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Potential 1/17-1/18 threat


BullCityWx

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RAH's afternoon discussion (ratios discussed as well):

.NEAR TERM /THROUGH WEDNESDAY NIGHT/...

As of 318 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 snow
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.
 

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2 minutes ago, SEwakenosnowforu said:

Should we expect temps to maybe fall into the upper teens tomorrow? I mean...it is 16 in Memphis right now??

basically kuchera works on an algorithm that takes the entire column of air and decides the ratio. It screwed totals out in KY and TN so badly because of the upper air. Once precip starts the frigid upper air will crash down to the surface.  Hence the 12-15:1 ratios instead of 8-10:1.  

 

I expect 10-14:1 ratio across Wake county tomorrow. start at 10:1 before quickly going up to 14:1 so .6 of qpf will be between 6-8 inches

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3 minutes ago, mackerel_sky said:

Temps made it to 50 when we got that big clipper/ storm in 2003. By midnight, it was hammering snow as temps dropped through the 20s! Very good analog storm for temps, IMO 

Hope you get a few inches Mack.  I just want to see some flakes falling.  I was working out of town last storm we had.  Hoping for a dusting on the Harnett/Cumberland line.

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Here's the latest snowfall meteogram for RDU, taking the 18Z NAM runs into account. Model average now just above 5". Hmm.

EDIT: here's the link: http://www.meteor.iastate.edu/~ckarsten/bufkit/image_loader.phtml?site=krdu&nam=on&nam_mos=on&namm=on&gfs_mos=on&gfs=on&gfsm_mos=on&gfsm=on&nws=on&rap=on&obs=on&nam4km=on&con=on&ratio=11

Screen Shot 2018-01-16 at 3.56.53 PM.png

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2 minutes ago, griteater said:

Don't shoot me for posting this, but you can get your old school 1980's weather channel local forecast here at this site.  Just plug in your city - http://weatherdaddy.us/weatherdaddy/index.html?q=raleigh%2C+nc

1.gif

That is awesome!! Thank you for posting this... I miss that old look.

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4 minutes ago, rjtysinger said:

Hope you get a few inches Mack.  I just want to see some flakes falling.  I was working out of town last storm we had.  Hoping for a dusting on the Harnett/Cumberland line.

NWS is calling for 3-4" in Lillington.  I am 5 miles south of the Harnett/Cumberland line near Linden, so watching this area closely.

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3 minutes ago, JovialWeather said:

I've gotten to learn my around Tropical Tidbits now, but what sites/resources do you guys use for tracking real-time stuff? What radars/links do you find most helpful for nowcasting?

For real-time my two main sites are

 

https://radar.weather.gov/Conus/full_loop.php      National radar

 

www.spc.noaa.gov/exper/mesoanalysis/new/viewsector.php?sector=19

Real-time atmospheric conditions

 

Also add pivotalweather to your model watching.   They have great maps for snow

www.pivotalweather.com/

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Latest rgem is out and it smokes the Upstate tomorrow morning! Also huge totals for Central, NC. It does look like they're might be a minima east of Raleigh as that band dies out and quickly pivots east. Edit to add: it actually looks like an area just Southeast of Raleigh gets almost completely shut out on this run, with very heavy totals just to the west of that boundary.

I_nw_EST_2018011618_018.png

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1 minute ago, The Alchemist said:

At the bottom of the page the download this font link takes you to a site where you can search for audio by year.... its all there man... 

Nice!  Thank you sir!!

 

1 minute ago, burrel2 said:

Latest rgem is out and it smokes the Upstate tomorrow morning! Also huge totals for Central, NC. It does look like they're might be a minima east of Raleigh as that band dies out and quickly pivots east.

Burrel, don't you dare say that to me right now!

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