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Central PA - Winter 2018-19


pasnownut

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3 minutes ago, pawatch said:

4 models South now; #ICON, #CFS, #UKMET, and #IBM Deep Thunder.

Next up the Euro??

Unfortunately not having one of the biggies on our side is a concern. If one caves of starts back the other way by tomorrow night my white flag may fly. 

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Sounds like CTP didn’t shut the door on us.....yet. Good read and what I’ve been driving at. (Ok they MAY know a little more that I do). 

 
.NEAR TERM /UNTIL 7 AM WEDNESDAY MORNING/...
Clouds will continue to increase tonight, creeping eastward and
lowering slightly. The problem of the night will be if freezing
drizzle will form instead of snow flakes. The soundings off the
NAM and RAP show temps getting colder as the thickness of the
low-moist layer increases/deepens. While the temp of the clouds
never quite gets into the preferred DGZ, it is well below
freezing through the entire layer. Not enough of a signal to
drop mentions of FZDZ, but enough that we will keep away from an
advy at this point. Will continue to watch the obs and seek
reports to discern p-type this evening and overnight.

Prev...
Weak isentropic lift/WAA ahead of northern stream shortwave
pivoting eastward from southern Ontario into Quebec and
associated surface cold front moving southeast through the Great
Lakes should promote some light snow across the western
mountains tonight into early Wednesday. Soundings indicate
shallow moisture profiles with weak low level upslope flow
supporting very light snow or patchy freezing drizzle. A coating
of snow/snizzle is possible by 12Z Wednesday and could make for
some slippery travel mainly west of US-219 for the AM commute.

&&

.SHORT TERM /7 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
*Widespread light to moderate snowfall Thursday PM-Friday AM

The passage of cold front will shift winds to the WNW direct
colder air downwind of the Great Lakes. Expect a brief period
of lake-effect snow showers gusty winds through Wednesday
afternoon before high pressure arrives Wednesday night. Any
additional snow accumulation should be very light/less than 1
inch.

Thursday will start dry but end white as a broad swath of snow
spreads southwest to northeast across central PA by late
evening. MaxTw`s aloft increase rather steadily Thursday night
and approach 0C early Friday morning so can`t rule out a period
of mixed precip over the southern tier given marginal profiles
at the tail end of the event. Used a blend of NBM/WPC for QPF
and snow amounts which support a widespread 1-3" accumulation.
The Friday morning commute could be impacted with bulk of snow
expected Thursday night.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
*likelihood of a major winter storm for the holiday weekend
 followed by arctic cold snap and dangerous wind chills into
 early next week. Snowfall in excess of 1 foot possible over the
 Northern Mountains of Pennsylvania.

Round 1 contain the upcoming 1-2 punches of winter weather will
occur Thursday evening through the mid morning Friday as a flat
wave aloft and weak sfc low reflection tracks NE from St. Louis
at 18Z Thursday to Syracuse NY by 12Z Friday. Periods of
moderate large-scale UVVEL and fairly low amounts of available
moisture will lead to a widespread 1.5 to 3 inch snowfall across
the majority of the CWA though a few spots across the higher
terrain of Central and Nrn Pa could end up with around 4" over
the 6-10 hour period of light snow. The least amounts of snow
(around 1.5") will likely fall across the far southeast zones.

Friday late morning right through early Saturday looks quiet as
a ridge of high pressure extends from the Upper Great Lakes
southeast through the Mid Atlantic Region. The focus will shift
to a major winter storm that`s likely to impact much of the
state Saturday afternoon through Sunday.

Confidence remains high for winter storm impacts this weekend,
however the exact details of the storm with respect to the
timing, location and depth of the above freezing layer of air
advecting north into the state are still imprecise.

Much of this is a result of slight variations in the speed and
track of the storm which will play a crucial rule in determining
precipitation types and amounts.

Highest confidence in heavy (even excessive) amounts of snow of
over 1 foot are across the northern third of the CWA where
multi-model consensus continues for the potential of mixed
precip during just a short few hour period Sat night.

06Z/12Z Operational GFS and it`s EFS mean storm track are at the
southeastern end of the envelope of solutions, While the 12Z
operational EC, Canadian model and GFS-FV3 tracks the 994-998MB
SFC low up the Ohio River Valley northeast across either
southern or even Central PA late Sat night and early Sunday
morning (which would even greatly trim the snowfall across the
North- Central Mtns of the state.

