Storms split around NYC?

[JohnHuntington]

I love chasing in the plains but I also try to get on everything I can that passes closer to home (Brooklyn--here's some photos from a severe-warned storm in Coney Island the other day).

Last night that big line came across the northeast, and it did something I've seen probably dozens of times--it split north and south of the city.

Here's the line when our severe watch was issued:


And here's the line when it finally got to us:

(Not sure why that resolution got degraded, but you get the idea)

Of course this may have been anomalous, and may have only happened when I've been out with my camera waiting for the lightning But I've been living in this apartment where I have roof access for about 13 years and have attempted to shoot lightning every single storm that I could, and this split has happened--at least for big organized lines of storms--more often than not, in my experience.

I googled around and found this article, the abstract of which says, "Moving thunderstorms, however, tended to bifurcate and to move around the city, due to its building barrier effect".

I didn't pay the $35 to read the whole article, but it seems to me that the buildings, while tall, wouldn't really impact something as big as the atmosphere?

And, it seems to me, with my limited understanding, that with an urban heat island, a pool of stronger warm, humid air in front of an approaching cold front would actually provide fuel for storm development, rather than cause it to split? I'm confused by those mechanics.

Has anyone else experienced this phenomena in other cities?

Thanks!

John
http://www.johnhuntington.photography/

 

[Royce Sheibal]

The heat island does exist, as heavily concreted areas tend to be 5F+ compared to areas around the city. Here in Omaha for example, Eppley Airport is the offical temp, but it's about 5 miles away from downtown, and surrounded by greenery and river. Mid town will often by 5F+ above during the spring and summer on a sunny day.
While the heat island does add heat, it does not add moisture. A lack of greenery means less evapotransperation, and lower relative humidity. This effectively ruins cape, and rising heat from the city will ruin lapse rates and create caps.
This effect seems to be most viable when there is minimal storm inflow in the horizontal plane, such as with bow echoes / derechos / MCS. A well inflowed storm like a supercell with tornado would likely disrupt the heat bubble and make it negligible, possibly even digesting the heat into the storm's upflow.
It's also worth noting that most big cities are a few hours east of the main axis of storm initiation. This means that storms will be fully matured, cycling, merging, or dying by the time they get to you. I'd like to see SPC do some climate data on this.

 

[Stan Rose]

it seems to me that the buildings, while tall, wouldn't really impact something as big as the atmosphere?

I'm sure they could cause local effects--I live on a slight hill on the plains maybe only 50-100 feet higher than the surrounding area, and the precip is significantly affected by the slight rise. One building might not do much, but a whole skyline might. It's probably been modeled...

 

[JamesCaruso]

John, those are some great shots you got over Coney Island! Nice to know another chaser from the east coast; I am originally from Queens and still have family back in NY (I am now in the Philadelphia area).

I don't feel qualified to comment on whether there is an actual effect from the city. But I will throw out there that I think everyone feels that storms always miss them... I know I feel like I always end up within a gap of a previously solid line, here in my neighborhood 35 miles northeast of Philly. There is simply a lot more land outside of your area than there is inside of it, so the likelihood is that your immediate area is NOT going to get hit. Now I know you are talking about a line and not an individual cell, but for a line to remain that solid is not a "natural" state, meaning that many variables have to be in equilibrium for that to occur and sustain itself, and the tendency is for it NOT to hold together - just like most supercells are not going to remain classic and discrete for too long before tending to go HP and/or merge. Like Royce said, the line is simply more mature by the time it gets to the city so is tending to weaken and break up by then.

Also NYC is relatively near to the coast, so there could be a stabilizing sea breeze effect as well.




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[Dan Robinson]

While the heat island is a known phenomenon, I don't believe that such a relatively subtle near-surface temperature change in urban areas has an appreciable impact on an established MCS. With east coast locations, I think most weakening has more to do with storms approaching the more stable marine layer near the coast. I happened to look at a radar loop at the time the NYC squall line was falling apart - and it started doing so well to the east in NJ, long before reaching the city.

I've been paying a lot more attention in recent seasons to the "MCS maintenance" parameter on the SPC mesoanalysis page. This has done surprisingly well in predicting when and where a squall line/MCS will begin to lose steam. Most of the time, weakening is simply due the storms moving out of a zone of instability, which is common along coastal areas along oceans and the Great Lakes. It's not always related to outrunning the CAPE axis though - it can be a loss of upper level support, encountering stronger capping, losing surface convergence, etc. When an MCS begins to weaken over a city here in the Midwest, it's usually just a coincidental juxtaposition of the synoptic/surface features. As long as an undisturbed CAPE reservoir is present in a largely uniform synoptic environment, an MCS will pass over cities with no noticeable change. When they do weaken, there is usually something else going on with the larger-scale environment rather than something as (relatively) small as a heat island.

 

[Royce Sheibal]

I agree, Dan, that local heat islands are small in size (100-1000sq mi), but the effects of localized evapotranspiration due to rain have been shown to have significant impacts on instability from the cellular level up to meso. If we already know that localized moisture has some impact, why not localized heat? Again I'm no expert on dynamics but I think this is a field that really hasn't been researched well and would make a great thesis paper for someone.
http://journals.ametsoc.org/doi/pdf/10.1175/1520-0450(2003)042%3C1273%3APACOAU%3E2.0.CO%3B2
Interesting paper on the theory that the heat island over Atlanta causes localized heavy rain events.

 

[JohnHuntington]

While the heat island does add heat, it does not add moisture. A lack of greenery means less evapotransperation, and lower relative humidity. This effectively ruins cape, and rising heat from the city will ruin lapse rates and create caps.

Aha, makes perfect sense, thanks!

John
www.johnhuntington.photography

 

[JohnHuntington]

One building might not do much, but a whole skyline might. It's probably been modeled...

Thanks!

John
www.johnhuntington.photography

 

[JohnHuntington]

John, those are some great shots you got over Coney Island!

Thanks!

Nice to know another chaser from the east coast; I am originally from Queens and still have family back in NY (I am now in the Philadelphia area).

Definitely! It's always amazing to me watching storms come in on Radarscope or something that I'm like one or two of 8 million people in the area on spotter network.

Of course Scott McPartland lives in Queens too. It's funny, he and I live like 10 miles apart but have never met. I even randomly stayed in an adjacent hotel to him in Texas this year but we still missed each other

I don't feel qualified to comment on whether there is an actual effect from the city. But I will throw out there that I think everyone feels that storms always miss them...

Oh I definitely suffer from that, but I've seen this over and over and over here so I think it's not just my imagination

Also NYC is relatively near to the coast, so there could be a stabilizing sea breeze effect as well.

I think this is a major factor too, I've seen lots of things just come in and die when it gets over here, while rolling along through the counties north of the city and on into Connecticut.

I'm likely going to be out chasing somewhere Tuesday, if I go south I often end up near Lancaster where it's flat and there's a lot of open fields. If you're out, drop me a line!

John
www.johnhuntington.photography




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[JohnHuntington]

I've been paying a lot more attention in recent seasons to the "MCS maintenance" parameter on the SPC mesoanalysis page.

Thanks! I didn't know about this one, I'll definitely check it out.

John
www.johnhuntington.photography