Sun-Mon 12/11-12/12 Discussions and Observations

I started a thread for this event. I'm still not sold on any one soln just yet. Energy comes on shore over the next 24-48hrs

I'll have a write up explaining this event either late today or tomorrow. I've been talking about it for awhile, and right now it looks minor, but it's worth tracking.

Frank_Wx wrote:I'll have a write up explaining this event either late today or tomorrow. I've been talking about it for awhile, and right now it looks minor, but it's worth tracking.

Any snow in my backyard is significant as it will be my first. I'll take anything in December. But the possibility for moderate event is real....for now.

I think this going to be another situation where the "poor get poorer, and the rich get richer", meaning northwestern zones are favored yet again for this event, where the I-95 corridor sees another miss. I also don't think this will be a very large event; maybe another 2-5". I'll either do a writeup or a video explaining why I feel this way.

The coast mat see no snow this year next 16 days gfs has cutters interior snow coastal rain. I'd rather it just be dry and cool temps but not freezing.

jmanley32 wrote:The coast mat see no snow this year next 16 days gfs has cutters interior snow coastal rain. I'd rather it just be dry and cool temps but not freezing.

This is banter Jman

12z GFS a bit stronger (warmer) of a solution, 1-3" NYC Metro this run. Interior does much better.

Have to watch the HP to the NE over next few runs. Not in ideal position to start, If it holds longer cold air will win, if it trends weaker and retreats sooner more of he same...N&W with coastal plain getting OOGOTZ!

So, I am doing a writeup because I'm still working with a crappy internet connection at my parents' lol Here goes:

I first want to start out with a look at the broad picture. The image below is a look at last night's EURO Ensemble mean 500 hPa heights (black contours) and anomalies (color shadings; blues indicate anomalous roughing, reds indicate anomalous ridging), valid 12z Sunday.



The regions of interest are highlighted in the green circles. Starting in the west (WPO/EPO domain), it's clear that we have a stout -WPO ridge across the north-central Pacific and into Alaska, with a shortwave trough near Hawaii that's attempting to bridge with the trough over the northeastern Pacific and northwestern North America. With this configuration, we also have a -EPO, although it is not the cleanest setup I have ever seen. Both of these indices with these phases support troughing and colder air in the eastern U.S. Looking quickly in the Arctic, notice that there is an approximate neutral state, as evidenced by the relatively equal spatial distributions of anomalous troughing and ridging. Moving into the east (NAO domain), you can see that there is a transient 50/50 (south-southwest of Greenland) low which is pumping a transient slightly negative to neutral NAO. The presence of the 50/50 low and associated NAO phase also supports a minor amount of troughing and cold air in the East.

Now take a look at the same map but valid for 12z Monday:



Notice how the EPO/WPO domain trended a bit stronger, as there are now more negative height anomalies bridging between the Hawaiian and North American troughs, but the NAO and 50/50 anomalies are now shifted northeast of where they were. With this configuration, we've lost the best properties of both components in the NAO domain. The 50/50 low is now too far northeast to promote the slightly negative to neutral NAO phase, and is now promoting a neutral to slightly positive phase. This means that we have lost one of the mechanisms for driving colder air into the East. Also, with the location of the 50/50 low, its wave spacing is far enough ahead of the main North American trough in the western part of the continent such that systems will be able to start sneaking behind it, as they will start to be more influenced by the main trough instead of being suppressed by the blocking attribute of the 50/50 low. Also notice how there is now a circle over the Mid-Atlantic signifying the height rises in this region, which is supported by the transience of the 50/50 low and favorable NAO state it forced. Lastly, the AO phase remains generally neutral to even slightly positive throughout this event, which also favors marginal cold in the East (at best).

For comparison, here are the GFS Ensembles for the same time frames:




And the GEM ensembles:




The higher height anomalies coming into the East as the event occurs are also supported, although admittedly weakly, by the possible emergence of the MJO into a weak phase 3 as suggested by the most recent guidance. An MJO pulse in phase 3 generally corresponds to the following temperature composites for November-January:



However, with the statistical significance:



and the fact that if it does emerge it will be weak (<1 St. Dev.), I think it only argues for a very muted Mid-lattitude response; but a response nonetheless.

