Tale Of Two Storm Scenarios

The weather in the early phase of this period is rather inconsequential compared to the cat's-out-of-the-bag developments looming for this weekend and beyond. Have a look.

Welcome to your Wednesday! :-)

Skies continue to stay well above normal, with mostly sunny skies, and little threat of rain going right into the end of the week. So, let's take care of that part of the forecast real quick-like...

"It's Gon' Be Fine!"

Okay, now that's done with... let's fast-forward to the end of the week.

Our storm system we've been talking about will finally make its first approach. We'll be talking about showers coming in late Friday (more like the overnight).

There's two main veins so far regarding how everything's going to happen. I'll talk about each and then offer my preference.

1. The tamer "big change on the way" scenario

This one is brought to us by the GFS. Here are some relevant maps:

GFS - Friday Night GFS - Saturday Night GFS - Sunday Night

Okay, I want to stress at the outset that meteorologists look at a ton of model imagery, and there's just not enough space on this blog to specifically lay out every single graphical combination of weather variables for each day. I'm trying to keep it simple and pick out a few, but I'm open to suggestions as to what you'd like to see (if it exists). This is a simple surface pressure map, with green and red dashed lines analogous to temperature laid on it as well. I have drawn in the relative position of fronts, with the exception of the final map, which I will get into soon enough.

Here's how this scenario plays out: We get a strong storm system into the area late Friday, bringing a thin not-a-big-deal amount of rain, lasting into parts of Saturday. The main system is near the Hudson Bay in Canada, but the front itself is stalling. This gives rise to some secondary development, but that will occur far to our north nearer to New England. This removes much of the moisture from our area, and doesn't permit a deeper plunge of cold air into the region. On the last map, this secondary low pressure system is absorbed into a large area of general low pressure that exists between the remnants of Tropical Storm Sandy over the Atlantic, and the parent low pressure system still swirling strongly in interior Canada. The blue blob on that map indicates what I see as the farthest penetration of the cold-enough-for-snow air toward our region. No doubt it will get much colder around here (30-degrees colder in fact), but this scenario does not look good enough for snowflakes. The cold air needs to be here, and the moisture needs to be in place, and both are missing each other at this point.

2. The crazy "big change on the way" scenario

This one comes via the European and Canadian Models (the Canadian traditionally volatile, but the Euro keeps trying to hold onto this whacky rendition through a few different runs and I keep expecting it to change...Since it's not, I might as well throw this one out there as the one y'all would be salivating over :-)

ECMWF - Saturday ECMWF - Monday ECMWF - Tuesday

Now, I agree there is a whole bunch of messy lines on these maps... but it's because the highs and lows are dramatially different from one another (lots of wind / movement of air going around here). Again, I've drawn on the fronts with this.

Initially, the system starts out much like that of the GFS model, with some pedestrian showers moving through for part of Saturday. We also have that secondary development far to the north, which would initially limit the push of cold air toward the Ohio Valley. But, here's the rub: This model wants to drive the remnants of Tropical Storm (well, on this model, more like "Hurricane") Sandy right into this parent system, combining forces similarly to the "Perfect Storm". This new situation not only shoves a whole lot more moisture onshore (and wraps it around back to the Appalachian Mountains), but it would also re-fire the engine that drives colder air down through the Mid-West and all the way to our neck-of-the-woods.

This scenario would generate huge headlines on the upper eastern seaboard (we'd be talking about near hurricane-force gusts, coastal flooding, erosion-- the works)... and smaller headlines out our way about chilly breezes and wet snowflakes. Were this to occur, it would probably amount to a once-in-decades kind of thing.

The CMC is less bull-ish on this scenario-- It keeps the Tropical system separate and offshore, but still manages to yank in the colder air (albeit without the moisture laying around).

My Preference...

The first thing I would say about this, is that the computer models that mobilize and resolve mid-latitude cyclones of non-tropical origin do very well at that, and the models that deal with tropical systems do well at their thing. Each one doesn't do well at the other. I like to keep in mind the National Hurricane Center's perspective on what they think tropical systems are going to do-- particularly ones that are days and days away from being relevant for our weather.

National Hurricane Center - Tropical Storm Sandy - Projected Track

According to the track projections of the National Hurricane Center, the system eventually tracks along the Gulf Stream current (common), passes near Bermuda (common), and then transitions to a strong "extra-tropical" system (common). It can certainly become absorbed into a "mid-latitude cyclone" (what we refer to as a warm-front/cold-front low-pressure system that is not tropical in origin), but the general direction of travel combined with its conviceably reasonable mechanics makes me believe this is probably the most likely scenario as it relates to Sandy.

This would throw a fatal wrench into the European perspective, not delivering the moisture and not providing a shot in the arm for cold air advection. The Canadian model doesn't have this either, and yet still gets the cold air in here. That's all well and good, but without the moisture, you're not going to get snow that way either.

A combination of the GFS / CMC seems most plausible now, with showers moving in Saturday, followed by colder air that simply continues to get colder through Monday. Temperatures will approach the threshold needed for snow, but stay marginal (as it stands now). If you want snow, you're going to have to hope that the "cold" and the "moisture" get to be a little closer friends-- or hope that that longshot scenario of the crazy perfect storm becomes a reality.

The best news is that we're still days away from verification, so future model runs will be coming in to further solidify or distance themselves on various solutions. Check the 7-Day forecast below for our general perspective on what's going to take shape.

I want to also open the floor to questions and comments. We have yet another new improvement to our comments section, so I'd like to see it in action. If you've got a request for different maps and/or questions about the ones I've already shown, or the forecast in general... Lay them on me, and I'll try to get to whatever I can, when I can. As you can imagine, this sort of thing requires a lot of work :-)

Regional Radar/Satellite with Warnings Tracking

Accuweather Radar

From the Storm Prediction Center (below): Click For a Larger Image

Activity Overview Storm Outlook Watches Potential Watches Storm Reports
Temperatures HD Doppler Radar Estimated Rainfall Active Warnings
Current Temperatures HD Doppler Radar Estimated Rainfall Active NWS Warnings
Click For Larger Click For Interactive Radar Click For Larger Click For Larger

Have a great day everyone!

-B

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