GSP Discussion
SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
As of 100 PM New Year`s Day: Flat upper ridging will traverse the
CFWA Tuesday night, ahead of a potent
shortwave trough moving in
from the west across the Southern Plains. Model guidance are in
good agreement with the
shortwave traveling along the Gulf Coast,
inducing weak surface
cyclogenesis as a coastal low develops
underneath. Expect increasing mid to
high clouds late Tuesday night
into Wednesday before completely blanketing the CFWA by Wednesday
afternoon. Temperatures are expected to drop 5 or so degrees below
normal for lows Tuesday night. Temperatures will remain a few ticks
below
normal for highs Wednesday afternoon due to being disrupted
by the increasing cloud cover.
Conditions start to change relatively quick later Wednesday as the
coastal low pushes south of the CFWA, across the Florida Panhandle
late Wednesday into Thursday morning. Good upper
divergence will
settle over the region as a piece of the southern stream
jet to
the south settles over the southeastern
CONUS. Factor in weak
isentropic lift and a decent
moisture transport from deep layer
southwesterly
flow will support at least mentionable
PoPs in the
forecast across most of the area. Profiles will be saturated enough
from the top-down to support ice nucleation in the cloud tops. With
dry air in place ahead of the system, the process of evaporational
cooling will occur before any precip makes contact with the surface,
which will lead to wet-bulbing as the low-levels cool to a point
that will support snow across the mountains Wednesday night into
Thursday morning. 850mb temperatures are in question outside of the
mountains, but will linger close to the freezing point. Wet-bulb
temperatures will be above freezing when the primary
QPF response
is expected late Wednesday night across the Piedmont. Can`t fully
rule out rain with mixing with snow/sleet across the Piedmont zones,
but with guidance pushing the precip out sooner than previous runs,
temperatures won`t have enough time to cool enough for a complete
changeover, despite what the 06Z run of the
NAM suggests, and now
the 12Z
NAM has barely any wintry precip-types at all outside of the
mountains. This lowers confidence even more for wintry precipitation
outside of the mountains. Only light accumulations in the mountains
are expected as the better
QPF amounts and lift reside south of the
CFWA. Temperatures will be near-
normal for lows Wednesday night. Dry
high pressure will move in from the northwest as the
shortwave
trough axis shifts offshore by mid-morning Thursday.
CAA filters
in behind the departing system, which will keep the mountains cold
during the day Thursday with highs in the 30s and low to mid 40s
in the major mountain valleys. Temperatures should rebound close
to
normal for the Piedmont zones.