January 25-26 Winter Storm Potential

[Hurricane Agnes]

7z NBM.

[MickeyTim6533]

geez, gfs at hour 228....wow

[Duca892]

I think there is almost a diving line in the Lehigh Valley between who sees 8+ and who doesn’t when all the trending and everything is said and done. My expectations for Allentown/Bethlehem etc is these areas top out around 7/8in and then get dosed with slop 

[MickeyTim6533]

3 minutes ago, Duca892 said:

I think there is almost a diving line in the Lehigh Valley between who sees 8+ and who doesn’t when all the trending and everything is said and done. My expectations for Allentown/Bethlehem etc is these areas top out around 7/8in and then get dosed with slop 

I'm new to the boards, are you always this pessimistic? LOL

[Thesmithsinde]

"Long" time lurker, learner, thank you !

What's is a time frame for start up in Mid Delaware?

We'll be at a wedding in KOP area Sat Night and trying to plan out what time to bug out of it to get home.

Thanks again.

 

[Duca892]

10 minutes ago, MickeyTim6533 said:

I'm new to the boards, are you always this pessimistic? LOL

I lol'd, I always remind everyone i don't know jack, but it always feels like in these scenarios warm air aloft is under modeled. I can't remember many times where a mix was involved and it was either delayed further out or didn't happen. Sorry will clean that up because I don't want to creative a negative experience here as I too love this forum 

[The Iceman]

Trust the pro’s

 

 

[MickeyTim6533]

Stolen from Central PA forum, great write up from CTP:

 

Excellent write up by NWS State College in their AFD:

“All in all, the probability of snowfall amounts exceeding 12
inches has increased to 60-80 percent across much of central
PA. The probability of more than 18 inches ranges from 15 to 40
percent. Amounts near 24 inches can`t be ruled out (10 percent
chance) especially if the comma head sits over central PA Sunday
night. Always prepare for the worst case scenario and continue
to check the forecast as it evolves. Now is the time to prepare.
Think snow blowers, re-arranging travel plans to avoid travel
during the storm, what to do in case of a power outage, etc.
Remember it will be very cold before, during and after the
storm. Never run a generator indoors due to carbon monoxide.

Now if you really enjoy meteorology and want to know *why* we
are predicting the most significant accumulations in the past
5+ years, feel free to read on through the remainder of this KEY
MESSAGE 2 discussion. We`ve had our fair share of cold snaps
this winter season, and tomorrow (Friday) will be no exception
after the next Arctic front pushes through. A large factor
driving all this cold weather has been the Polar Vortex
displaced from the North Pole, with a tendency for the vortex to
find itself over Hudson Bay and northern Quebec. With
displacement that far south, we`ve gotten plenty of cold air,
but it`s also nudged the storm track south of our area for many
of the recent events. If you`ve ever heard people say "it`s too
cold to snow", it`s not that it`s physically too cold to snow,
it usually just means that the storm track has shifted far
enough to the south that we end up under dry high pressure while
our temps are cold.

One key difference this time is the influence of a Pacific
storm, located off the coast of southern California this
evening, and a strengthening subtropical jet to its south. Over
the next 24 hours these features will cross the Baja Peninsula
of Mexico and then into Texas. Southwesterly flow out ahead of
this southern stream feature will pump warmer air into the Gulf
Coast and Southeastern US Saturday night into Sunday. At the
same time, a northern stream shortwave trough coming down from
western Canada into the Great Plains will bring a reinforcing
shot of cold air to the back side of the northern longwave
trough. The increasing temperature gradients will result in an
overall increase in wind speed aloft at jet stream altitude, and
an amplification of the northern stream trough and ridge. By
Sunday, the right entrance region of the northern jet and the
left exit region of the southern jet will align to produce
enhanced upward motion through the troposphere. Remaining
uncertainty in the forecast largely depends on the degree of
phasing of these two jets, the angle at which they align, and
how much amplification there is of the ridge out ahead of the
deepening trough.

The very cold air in place ahead of this system also plays other
crucial roles to increase impacts. At 00Z Sunday, model
consensus depicts a 1040+ mb high over New York State, which
only slowly moves northeastward across New England over the next
24 hours. The deep, cold blocking high to the northeast of a
winter storm is a textbook feature that supplies a stream of
cold air down the Alleghenies and provides a cold dome for
warmer, less dense air parcels streaming in from the southwest
to ascend over. That upward motion is key to production of
hydrometeors - in this case snow. And then there is the key role
that cold temperatures have on ice crystal habits. The so
called "dendritic growth zone" exists where temperatures are
between roughly 0F and 10F. Given low temperatures Saturday
night in the single digits, some spots might start off with a
DGZ that extends from the ground up 10,000 to 15,000 feet which
is pretty remarkable for a large synoptic storm in this region.
As long as the column saturates quickly enough, any snow that
falls late Saturday night and into early Sunday morning could be
very high ratio, fluffy, rapidly accumulating snow that
consists of many pristine dendrites (SLRs 15-20:1, could be
even higher if the column saturates faster but there is dry air
at low levels to overcome at onset). So after a few hours of
virga, accumulations have the potential to begin with a
vengeance in the predawn hours Sunday, especially from I-80
south.”

