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Wintry February 19-21, 2020 Winter Storm

Poimen said:
NAM keeping the snow going a tad longer over the NW Piedmont than before. Nice little tail/deform band of some kind.

ref1km_ptype.us_ma.png
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Going to be some stupid totals up this way.... I just can't buy into it yet
 
Poimen said:
NAM keeping the snow going a tad longer over the NW Piedmont than before. Nice little tail/deform band of some kind.

ref1km_ptype.us_ma.png
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Looks like it's going to be a balancing act between how far north the warm nose gets, how long it lasts, and how long the precip falls once the warm nose is gone.
 
How long are the models saying we’ll see rain and rain/snow before transition to all snow for RDU folk?
 
GSP WWA likely gonna be issued for northern upstate through Charlotte soon



.NEAR TERM /THROUGH THURSDAY/...
As of 300 PM: We continue to be on track for our winter storm
starting late tonight and continuing through much of the day
Thursday. An impressive 1045+ mb Canadian high pressure will
continue to gradually build into the area, supplying colder and
drier air through tonight and really into the day Thursday
(especially near the surface). The upcoming system was organizing
over Texas early this afternoon and seems a bit more well organized
than some guidance suggests. As a result, have trended rain/snow
chances increasing a bit earlier than previous forecast, now
starting by sunrise for northeast Georgia and the western Upstate of
South Carolina into much of the mountains. Thermal profiles should
support mainly snow above 2000 feet on the onset across the
mountains. Snow should also prevail as precipitation reaches the
foothills into the I-40 corridor, although rain/sleet may mix in at
times. Heavier showers and continued cold air filtering in on breezy
northerly winds is expected to support a gradual change over to snow
from the I-40 corridor to the I-85 corridor from around noon into
the afternoon with lingering precipitation (possibly taking a banded
look) becoming all snow along the I-77 corridor late in the
afternoon into the evening hours. All told, we are expected one to
three inches with locally four inches across the mountains with one
half of an inch to two inches, locally three for the North Carolina
foothills to Piedmont. One half to one inch is possible in and
around Charlotte into northern portion of the Upstate of South
Carolina. A winter weather advisory will be issued shortly for most
of these areas as a result. Temperatures will fall through the 40s
tonight with Thursday daytime highs likely in the morning as wet-
bulbing will support temperatures falling through the 30s for most
late morning into the afternoon.
 
Stephenb888 said:
It’s gonna be around abbeville/greenwood this go around. Below I-85
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I agree. Once that coastal takes shape cold air will dive south and flip areas in the southern part of the upstate to snow. The good thing is those areas will still have moisture to work with while the northern upstate is beginning to dry out. Backend looks promising as well
 
Jimmy Hypocracy said:
I agree. Once that coastal takes shape cold air will dive south and flip areas in the southern part of the upstate to snow. The good thing is those areas will still have moisture to work with while the northern upstate is beginning to dry out. Backend looks promising as well
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That's a nice thing about cold conveyor belt with these mid-latitude cyclones :)
 
RDU is a little more gung ho with their afternoon discussion:
.SHORT TERM /THURSDAY AND FRIDAY NIGHT/...
As of 200 PM Wednesday...

...
Winter Weather Advisory

in effect from 10 AM Thursday to 7 AM
Friday...

Changes: Still a good bit of uncertainty with respect to amounts,
though there will
likely

be a "sweet spot" and a tight
gradient


somewhere across central
NC

. Primary changes for this forecast
issuance include an earlier start time for snow, particularly across
the northern half of the area and an uptick in amounts along the I-
85/US-64 corridors. While the overall weather pattern remains
similar to previous model runs, changes to the temperature profile
aloft have resulted in a bit more p-type uncertainty. There will
likely

be a stripe of wintry mix across the area as the rain mixes
and transitions to snow across the area.

Overall pattern: A cold
front

will settle south of the area, laying
across SC/GA Thursday morning with cool high pressure ridging
southward and advecting cold air into central
NC

. While the surface
front

will remain south of the
NC

/SC border, albeit pivoting some to
more SW/NE orientation, the H85
front

will stall over
NC

. As a s/w
aloft rides along the H85
front

from the MS Valley toward the mid-
Atlantic during the day, a surface low will develop over the Gulf
Coast/Southeast US in response. With abundant
moisture


advection


aloft and and strong
cyclogenesis

at the surface off the Carolina
Coast there will
likely

be an area of strong
frontogenesis

over
NC


during the
aft

/eve. The coastal low will lift northeast along the
NC


coast then eastward out over the Atlantic through Thursday
eve/night. Meanwhile, the parent upper
trough

will swing eastward
through the
OH

/TN Valley toward the mid-Atlantic/NE Thursday night.
Precipitation will quickly taper off as the upper
trough

swings
through the area, exiting the region early Friday.

Precipitation: Rain will move into the area from the south-southwest
early Thursday. With the cool, dry air in place this rain will help
lower temperatures to the wet bulb temperature (which should be in
the 29-32 degree range), especially across the northern half of the
area. The tricky part of the precipitation will be determining the p-
type and transition times. There is a big potential for error in
this regard, but the most
likely

scenario will be a quicker
transition to snow across the north with lower liquid equivalent
precipitation totals than across the south. In between there will be
higher chances of
mixed precipitation

which could lower the overall
snow accumulation but potentially cause more issues travel-wise.
Based on the model simulations from this morning, there should be a
period of all snow, more brief in some areas than others, across
central
NC

between Thursday morning and daybreak Friday. While
generally 0.5" to 3" are most
likely

across central
NC

, the more
realistic scenario will be a very localized area of higher amounts
and a tight
gradient

from that to
trace

amounts. Of course, the
thermal

profile and snow-liquid ratios will both impact the overall
snow totals when it`s all said and done. As per usual, the most
significant accumulations will occur on elevated/grassy surfaces.

Temperatures: Highs on Thursday will occur in the morning, topping
out in the upper 30s north to mid 40s south. Temperatures will lower
with the onset of
rainfall

, more quickly across the north with
temperatures in the mid 30s across the area expected by sunset.
Overnight lows will depend on how quickly the low moves away and the
precip ends, but generally expect a steady decrease to around
freezing until the rain ends, with more rapid cooling in its
wake

.
For now, expect temperatures could be in the mid 20s NW to upper 20s
SE by daybreak Friday.

Winds: Winds should be northeasterly throughout the period. While
sustained winds will remain in the 5-10
kt

range in the NW, gusting
to 10-15
kts

in the eve/night, winds across the southeast (in closer
proximity to the coastal low) will be quite a bit stronger and
gustier. Expect sustained winds across the Sandhills and Coastal
Plain around 15
kts

with gusts into the mid 20s
kts

.

Friday and Friday night: The precipitation should quickly exit the
area early Friday, with cool, dry weather expected in its
wake

.
Winds will continue to be a bit breezy/gusty, strongest in the east
and southeast during the day and tapering off overnight. Skies
should rapidly clear during the day, but with the winds highs may
reach low 40s west while topping out in the upper 30s east.
Overnight, clear skies and light winds will result in good
radiational cooling

conditions with lows in the mid 20s expected.

&&
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