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Orangeburgwx

December 8-10, 2018 Winter Storm

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6 minutes ago, Blue_Ridge_Escarpment said:

What are they looking at? Euro, UK, FV3, CMC all show a foot and a half here. 

Just scrolled through their maps, the high end matches up with model output but then  when you look at expected and then scroll through the “% of x inches”, it makes no sense why they went with what they did.  only thing I can figure is they see this mainly a CAD region storm in regards to snow as the ice accumulation map is highest SW of Asheville.

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RAH just wrote a book!

.LONG TERM /SATURDAY THROUGH THURSDAY/...
As of 330 PM Thursday...

...A significant winter storm is expected Sat night through Mon; 
a winter storm watch is being issued for the NW Piedmont...

Overview for Sat-Mon: A significant wintertime storm for NC is 
growing more likely with every model run. Differences among the 
models regarding timing, track, precip amounts, and the vertical 
thermal structure and advection patterns persist, which makes it 
challenging to pinpoint the details, but the models are coming into 
better agreement now. It's very likely that parts of central NC, 
primarily N and W of the Triangle, will see several inches of snow, 
at least, along with some icing. Lesser (but still impactful) 
accumulations of ice and snow are expected at some point of the 
event over all but the far SE.

-Synopsis: A potent mid-upper trough/low will cross the S Plains, 
Gulf States, and Southeast during this period, as a surface low 
tracks along the Gulf Coast/S GA/FL Panhandle, evolving into a 
Miller B configuration as this energy transfers to a deepening low 
just off GA/SC on Sun. This low should then intensify as it tracks 
NE just off the NC coast through Mon. A second, strong polar stream 
wave will dive through the Midwest and lower Miss Valley Sat night 
through Mon, shearing across the Southeast states and prolonging the 
lift and moisture over central NC as yet another deepening low 
pressure center holds just off NC. 

-Timing: Model agreement has improved since yesterday, with the 
ECMWF/Canadian still the preferred solution, while the NAM is quite 
close and the GFS still a fast solution. Leaning toward the 
ECMWF/Canadian/NAM, have brought chance pops gradually into the SW 
CWA on Sat, expanding slowly to the N and NE late day and overnight. 
The heaviest precip is expected to fall from early Sun morning to 
mid afternoon Sun, in conjunction with the most intense upper 
divergence/mid level DPVA and most vigorous and deepest moist 
upglide. After this time, drying aloft (in the -12C to -18C layer) 
and waning forcing for ascent should mean a trend to lower precip 
rates, although high pops will persist. 

-Precip types: Increased confidence in a cold column has prompted 
expansion of the areas likely to be impacted by wintry weather. The 
far SE is still likely to see mostly rain through Sun, albeit with a 
little wintry precip early in the event and again on Mon. Roughly 
along the Highway 1 corridor including the Triangle, a longer 
duration of a wintry mix is anticipated, with a light glazing 
possible along with some snow and/or sleet accumulation ranging from 
one half inch to a few inches (this is the area that could see a 
tight gradient of lighter to heavier accumulations over a short 
distance). We could see a trend to a cold rain sometime on Sun in 
this zone, if low level warm advection on the N side of the coastal 
low becomes more prominent. For the NW Piedmont including the Triad, 
snow and sleet will be the predominant precip type for most of the 
event, with accumulations from several inches to just under a foot 
not out of the question. Some low level drying is expected by Mon, 
but continued lift and moisture in the -12C to -18C depth should 
result in a secondary chance of some light snow or a wintry mix 
associated with the polar wave and some additional light 
accumulations. 

-Temps: Expect highs in the upper 30s to mid 40s Sat and Mon, with 
around 30 to the mid 40s for highs on Sun. Lows will be mainly in 
the upper 20s to mid 30s. The diurnal range in most areas will be 
very low. 

