Snow Events Week of 02/17

jimv45 wrote:Hyde I am thinking more of the 1 then the 3 and some sleet. Can't wait!!!

I'll take what we can get but doesn't look promising. How much did you get from last night? I wound up with 3.

hyde345 wrote:NWS Albany is not impressed with next system.


Wednesday into Thursday, the focus will be on a deamplifying
midlevel trough moving from the Upper Midwest into southeast
Canada. Attendant primary surface low will remain well to our
west, with possible secondary low development off the southern
New England coast on Thursday. This is a pattern we have seen
often this winter. Isentropic lift will begin Wednesday
afternoon into the evening as the 850 mb winds increase to 40-50
kt out of the south-southwest. Thermal profiles appear cold
enough to support snow everywhere at the onset. Depending on the
timing, it could be working in during the end of the evening
rush hour, especially south and west of Albany. Warmer air aloft
will change p-type to sleet and freezing rain Wednesday night.
The departing high isn`t in an ideal position to keep cold air
locked in place, but it looks like at least light icing is
possible before temperatures rise late Wednesday night into
Thursday morning. Midlevel dry slot will be rapidly approaching
as well for late Wednesday night or Thursday morning, so we
could see steadier precip turn to drizzle and freezing drizzle.
Overall it does not look like a major event from a QPF
standpoint, and the timing does not look favorable for big
impacts, but it could be just messy enough for winter weather
headlines to be necessary with around 1-3 inches of snow/sleet
combined with up to a tenth of an inch of ice.

Upton is in the same boat:

The synoptic pattern for the first storm system is not favorable for
a significant winter storm across the region. The antecedent air
mass is the main ingredient to bring about a concern of front end
wintry precipitation before a wintry mix and then eventually rain.

High pressure gradually shifts from overhead Wednesday morning to
just along the New England coast Wednesday evening. The air will
initially be dry with dew points in the teens. Some concern that the
models are saturating this air mass too quickly due to the proximity
of the high pressure. Another factor of concern is deep layered
ridging aloft. The main shortwave trough and parent low is progged
to be located over the Northern Plains at 00z Thursday. The main
source of lift will be from warm advection/frontogenesis and the
potential of secondary low pressure to develop somewhere along the
Middle Atlantic Wednesday evening. The 12z NAM appears to be too
aggressive in developing precip early Wednesday afternoon and has
therefore been discounted. Have followed a GFS/ECMWF blend for
timing. Another factor to weigh in here is overall model performance
this winter has been subpar regarding similar PTYPE events, with too
much wintry precip forecast versus actual observations (the most
recent occurring last night into this morning).

This new forecast package shows the potential for snow to develop
for the Wednesday evening commute across the southern half of the
area. Its north and eastward progression will be determined by how
quickly it can overcome lingering dry air and surface and upper
ridging. The snow should overspread the rest of the region after 00z
Thursday. However, due to the unfavorable position of the high and
factors noted above, the snow should quickly transition to a wintry
mix and plain rain at the coast before midnight. This progression
will continue northward through early Thursday morning as warmer
air moves in both at the surface and aloft. Some lingering freezing
rain is possible across the NW interior if surface temperatures take
a bit longer to rise above freezing.

Have followed a conservative approach to snow/sleet amounts with
generally 1-2 inches across the region, with lower amounts across
eastern Long Island and SE CT. A reasonable worst case scenario with
a snowier outcome is for 1-3 inches east and 3-4 inches from NYC on
west. Of note is the 12z ECMWF EPS mean probability for greater than
3 inches is generally less than 30 percent. A tenth of an inch or
less of freezing rain is forecast across the interior. Overall
liquid equivalent amounts are around a half inch.

OK, so why does this look so bad for the coast? At least as of now?

Well, according to Mt Holly:

"snow will accumulate for a good portion of the forecast area for a good part of the day. Midlevel warm air starts to lift into far southern portions late in the afternoon, allowing for a wintry mix over southern Delmarva and southeast New Jersey, but surface midlevel temps remain cold enough for all snow across the southern Poconos, northern NJ, and down into the Delaware Valley."

"Winds turning onshore should usher warmer and above freezing temperatures to these coastal areas earlier than inland locales."

And wow, it looks like the GFS really depicts this:





The snow arrives at the same time as the warm air for the Shore. It looks like the warm air might even beat the snow outright for NENJ and NYC. So, if this happens, we are all DOA, no?