 

 

 

[The Iceman]

Just now, Duca892 said:

I lol'd, I always remind everyone i don't know jack, but it always feels like in these scenarios warm air aloft is under modeled. I can't remember many times where a mix was involved and it was either delayed further out or didn't happen. Sorry will clean that up because I don't want to creative a negative experience here as I too love this forum 

You’re not wrong, in this area most of the time the mixing is way stronger than modeled. However, most of the time we also don’t have a giant arctic high providing highs in the teens either. I totally get the “pessimism” so to speak though, I just think that this situation is a bit different than other events where we mix. We shall see though!

[geeter1]

28 minutes ago, Duca892 said:

I think there is almost a diving line in the Lehigh Valley between who sees 8+ and who doesn’t when all the trending and everything is said and done. My expectations for Allentown/Bethlehem etc is these areas top out around 7/8in and then get dosed with slop 

I believe there are equal chances this storm could also over perform. We'll know on Monday...

[Lucy Pull]

9 minutes ago, Duca892 said:

I lol'd, I always remind everyone i don't know jack, but it always feels like in these scenarios warm air aloft is under modeled. I can't remember many times where a mix was involved and it was either delayed further out or didn't happen. Sorry will clean that up because I don't want to creative a negative experience here as I too love this forum 

Tend to agree, especially with NAM being so excited about the warm nose. I’ve only really seen these over-perform when rates stay high.
 

I think if we keep rates up it could slow it down. If they slow up i think the opportunity is there for that warm tongue to shoot north. 

[JTA66]

25 minutes ago, Thesmithsinde said:

"Long" time lurker, learner, thank you !

What's is a time frame for start up in Mid Delaware?

We'll be at a wedding in KOP area Sat Night and trying to plan out what time to bug out of it to get home.

Thanks again.

 

Welcome. Start times vary across the guidance and of course it will be snowing in DE before PA. I’d guess you’re good if you get home before 2-3am

(But I’m not a met.)

[Violentweatherfan]

22 minutes ago, The Iceman said:

Trust the pro’s

 

 

Look at the timestamp it’s early and before the most recent model runs

[ChescoWx]

38 minutes ago, Duca892 said:

I think there is almost a diving line in the Lehigh Valley between who sees 8+ and who doesn’t when all the trending and everything is said and done. My expectations for Allentown/Bethlehem etc is these areas top out around 7/8in and then get dosed with slop 

I am sure you know but that slop will likely be accumulating sleet which counts as snow....

[ChescoWx]

Updated and latest NWS Forecast

[Violentweatherfan]

Ninja’d

[JTA66]

Ah man, big bust heading for NYC. Cantore is there!  

[Hurricane Agnes]

6z 12k NAMs still wants to put other frozen in there.

[Physicsteve]

Based on the map Paul just posted, which i had to double and triple check all the time stamps, maybe the real mets are also thinking the models are overdoing the non-snow. Paging @MGorse, as if he’s not busy or anything. 

ETA: Does that map *include sleet* as snow like some other models? Also off topic and apologize if bantery, but how does the NBM account for some including sleet as 3:1 snow and not others?

[Hurricane Agnes]

Some other 6zs - ICON, Canadian & Ukie.

[Albedoman]

54 minutes ago, MickeyTim6533 said:

Stolen from Central PA forum, great write up from CTP:

 

Excellent write up by NWS State College in their AFD:

“All in all, the probability of snowfall amounts exceeding 12
inches has increased to 60-80 percent across much of central
PA. The probability of more than 18 inches ranges from 15 to 40
percent. Amounts near 24 inches can`t be ruled out (10 percent
chance) especially if the comma head sits over central PA Sunday
night. Always prepare for the worst case scenario and continue
to check the forecast as it evolves. Now is the time to prepare.
Think snow blowers, re-arranging travel plans to avoid travel
during the storm, what to do in case of a power outage, etc.
Remember it will be very cold before, during and after the
storm. Never run a generator indoors due to carbon monoxide.

Now if you really enjoy meteorology and want to know *why* we
are predicting the most significant accumulations in the past
5+ years, feel free to read on through the remainder of this KEY
MESSAGE 2 discussion. We`ve had our fair share of cold snaps
this winter season, and tomorrow (Friday) will be no exception
after the next Arctic front pushes through. A large factor
driving all this cold weather has been the Polar Vortex
displaced from the North Pole, with a tendency for the vortex to
find itself over Hudson Bay and northern Quebec. With
displacement that far south, we`ve gotten plenty of cold air,
but it`s also nudged the storm track south of our area for many
of the recent events. If you`ve ever heard people say "it`s too
cold to snow", it`s not that it`s physically too cold to snow,
it usually just means that the storm track has shifted far
enough to the south that we end up under dry high pressure while
our temps are cold.