Based on these factors, I am actually thinking that we could see this system trend northward in coming runs, or at least a northward shift of the lower-level thermal gradients, as the sensible effects of the points I just outlined are realized in the models, assuming that what they are currently showing is correct.

Getting into more detail and discussing why I don't feel that this will be an event any larger than the one that we just saw yesterday, let's start with a map of precipitable water anomalies from last night's GFS Operational valid for Monday at 12z. The anomalies are depicted by the color shadings, where blues indicate drier than normal air and reds indicate higher than normal water content, and 700 hPa winds are denoted by the black wind barbs:



Notice how the boundary of weakly anomalous moisture essentially stops around the I-84 corridor, and the higher anomalies (above 1 St. Dev.) don't even make it much further north than the Mason-Dixon line. If you're looking for significant snow, that's a problem.

Working deeper in detail, here's a look at the EURO Operational surface 6-hourly QPF in the greens, pressures in the black contours, and 1000-500 hPa thicknesses in dashed color contours:



What follow will be temperature maps at 925, 850 and 700 hPa with contours every 2°C, where the purple line is the 0°C line, blue lines are below freezing and red lines above, heights in black contours, relative humidity in the green color fills, and winds in the black wind barbs:





The green outlines show the region(s) of best temperature advection (isentropic/upglide forcing for ascent) at all levels, with areas of red showing meager advection (700 hPa). When you overlap these regions, you get something like this (outlined in red on the last image to the right):



Looking at 500 hPa, where the heights are in the black contours, winds are denoted by the black wind barbs, the vorticity (energy) is depicted by the color fills, and the positive vorticity advection (forcing for ascent) is shown in the blue outline:



Lastly, looking at the 300 hPa jet structure, where the wind directions and speeds are shown by the black wind barbs, the speeds are more clearly shown by the color fills (in knots), and the region of best upper-level divergence forced by the jet (forcing for ascent) is outlined in green:



If we overlap the mid- and upper-level forcings for ascent, we get this (outlined in red on the last image to the right):



Finally, if we look at how all of the forcing mechanisms for ascent align, we get this (most overlap is outlined in red):



My argument is that even though the model is showing a wide swath of moderate precipitation, I feel that the steadiest, and heaviest, will end up in the region in red above. That's not to say that we will stay dry. I do think that there will be low-topped precipitation in the form of showers that are forced where the lower-level forcings align, but the best column-deep forcing for ascent is mainly across the body of New York State, which is where I think the highest threat of seeing accumulating snowfall will be. In terms of accumulations, I think a general 2-5" is a reasonable guess for the regions north of the red line seen below:



Not only is that the region of best column-deep forcing, but I am also expecting this system to trend northward in time, which will allow an increase in the meridional (north-south) advance of the lower-level warm advection (keeping areas to the south and towards the coast mainly wet), as well as a further northward extension of the weak moisture belt so it can overcome the lack of decent forcing at 700 hPa and realize the positive forcing above it. It would also not surprise me to see the energy itself trend stronger in the modeling once it crosses the Rockies, as such a setup argues for an enhancement of vortex tube stretching, and a strengthening of the spin of the energy once it crosses the mountains.

Hopefully this wasn't too long or confusing, but I figured this was better than waiting hours for a video to upload haha If you have any questions, comments, or concerns, let me know and I'll do my best!!

12z GGEM drops half a foot of snow on Manhattan Monday. I'll take this solution please.

