Discussion-OBS snow event sometime between 06z Thu 2/20-12z Fri 2/21?

[LibertyBell]

1 minute ago, weatherpruf said:

Supposedly it was that NW wind that killed us in Feb 89...

Yes I only like NW winds in the summer (dry and hot, love that low humidity heat!)

[weatherpruf]

12 minutes ago, LibertyBell said:

Yes I only like NW winds in the summer (dry and hot, love that low humidity heat!)

It's the best for fishing too; unless it is too strong. 10-15 NW is just great, preferably with an outgoing tide. 

[wdrag]

Headline may adjust Monday based on consensus for whatever-whenever. Right now the goal posts are very wide for possibly a 2 part event... instead of one major Nor'easter (or distant OCEAN storm?).  Its's good enough for this weekend unless WPC ensembles upshift to say 70% or greater for .25 frozen w.e NYC-LI. 

[brooklynwx99]

Next week's system has become increasingly ominous and holds potential for significant to major impacts from DC - NYC and even BOS. There are a few features that make this such a favorable setup, mirroring past major and even historic storms:

1. The most important feature of this setup is the retrograding and decaying west-based -NAO that migrates into central Canada. This is perhaps the most important feature for major EC snowstorms, and it is a huge factor here, as it slows the pattern down and locks in confluence. It also leads to the "banana" HP that often develops in these setups due to NVA downstream of the block.
2. This is a lobe of the polar vortex (PV) that is the impetus for the storm threat. This lobe becomes trapped under the block and will be forced to pivot under it, leading to a potential phase with the southern stream vort (x) over TX/OK. This kind of slow-moving, amplified ULL is also a main feature of major storm threats.
3. As is common in these setups, a disturbance, either coastal or otherwise, amplifies into the northern Atlantic and becomes trapped by the block, leading to a 50/50 ULL that departs. This is crucial for establishing confluence, which keeps heights in check downstream of the amplifying trough. Note how heights are zonal over ME and Atlantic Canada.
4. Last but not least, there is a transient spike in heights over the Pacific NW that links up with the blocking. This is a crucial piece of the puzzle... if that disturbance offshore destructively interferes with the blossoming +PNA, you get a weaker solution. However, the trend has been for constructive interference, which helps lead to downstream amplification.

It's also worth noting that this setup very closely mirrors past setups that delivered historic snowfall to the northern Mid-Atlantic. Notice the 500mb composite that has all four main features... the retrograding and decaying block, the amplifying trough over the MS River Valley, departing confluence, and a brief PNA spike as the storm is getting its act together.

Suffice it to say, this is probably the best synoptic setup that we have seen enter the medium range since February 2021 and it does hold the potential to be just as impactful. The GFS not being on board is pretty common in these setups. However, we will want to see this amplification signal enter the 96 hour window, so if we see this signal last into Monday, talks about a legitimate major snowstorm will hold more weight. Right now, it's worth being cautious, but the pattern has been screaming this kind of outcome for a week now, and it is bolstered by past outcomes.

[LibertyBell]

7 minutes ago, brooklynwx99 said:

Next week's system has become increasingly ominous and holds potential for significant to major impacts from DC - NYC and even BOS. There are a few features that make this such a favorable setup, mirroring past major and even historic storms:

1. The most important feature of this setup is the retrograding and decaying west-based -NAO that migrates into central Canada. This is perhaps the most important feature for major EC snowstorms, and it is a huge factor here, as it slows the pattern down and locks in confluence. It also leads to the "banana" HP that often develops in these setups due to NVA downstream of the block.
2. This is a lobe of the polar vortex (PV) that is the impetus for the storm threat. This lobe becomes trapped under the block and will be forced to pivot under it, leading to a potential phase with the southern stream vort (x) over TX/OK. This kind of slow-moving, amplified ULL is also a main feature of major storm threats.
3. As is common in these setups, a disturbance, either coastal or otherwise, amplifies into the northern Atlantic and becomes trapped by the block, leading to a 50/50 ULL that departs. This is crucial for establishing confluence, which keeps heights in check downstream of the amplifying trough. Note how heights are zonal over ME and Atlantic Canada.
4. Last but not least, there is a transient spike in heights over the Pacific NW that links up with the blocking. This is a crucial piece of the puzzle... if that disturbance offshore destructively interferes with the blossoming +PNA, you get a weaker solution. However, the trend has been for constructive interference, which helps lead to downstream amplification.

It's also worth noting that this setup very closely mirrors past setups that delivered historic snowfall to the northern Mid-Atlantic. Notice the 500mb composite that has all four main features... the retrograding and decaying block, the amplifying trough over the MS River Valley, departing confluence, and a brief PNA spike as the storm is getting its act together.

