday night.
...Discussion...
A more prominent blocking regime centered across the northern
Atlantic continues to evolve. Models indicate that this will
include the development of a broad cyclonic regime centered across
the Canadian Maritimes by early Friday, which will persist through
the remainder of the period. Some amplification of large-scale
troughing extending southward offshore of the remainder of the
Atlantic Seaboard is forecast, downstream of a significant mid-level
trough and embedded cyclone migrating northeast and east of the
Canadian Maritimes, on the leading edge of a more progressive
regime.
Upstream, broad short wave ridging appears likely to shift inland of
the British Columbia coast, across and east of the Canadian/northern
U.S. Rockies, to the north of an increasingly cut-off low offshore
of the central and southern California coast.
Models continue to indicate that the modifying mid-level cold core
of the eastern Pacific low (including coldest 500 mb temperatures
warming above -24 C) will generally remain offshore through this
period. While it may tend to pivot away from coastal areas
near/south of San Francisco Bay, and slowly toward southern
California coastal areas Friday night, the leading edge of stronger
forcing for ascent/cooling aloft supportive of low-topped
thunderstorm development appears likely to remain well west of the
southern California coastal waters through 12Z Saturday.
Potential for thunderstorm development Friday through Friday night
appears largely confined to a plume of lower latitude eastern
Pacific moisture return, advecting ahead of the low into the
southern periphery of the stronger mid-latitude westerlies. Models
suggest that this may contribute to developing layers of weak
conditional instability rooted in the lower/mid-tropospheric, across
the southern California coast through portions of the southern
Sierra Nevada and Mojave Desert, Great Basin, northern Rockies, and
northern Great Plains. Weak convection becoming briefly capable of
producing a few lightning strikes may not be entirely out of the
question anywhere within this corridor. However, due to likely
sparse coverage and rather low predictability, probabilities for
thunderstorms still appear generally less than 10 percent.
..Kerr.. 11/13/2025
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SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0100 PM CST Thu Nov 13 2025
Valid 151200Z - 161200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE SATURDAY
AFTERNOON AND EVENING ACROSS PARTS OF EASTERN OHIO...WESTERN
PENNSYLVANIA AND NORTHERN WEST VIRGINIA...
...SUMMARY...
Showers and a few thunderstorms may be accompanied by strong wind
gusts across parts of the upper Ohio Valley late Saturday afternoon
and evening.
...Discussion...
Saturday into Saturday night, it appears that the more progressive
flow emanating from the northern mid-latitude Pacific will begin to
impinge on the blocking regime now evolving across parts of eastern
North America into the Atlantic. While an initially prominent
cyclone on the leading edge of this regime is forecast to undergo
considerable deformation and weakening, models continue to indicate
that a notable perturbation emerging from it will dig across the
upper through lower Great Lakes, accompanied by secondary surface
cyclogenesis.
Upstream, the westerlies may undergo notable amplification,
including digging mid/upper troughing offshore of the British
Columbia and northern Pacific coast and building ridging across and
east of the Canadian/northern U.S. Rockies. As this occurs, an
initially cut-off low offshore of the southern California/northern
Baja coast is forecast to accelerate into the Southwest late
Saturday through Saturday night.
...Upper Ohio Valley...
Within the warm sector of the developing surface low, NAM forecast
soundings indicate that modest low-level moisture return may become
supportive of the development of thermodynamic profiles
characterized by weak conditional and convective instability in the
lowest 5-6 km AGL. It appears that this environment could become at
least marginally conducive to boundary-layer based convection
capable of producing lightning by late Saturday afternoon, mainly
near the southern periphery of the colder mid-level air, across
parts of northeastern Ohio into the western slopes of the Allegheny
Mountains.
In the presence of strengthening lower/mid-tropospheric wind fields
(including 40-50+ kt west-northwesterly mean flow in the lowest 6 km
AGL), the development of a relatively compact band of stronger
showers and thunderstorms appears possible. This activity, perhaps
aided by latent cooling in downdrafts associated with melting small
hail, may contribute to the downward transfer of stronger winds to
the surface, before convection weakens while crossing the Allegheny
Mountains Saturday evening.
...Southwest...
Models suggest that a mid-level cold core, characterized by 500 mb
temperatures as cold as near or just below -20 C, will finally shift
inland late Saturday through Saturday night. These temperatures
appear on the relatively warm side compared to cool season
environments typically conducive to low-topped convection capable of
producing lighting across and inland of Pacific coastal areas.
However, it is possible that low-level moisture return emanating
from the lower-latitude eastern Pacific and Gulf of California may
compensate.
Otherwise, it might not be out of the question that preceding
elevated moisture return contributes to layers of weak conditional
instability minimally supportive of convection capable of producing
lightning across parts of the Mojave Desert/lower Colorado Valley
vicinity.
..Kerr.. 11/13/2025
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