FROM NWS BIRMINGHAM
.LONG TERM...
(Sunday night through next Friday)
Issued at 414 AM CST
SAT JAN 13 2024
A broad
trough will remain across much of the
CONUS through Tuesday,
with a deep upper low over Hudson Bay, associated with the
extratropical cyclone currently over the Great Lakes which will be
occluded by that time. A series of weak shortwaves will be rotating
through the base of this
trough. At the surface, a strong cold
front
will have moved through during the short term period, with an Arctic
air mass covering much of the central
CONUS. The first weak wave
moves through Sunday night. A band of light snow is expected to set
up along an 850-700mb
frontogenesis zone over the Mid-South region
Sunday night northwest of the forecast area, though there is a
chance some of this light snow makes it into our far northwest
counties prior to sunrise Monday morning. At this time
accumulations are not expected during the overnight hours Sunday
night in our far northwest counties, but will need to monitor as
temperatures will be below freezing during this time. A stronger
shortwave moves through during the day on Monday, and this band of
precipitation should sink southeastward into our far northwest
counties, especially Marion and Winston counties. Temperatures
will also remain at or below freezing in that region. Global
models all indicate temperature profiles in this region being
supportive of snow, with the potential for 1 to 2 inches of snow
in the far northwest counties, but the
NAM indicates a warm nose.
Overall the
NAM appears to be too amplified with the system and
850mb winds with the 925-850mb
front further to the northwest,
though it is certainly possible there could be a warm nose not
depicted in the global guidance. Still, with precipitation falling
with temperatures at or below freezing, there would be impacts
from sleet or freezing rain if the precipitation there ends up not
being snow. Have therefore issued a Winter Storm
Watch for Marion
and Winston Counties starting Monday morning, though this could
move earlier into Sunday night if precipitation starts earlier.
The
shortwave moves past the area Monday evening, with mid-levels
drying out including in the
dendritic growth zone. This will result
in overall less favorable conditions for accumulating snow Monday
night.
Isentropic lift will persist at low-levels, however, with
southwest low to mid-level
flow continuing
downstream of a
trough
digging into the Plains. Soundings remain saturated up to around
700mb, but generally below the -10C level. At the same time cold
advection at low-levels will cause sub-freezing temperatures to
advance southeastwards. With a warm nose present in soundings, this
indicates more of a wintry mix with rain changing over to freezing
rain, possibly mixed with sleet or light snow. Therefore
accumulations south of the far northern counties will mainly be in
the form of
icing rather than sleet or snow. While
PoPs (
probability
of measurable precipitation) are currently only in the 20 to 30
percent range, at minimum freezing drizzle appears possible with
these soundings, which while not "measurable" can still cause
travel impacts. A
winter weather advisory will
likely be needed in
future updates for icy road conditions by Tuesday morning for at
least the northwest half of the forecast area. As we go into early
Tuesday morning, uncertainty increases regarding whether there is
an uptick of precipitation over our southeast counties, with
temperatures along the I-85 corridor near freezing. Will hold of
on mentioning wintry impacts in these areas but will need to
continue to monitor this.
A very cold
air mass will move into the area behind this system.
High temperatures will be at or below freezing along and north of I-
20 on Tuesday, which could prolong travel impacts. A hard
freeze
warning will probably be needed for some of our northwest counties
Tuesday morning, and areawide by Tuesday night/Wednesday morning.
Winds will become light across the far northwest/northern counties
Tuesday night, where forecast lows are in the mid to upper single
digits. They could trend a bit lower if there is snow on the ground.
Wind chills will also be at or below zero across northern and
western portions of the area Wednesday morning, so a
wind chill
advisory may become necessary. Some far northern areas may not go
above freezing Wednesday either. Another hard
freeze warning may
be needed for portions of the area Wednesday night. The next
system moves in Thursday night into Friday. There are some model
disagreements in temperatures with this system and precipitation
types. Will hold off on mentioning any wintry impacts in the HWO
at this time.
32/Davis