The UKIE along with the CMC and Euro all have weak system for the Monday event. The GFS is the only amped up solution at the moment similar to what yesterday's Euro showed. We want the weakest solution with over-running precip which I favor at this time as the flow is very fast. Light to moderate snow accumulations across the area with maybe a change over to drizzle at the end along the coast

Also whatever snow that falls should stick immediately as it will for early Monday morning and the ground should be frozen outside of the immediate urban areas with low's this weekend well down into the twenties

Euro looked pretty good overall. HP trying to hold strong with LP to the NE likely preventing it from retreating. At work so cant get into details

I have no maps but am hearing the EPS are out of control snowy for most of us over the next 8 days!

NWS forecast for Sunday and Monday just changed at 4:00 p.m. (which is about the time they update every day) Earlier today it was for snow turning to rain Sunday night and rain on Monday here on LI. Now it is rain late Sunday afternoon going over to snow quickly Sunday night and remaining all snow through Monday morning before mixing with rain late in the AM. Pretty significant change. Precip. chances also increased to 70%. This could be our first area wide event. 72 hours out only

Its going to be close for us Syo.  There is no doubt trends have been a slightly weaker system that initially develops over the Ohio preventing from any sigificant height rises out ahead.  This is key. The frontal boundary looks like it "should" remain to our south.  Some level of CAD is likely to happen as the HP to the N looks pretty darn good on modeling, but us surrounded by still pretty warm waters could be the Achilles.  IMO trends have been favorable for LI esp N shore.  North Shore vs South shore could be the difference.

Can someone help me out with temperatures on the Jersey shore coast is there any chance we see some snow or it's pretty much a done deal for rain as most maps show us rain for now?

SoulSingMG wrote:I have no maps but am hearing the EPS are out of control snowy for most of us over the next 8 days!

OOOOFAAAA!!!!!!!!!!

sroc4 wrote:Its going to be close for us Syo.  There is no doubt trends have been a slightly weaker system that initially develops over the Ohio preventing from any sigificant height rises out ahead.  This is key.  The frontal boundary looks like it "should" remain to our south.  Some level of CAD is likely to happen as the HP to the N looks pretty darn good on modeling, but us surrounded by still pretty warm waters could be the Achilles.  IMO trends have been favorable for LI esp N shore.  North Shore vs South shore could be the difference.

well if you are right (and I agree) then at least you and I are both on the N shore.

Upton:
For Sunday-Monday night the models are coming into better agreement
that fast zonal flow will produce a weaker/flatter (more sheared)
system moving in from the Intermountain West starting Sunday
morning. The reduced amplification will result in weaker warm
advection ahead of the system, with the warm front now likely
staying S of Long Island through the event, with a secondary low
tracking to the S of Long Island along the front. Northern stream
ridging ahead of the system will support the forming of a high over
SE Canada which should server as a source for low level cold air by
Monday (NE- E flow over the region - typical of a cold air damming
pattern).

In terms of sensible weather, the aforementioned shortwave ridging
passing to the north Sunday should hold off anything other than very
light precipitation into Sunday afternoon - with snow across the
interior and rain elsewhere. The precipitation will become more
widespread and steady Sunday night and should chance to all snow
from N to S Sunday evening across the Tri-State. Snow continues into
Monday, with precipitation mixing with then changing to rain over
Long Island and at least Southern portions of NYC and maybe coastal
SW CT Monday morning and then to all rain Monday afternoon, except
for maybe far Northern portions of the CWA where a rain/snow mix
could linger. Precipitation should taper off from W to E Monday
night as the low exits to the southeast of Cape Cod mainly as Snow
N of Long Island Sound and Rain to the south.

sroc4 wrote:

jmanley32 wrote:The coast mat see no snow this year next 16 days gfs has cutters interior snow coastal rain. I'd rather it just be dry and cool temps but not freezing.

This is banter Jman

yeah sorry sroc please move it. I should known better but when I realized a reply had been made.

Joe Cioffi A EARLY CALL

I am in the 1 to 3 inch range I say go higher I know it's early when do u think the city will change to rain and will ice be an issue

Looking at the soundings on the 18z GFS it is expecting freezing rain at Teterboro, then going to rain, so I think it is going to be close....

Is anyone doing a write up on this one.