-What to watch out for/what could change: First, the inland 
penetration of warm air on the N side of coastal lows is always 
problematic. This could cause a significant warm nose to develop 
aloft, shifting snow over to more sleet or freezing rain in some 
areas. Second, if surface temperatures don't warm up as advertised 
on Sun, especially along and E of the Highway 1 corridor, wintry 
precip could last longer, increasing accumulations of both snow and 
ice. Third, there are indications in the models that a band of 
heavier convective precip is possible over the Southeast, just 
inland to just off the Southeast coast, and this could serve to 
interrupt transport of high moisture into central NC; if this were 
to occur, liquid equivalent precip amounts would be lower. Finally, 
if we can achieve banded snow at any point in this event, we could 
potentially see localized zones of very heavy snowfall over portions 
of the Piedmont. 

 

 

 

 
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Just now, Brick Tamland said:

Big turnaround with the NAM.

namconus_asnow_seus_27.thumb.png.cc1e448f2d2922ab95e8752564c1e765.png

That map is highly inaccurate with all of the sleet and ZR included 

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Here is GSP's reasoning:

.SHORT TERM /SATURDAY THROUGH MONDAY/...
As of 250 PM Thu: Still high confidence on the occurrence of a
winter storm developing late Saturday into early Sunday across
the region. Trends in the models unfortunately do not lend much
additional confidence to precip types or transitions. Cold-air
damming still is a key component of the event. The models suggest
the CAD will be a bit stronger at the onset of precip, which
looks most likely Saturday afternoon as a stationary front sets
up between the incoming continental sfc high and the developing
coastal low. The general track of the low is still expected to be
across the Coastal Plain to our south, so the timing of the event
has changed little.

One appreciable difference with this fcst package is lower
overall QPF. Unfortunately for the sake of forecasting p-type
distribution/transitions, models continue to show midlevel temps
flirting with 0C for much of the event. Temps are expected to
remain above freezing for most of the area Saturday afternoon,
though the trend has been colder in latest guidance. A deep but
relatively cool warm layer aloft implies a mix of precip types
is possible late Saturday; increasing precip should strengthen
the wedge through diabatic cooling and profiles will support all
snow over an increasing portion of WNC through Sunday morning. Sfc
temps Sunday are especially tricky given guidance split across
the freezing mark. Have biased the fcst in favor of a GFS-based
blend that did well in last month`s wintry wedge event. Still,
where temps are above freezing sleet is expected to be the main
p-type. The NAM is substantially warmer with temps aloft than
any of the global models we have at our disposal. For now the NAM
profiles are being discounted and not used in the fcst process,
not only due to the consensus in the other guidance, but to help
maintain better forecast continuity--i.e. not to shift too much of
the accumulation from the snow to ice category. But this is a trend
that we will have to monitor in subsequent fcst shifts. We continue
to expect 8-12" of snow over the climatologically coldest part of
the CWA during CAD, i.e., the east-facing Blue Ridge Escarpment
and area extending east along I-40. "Snow" totals have declined by
a few inches over the northern GA/SC zones and in the more western
NC mtns, as more of the QPF is now expected to fall as sleet. Ice
accums remain at least advisory criteria along the fringe of the
sleet area. Confidence is already high enough to warrant a Winter
Storm Watch for all of our NC zones; one is being hoisted with
this package. This is at least 12 hours earlier than we would
normally issue a watch. We thus have decided to leave out all the
GA/SC zones for now and perhaps try to better define the p-type
transition zone. The expected sleet/ice amounts in these zones
will be more sensitive to forecast QPF and therefore a downward
trend could keep some areas out of warning crtieria altogether,
thus not warranting a watch there. Stay tuned.

WAA continues, albeit more weakly, as the sfc low pushes out to sea
Sunday night. At that time we will begin a slow transition from the
CAD/Miller-A forcing to that supplied by a shortwave/deformation
zone transitioning over the area. PoPs decline very slowly thru
Monday as a result. With the WAA, whereas we might normally expect
a transition to all snow across the area, we will continue to see
mixed p-types toward the south and east, wherever sfc temps remain
near or below freezing. Moisture becomes more shallow during this
time, too, putting the possibility of additional snow/sleet in
question as ice nuclei become scarce.

