Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0404 AM CST Tue Dec 28 2021
Valid 311200Z - 051200Z
...Day4/Friday - Arklatex to the Mid-Mississippi Valley...
A mid-level shortwave trough will move from near the Baja Peninsula
Friday morning to the southern Plains by late Friday night. This
approaching shortwave and deepening lee cyclone across the southern
High Plains will elicit a strong mass response across the Arklatex
late Friday and into Friday night. As the low-level jet strengthens,
storm coverage is expected to increase in a broad zone of isentropic
ascent north of a warm front from southeast Oklahoma to the
Tennessee Valley. In addition to this elevated storm activity, most
guidance also shows surface-based storm development on the warm side
of the boundary Friday evening into the early morning hours
Saturday. A very moist boundary layer will be in place ahead of this
storm activity with mid-60s dewpoints as far north as southern
Kentucky at 06Z Saturday. Therefore, convection will form and
propagate into an unstable environment which will allow
thunderstorms to continue through the overnight hours and into the
Day5 period with a severe threat throughout. Strong deep-layer and
low-level shear will support all severe hazards.
...Day5/Saturday - Mid South and the Tennessee Valley to the
Severe weather will likely be ongoing at the beginning of the period
from the early morning thunderstorms across Arkansas and vicinity.
There may be a slight lull in storm coverage/intensity during the
diurnal minimum Saturday morning, as the lead wave continues
northeastward and the primary trough approaches from the west.
However, by midday, significant height falls will start to
overspread the warm sector and widespread storm development is
anticipated. The location of overnight convection will have a
significant impact on the zones within the broader risk area where a
higher severe weather threat will exist. However, all guidance shows
a broad warm sector with a broad 50 knot low-level jet, which would
foster an environment favorable for all severe weather types. The
greatest uncertainties are related to the northward extent of the
risk and the surface low track. Given the widespread convection
expected north of the warm front, a convectively reinforced warm
front could set up farther south than the surface low track may
suggest. Also, global guidance still varies with the intensity and
location of the surface-low as it tracks northeast. The track and
intensity of this surface-low will have some impact on the storm
evolution and intensity within the warm sector, especially as it
relates to storm mode and the tornado threat. Maintained 15 percent
probabilities from the previous Day 6 forecast with an expansion on
the southern and eastern extent to account for the threat continuing
late Saturday night.
...Day6/Sunday - Portions of the Southeast into the Carolinas...
A severe-weather threat will likely persist into the Southeast and
Carolinas after 12Z on Sunday, but the magnitude of the threat
varies greatly. Most guidance shows a remnant squall line moving
through the region. With extensive cloud cover, slightly lower
moisture quality, and decreasing ascent, a significant severe threat
would not necessarily be most likely. However, there is still
considerable uncertainty during the Day 6 timeframe, and several of
the GEFS members, including the operational GFS, have a deepening
surface cyclone somewhere east of the Appalachians on Sunday. This
would lead to a more significant severe-weather threat than ECMWF
guidance would suggest and will need to be monitored as a
...not to mention the fact that the strongest dynamics lag behind the warm sector on Saturday, given a surging cold front that tends to undercut LL thermodynamics.Mid and upper level temps don’t look nearly as favorable as the last few systems (especially December 10/11). Looks like some entrainment of the subtropical jet with that cut off that gets absorbed by the main trough down near the Baja of California.
Is it too early to get a location/region that might be affected?I know we have to get past today's threat, but concern should be increasing substantially for this one. Euro, UKMET, GFS op, GFS ensembles, NAM, SREF, and even the 15k of our in-house Baron are ALL trending toward a stronger, slower, more consolidated system with a surface low farther west during peak heating, a trend toward less low-level veering, and a trend toward higher shear co-located with prefrontal activity with an upper trough that has large scale ascent well ahead of the front. It's looking more and more like trying to buy into the faster surface low track/evolution and a veering low-level flow was a potentially dangerous idea...
I know we have to get past today's threat, but concern should be increasing substantially for this one. Euro, UKMET, GFS op, GFS ensembles, NAM, SREF, and even the 15k of our in-house Baron are ALL trending toward a stronger, slower, more consolidated system with a surface low farther west during peak heating, a trend toward less low-level veering, and a trend toward higher shear co-located with prefrontal activity with an upper trough that has large scale ascent well ahead of the front. It's looking more and more like trying to buy into the faster surface low track/evolution and a veering low-level flow was a potentially dangerous idea...