Historic (?) Southeast Storm Could Be Next Northeast Snow Threat

Overall pleased with the forecast for the current storm for the Big Cities. Definitely underestimated parts of CT that saw 8-16″ of snowfall on average in the western part of the state, even down to New Haven County. Just a reminder… State of Occlusion is on Facebook. I’ve posted some additional cool links and snow maps early on that page. “Like” the blog by clicking here! On to the fun…

The Eastern 2/3 of the US are going to be peppered by winter events over the next five days or so. Let me run through things here.

Snowfall Forecast from Friday Overnight-Sunday Morning

First off, tomorrow, as all of the energy responsible for the unsettled eastern weather the last couple days starts to slide offshore, it will begin to develop into a nor’easter, but rapidly exit to the east. However, as it intensifies, it could produce a pretty well organized band of snow from about Southern NJ/Central DE through E Long Island and possibly Cape Cod. The snow map is over to the left if you want to enlarge it and see my thoughts through Sunday morning. Not a big storm, but there could be some heavy snow for an hour or two, especially east of Rt. 206 in NJ as the storm pulls away. Lingering snows will produce perhaps a couple more inches in New England, with upslope areas of the Green Mountains and Berkshires more favored. I don’t believe accumulations will be that high. There is some chance the Cape and Islands, as well as the Boston area may see some enhancement too.

GFS Forecast of Total Ice Through Tuesday Morning (Credit: wxcaster.com)

That will exit tomorrow night and by Sunday morning or so, things will be quiet. But that sets the stage for the next event, and this one might be an absolutely punishing doozy of a storm. The map to the right shows the GFS forecast for total accumulated freezing rain through Monday. A strong storm system is going to trek across the Southeast in an unusually cold air mass, and with it will come plenty of moisture…almost an El Nino type storm. Winter Storm Watches are posted almost to the Gulf Coast for Mississippi and Alabama, and for most of northern Georgia and Louisiana, as well as Arkansas. This amount of ice this far south would be absolutely crippling…that isn’t hyperbole either…these are places that almost never see frozen precipitation of any kind, let alone to this extent. The raw model outputs in some of these places is absolutely mind boggling. Atlanta is showing anywhere from 6-12″ of snow, with 1/4″ of ice! Of course, that’s raw model and has to be taken with a grain of (road) salt. But still, that’s absolutely insane, The all-time snow record for Atlanta is (I believe) 10″ in January 1940. It’s tough for me to put this in historical context, as I’m not THAT familiar with Southeast wintry climatology, but this would be, from a meteorological perspective, one of the most incredible things we’ve seen over the last couple winters (and we’ve seen a LOT). Check out the total snowfall forecast through Tuesday morning in the Southeast below (from http://wxcaster.com/regional_snowfall.htm).

Southeast NAM Snowfall Forecast Thru Monday Night (Credit: http://wxcaster.com/regional_snowfall.htm)

The next question becomes, where does it go? The three main models to look at for tonight, taking them (since the NAM only goes out 84 hours) to Tuesday morning shows the low sitting somewhere off the northeast South Carolina coast. Not surprisingly, where this storm sets up, will determine how it impacts areas up the coast. The European model sets up the furthest northwest. Not surprisingly, as you run it out further in time, the European delivers a quick moving, but solid snow event (6-12″ish) for most areas from I-95 south and east. The GFS is a glancing blow, but mainly a miss (not bad for New England). The NAM stops at hour 84, but is a little closer to the European model than the GFS. So my feeling is that despite model flip flopping the last couple of days, we could still see a pretty potent little storm from the Carolinas up into New England. The timing on the snow would be later Tuesday to the south, ending Wednesday from Jersey through New England. Stay tuned on this, especially if you have midweek plans. I’ll do my best to keep you posted.

 

Norlun Troughs?