That being said regarding the changeover timing from snow and
potential amounts up north, most if not the entire area will see
a several...6 hour period of snow Sat afternoon and evening well
ahead of the main South-Southwesterly LLJ axis. This first shot
of snow will amount to anywhere from 2-7 inches with the most
likely falling near and to the north of a KJST to KUNV and KIPT
line. Steep q-stnry boundary for ascent will be located WSW to
ENE across the CWA Sat night with mean 925 to 850 mb wet bulbs
temps around zero near the I-80 corridor. Beneath the thicker,
above freezing layer aloft across Southern PA will be sun-
freezing sfc wet bulbs right down to the PA turnpike in southern
PA through 06Z Sunday (thanks to strong LLVL Ageostrophic
component of 30-35 kts from the NNE - helping to lock in the
LLVL cold air). Temps may warm several deg F during the predawn
hours Sunday lifting the FZRA/Rain line north to near a
KIDI...KUNV and KAVP line. However, a multi-model blend,
incorporating the colder members of the GFS model suite, keep
sfc temps below freezing longer/further south early Sunday.

There is "some" similarity of this storm to the other big
snowmaker back on Nov 15-16th (with respect to potentially high
precip rates, and the location, timing and depth of the above
freezing layer aloft). The mid-November storm did have a bit
more negative tilt to the upstream trough and a several hour
period of strong upper level divergence and deep/strong UVVEL
that delayed the changeover to mixed precip by a few hours
during the time of heaviest precip rates.

A zone of mixed precip (several to 6 inches of snow, topped by
a layer of sleet and freezing rain and even a brief, few-hour
period of plain rain) appears most likely near and just to the
south of Interstate 80.

Further south near the I-76, I78 and I-81 corridors should see
a general 1-4 inches of snow Sat afternoon and evening followed
by a changeover to sleet, FZRA then a period of moderate to
ocnly heavy rain later Sat night/early Sunday with rapid stream
rises possible.

Even without the exact details, this storm will likely result
in significant disruptions to travel and daily activities so
please be prepared and plan accordingly.

Brutally cold, arctic air will blast into the area during the
day Sunday into early next week. GEFS shows temps falling
steadily during the day sunday with NW winds gusting between
30-40 mph.

GEFS guidance shows low temps Sunday night in the single digits
above and below zero. Gusty winds combined with the frigid
airmass should result in potentially dangerous wind chills in
the -10 to -20F range.

After taking a leave of absence over the last month and a half,
winter is poised to make a big comeback with odds heavily
favoring cold weather/below average temperatures through the
second half of January into early February.

&&
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18 minutes ago, Atomixwx said:

Thanks for posting that in 26pt font, so that us old facks can read. You really look out for us. That's why we used the hashtag #Anused. You get the job done when nobody else will. You really #Anused us there. And for that, I thank you. 

Ur whacked..........

 

I like that about you.

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Great write up by CTP !

I see that they mentioned the November storm that we had 2 months ago in regard to the potential of a good front end snow thump due to heavy precip rates. They also mention cold air staying anchored in for a good duration across most of our region.

I think If we get great precip rates to start, we can over perform on the front end.

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1 minute ago, Blizzard of 93 said:

Great write up by CTP !

I see that they mentioned the November storm that we had 2 months ago in regard to the potential of a good front end snow thump due to heavy precip rates. They also mention cold air staying anchored in for a good duration across most of our region.

I think If we get great precip rates to start, we can over perform on the front end.

yup....thats what I'm hangin my hat on for now.  Some models show a good front end thump, and with any luck and flattening out front, it could pull of the XMAS 06' miracle in evolution.  (i think it was 06). 

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We should root for a stronger system to move in Thursday night into Friday since that would shift the baroclinic zone farther south, allowing this weekend's event to track farther south. Thursday night's system seems like a general 2-4" event across most of the region.

For this weekend, I would definitely be more concerned about the ice threat as opposed to snow, especially if I lived N and W of Interstate 81. There is a definite cold air damming signal, which CTP alluded to in the discussion, and it is often underestimated by the models leading up to events of this nature. That being said, strong frontogenetic lifting associated with warm air advection could lead to a solid burst of snow at the start across Central PA Saturday night, as hinted by the 18z GFS. The key to overperforming in this system would be to get strong rates at the start, which would cool the column and allow cold air to stick around longer. Definitely something to watch over the next few days. 

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3 minutes ago, bubbler86 said:

It has to finish reading the MA Long Range thread to figure out its next move.

 

 

waiting for PSU's approval

edit - i like him and all, but man he can be like a debate moderator (which he is at school or something).  Its a discussion forum, not debate club.  we all know we can be right or wrong for the right or wrong reasons in this sport.

 

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