SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0654 AM CST Fri Dec 08 2023
Valid 081300Z - 091200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
THE ARKLATEX REGION TO THE OZARKS...
...SUMMARY...
Isolated large hail is possible this evening and tonight from parts
of the Arklatex region to the Ozarks.
...Synopsis...
An eastward-moving, amplifying, mid/upper-level trough is expected
to shift into the central CONUS during the period, spreading an
extensive field of height falls and strengthening flow aloft across
much of the Plains States and Mississippi Valley. Within the
associated cyclonic flow, two main shortwave troughs will exert the
most influence on large-scale lift and low-level mass response:
1. A northern-stream perturbation, apparent in moisture-channel
imagery over the northern High Plains, forecast to move eastward and
evolve to a closed 500-mb cyclone over MN by 12Z tomorrow.
2. An elongated, initially negatively tilted trough from the
southern ID/northern NV region southeastward toward the Four
Corners. The southeastern part will break eastward/northeastward
across the south-central Rockies today, reaching the MKC area around
06Z, then accelerating northeastward into confluent flow fringing
the northern-stream shortwave trough. Meanwhile, the remainder
should dig southeastward, consolidate and amplify, reaching northern
NM and southern CO by 12Z.
At the surface, 11Z analysis showed a low over extreme northwestern
MN, with occluded/cold front arching across south-central IA and
south-central KS to a weak low over northwestern OK, then over
portions of the central/southern TX Panhandle and northeastern NM.
By 00Z, the main low should eject to northwestern ON, while the
southern one ripples northeastward along the trailing cold front to
southeastern KS. The front should extend from there southwestward
across south-central OK to northwest TX and east-central/
southeastern NM. By 12Z, the southern low should continue moving
northeastward along the front to the MKE vicinity, with front
trailing over east-central IL, southeastern MO, to near a line from
LIT-TXK-ACT-FST. An early-stage dryline was drawn from west-central
OK south-southwestward to near BPG, then southward into northern
Coahuila. The dryline should shift eastward and become better-
defined through the day, and by 00Z, extend from a frontal
intersection over northeastern OK across north-central TX to the DRT
area. Overnight, the front will overtake a then-quasistationary
dryline from north-south across OK.
....Ozarks to Arklatex...
Widely scattered to scattered thunderstorms are possible tonight
from western MO southward into parts of eastern OK/western AR,
becoming more isolated toward the Arklatex region. A few cells may
organize enough to produce severe hail, particularly where more
discrete convection is at least temporarily possible from the Ozarks
southward. Strong gusts also may penetrate to the surface from more
linear, frontal convection over MO, but boundary-layer instability
in that regime currently appears too limited to warrant an organized
severe threat.
Thunderstorms may develop over western parts of the outlook area
(eastern OK and perhaps northeast TX) between 00-03Z, then move
eastward to northeastward into portions of AR and the Arklatex
region, offering occasional hail near severe limits. In general,
deep shear will increase with time area wide, while still being
stronger with northward extent. Meanwhile, moisture and buoyancy
should increase southward. The environment over southern parts of
the outlook area -- around the Red River and Arklatex east of the
front and dryline -- will become increasingly moist throughout the
period, with 60s F surface dewpoints becoming common into parts of
eastern OK and western AR. This will support technically surface-
based effective-inflow parcels in forecast soundings overnight.
However, a nocturnally cooled (temperatures also in the 60s),
somewhat diabatically stabilized near-surface layer should be
present.
Frontal convection may be messy in mode, and lift sufficient to
force surface-based storms in the warm sector appears nebulous at
best. As such, a seemingly favorable parameter space (e.g., MLCAPE
around 1000-1500 J/kg collocated with 300-400 J/kg effective SRH
under the LLJ, and 250-300 J/kg of 1/2-km SRH), may not be fully
realized. For now, the tornado potential (dependent on sustained,
surface-based storm) is not zero, but still looks too conditional
and low-end to introduce an unconditional area for that hazard. The
bulk of convection should be at least slightly elevated, with
similar MUCAPE values and around 40-45 kt effective-shear
magnitudes.
..Edwards/Gleason.. 12/08/2023
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