Going to get a little technical briefly. Going to put this pretty plainly: What’s coming Friday will more than likely not be forecasted very well. Why? We’re dealing with a phenomenon that’s pretty common in the Northeast in winter…it usually rears its ugly head at least once. We call this an inverted trough…Norlun trough…or instability trough. What is it? Well, typically, when you think of an atmospheric trough, you think of a “U” or “V” shaped pattern. In an inverted trough, this, well, inverts. It looks more like an upside down U. The lower pressure, or lower heights end up on the north side, rather than the south side. These sorts of setups can produce some nasty weather, heavy precipitation, and thunder.

Here’s more info on Norlun troughs (recognized in the 90s and named for the meteorologists who discovered it).
A technical paper on Norlun trough events.
And here’s more on inverted troughs.

So what’s it to you? Well, the models are beginning to hone in on how this storm on Friday and Saturday is going to behave. And they are indicating that an inverted/Norlun trough type setup may occur. The bottom line is that there will be snow. The question is twofold: Will the Norlun event occur, and if so, where will it setup? This morning’s models pegged it right over North Jersey and NYC. This evening it looks to be shifted a little further north. This is important, because outside of the Norlun trough there will be a generic sort of snowfall. But under the narrow Norlun trough, there should be significant snow, with the possibility of thundersnow and more.

Right now, the NAM model (a mesoscale, small scale, higher resolution model) is showing extremely heavy snow (and has on three straight runs today) for areas immediately north of NYC, Long Island, the Catskills, and the Western Mohawk Valley. The GFS model is suggesting this will be further north and east into New England and the Adirondacks.

Latest Snowfall Risk Assessment for Friday and Saturday

So my snow “assessment” has a broad area of potentially significant snow showing in red. I right now have this from about the Bronx, east-southeast into Long Island (yes, that places the division of snow vs. heavy snow within NYC). It stretches up into the western Hudson Valley, Catskills, western Mohawk Valley and southwestern Adirondacks. I also include much of southwest Connecticut as well, including Bridgeport and New Haven. The problem is that it’s next to impossible to pinpoint exactly where within this idealized zone the prolific snow will be. The yellow territory indicates the basic “cone of error” of sorts. I don’t foresee the risk of heavy snow shifting south of NYC much, if at all. The risk to me is clearly on the northern and eastern sides. This could shift further north, so the axis of the heavy snow stretches from Syracuse/Utica through Albany, the Berkshires, and Central Connecticut to the coast. And it could even shift further north too.

The heavy snow band will be awesome though, with extremely heavy rates of snow, likely some thunder, lightning, and whiteout conditions. I could see max amounts of 10-15″ in this band. You will only need to go a few miles from that core of heavy snow however to find amounts of 6″ or less…that’s the type of storm we’re looking at: Very narrow gradient, very sharp gradient, with extremely variable snowfall totals. Thus, this makes forecasting this system extremely difficult, if not impossible at this point. So if you live from NYC into Central New York and all of Southern New England, stay tuned. As I said, the forecasts for this will more than likely be challenging, vague, and possibly even wrong initially. But that’s the story.

Outside of the heavy snows, expect a brief period of maybe some heavy snow, with a coating or so, up to about 3″ in spots across much of NJ, PA and central New England. Closer to the heavy snow axis, there may be some 3-6″ amounts. But those will be isolated.

New model data indicating the possibility still of a major snowstorm Tuesday of next week. There are still a multitude of questions as to whether it will track in the sweet spot for a DC-Boston hit, as tonight’s GFS is showing, or if it will pass further south. More on that after this first event passes.

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Why Snowfall is so Tough to Forecast

One of my favorite things to do after a snowstorm is to look and see where the most challenging gradient of snowfall occurs…in other words, the greatest change in snowfall totals over the shortest distance. This storm provided another good lesson in that. Check out the map below. I’ve plotted some select snow totals from the Mount Holly and Upton CWA’s from the event for Orange County, NY, and Sussex, Warren, Hunterdon, Somerset, Middlesex, Union, Essex, Morris, and Passaic Counties in NJ. Location on the map is approximate, and you can enlarge the map by clicking on it:

Check out some of the disparities. In one instance you go from 22″ to about 11″ over the course of *maybe* 10 miles. In the most extreme instance, Pottersville, NJ in extreme NW Somerset County reported 4.5″ (NWS Co-Op site). Elizabeth, NJ near Newark Airport in Union County reported 32.0″ (trained spotter). The distance between both locations is approximately 30 miles as the crow flies. That’s incredible. It’s common though. In snowstorms, especially ones of this intensity, you get intense areas of what we call mesoscale banding…bands of extremely heavy snow (sometimes with thunder) that impact small areas. To take this to another level, which I won’t do, you can also have something known intriguingly enough as “CSI,” or conditional symmetric instability…or slantwise convection. You often get this in intense snowstorms. I won’t bore you with details right now, but if you’re interested, a whole website is devoted to the topic here. It will be interesting to see the number of papers that I’m sure will come out in a year or three about this storm and the ones of last winter. Anyway, this basically means, some areas get absolutely walloped, while others get shafted.

Anyway, back to the topic at hand, you could probably replicate a map like this across southwest NJ and in parts of New England too. But this just goes to show you, for meteorologists making a snowfall forecast map, these are some of the complexities that we all have to deal with.

Lastly, the poll question continues. Do you all prefer the current system of occasional blog posts, or would you rather have occasional blog posts and a Facebook “like” page with occasional links/discussion/question areas? Vote below, and we’ll see where this goes.

The Boxing Day Blizzard

Well, it’s underway, and miraculously, there haven’t been any dramatic changes in the forecast in the last 12 hours. The main areas of concern to me seem to be:

  • Cape Cod/Providence/Boston/Long Island: How much falls as sleet/rain vs. snow, thus cutting down snow totals there. The low should ride the coast from about Montauk to Martha’s Vineyard, so this will both lead to a mix/changeover scenario on Cape Cod/southeast Connecticut/Rhode Island and may even have to a dry slot cutting down totals in general. Will this make it as far north as Boston? Doubtful, but we’ll see.
  • Jersey Shore from LBI south: There could also be some mixing issues here. In my experience there are almost always mixing issues in this region when a low passes this close to the coast. So this may cut down totals, and I’ve lowered the range a little to 7-14 (down from 8-16). It’ll still be a good storm, but the combination of a little less precip and this mixing scenario has me cutting back a smidge.
  • Philly-Morristown-Albany: The biggest question of all is regarding how far west the heavy snow will get. And this corridor stands the most to gain or lose depending on the exact amount the precip shield barges inland. I could see this being as little as 6″ in Philly to as much as 12-16″ there depending on the exact track (same goes for the I-287 corridor in Jersey and I-87 from Newburgh to Albany.
  • NYC-Hartford-Interior New England: This could be an absolute wallop for places like Worcester, the Berkshires, the Litchfield Hills, etc. A lot of potential for a lot of snow in these areas, and there could be a cluster of significant 20″+ amounts anywhere between NYC and Boston depending on where the best mesoscale banding sets up.

Lastly, the wind impact from this cannot be stated enough. This is a storm which is going to see its barometric pressure fall from about 996mb off Cape Hatteras to perhaps 970 mb or lower south of Long Island. In meteorological terms, we call this an atmospheric “bomb.” In other words, it’s going to be rapidly deepening, and it will be progressing along close to shore. This is going to create absolutely ferocious winds all the way up the coast and rather far inland. With everyone’s Christmas lights up, coupled with heavy snow, the wind has the potential to cause a LOT of damage/mess. It may not be a bad idea to secure some of the holiday displays Sunday morning. There will also be the potential for significant power outages as well, so be prepared, especially because temperatures will drop into the low 20s to teens Monday night and Tuesday morning, with wind chill on top of that.

Travel is going to be next to impossible and is not recommended, especially from Northeast NJ into New England after about 9 AM-Noon tomorrow. And it may be that this is the case throughout most of eastern PA/NJ/DE/eastern NY as well. This really to me seems like last February, shifted a couple hundred miles further north. So please use caution if you have to travel, and be prepared for numerous road closures/states of emergency by Sunday evening.

