So What Will It Be? The "Norlun" or the "Tractor Beam"...

The latest perspective on the dynamic storm system developing in the coming days. Models are converging, but more than one possibility still exists-- including one that brings flakes to parts of our area.

Welcome to your Thursday... Creeping ever-so-closer to the weekend!

Thank you very much for stopping by the weather blog. I update this site at least daily, and sometimes multiple times per day. The "tracking maps" below are for your benefit, providing important weather information that updates all the time. Also, feel free to leave comments and/or questions at the bottom of the blog-- I do look at every one and often get a chance to respond.

With that... let's take a look at our weather picture for the day.

HPC - Surface Map - Thursday PM

For such a peaceful day locally, there is ...a LOT going on.

In the tri-state area, we're still receiving the benefits of high pressure, albeit on the waning end. Expect gentle warm breezes and temperatures cresting a hair above 80 in the afternoon. This one will be the most summer-like of all the days, which is fitting, as it's the last day before the wheels are set in motion for a multi-day event that will occupy many-a forecaster's time into next week.

I know you all want to talk about it... so let's talk about it ;-)

One of the things you might want to do, is refresh yourself with the perspective of yesterday's blog post, just because you'll have a better foundation to go to understand any sort of adjustment today's perspective brings. Some of the models have certainly changed.

On the above map, you'll notice the two main features of the storm variety-- Hurricane Sandy in the Bahamas, and the non-tropical mid-latitude cyclone spinning in the Northern Plains heading into Canada. An interesting thing to notice about this scenario is that BOTH systems have the same low central pressure (around 985mb), quite decent for late October standards.

What all the models are converging on is a situation where high pressure is essentially pinched out by the two storm systems as they approach each other. My own confidence is growing on this set-up as well, but the key is what will this look like?

Here's an image I've drawn to show the general scenario as it unfolds in terms of a "cross-section". This means I slice a section of the atmosphere over a straight line of land, and stare at some weather variable(s) to look at things from a different angle (got to use all the tools in the bag when it comes to this approaching event).

Cross-Section - Surface Pressure - Thursday
Cross-Section - Surface Pressure - Tuesday

As you can see with this cross-section, I've picked a straight line from Eastern Canada, over the Mid-Atlantic States, and on to the waters offshore where Sandy will eventually end up. Notice that by early next week, a general area of lower pressure exists throughout the entire region, which presents an interesting issue of where to put the "Ls" (low pressure centers) across a sea of unsettledness. This is actually significant in its own right, because the computer models have to figure out the same thing-- and in my mind there are two roads to the same destination.

The Computer Models Are Converging...

One important change between yesterday and today is that the major computer models that we look at are coming into a closer alignment as to what they think are going to happen, though they may not all exactly agree on the timing. Check out yesterday's blog post for the highlights in how the GFS and European models were disagreeing. Here, I'm going to post single-point-in-time snapshots of the various models and what they're showing...

GFS - Wednesday AM CMC - Tuesday PM ECMWF - Tuesday AM

I've highlighted in blue the areas where I see "no-joke" areas where conditions are favorable for snowfall in each of these maps. Each one of these models, despite phasing everything together at different times (note each map has a different time-stamp), generally show the same thing-- a historic storm system that combines a mid-latitude cyclone with a "post-tropical" system (the still-strong remnants of "Sandy") and forces it against the grain inland through the Mid-Atlantic States and New England.

Another tidbit of information is that the most recent track from the National Hurricane Center regarding the path of Sandy has also shifted more favorably toward this scenario:

NHC - Projected Track - Hurricane

At this point, it is important to offer a few guiding principles that I've learned over the years-- and probably many meteorologists adhere to them as well...

1. When the models all agree-- this must be respected

2. The model that shows the most consistency (here, it's the Euro), should be respected the most

but also... (no particular order with these things by the way)

1. More often than not, the solution that leads to the more "meteorologically common" outcome is the one to head toward

2. Be suspicious of ever-slowing storm development in the models

There are others, but those are the bells that are ringing in my head right now :-)

I'm definitely suspicious of the models right now, because (a) they keep pushing this 'grand culmination' of whats going to happen into the tail end of their forecast range; and (b) they are all calling for something that's certainly not very common, no matter how it all develops.

That is not to say there is no precedent with any of these.

