SPC has added a ton of language to the outlooks . day 1 includes a hatched tornado risk. day 2 has some limiting factors but could be upgraded depending on evolution
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0654 AM CST Fri Nov 30 2018
Valid 301300Z - 011200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS CENTERED OVER
THE ARKLATEX REGION...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
ENHANCED RISK AND SEPARATELY OVER THE LOWER MISSISSIPPI DELTA
REGION...
...SUMMARY...
Severe thunderstorms are forecast from parts of the southern Plains
to the lower Mississippi Valley this afternoon into tonight, with a
risk for tornadoes, damaging gusts and occasional hail.
...Synopsis...
The mid/upper-level pattern this period will be dominated by a
southern-stream wave train, featuring a strong shortwave trough now
located over portions of AZ and Sonora. This trough is expected to
move eastward across NM and Chihuahua today, reaching the eastern
border of NM and the TX Big Bend by 00Z. A 500-mb low should
develop in the northern parts of the trough around 00Z, near the
OK/NM border, then follow a curving path across southwestern/central
KS through 12Z. By then, the accompanying trough should assume more
negative tilt across portions of eastern OK and north-central/
northeast TX, with cyclonic flow covering a vast area from northern
MX to the mid/lower Mississippi Valley. A 110-140-kt 250-mb jet
will flow through the trough, extending/expanding from far west TX
to east-central TX and the LA/AR border by the end of the period.
In response to those developments, surface lee troughing now located
over the central/southern High Plains will intensify. A cyclone
should develop through afternoon over the southeastern CO/extreme
northeastern NM area, occluding as it deepens, with warm front
across northern OK and the Ozarks. A "Pacific" cold front will move
out of the southern Rockies today and overtake the dryline from
north to south, southeast of the surface low. By 00Z the combined
boundary should arc from west-central/southwestern OK across
northwest/west-central TX. By 12Z, the boundary should reach
southeastern KS, extreme eastern OK, extreme northeast TX, to the
PSX/CRP areas.
Three distinct convective processes contribute to this outlook, the
first two overlapping spatially.
...Warm-advection conveyor, east TX to southeast OK and AR...
Thunderstorms are expected to develop gradually today into this
evening within a broad area of clouds and precip from east TX across
northern LA and AR into the Mid-South region. The severe threat
should ramp up from mid/late afternoon into tonight and spread
northward across the Arklatex, eastern OK and AR, with some storms
becoming supercells capable of tornadoes, damaging gusts and large
hail. A few strong/EF2+ tornadoes may occur given the favorable
parameter space forecast.
As supportive low-level warm advection and moisture transport
persist, low-level moist-layer quality, depth and theta-e each will
increase, while MLCINH weakens and temperatures aloft cool with the
approaching intense shortwave trough. This will steepen low/middle-
level lapse rates, leading to the development of MLCAPE of 500-1500
J/kg and very low LCLs. With this regime being in the eastern rim
of the warm sector, lapse rates will not be as large as in the
frontal process; however, very favorable low-level shear and
hodographs should develop beneath the strengthening evening LLJ,
with more sustained potential for at least semi-discrete supercells.
Effective SRH 250-400 J/kg should become common, with locally
higher values. The frontal arc will impinge on the western part of
this regime late tonight.
...Cold front/dryline, southern Plains eastward...
As the front overtakes the dryline and the combined boundary thrusts
eastward into favorable low-level moisture late afternoon and
especially this evening, at least a broken arc of convection is
expected to form over parts of central/eastern OK and north to
central TX. Strengthening of both convective-scale/low-level lift
and large-scale forcing aloft will support this development, while
deep-layer winds and shear strengthen. Early-stage convection may
be supercellular, with large hail and a few tornadoes possible.
Geometry of ambient flow, including backing with height in low/
middle levels, suggests mode could get messy where storms do form,
with limited time window for discrete cells. Regardless, this
activity will move into a setting of strengthening low-level shear,
moisture and lapse rates above the boundary layer, supporting a
continued tornado risk into tonight, perhaps from embedded
supercells or QLCS/leading-edge circulations.
...Gulf Coast, late in period...
Widely scattered to scattered thunderstorms should move onshore from
the Gulf overnight, posing an increasing risk for damaging gusts and
a few tornadoes as the supporting inflow layer becomes progressively
more surface-based and unstable. A wedge of marine air will spread
inland across portions of the central Gulf Coast from LA to AL and
perhaps the western FL Panhandle overnight, with dew points rising
through the 60s F, and a deepening moist layer with time. Although
weak midlevel lapse rates are expected to persist, boundary-layer
theta-e in the marine layer should offset that factor enough to
yield MLCAPE rising into the 500-800 J/kg range, with enlarged and
strongly curved low-level hodographs. Strengthening cyclonic flow
aloft and deep shear further will support supercell modes with this
convection, which may represent the northern part of a broad area of
supercell potential extending well southward over the open Gulf by
12Z.
.
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1151 PM CST Thu Nov 29 2018
Valid 011200Z - 021200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHEAST...
...SUMMARY...
A few severe storms will be possible on Saturday across parts of the
Southeast. Marginally severe storms could occur northward across the
Tennessee and lower Ohio Valleys into the mid Mississippi Valley.
...Southeast...
An upper-level low and an associated negatively tilted upper-level
trough will move northeastward into the mid Mississippi Valley on
Saturday. A strong surface low will move northeastward into the
lower Missouri Valley as a cold front advances eastward across the
southern Plains. A pre-frontal trough will move across the lower
Mississippi Valley as low-level moisture advects northward into the
central Gulf Coast States. In the central Gulf Coast States, a 50 to
60 kt low-level jet will move northeastward. To the west of this
feature, morning showers and thunderstorms are forecast develop from
south-central Mississippi into south-central Alabama. This combined
with abundant cloud cover, introduces uncertainty into the forecast
concerning instability. In spite of this, forecast soundings around
midday into southern Mississippi and southern Alabama show surface
dewpoints in the mid 60s F with MLCAPE values reaching the 800 to
1200 J/kg range. This combined with strong deep-layer shear of 50 to
60 kt should be sufficient for a severe threat. The type of severe
should depend upon which mode is favored. Wind damage and QLCS-type
tornadoes would be possible with line segments. If a cluster
organizes with discrete modes, then supercells along with a tornado
threat would also be possible.
Negative factors for this event include
1) The upper-level system and the associated large-scale ascent is
too far north
2) Widespread morning convection should hamper destabilization
For these reasons, an upgrade will not be issued for this outlook
and a slight risk will be maintained in the same general area.
...Tennessee and Lower Ohio Valleys/Mid Mississippi Valley...
An upper-level low and an associated negatively-tilted upper-level
trough will move northeastward into the mid Mississippi Valley on
Saturday. The exit region of a 75 to 90 mid-level jet will
overspread the Ohio Valley as a surface low moves into the lower
Missouri Valley. South to southeasterly winds are forecast across
the Ohio and Tennessee Valleys which will help maintain a corridor
of low-level moisture. Although instability will remain weak along
this corridor, large-scale ascent will be strong enough for
thunderstorm development during the late morning and afternoon. Deep
layer-shear of 70 to 80 kt along with the large-scale ascent and
cold air aloft, may be enough for a marginal hail threat during the
afternoon. A few strong wind gusts will also be possible.