And compare the placement of the Highs on the Nam and the GFS as the precip is approaching. On the Nam the high literally jumps from Lake George to South Philly. Whereas the GFS keeps the high at bm and then ots.





And it's the high pressure that keeps the cold air in place, right? so this makes sense now why the Nam is showing a colder solution, the high pressure is in the perfect spot on the Nam to create several more hours of thump from Ocean County on up to really Nassau County.

So, if the Nam happens, different story. But the only one buying the Nam right now is the Nam...lol.

Is that right in any way? by the way, if all this is just wrong, sorry! lol.  Seems like it makes sense...as I look at it anyway.

SENJsnowman wrote:OK, so why does this look so bad for the coast? At least as of now?

Well, according to Mt Holly:

"snow will accumulate for a good portion of the forecast area for a good part of the day. Midlevel warm air starts to lift into far southern portions late in the afternoon, allowing for a wintry mix over southern Delmarva and southeast New Jersey, but surface midlevel temps remain cold enough for all snow across the southern Poconos, northern NJ, and down into the Delaware Valley."

"Winds turning onshore should usher warmer and above freezing temperatures to these coastal areas earlier than inland locales."

And wow, it looks like the GFS really depicts this:





The snow arrives at the same time as the warm air for the Shore. It looks like the warm air might even beat the snow outright for NENJ and NYC. So, if this happens, we are all DOA, no?

And compare the placement of the Highs on the Nam and the GFS as the precip is approaching. On the Nam the high literally jumps from Lake George to South Philly. Whereas the GFS keeps the high at bm and then ots.





And it's the high pressure that keeps the cold air in place, right? so this makes sense now why the Nam is showing a colder solution, the high pressure is in the perfect spot on the Nam to create several more hours of thump from Ocean County on up to really Nassau County.

So, if the Nam happens, different story. But the only one buying the Nam right now is the Nam...lol.

Is that right in any way? by the way, if all this is just wrong, sorry! lol.  Seems like it makes sense...as I look at it anyway.

Man, you’ve been KILLING IT these last couple weeks!! I love it!! Now I have two questions for you (and again, not because I question your analysis, but to help advance your understanding):

1. Which evolution do you currently favor (and why?)

2. It’s understood that the high pressure will be the mechanism responsible for providing the cold air at the onset, but how/why does it do this?

Hyde I ended up with less then an inch.

rb924119 wrote:

SENJsnowman wrote:OK, so why does this look so bad for the coast? At least as of now?

Well, according to Mt Holly:

"snow will accumulate for a good portion of the forecast area for a good part of the day. Midlevel warm air starts to lift into far southern portions late in the afternoon, allowing for a wintry mix over southern Delmarva and southeast New Jersey, but surface midlevel temps remain cold enough for all snow across the southern Poconos, northern NJ, and down into the Delaware Valley."

"Winds turning onshore should usher warmer and above freezing temperatures to these coastal areas earlier than inland locales."

And wow, it looks like the GFS really depicts this:





The snow arrives at the same time as the warm air for the Shore. It looks like the warm air might even beat the snow outright for NENJ and NYC. So, if this happens, we are all DOA, no?

And compare the placement of the Highs on the Nam and the GFS as the precip is approaching. On the Nam the high literally jumps from Lake George to South Philly. Whereas the GFS keeps the high at bm and then ots.





And it's the high pressure that keeps the cold air in place, right? so this makes sense now why the Nam is showing a colder solution, the high pressure is in the perfect spot on the Nam to create several more hours of thump from Ocean County on up to really Nassau County.

So, if the Nam happens, different story. But the only one buying the Nam right now is the Nam...lol.

Is that right in any way? by the way, if all this is just wrong, sorry! lol.  Seems like it makes sense...as I look at it anyway.

Man, you’ve been KILLING IT these last couple weeks!! I love it!! Now I have two questions for you (and again, not because I question your analysis, but to help advance your understanding):

1. Which evolution do you currently favor (and why?)

2. It’s understood that the high pressure will be the mechanism responsible for providing the cold air at the onset, but how/why does it do this?

