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January 8th-9th threat


BullCityWx
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NWS GSP's overnight thoughts...

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.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 300 AM Wednesday: The weather topic of the short term will
be detailing the ins and outs of the incoming system that will
enter the area. An open upper trough currently sitting over the
Rockies will nosedive to the south and east as it tracks towards
the lower MS Valley by the start of the forecast period. Model
guidance evolves the trough into an upper low at this point as
it scoots towards the area with a sfc low developing underneath
once the upper low taps into the western portions of the Gulf of
Mexico. Expect this system to ride north of the Gulf Coast as it
approaches the Southeast by late Thursday into Friday. High clouds
will move into the region early Thursday with the clouds deepening
and lowering by Thursday afternoon. Ample moisture advection coming
off the Gulf of Mexico Thursday and the Atlantic once the sfc low
approaches the Southeast coastline by Thursday night/early Friday
will allow for the cwa to become relatively saturated. Thursday will
be fairly cool and dry with PoPs entering the southwestern portions
of the cwa by Thursday afternoon and spreading northeast through the
evening and into the overnight hours. QPF amounts still differ from
run to run per model guidance, but has not changed much overall.
Locations that remain mostly liquid should see QPF amounts of ~0.25"
- 0.50+" for the duration of this event.

The 850 mb low has trended slightly northward over the past
couple of model runs and would likely surge a warm nose into
the region, despite a surge of colder air aloft from the upper low.
Mixed p-types will likely occur at the transition zone and very
light accumulations of ice could be in store at locations that fall
under the zone. As of now, the mountains will have enough cold air
to support a mostly snow event as a broad sfc high sets up shop to
the north and pumps in colder air in the low levels. With a warm
nose being indicated by the NAM and trending that way with global
models, light ice accumulations could reach as far west as the
northern foothills and Escarpment during the first hour or two at
the onset of precip, which would lower overall snow totals. A mix of
rain/snow seems evident between the I-40 and I-85 corridor with the
transition zone likely to settle somewhere between the two
corridors. A shift slightly to the south could bring the transition
zone closer to the I-85 corridor and provide the lower Piedmont and
Upstate of SC a brief period of wintry precip Friday morning, when
temperatures are cold enough at the surface. A few inches of snow is
looking more likely for the higher elevations with some locations
receiving 6+" at the highest peaks. An inch or two is becoming more
apparent north and along the I-40 corridor, a tighter gradient of
snow/ice accumulations between I-40 and I-85, and a possible dusting
can`t be ruled out along the I-85 corridor when it`s all said and
done by Friday night.

Another factor to consider is determining where the deformation band
develops. Model guidance have hinted at placing the band between I-
40 and I-85, which would produce a few locations with more snow than
what is forecasted, but it is way too early to determine the exact
set up of the deformation band. Areas south of I-85 may see a few
snowflakes mix in, but temperatures from the sfc to ~850 mb will
likely be too warm to support any brief periods of snow, especially
with a warm nose becoming more apparent as the event closes in on
the area. Expect the upper low and sfc to exit the region by Friday
night as dry, NW flow builds in and dries the area out with the
exception of favorable upslope NW flow snow lingering in the
northern mountains and along the TN Border Friday night/early
Saturday. Temperatures will likely remain below normal for a good
portion of the short term.

 

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