Scenario A -- The "Tractor Beam"

This one would reflect the model consensus at this time. It involves drawing in a post-tropical storm system and making it "retrograde" (go against the natural flow of things due to the inertial spin of the Earth), and then combine with some serious non-normal cold air dropping in from the Arctic. There are some feedback processes at work here as well that synergistically enhance each ingredient such that if one or the other wasn't there, the house of cards would fall apart.

Here are some examples of things like this that have happened over the years (note, they may not be exactly the same-- little in weather is, so don't get too excited):

1. "The Perfect Storm" (Halloween Weekend, 1991) - This is the most famous example of just about every mean and nasty system coming together at the same time for one big party over the Mid-Atlantic and New England. This time of year is certainly the best time for this rare event to happen (because you've still got the impetus for tropical formation, combined with the ramped up cyclone activity that autumn temperature swings can bring. However, this typically occurs over the open waters, and not where the whole mess itself is brought deep inland.

2. Hurricane Audrey (June, 1972) - This is an example of a hurricane turning post-tropical and getting absorbed into a mid-latitude cyclone and being drawn back inland over the Mid-Atlantic states instead of continuing on a path farther away from the coast. However, the ingredients in this scenario are much farther apart from each other-- The hurricane is well offshore instead of already having made landfall, the polar cyclone is going to be near the Hudson Bay region of Canada, and any blocking area of high pressure to the north of the hurricane's path (that might help steer it inland) is actually north of the Canadian Maritimes, rather than within them.

3. The Thanksgiving Blizzard of 1950 - This is the Grand-daddy of them all, and what gave birth to modern computer-model meteorology in the first place. I encourage one and all to read up on this monster, but just because of the meteorological masterpiece that this became. We may never see something quite like this again (but never say never) ;-) ... Anyway, this is another example of the kinds of conditions and the severity of storm necessary to create this significant "retrograde" pattern that will generate that kind of representation on a weather map. Simply put, if any one of the above models verify as they stand, we'd be talking about tremendous headlines of hurricane-force wind gusts, beach erosion, coastal flooding, heavy rains, and yes, snow as well (though you have to understand that part is going to be the most minor element in our present situation compared to this apocalyptic ridiculousness that occured in 1950).

Pause for a breath...

So then, if every model is all in consensus calling for something big and nasty that simply doesn't happen (except maybe every 20 years-- the last one being about 20 years ago...), then what could possibly stitch all these elements together in a way that's more "meteorologically common", even if the models aren't showing it.

My answer is the "Norlun" Trough.

Scenario B -- The "Norlun" Trough

If you are interested in the finer workings of this still-unusual-but-not-nearly-as-rare weather pattern, I recommend checking out this video:

Admittedly, this is primarily a Winter-time phenomenon, but that's only because the ingredients aren't usually there until then. However, here we've got a situation where a post-tropical system (a deep area of low pressure) is traveling through the western Atlantic Ocean, and another deep area of low pressure exists in the Hudson Bay area of Canada. The most meteorologically common scenario for the tropical system is that it stay offshore and continue on its progress. The most common meteorological scenario for the Hudson Bay low is that it continue to just hang out there and look mean. Just as in the "norlun" scenario, eventually there will be a breakdown between the two, whereby an umbilical cord of sorts will link the two events together, essentially creating one elongated central area of low pressure that will extend from the remnants of Sandy all the way back into Canada, crossing parts of New England and the Mid-Atlantic States. This will focus the precipitation there and not here (sorry), but we can certainly find ourselves getting scraps from the table.

Either way, we still have much time to keep an eye on this (and remember, always be suspicious of things that loom only in the long range). Once we get closer to the weekend, we'll get a better look at what will end up coming to pass (especially when the NAM and other high-resolution models will get a crack at it-- they don't go out that far in time range). There's still a lot that can happen, and many ways things can change.

Both scenarios can still play out in such a way locally where flakes could fly (though we're talking about the WV mountains primarily). I'll touch on that tomorrow-- remember, we've still got several days to watch this. For now, I'll leave you with this apologetically long wall of text :-)  As you can imagine, it is nearly impossible to discuss this longer-range weather scenario on the air in the short time span that I need to use to also cover the important weather of the short term. That's why I want you all to come here as well for fresh information on any/all complicated weather patterns that may arise in the mid-long range.

Feel free to ask any questions, or include any comments/suggestions/complaints you may have, so that I can best make sure this blog is serving your needs.

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Have a great day everyone!



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