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Wintry January 29th-30th ARCC Slam Dunk Winter Weather Threat

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From Huntsville




By Monday, mid-level flow will quickly back to the west-southwest
once again downstream from a stronger northern stream trough progged
to dig southeastward into the mid-MS Valley. As the related surface
cyclone shifts eastward through the lower Great Lakes, an increase
in south-southwesterly winds in the boundary layer will lead to
another mild day with highs in the m-u 50s. Although temporal
differences remain among the latest suite of global models, a
consensus of the guidance suggests that a powerful arctic cold front
trailing southwestward from the surface low will enter northwest AL
at some point during the mid/late evening hours on Monday and push
steadily southeastward through the entire CWFA by 9-10Z. It still
appears as if prefrontal shower activity will increase as the front
intercepts a plume of deeper moisture across our region. However, of
more concern is the potential for postfrontal precipitation, which
could occur in a fairly wide band given strength of lift downstream
from the mid-level trough axis. The precipitation will initially
transition to a mixture of freezing rain/sleet as temperatures
drop immediately in the wake of the front, but should eventually
transition entirely to snow as temps fall below freezing through the
depth of the vertical column. At this point, we suspect most
locations could receive between 1-2 inches of snow, with up to one
hundredth of an inch of ice accumulation in a few spots. Even with
clearing skies, strong advection of arctic air into the region will
ensure that daytime max temps stay around 30 degrees or lower for
most of the region.
 
Snippet from GSP this morning:
East of the mtns,
still think the cold air will not get past the mtns before the
back edge of the significant precip departs. That being said, if
the timing of the NAM/ECMWF proves more correct, and that timing
slips into Tuesday evening, then it could get more interesting,
but for now that should be downplayed.
 
One thing to keep in mind, no matter if it snows or rains there will be a flash freeze Tuesday night. Moisture on the ground and roads will freeze quickly as temps drop into the teens and 20s behind the front.
 
Cad Wedge NC said:
topography.... the mountains delay the cold air from penetrating farther south and down-sloping has a tendency to dry out the atmosphere.
Click to expand...
So is it set in stone that this will happen or a chance that this could change somehow?
 
FFC going with NBM (National Blend of Models) and WPC QPF forecast.

000
FXUS62 KFFC 261128
AFDFFC

Area Forecast Discussion...Updated for Aviation
National Weather Service Peachtree City GA
625 AM EST Sat Jan 26 2019

.LONG TERM /Sunday Night through Friday/...

Primary concern in the extended forecast period continues to be the
wintry precipitation Tuesday. Still significant differences in the
medium-range models concerning mainly the amounts of precipitation
and the timing/duration of the mixing/change-over from liquid to
frozen precipitation. GFS and Canadian models continue to be faster
and noticeably lower in QPF than the ECMWF. This appears to be due
to the stronger, slower and more southerly track of the short wave in
the European solution. I have stuck with a model blend for now
(namely the NBM for most parameters and WPC QPF) with precipitation
type driven by a non-diurnal temperature trend during the day
Tuesday. This yields a potential for advisory-level or higher
snowfall amounts across the higher elevations of the far north.
Otherwise, only trace amounts are generated across north Georgia,
including into the northern and western metro Atlanta area. No
accumulations expected across central Georgia. Confidence that we
will see some kind of rain/snow mix across much of north Georgia is
fairly high, confidence on accumulations remains low at this time.
Cold and dry air moves across the forecast area from west to east by
late in the day with only lingering light rain in eastern portions of
the forecast area into the early evening. Wouldn`t be surprised to
see a few areas with a light rain/snow mix into central Georgia late
in the afternoon/early in the evening, but no accumulations across
that area.

https://forecast.weather.gov/produc...FC&product=AFD&format=CI&version=1&glossary=1
 
Webberweather53 said:
You can see exactly what I'm talking about on the 48 hour z500 trend on the GFS. The bigger Carolina wave is strengthening the downstream ridge over Atlantic Canada and allows the trough many are concerned about for this arctic front to slow and become neutrally tilted sooner.

View attachment 13455
Click to expand...
Doesn't this same process also potentially cause areas to the west, such as N AL, to see less precipitation as the energy transfer to the coast?
 
Per FFC & the 0z Doc, I’d say the best chance @ seeing the ground white in Georgia will be North of I-20 & west of the hooch. This sucker doesn’t appear to have quite enough juice to be more than a novelty for areas further east
 
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