7:30 AM Sunday Update: I would likely trim some of the snow totals back east a bit in the 3-7″ range, esp in NY/PA. The storm is moving along at a decent clip. The real intensification takes place this evening…that’s when the “blizzard” aspect will begin to take shape. In terms of the actual amounts, I might be apt to trim back south Jersey/Delaware a bit (more like 6-12 now to me). Overnight models (not going to read into them too much at this point) did cut back snow totals there to the 6-10″ range). Still looks good that the bullseye is between NYC and Boston..but not IN NYC or Boston. Boston may end up on the lower end of my forecast range, but inland areas will push the higher end. The western extent of the snow between the Delaware River and the Hudson River is going to be EXTREMELY sharp now it appears. Could easily go from 2-4″ far west to 12″+ over a very short distance. Whether that gradient is centered over the Delaware Water Gap or Denville in North Jersey, I’m still not sure. Still a tough forecast. Keep an eye on things throughout the day. Also, from northeast NJ into New England, the bad travel may not start until more like 11-2, rather than 9-12.

1:30 PM EST Update:  Everything still on track. Morning model guidance and current radar trends validating a major storm that’s underway. Latest SPC Mesoanalysis showing that the storm is rapidly deepening off the NC coast as it gradually pulls north. This will bring blizzard conditions to most of coastal NJ/Delmarva and inland to about Rt. 206. The blizzard conditions will spread north into NYC and New England this evening. The worst of the weather will be bounded on a line south of I-90 in New England and east of I-287 in NJ-I-87 in NY.

If you live in Southeast Jersey, snowfall rates of at least 1″/hour are occurring and those heavier bands will continue to push onshore from time to time this afternoon and evening. Heavier snow continues to gradually push inland, and to be honest, the snowfall map from last evening doesn’t look too bad at this point (though I’d still shift the 4-8″ area a little further east). Some totals so far include Somers Point at 6″, ACY at 4.3″, a little over 3″ at Ocean City, MD, and 6-10″ in the Hampton Roads area of Southeast VA and parts of Northeast NC, back through Raleigh/Durham. The DC/Baltimore areas have been for the most part “shut out” of the storm so far, and it’s not looking likely that those areas will be hit nearly as hard as others north and east.

Travel and conditions in general will continue to deteriorate this afternoon. Be safe!

Here’s your map for new snow tonight-Monday (click to make it bigger). Feel free to add any questions in the comments, and if you like the updates or have any comments/ideas for future items, let me know! And Happy Boxing Day!

Final Snowfall forecast for Boxing Day Blizzard (click to enlarge)
The storm is moving along at a decent clip. The real intensification takes place this evening…that’s when the “blizzard” aspect will begin to take shape. In terms of the actual amounts, I might be apt to trim back south Jersey/Delaware a bit (more like 6-12 now to me). Overnight models (not going to read into them too much at this point) did cut back snow totals there to the 6-10″ range). Still looks good that the bullseye is between NYC and Boston..but not IN NYC or Boston. Boston may end up on the lower end of my forecast range, but inland areas will push the higher end. The western extent of the snow between the Delaware River and the Hudson River is going to be EXTREMELY sharp now it appears. Could easily go from 2-4″ far west to 12″+ over a very short distance. Whether that gradient is centered over the Delaware Water Gap or Denville in North Jersey, I’m still not sure. Still a tough forecast. Keep an eye on things throughout the day.

Let’s Talk Snow

If the morning computer model guidance is right, it’s game on for snow this weekend in much of the Mid-Atlantic and Northeast. This is not uncommon…just a few days ago, the models were basically offshore with the storm, but as the energy is now moving over the Western US (with observations) and not the ocean, it’s gradually bringing the models closer to each other in terms of track, confidence, etc.

I’ll try not to bore you with the details, but here’s a quick synopsis of each model’s morning run.

Morning GFS Forecast for Monday Morning, from Penn State E-Wall (click to enlarge)

AM GFS: Moderate to heavy snow starts in southeast Virginia Sunday morning after midnight.  Light to moderate snows continue through the day Sunday south and east of I-95. Moderate to heavy snow spreads into Southern New England east of I-91 Sunday evening and tapers off Monday afternoon. Additional lighter snow is possible with another system later Tuesday through Thursday. Impacts would be minor for most of the I-95 corridor until you get to Connecticut, minor in NJ, and significant in interior southern New England.

