Day 4-8 Outlook
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0345 AM CST Thu Dec 23 2021
Valid 261200Z - 311200Z
...DISCUSSION...
Overall, the large scale pattern will feature an upper-level trough
in the western CONUS with an upper level ridge near the East Coast.
This pattern could be favorable for severe weather events,
especially as a higher moisture content airmass over the Gulf of
Mexico moves inland. Southerly winds have started to strengthen in
the western Gulf of Mexico Thursday morning which will start the
process of moisture recovery across portions of south Texas and
Louisiana. Winds across the eastern Gulf will turn easterly by early
Friday morning and will start the long-fetch moisture feed which is
expected to persist for the entire long term period.
...D4/Sunday - Eastern Plains into the Midwest...
A mid-level shortwave trough is expected to eject from near Southern
California on Sunday morning to parts of the Great Lakes by early
Monday morning. There are differences in timing and amplitude of the
trough with complicate the forecast somewhat, but a weakening
surface low is expected to track from somewhere in the Plains into
the Great Lakes during the Day Sunday. There is agreement in upper
50s to near 60 degree dewpoints to move in ahead of this system.
This may provide enough moisture for some thunderstorm activity near
the surface low, but instability is expected to stay too limited for
a greater severe weather threat.
...D6/Tuesday - Midwest into the Ohio Valley...
The next weak shortwave trough will move through the Midwest and
into the Great Lakes on Day 6/Tuesday. By this time, surface
dewpoints are forecast by most guidance to be in the low to mid 60s
for much of the warm sector. This will result in a more unstable
warm sector and slightly higher chances for severe weather. At this
time, instability does not appear high enough to support severe
weather probabilities, but trends will continue to be monitored.
...Beyond Day 6...
The chances for more significant severe weather will increase beyond
Day 6. Most guidance suggests 70 degree dewpoints across the entire
Gulf of Mexico by D6/Tue. This is anomalously high Gulf moisture
content for this time of year and will set the stage for severe
weather potential. The exact magnitude of any severe weather threat
will depend on the evolution of the upper-level and surface pattern,
but with a broad warm sector in place across the Southeast and
mid-Mississippi Valley it is more likely than not that there will
eventually be a severe weather episode somewhere from the Southeast
into the Midwest/Great Lakes.
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