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Wintry More SE Snow ? (1/16-1/18)

NWS Atlanta increased local totals to up to 2". This is great for everyone in south metro who were screwed on last storm.

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GaWx said:
Hopefully, any snow in ATL waits til after 5 PM or so.
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Yeah, Larry, I'm at 51.3 at 3. So it warmed up good today, but now the sun is gone, it should start dropping, and by the time the front eeks on thru here, I expect things will go down hill on roads pretty fast once we get into some flakes. My past experience with these things is it will give everyone else hours of snow, and blast thru here in the last hour of an ever skinnier front, lol. Of course, Ptree City says we'll do better than that, and since they are close by, and always good in my point forecast, I'm hoping for something to exceed my low expectations :) I'll be looking to Greg to give me some indication as to how things are up north of here :) So Greg, I want big totals from you, while I wait, and wait....and wait :)
 
000
FXUS64 KBMX 162005
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
205 PM CST Tue Jan 16 2018

.UPDATE...
MESOSCALE UPDATE.

&&

.SHORT TERM...

Snow is starting to move into the Birmingham Metro here just
before 2:00pm. A stronger band of heavier snow is stretching
through Pickens and Northern Tuscaloosa County now and should
start moving into the Tuscaloosa area in the next hour. Soundings
using any of the well-initialized models show completely saturated
profiles well into the dendritic growth zone. Temperatures aloft
remain well below freezing, which will not allow any melting of
the snowflakes. This combined with the saturated profiles not
allowing much evaporation is resulting in some fairly large
snowflakes that exhibit the "classic" dendrite snowflake shape.
One impressive feature is just how quickly the temperatures are
dropping as this band of snow approaches. In the last 40 minutes
or so, we`ve dropped 5 degrees here at the Shelby County Airport.
Birmingham has already dropped into the upper 20s while Anniston
is sitting at 41 degrees. We have gotten some reports of a brief
winter mix at the onset of precipitation, but this will quickly
transition to all snow as the colder air filter in.

The concern continues to be the icing of roads and bridges as the
initial snow melts then re-freezes when temperatures plummet.
We`ve already seen this occur in the northwestern counties as the
temperature in Hamilton is sitting at 20 degrees now. Travel is
highly discouraged throughout central AL this afternoon and
evening with some roads in the northwest already being deemed
impassable.

Overall, the current forecast seems to be on track with the
timings across Central AL. Some high resolution guidance still
hinting at re-development of the snow bands in the southeastern
counties tonight, so will continue mention of impacts through this
evening as the system moves south and east of the I-85 corridor.

25/Owen


Previous short-term discussion:
Despite surface temperatures that have risen above freezing over
the past few hours roughly along and southeast of the Interstate
59 corridor we continue to observe noticable temperature decreases
across our west-central and northwest counties as the
precipitation has started to fall. The main concern continues to
be the risk of snow melting when it comes into contact with road
surfaces and then the moisture will freeze onto the pavement as
temperatures fall below freezing, creating icy patches and slick
spots on roadways. A winter weather advisory remains in effect as
snow will continue affect our northwest counties with snow
eventually impacting more of our central counties early this
afternoon along with portions of our south and eastern counties
this afternoon and evening.

Changes in the overall thinking is not huge. The one difference
is that the area of rain that is developing over southwestern
AL/southeastern MS will move into the southeast ahead of the front
and may provide a brief window of rain before the snow starts.
This will do two things. One it will moisten the overall column
and two it will begin to cool down the airmass ahead of the Arctic
air.

So we are still expecting a significant impact to the area even with
light amounts (2 inches or less). This a slow moving band and will
take almost sort of a staircase approach through the state.
Currently watching another band developing further south in MS
and this will then slide east into the area.

The approaching vort max at 500mb appears very impressive this
afternoon into tonight and will have an opportunity to enhance the
snow band as it moves east of I-59. PWAT values will surge in
this zone, and additional lift could result in snowfall amounts
exceeding our current forecast. The ECMWF, several European
Ensemble members, and the Regional Canadian indicate the potential
for 2-4 inch amounts along and east of I-59 all the way to our
eastern and southern borders. This scenario will be monitored for
a possible upgrade to a Winter Storm Warning. Impacts could be
significant across our entire forecast area due to temperatures
falling into the 20s and teens as the snow falls. A Wind Chill
Advisory has been issued for the entire area for tonight and
Wednesday morning for wind chills of 5 above zero to 5 below zero.

05/16/87
 
packfan98 said:
This is a great AFD discussion from the NWS in Raleigh. Fun reading!