One key difference this time is the influence of a Pacific
storm, located off the coast of southern California this
evening, and a strengthening subtropical jet to its south. Over
the next 24 hours these features will cross the Baja Peninsula
of Mexico and then into Texas. Southwesterly flow out ahead of
this southern stream feature will pump warmer air into the Gulf
Coast and Southeastern US Saturday night into Sunday. At the
same time, a northern stream shortwave trough coming down from
western Canada into the Great Plains will bring a reinforcing
shot of cold air to the back side of the northern longwave
trough. The increasing temperature gradients will result in an
overall increase in wind speed aloft at jet stream altitude, and
an amplification of the northern stream trough and ridge. By
Sunday, the right entrance region of the northern jet and the
left exit region of the southern jet will align to produce
enhanced upward motion through the troposphere. Remaining
uncertainty in the forecast largely depends on the degree of
phasing of these two jets, the angle at which they align, and
how much amplification there is of the ridge out ahead of the
deepening trough.

The very cold air in place ahead of this system also plays other
crucial roles to increase impacts. At 00Z Sunday, model
consensus depicts a 1040+ mb high over New York State, which
only slowly moves northeastward across New England over the next
24 hours. The deep, cold blocking high to the northeast of a
winter storm is a textbook feature that supplies a stream of
cold air down the Alleghenies and provides a cold dome for
warmer, less dense air parcels streaming in from the southwest
to ascend over. That upward motion is key to production of
hydrometeors - in this case snow. And then there is the key role
that cold temperatures have on ice crystal habits. The so
called "dendritic growth zone" exists where temperatures are
between roughly 0F and 10F. Given low temperatures Saturday
night in the single digits, some spots might start off with a
DGZ that extends from the ground up 10,000 to 15,000 feet which
is pretty remarkable for a large synoptic storm in this region.
As long as the column saturates quickly enough, any snow that
falls late Saturday night and into early Sunday morning could be
very high ratio, fluffy, rapidly accumulating snow that
consists of many pristine dendrites (SLRs 15-20:1, could be
even higher if the column saturates faster but there is dry air
at low levels to overcome at onset). So after a few hours of
virga, accumulations have the potential to begin with a
vengeance in the predawn hours Sunday, especially from I-80
south.”

 

 

 

Note this.  I am NOT chuckling:  

 

As long as the column saturates quickly enough, any snow that
falls late Saturday night and into early Sunday morning could be
very high ratio, fluffy, rapidly accumulating snow that
consists of many pristine dendrites (SLRs 15-20:1, could be
even higher if the column saturates faster but there is dry air
at low levels to overcome at onset). So after a few hours of
virga, accumulations have the potential to begin with a
vengeance in the predawn hours Sunday, especially from I-80
south.”

[Albedoman]

28 minutes ago, JTA66 said:

Ah man, big bust heading for NYC. Cantore is there!  

thundersleet 

[MGorse]

12 minutes ago, Physicsteve said:

Based on the map Paul just posted, which i had to double and triple check all the time stamps, maybe the real mets are also thinking the models are overdoing the non-snow. Paging @MGorse, as if he’s not busy or anything. 

ETA: Does that map *include sleet* as snow like some other models? Also off topic and apologize if bantery, but how does the NBM account for some including sleet as 3:1 snow and not others?

Looking at some of the model forecast soundings, some  of the guidance is showing freezing rain or even plain rain (depending on location) however the sounding looks more like sleet. Model snowfall graphics typically include sleet as snow and sleet are counted together. The FRAM graphic above is strictly ice accretion from freezing rain. The Kuchera snowfall maps be careful with as it only uses the maximum temperature aloft to calculate snowfall. The 10:1 ratio maps also use with caution as that ratio is not usually representative during a storm as the ratios certainly change up and down as the storm evolves.

[Albedoman]

1 hour ago, Duca892 said:

I lol'd, I always remind everyone i don't know jack, but it always feels like in these scenarios warm air aloft is under modeled. I can't remember many times where a mix was involved and it was either delayed further out or didn't happen. Sorry will clean that up because I don't want to creative a negative experience here as I too love this forum 

Yes the LV has been burned many times Duncan892 with warm nose intrusions, but that is to be expected in the LV, but not this time. The Quebec high is too strong. The sleet line will be around th eMid Montgomery Bucks lines  on the other side of the S mtn range. If we do get any ice, it will be sleet mixed in with the heavier bands of snow or freezing drizzle. This only comes with experience with doing this for 40+ years and seeing every historical pounding snowstorm the LV has received since 1983 most  infamous dumping  where we got 5" inches in one hour and ended up with 23 inches.