GSP
.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 240 pm EST Tuesday: Looking ahead to the weekend, all
attention turns toward the possibility of a winter storm that would
affect the western Carolinas and northeast Georgia beginning perhaps
as early as Saturday afternoon and possibly continuing through the
better part of Sunday...emphasis on the word "possible". It is worth
noting that the 12Z ECMWF has come around to the GFS idea that a
strong short wave dropping southeastward along the High Plains would
ultimately cut off an upper low over the central/srn Plains Friday
night into Saturday. Also worth noting is the relative run-to-run
consistency seen in the operational GFS with this feature. The
setup begins Friday night into Saturday as the developing split in
the flow helps to slow the progress of a large continental sfc high
moving from Ontario, down across the lower lakes, to Upstate NY/New
England Saturday/Saturday night. This would provide the necessary
source for cold air prior to the arrival of the precip associated
with the upper low, which operational guidance suggests will come
across the lower MS Valley region Saturday night. The operational
models show partial thickness values low enough to support at least
a mix with wintry precip as we acquire isentropic lift on Saturday
that could force the development of said precip by the afternoon. If
this develops as it could, essentially as an activating warm front,
it would help to lock in the cooler sfc temps before the main
mid/upper forcing arrives from the west. The operational models all
show a closed upper low rolling east on Sunday, moving overhead or
to the south of the fcst area, then offshore/northeast on Sunday
night. Be that as it may, this is not the only possible solution,
and some of the ensemble members show very different outcomes
to the upper/sfc pattern. Looking at the GEFS...there has been
a definite trend toward more wintry precip across more of the
fcst area, with the majority of ensemble members at 12Z showing
wintry precip affecting nearly the entire fcst area Saturday
night/Sunday. The plume diagrams, and their supposed total snow
accumulations, appear most tantalizing. However, there are as many
ensemble members showing minimal wintry precip as there are showing
a great deal, and some still showing none at all. Our forecast will
reflect developing confidence in the wintry scenario but limits
the precip probs to the chance range for the time being. The trend
is toward more of a snow possibility along/north of I-85 and more
mixing/changing to sleet/freezing rain south of I-85, but this is
only one scenario. The track of the low will determine how strong
of a warm nose might develop from the south, which would greatly
affect the precip-type distribution. The QPF blend right now is
especially modest, and the conservative approach is preferable
for a system that is still out on Day 4/5. In spite of the trend,
readers are cautioned to manage their expectations...at least for
the time being. Stay tuned.
If this system develops as it could, we would be in for some NW
flow snow on the TN border Sunday night into Monday, otherwise
the remainder of the period would be quiet with a large sfc high
settling across the region Monday into Tuesday.