Suffice it to say, this is probably the best synoptic setup that we have seen enter the medium range since February 2021 and it does hold the potential to be just as impactful. The GFS not being on board is pretty common in these setups. However, we will want to see this amplification signal enter the 96 hour window, so if we see this signal last into Monday, talks about a legitimate major snowstorm will hold more weight. Right now, it's worth being cautious, but the pattern has been screaming this kind of outcome for a week now, and it is bolstered by past outcomes.

ominous to me means dangerous.... do you foresee widespread power outages with this? we haven't discussed how high the winds will be.

 

[NEG NAO]

16 minutes ago, wdrag said:

Headline may adjust Monday based on consensus for whatever-whenever. Right now the goal posts are very wide for possibly a 2 part event... instead of one major Nor'easter (or distant OCEAN storm?).  Its's good enough for this weekend unless WPC ensembles upshift to say 70% or greater for .25 frozen w.e NYC-LI. 

wouldn't that lessen the impact and open the door to mixing changeover issues in parts of the region? the December 5-6 , 2003  storm was 2 parts so could it be similar to this ?

Snow and ice storm, December 5-6, 2003 - Storm Summary

[LibertyBell]

2 minutes ago, NEG NAO said:

wouldn't that lessen the impact and open the door to mixing changeover issues in parts of the region? the December 5-6 , 2003 was 2 parts so could it be similar to this ?

Snow and ice storm, December 5-6, 2003 - Storm Summary

we had this in the late January 2011 storm too.

We never changed over in the December 2003 storm but the mix line was 5 miles south of us on the first day of the storm (we had our best snowfall rates that day too.)

we did change over to sleet and thundersleet in the late January 2011 snowstorm and to very heavy snow that night.

 

[NEG NAO]

How often do you see the words "Snow Likely" in a forecast 6 days in advance ?

ZFP from KOKX

[nycsnow]

LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Key Points:

* Colder and windy conditions expected early next week after a cold
  frontal passage Sunday night.

* Potential is increasing for a major winter storm from Wednesday
  night into Thursday night.

Complex pattern developing over North America during this time
should help lock in cold air, with one large closed low developing
over eastern Canada and another in its wake over the northern Plains
and upper Great Lakes. At the surface, strong low pressure moving
from upstate New York toward the Canadian Maritimes Sunday night
will bring a cold front through, with colder and brisk conditions
for Monday and possibly into Tuesday via a tight pressure gradient
between the low and strong high pressure off to the west.

Meanwhile, shortwave energy moving onshore the West Coast early next
week should dive toward the southern Plains by Wed AM and initiate
sfc cyclogenesis along the northern Gulf coast daytime Wed. The
degree to which this system phases with the northern Plains closed
low will determine the track and intensity of the developing sfc low
as it moves up the Southeast coast Wed night and then off the Mid
Atlantic coast Thu/Thu night, pulling away on Fri. There is
increasing potential for a major winter storm to impact the area
from Wed night into Thu night with heavy snow during this time, also
strong N winds Thu night--the 12Z ECMWF ensemble control run shows
an intense low off the Mid Atlantic coast passing just outside the
40N/70W benchmark Thu night, bringing major snowfall for all the I-
95 cities from DC to Boston, with its axis of heaviest snowfall very
close or just south and east which make sense given that storm
track, while the ensemble control run shows widespread 50-60%
potential for 6 or more inches of snow during this time. The
Canadian model and its ensemble are in close agreement, while the
deterministic GFS/ICON are suppressed, showing the heaviest snow
mostly away from the big cities, impacting eastern Delmarva and
southern NJ over to the Cape and Islands of MA. That said, the GEFS
does show some ensemble members supporting the ECMWF/Canadian
solution. Enough confidence in winter storm potential exists to
include mention in the HWO.

[LibertyBell]

50 minutes ago, NEG NAO said:

How often do you see the words "Snow Likely" in a forecast 6 days in advance ?

ZFP from KOKX

about as often as you see rain likely or wind likely

[BoulderWX]

Gfs looks like it will go OTS after nailing Delmarva pretty good but the idea is still there. 

[NEG NAO]

7 minutes ago, LibertyBell said:

about as often as you see rain likely or wind likely

6 days in advance ? lots can go wrong why do you think Walt is playing it conservative ? Also Mt. Holly shows likely so they probably had a conference call with Upton

[NEG NAO]

2 minutes ago, BoulderWX said:

Gfs looks like it will go OTS after nailing Delmarva pretty good but the idea is still there. 

18Z uses same data from  12Z no big surprise

[LibertyBell]

1 minute ago, NEG NAO said:

6 days in advance ? lots can go wrong why do you think Walt is playing it conservative ?

likely isn't a certainty, likely to me means a 50% or higher probability.

everything is  a probability.... perhaps a chance of snow would be more accurate but maybe they wanted to convey a higher degree of likelihood.  Our local channels are also doing it, Lee Goldberg just said the probabilities of significant snowfall have increased on WABC 7.

[Nibor]

5 minutes ago, BoulderWX said:

Gfs looks like it will go OTS after nailing Delmarva pretty good but the idea is still there. 