 

Raw model output is:

4-8″ with a mix for Boston and Providence
12-18″ for the interior parts of Mass/NH/RI/NE CT
Hartford is about 3-6″
Jersey/NYC is about 2-4″
Less in NW NJ through Philly and DC.

Morning European Model Forecast for Monday Morning, from PSU E-Wall (click to enlarge)

AM European model:  The timing is similar, with snow overspreading eastern VA Sunday night after midnight, and DC/Baltimore/Philly/South Jersey Sunday morning, into New England by late morning. Snow would taper off Sunday night in Balt/DC, Monday morning in NJ/Philly, and Monday late morning in NYC, with gradually ending snow Monday afternoon in New England. Impacts would be significant on the immediate coast from Long Beach Island south into the Virginia Tidewater, severe in interior South Jersey and Delaware, up through NYC and then in between I-87 and I-91 in NY/CT/southern VT/NH and MA.

Raw Model output/my manual adjusting is roughly:

4-8″ DC/Baltimore
6-12″+ in far Eastern VA
12″+ for interior South NJ/Delaware
6-12″+ coastal South Jersey (some mixing with sleet likely)
6-12″ for Philly
8-16″+ for NYC/interior southern New England, with potentially high end or more on Long Island depending on mixing.
7-14″+ for the mountains in NW NJ
6-12″ Albany
7-14″+ Boston area

These are just rough and subject to change obviously.

My thoughts? Both models are trending toward each other, so very often, you find the answer in the middle. So somewhere between these two current solutions (the offshore GFS and and closer to the coast/bigger hit Euro) likely lies what will ultimately happen. The European model is next to lethal in this timeframe though, so this close to the coast/high impact solution cannot be ignored. Right now I would say the odds for significant snow are:

Very High in interior southern New England
High south and east of I-95 from NYC-South Jersey
Moderate from Philly to DC
Moderate-high for VA through Richmond
High east of Richmond to Delmarva

So stay tuned, and consider getting prepared for a bigger storm than usual (though likely a little under the big ones from last winter). More on this as we get closer!

Monday Evening Storm Update

PSU E-Wall European Model Forecast for Next Weekend

So here’s my evening update on the storm and more. I won’t get to analyze the 00Z Euro til I’m at work tomorrow. But we can look at the 12Z Euro and the 00Z GFS. The 00Z Euro had backed off last night and sent the storm out to sea. This morning’s run was a little further West, but still primarily offshore enough to only impact the coast north of Delmarva with some light snow and hits Maine pretty good. The map to your left is the12Z run, showing the position of the low. Frankly, it’s not in a bad spot right now on the models. Sure, you’d like to see a big hit, but this far out (138 hours), I like having a track just offshore from my own personal experience. Last winter there were a few instances where the storm tracked like that this far out and then bounced back in the last 72 hours and ended up hitting. This is not last winter (despite the similarities), but still I like this. Again, the west will be what to watch…how the energy shoots in this week (almost a pineapple express scenario…not classic, but close) and how that weak ridge over the intermountain region sets up as well.

Watching the GFS come in and it’s clearly a bit deeper and wetter and probably further west, closer to the coast with this. The big, big question to me is what happens with this Pacific energy undercutting everything out here Thursday…the system actually goes into Baja, Arizona, and New Mexico, which is extremely odd to see in Nina I think. That’s your key right now, because it hits the block and explodes off the coast.

So the GFS is further west…good trend for snow lovers. Literal solution is mod snow for most of VA, southern 2/3 of NJ, and maybe Long Island/Cape Cod, with a secondary blast for Norfolk/NE North Carolina and Delmarva as the storm bombs offshore. This is really in the sweet spot this far out. Timing is Saturday night to Sunday, and again I think the key is almost entirely the energy in the Southwest. Stay tuned.