Impacts from the combination of what is expected to be a very wet
snow, combined with icing in some areas, are not looking any less
significant than what the previous shift expected, even though
total amounts may have come down with this package. Very windy
conditions are expected Saturday night and most of Sunday, which
makes falling trees/powerlines likely.
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3 minutes ago, WxKnurd said:

Just scrolled through their maps, the high end matches up with model output but then  when you look at expected and then scroll through the “% of x inches”, it makes no sense why they went with what they did.  only thing I can figure is they see this mainly a CAD region storm in regards to snow as the ice accumulation map is highest SW of Asheville.

They're showing more for Salisbury than atop Mt. Mitchell. 

I'm sorry, but there is no on this earth that I am going to buy into that map right now.

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2 minutes ago, Solak said:

RAH just wrote a book!

.LONG TERM /SATURDAY THROUGH THURSDAY/...
As of 330 PM Thursday...

...A significant winter storm is expected Sat night through Mon; 
a winter storm watch is being issued for the NW Piedmont...

Overview for Sat-Mon: A significant wintertime storm for NC is 
growing more likely with every model run. Differences among the 
models regarding timing, track, precip amounts, and the vertical 
thermal structure and advection patterns persist, which makes it 
challenging to pinpoint the details, but the models are coming into 
better agreement now. It's very likely that parts of central NC, 
primarily N and W of the Triangle, will see several inches of snow, 
at least, along with some icing. Lesser (but still impactful) 
accumulations of ice and snow are expected at some point of the 
event over all but the far SE.

-Synopsis: A potent mid-upper trough/low will cross the S Plains, 
Gulf States, and Southeast during this period, as a surface low 
tracks along the Gulf Coast/S GA/FL Panhandle, evolving into a 
Miller B configuration as this energy transfers to a deepening low 
just off GA/SC on Sun. This low should then intensify as it tracks 
NE just off the NC coast through Mon. A second, strong polar stream 
wave will dive through the Midwest and lower Miss Valley Sat night 
through Mon, shearing across the Southeast states and prolonging the 
lift and moisture over central NC as yet another deepening low 
pressure center holds just off NC. 

-Timing: Model agreement has improved since yesterday, with the 
ECMWF/Canadian still the preferred solution, while the NAM is quite 
close and the GFS still a fast solution. Leaning toward the 
ECMWF/Canadian/NAM, have brought chance pops gradually into the SW 
CWA on Sat, expanding slowly to the N and NE late day and overnight. 
The heaviest precip is expected to fall from early Sun morning to 
mid afternoon Sun, in conjunction with the most intense upper 
divergence/mid level DPVA and most vigorous and deepest moist 
upglide. After this time, drying aloft (in the -12C to -18C layer) 
and waning forcing for ascent should mean a trend to lower precip 
rates, although high pops will persist. 

-Precip types: Increased confidence in a cold column has prompted 
expansion of the areas likely to be impacted by wintry weather. The 
far SE is still likely to see mostly rain through Sun, albeit with a 
little wintry precip early in the event and again on Mon. Roughly 
along the Highway 1 corridor including the Triangle, a longer 
duration of a wintry mix is anticipated, with a light glazing 
possible along with some snow and/or sleet accumulation ranging from 
one half inch to a few inches (this is the area that could see a 
tight gradient of lighter to heavier accumulations over a short 
distance). We could see a trend to a cold rain sometime on Sun in 
this zone, if low level warm advection on the N side of the coastal 
low becomes more prominent. For the NW Piedmont including the Triad, 
snow and sleet will be the predominant precip type for most of the 
event, with accumulations from several inches to just under a foot 
not out of the question. Some low level drying is expected by Mon, 
but continued lift and moisture in the -12C to -18C depth should 
result in a secondary chance of some light snow or a wintry mix 
associated with the polar wave and some additional light 
accumulations. 