Coastal scraper like 12z. Wouldn’t take much for it to come in line with other guidance. 

[LibertyBell]

1 minute ago, NEG NAO said:

18Z uses same data from  12Z no big surprise

yep, 6z and 18z don't include the new upper air data

[BxEngine]

No, thats not true. They have less new data, especially upper air, but they still incorporate new data in between. 

[BxEngine]

https://ams.confex.com/ams/27WAF23NWP/webprogram/Handout/Paper273676/GFS4cycle_2015_NWP_Chicago_15A.pdf

[Monmouth_County_Jacpot]

1 minute ago, Nibor said:

Coastal scraper like 12z. Wouldn’t take much for it to come in line with other guidance. 

Bottom line you want that trof further west in the Midwest. The further east it is more likely storm gets pushed south

[EastonSN+]

GEFS took a step back. On to 0z.

[wdrag]

1 hour ago, NEG NAO said:

wouldn't that lessen the impact and open the door to mixing changeover issues in parts of the region? the December 5-6 , 2003  storm was 2 parts so could it be similar to this ?

Snow and ice storm, December 5-6, 2003 - Storm Summary

I'm not thinking rain at all...  looks too cold... my main concern is that 5H closes off to our nw in NYS..  otherwise if it closes too late over BOS, most of this is to our south and southeast---just my thinking.  18z GEFS has snow (despite the nil op) but max axis Southeast of us... that's my concern... if it doesn't amp, it slides out to our se. 

[LibertyBell]

50 minutes ago, BxEngine said:

No, thats not true. They have less new data, especially upper air, but they still incorporate new data in between. 

yes it's specifically less new land RAOBs, but still some new data

I posted a pdf about it a few years ago

 

file:///C:/Users/CosmicQuantum/Pictures/GFS4cycle_2015_NWP_Chicago_15A.pdf

 

I don't know if this is the same paper you posted but I'll take a look

All cycles have been steadily improved. • 12Z cycle is comparable to 00Z cycle. • 06Z and 18Z cycles are worse than 00Z and 12Z cycle

 

GFS 06Z and 18Z cycle are less skillful than the 00Z and 12Z cycles. • The difference in the NH is the largest

 

06Z data count is always less (10~30%) than other cycles. • Even though the 18Z-cycle forecast score is worse than that of the 00Z cycle, 18Z conventional data count is not less than 00Z data count!

 

 

Note even though the total number of land soundings is almost the same among the four cycles, 06Z and 18Z have much less land RAOBs than the 00Z and 12Z cycles !

 

 

18Z and 00Z have the same amount of conventional data, but 18Z has worse forecast skills than 00Z. On the other hand, 12Z has less conventional data than 00Z, but 12Z and 00Z have similar forecast skills.

 

 

 

06Z and 18Z cycles have 10 to 20 times less land rawinsonde observations than the 00Z and 12Z cycles. Is the lack of RAOBS responsible for the lower forecast scores of the 06Z and 18Z cycles? More investigation is required to understand its impact.

 

 

 

The forecast skills of GFS 06Z and 18Z cycles are not as good as that of the 00Z and 12Z cycles.

 

 

 

 

[NEG NAO]

5 minutes ago, wdrag said:

I'm not thinking rain at all...  looks too cold... my main concern is that 5H closes off to our nw in NYS..  otherwise if it closes too late over BOS, most of this is to our south and southeast---just my thinking.  18z GEFS has snow (despite the nil op) but max axis Southeast of us... that's my concern... if it doesn't amp, it slides out to our se. 

 other METS say that is a common error the GFS makes - you don't agree ?  Also what is your opinion about Upton and Mt. Holly forecasting "snow likely" for Thursday ?- so far out........

[LibertyBell]

46 minutes ago, BxEngine said:

https://ams.confex.com/ams/27WAF23NWP/webprogram/Handout/Paper273676/GFS4cycle_2015_NWP_Chicago_15A.pdf

it's the same paper but I can't post the link so I just quoted from it, it shows the lower verification scores of 6z and 18z and which type of data are not ingested in those runs.

[NEG NAO]

1 minute ago, LibertyBell said:

it's the same paper but I can't post the link so I just quoted from it, it shows the lower verification scores of 6z and 18z and which type of data are not ingested in those runs.

it says the 18Z and 6Z are less skillful so thats why many METS discount them.........

[BxEngine]

Saying they are less skillful is a completely different argument than “they receive no new data”. Thats simply not true. Back to the storm thread. 

[NEG NAO]

I wouldn't forecast snow likely on Thursday 6 days out because there is a possibility there could be a timing change - especially if it is a 2 part storm as Walt has suggested ......I would just leave it at a 40 or 50% chance for now

[MJO812]

Another big hit by the euro

[NEG NAO]

2 minutes ago, MJO812 said:

Another big hit by the euro

18Z ? Got Graphics ?

[MJO812]

Just now, NEG NAO said:

18Z ?

Yes