I too agree SENJSnowman. You are nailing the this analysis. VERY Well done. I will let you answer rb's questions, but a hint would be follow the wake of the confluence at 500mb to help you answer the question as to why the HP provides the cold air at the onset. But also to help you answer which model you believe is correct. Ultimately where the HP shifts and is centered plays a huge role in determining the timing to the warming of the midlevels. Two words: source region. Why does the HP, which starts out in perfect position, instead of lifting out to the NE, shifts east and even SE instead? Again Follow the confluence. The HP builds in the wake of the confluence.

CNJ and PHI are in a prime spot for this storm IMO. Good work SE NJ on the maps and discussion. 

GEM LAM goes bezerk this run with many LP and HPS LOL.
It would be a secs for philly through CNJ this run. Is it onto something ?? Snow rate bands it's showing would be 1-3" per hour again as per this run

Ray, I'm working on #1 next, but I gotta clock in for a few hours tonight, so I hope to get back to this one later.

2. High pressure areas in northern latitudes in the winter time are typically associated with arctic air masses. When the high pressure area meets the low pressure area, the colder air from the high sinks toward the surface (warming a bit as it does) and the warmer air from the low rises to the top (cooling and also saturating the air column as it does). So the warmer low pressure air closer to the surface is literally replaced with the colder sinking air.

That took a bit of googling to pull together my thoughts and to find the right actual terms, but that's pretty much what I'm digesting at this point. ha ha

Meantime, what about my #2? I can take it...give it to me straight rb!

Thanks SROC...I look forward to trying to work thru your issues/questions tonight and see if I can weigh in!

I’d love to buy into the NAM as it gives me a 3-6” snow event and it did handle last Tuesday well. But I don’t. It’s placement of the High Pressure center is the first clue to me something is amiss.

Interesting thing about this event is that the timing is much more similar to the November event which is problematic for commuters. Nobody is going to close Wednesday for a storm not expected to start until afternoon. But, if it does start snowing heavily around 2 or 3 pm, people could be caught in the same traffic nightmare as November on their way home.

0z NAM holds serve. Still showing extended snow and sleet with pretty much a general statewide 3-6”.

Interestingly the 0z NAM now places the High off New England, which is more consistent with GFS (and logical). I still don’t think that’s a great spot for it to keep cold air in place; but I guess I could be wrong.

SENJsnowman wrote:Ray, I'm working on #1 next, but I gotta clock in for a few hours tonight, so I hope to get back to this one later.

2. High pressure areas in northern latitudes in the winter time are typically associated with arctic air masses. When the high pressure area meets the low pressure area, the colder air from the high sinks toward the surface (warming a bit as it does) and the warmer air from the low rises to the top (cooling and also saturating the air column as it does). So the warmer low pressure air closer to the surface is literally replaced with the colder sinking air.

That took a bit of googling to pull together my thoughts and to find the right actual terms, but that's pretty much what I'm digesting at this point. ha ha

Meantime, what about my #2? I can take it...give it to me straight rb!

Thanks SROC...I look forward to trying to work thru your issues/questions tonight and see if I can weigh in!

Ok, so your train of thought is definitely on the right track, but it's a little off. Let's break it down piece by piece:

"High pressure areas in northern latitudes in the winter time are typically associated with arctic air masses."
YES. And even during the warm season, these high pressures are typically associated with cooler air relative to that further south. Same concept.

"When the high pressure area meets the low pressure area, the colder air from the high sinks toward the surface (warming a bit as it does) and the warmer air from the low rises to the top (cooling and also saturating the air column as it does). So the warmer low pressure air closer to the surface is literally replaced with the colder sinking air."
You've just described one of the fundamentals of Meteorology: The Law of Conservation of Mass. Let's now take this a step further, though. WHY is the flow of air directed from the cooler high to the "warmer" low? It's all about density. Cooler/colder (and therefore also drier) air is much more dense than warmer/hotter (and therefore more moisture-laden) air, and it is this density GRADIENT that determines the direction in which the colder air will "flow". The direction of "flow" will always act perpendicularly to this gradient. *Keep in mind that this is NOT necessarily the same as the actual wind direction*, though in some cases, like the one coming up, it can be. This is a separate and fairly abstract idea to comprehend, but it gives you an idea of how the cold air will tend to behave independently of its surrounding environment. This is known as the ageostrophic component (technically isallobaric because we are discussing it in terms of the pressure field, not heights) of the lower-level flow, and it must be considered independently of the actual wind direction.