-Temps: Expect highs in the upper 30s to mid 40s Sat and Mon, with 
around 30 to the mid 40s for highs on Sun. Lows will be mainly in 
the upper 20s to mid 30s. The diurnal range in most areas will be 
very low. 

-What to watch out for/what could change: First, the inland 
penetration of warm air on the N side of coastal lows is always 
problematic. This could cause a significant warm nose to develop 
aloft, shifting snow over to more sleet or freezing rain in some 
areas. Second, if surface temperatures don't warm up as advertised 
on Sun, especially along and E of the Highway 1 corridor, wintry 
precip could last longer, increasing accumulations of both snow and 
ice. Third, there are indications in the models that a band of 
heavier convective precip is possible over the Southeast, just 
inland to just off the Southeast coast, and this could serve to 
interrupt transport of high moisture into central NC; if this were 
to occur, liquid equivalent precip amounts would be lower. Finally, 
if we can achieve banded snow at any point in this event, we could 
potentially see localized zones of very heavy snowfall over portions 
of the Piedmont. 

 

 

 


 

At least now they are saying a big storm could be a possibility instead of 1 to 2 inches.

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1 minute ago, wncsnow said:

NAM is a nasty ice storm for many 

zr_acc.us_ma (1).png

Upstate SC folks better get the generators gassed up!  I cant even imagine how many nights we will be without power if this verifies.  Cold rain would be MUCH better than that...

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4 minutes ago, Solak said:

RAH just wrote a book!

.LONG TERM /SATURDAY THROUGH THURSDAY/...
As of 330 PM Thursday...

...A significant winter storm is expected Sat night through Mon; 
a winter storm watch is being issued for the NW Piedmont...

Overview for Sat-Mon: A significant wintertime storm for NC is 
growing more likely with every model run. Differences among the 
models regarding timing, track, precip amounts, and the vertical 
thermal structure and advection patterns persist, which makes it 
challenging to pinpoint the details, but the models are coming into 
better agreement now. It's very likely that parts of central NC, 
primarily N and W of the Triangle, will see several inches of snow, 
at least, along with some icing. Lesser (but still impactful) 
accumulations of ice and snow are expected at some point of the 
event over all but the far SE.

Or as the rest of us call it, the Triad.  :rolleyes:

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4 minutes ago, BlueRidgeFolklore said:

They're showing more for Salisbury than atop Mt. Mitchell. 

I'm sorry, but there is no on this earth that I am going to buy into that map right now.

Oh I agree, just pointing out that the expected map makes no sense when you factor in all the other product maps they put out with it.  And that’s the only reasoning I could think of, which makes sense when you look at the disco about QPF and sleet SW of Asheville.  Seems like their reasoning is banks on snow being rate driven given the thermal profile.

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The NAM is a raging sleetstorm for many with the big warm nose. Thats why the kuchera maps look so much different than the one brick posted..

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GSP is discounting the NAM’s thermal profiles:

 

 

“The NAM is substantially warmer with temps aloft than

any of the global models we have at our disposal. For now the NAM

profiles are being discounted and not used in the fcst process,

not only due to the consensus in the other guidance, but to help

maintain better forecast continuity”

 

Also, they are thinking the mountains are going to see a larger percentage of the precip fall as sleet:

 

“"Snow" totals have declined by

a few inches over the northern GA/SC zones and in the more western

NC mtns, as more of the QPF is now expected to fall as sleet.”

 

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4 minutes ago, wncsnow said:

The NAM is a raging sleetstorm for many with the big warm nose. Thats why the kuchera maps look so much different than the one brick posted..

Once that warm nose makes an appearance for the RDU area, I've learned to count on it.  It's usually worse than modeled.  I'm not saying that's the case for this storm but I've found that mostly true for past storms.

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