As of 250 PM Tuesday...
Summary and Main Points:

NWP models have trended wetter over the past couple of runs, which
has boosted forecast confidence that the strong dynamic support
aloft associated with the vigorous shortwave trough will support a
quick burst of significant snowfall across central NC between 12 to
18z Wednesday, with an increasing likelihood of seeing a broad now
swath of 2 to 4 inches, with locally higher amounts of 5 to 6
possible across the interior portions of the RAH CWA. As such, have
upgraded all but the 2 most SE counties(Sampson, Wayne)to a Winter
Storm Warning. Due to the west-east difference in onset and ending
timing of precip, will segment the warning/advisories maps, with an
earlier start in the west and later ending in the east.

Details:
The well-advertised blast of Arctic air, that`s currently supporting
daytime highs in the teens and 20s across central and eastern TN, is
well on it`s way. There has been little change in the model timing
of the frontal passage through the area; between 06z-09 through the
NW Piedmont, to 12 to 15z across the southern Coastal Plain. On the
heels of this front, the high-amplitude positively-tilted trough
that currently extends from SE Canada back into the Southern Plains,
will assume a neutral tilt as it traverses the region on Wednesday,
a signal of the strengthening deep layer lift(coupled ascent from
strong s/w dynamics, vigorous jet divergence and deep layer f-gen)as
depicted by bufkit soundings that shows a classic cross-hair
signature(moderate to strong lift intersecting with the dendritic
growth zone(-10C to -18C))across central NC between 12 to 18z. As
such, expect the ana-frontal precip band to fill in and blossom
across the area during that time frame. So, it`s not a surprise to
see that models have trended wetter over the last 24 hours, with
average liquid equivalents now in the 0.20 to 0.40"range.

While we could see a brief period of rain or rain-snow mix at onset,
especially east of the US 1 where precip will move in after
daybreak, deep layer cooling will result in a quick change-over to
snow, with high snow:liquid ratios of 12:18 expected in the 3 to 6
hour window of strongest forcing, similar to the upstream ratios we
saw across Middle Tn and Central-Eastern Tn earlier this morning.
This would support a broad swath of 2 to 4 inches(0.5-1.0"/hour
rate)across interior sections of the state, with localized higher
amounts of 5 to 6 inches certainly possible given the favorable set
up for banding precip. Elsewhere, along the western and SE fringes,
1 to 3 inches are possible. Aggressive drying aloft will overwhelm
the area as early as late morning in the west to mid afternoon in
the east. This would support a brief transition of freezing drizzle
before ending, resulting in only trace ice amounts. The drying and
subsidence aloft is so strong and abrupt, that western portions of
the forecast could see sunshine by the afternoon, indeed a quick
hitting system.

Additionally, the Arctic high building in the Southern US in the
wake of this system will support very cold temperatures and wind
chills Wednesday and Wednesday night. Daytime highs will likely
occur during the early morning at most locations, with wet-bulb
cooling and CAA leading to a quick drop into the 20s by midday. NWLY
wind gusts of 15 to 20 kts will make it feel even colder, producing
wind chills in the teens and 20s.

Lows Wednesday night are expected to be in the teens, with wind
chill values approaching the single digits across much of central
NC. Given these frigid temperatures, any snow or slush on roads and
bridges/overpasses will freeze, making for treacherous road
conditions Thursday morning.
Click to expand...

Now THIS is how to write an AFD! Well done
 
Seems Bham is thinking that they redevelopment of that band won't be at the 1-59 corridor and more along and southeast of the I-85 corridor with new model guidance. (Not sure which because most still show it in the I-59 corridor east and south.)
 
SCweather said:
Didn't end badly last night when it happened.
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Heck, I'm thinking a half inch to an inch maybe and I'm very concerned about the warm nose with me west of y'all. The main reason why the NAM wasn't great this time was bad initialization. I don't think we can use that excuse here.
 
New 3km nam (so far) vs old run...big increase especially I85 AL to ATL corridor..
SmartSelectImage_2018-01-16-15-15-34.jpg SmartSelectImage_2018-01-16-15-15-59.jpg
 
Lynsy said:
Seems Bham is thinking that they redevelopment of that band won't be at the 1-59 corridor and more along and southeast of the I-85 corridor with new model guidance. (Not sure which because most still show it in the I-59 corridor east and south.)
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I think they are just looking at the trends to the west....its just not happening along I-59 right now. Lots of moisture back near Jackson, MS streaming eastward and not north-eastward...just my guess.
 
GeorgiaGirl said:
Heck, I'm thinking a half inch to an inch maybe and I'm very concerned about the warm nose with me west of y'all. The main reason why the NAM wasn't great this time was bad initialization. I don't think we can use that excuse here.
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Warm nose isn't the problem, it's the timing of the day. The NAM slowed it down which brings the precip through later and later in the morning. I'm still hoping for a inch here in Lexington. Not going to get greedy and ask for any more.
 
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