How do you figure out how this gradient and associated ageostrophic/isallobaric flow are oriented? This is a complicated question, because it actually varies as you look throughout the entire atmospheric column; however, for our purposes, we will only focus on the lowest levels, which are within the first few thousand feet of the surface. Generally speaking, you can assume that the gradient that exists between the warmer and cooler airmasses is essentially the same as the lower-level pressure field (i.e. the shapes of the isobars outlining the surface high(s) and low(s) can serve as a pretty good proxy, and even more so, the surface pressure anomalies). The first image below is just of forecast precipitation types from 00z NAM, but the second image is of the surface pressure anomalies with the direction of the ageostrophic/isallobaric flow annotated in green:




Now, taking your initial statements into account with the above, continue expanding......

billg315 wrote:Interestingly the 0z NAM now places the High off New England, which is more consistent with GFS (and logical). I still don’t think that’s a great spot for it to keep cold air in place; but I guess I could be wrong.

Fully agree here.

Also, thank you CP, heehaw, and mugsy

Lee wth?? Is he smoking the cannibas?
That precip has to.move in by 1-2pm and snow till 5-6 and then transition to sleet, sleet ratio is 3:1 at best.
Is it possible, possible but the trends and the players positions as proggged don't show this. Zoo and I in NENJ see about 1-2" most.
What we'd need is the HP to track NE not E or SE. 
CNJ to PHI again do best for our area overall unless we see a sizable shift in the HP or the speed of the precip.
Very Nina like type storm or warm neutral Nino which we have been and are in.

At the moment, I am seeing a setup similar to the system from last week. Maybe an hour or two of snow for NYC, then a prolonged period of sleet. Of course, the wild card is how long can the upper levels stay cold all the way through. During the November 15th event, they stayed cold for five hours, more than enough to wreak havoc on the evening commute. The precipitation from this event may actually start around the same time as that November event. But given the overall pattern over the past three months, there's every reason to be skeptical about 3-6" of snow in NYC.

docstox12 wrote:

heehaw453 wrote:

SoulSingMG wrote:Lee's feeling bullish!

This is what I have felt for a few days. DC will be too warm at midlevels and will mix too quickly. Above nyc will not be heavy enough rates. Phl-nyc special with Monmouth county finally getting a taste sounds about right.  

I hope Mom sees this she had two fingers on the towel yesterday,LOL.Central and Central Shore NJ folks really deserve this one, they have done really bad this season.good luck everybody there!

Just to give you an idea of just how bad us along the coastal plain have done check this image out. Nov18-Feb16th.  Ugg!  

sroc4 wrote:
I too agree SENJSnowman.  You are nailing the this analysis.  VERY Well done.  I will let you answer rb's questions, but a hint would be follow the wake of the confluence at 500mb to help you answer the question as to why the HP provides the cold air at the onset.  But also to help you answer which model you believe is correct.   Ultimately where the HP shifts and is centered plays a huge role in determining the timing to the warming of the midlevels.  Two words:  source region.  Why does the HP, which starts out in perfect position, instead of lifting out to the NE, shifts east and even SE instead?  Again Follow the confluence.  The HP builds in the wake of the confluence.    

OK, sroc, gonna do my best here. I'm sure I'll have some gaps and errors, but I think I understand the basics and how it applies in the case.

First, let's get our terms straight:

Confluence: Two streams flowing together concurrently, not necessarily joining as one (convergence), but flowing together, not apart (difluence)
500 mb level: About 18k feet up
Wake: the vortex that's created as a moving force leaves an area.

Here is the GFS for 12z on Wed:




It looks to me like the cold Canada air is going straight for the HP center. That HP is too far north though, so the really cold air stays well above us. It looks like most of the 500mb air flow that comes over our area is actually warm source air that travels north from the Gulf to the midwest and then over to us.



And here is the NAM for the same time:



The Nam looks only slightly different, but that slight difference looks important. The more southern placement of the HP seems to bring the arctic air much further south. But still not south enough. And we still get overrun by the abundance of warm gulf air being brought up by the storm system.

And in both cases confluence is E or SE. No where close to N or NE.

So based on that analysis, this storm should track SE, which will help pull more cold air into our region. Or closer into our region anyway. But there will always be a direct flow of warmer gulf air coming directly over the top of us.

So would the result be something like this in that case?



That outcome puts our area largely on the border of the cold, and would create a nowcast situation?

rb is the hi pressure to lo pressure movement of air what causes the onshore wind? The offshore placement of the high due east from the low means an easterly flow?