A flag is placed in the foundation of a flattened home in Moore. (Reuters)

Today’s topic is rather timely:

Q: What city has been hit the most by tornadoes?

A: The answer appears to be Oklahoma City, says Brent McRoberts of Texas A&M University. “Oklahoma City is almost in a class by itself when it comes to tornado activity,” he explains. “According to the local National Weather Service office, the capital of Oklahoma has been hit more than 140 times since records began in the early 1890s. OKC added to that total this month when at least five other tornadoes hit just recently, and the deadly Moore storm on May 20 struck just south of Oklahoma City. There seems to be no explanation other than Oklahoma City is smack in the middle of Tornado Alley, and conditions in and around the town are perfect for tornado formation during the spring months.”

Q: What are some other oddities about tornadoes and cities?

A:  One of the strangest has to involve the small town of Codell, Kans., McRoberts notes. “Codell was hit by a tornado on the exact same day – May 20 – for three consecutive years, 1916, 1917 and 1918,” he says, adding that records are sketchy about how much damage was done. “Also, the small town of Murphysboro, Ill., holds the record of most deaths from a single tornado – 234 people died in the March 1925 famous ‘Tri-State’ tornado that killed 695 people over three states. The tornado was measured at more than one mile in width.”

Nearly half of Oklahoma City’s tornadoes have come during the month of May.

This means the tornado had winds estimated at 200 to 210 mph, as determined by damage to structures in its path.

Prior to the Moore tornado there had been 58 EF-5 tornadoes recorded in the United States since 1950, when reliable record keeping began. The following map, from the Tornado History Project, shows their location:

Location of 58 EF-5 tornadoes in the United States. (Tornado History Project)

These tornadoes have killed 1,323 people, or an average of 21 per twister. The deadliest EF-5 tornado on record occurred in 2011, with the devastating Joplin tornado. Unfortunately the Moore tornado will be closer to the maximum number of deaths than the mean.

Since 1950 there have been six EF-5 tornadoes in Texas, the most recent one north of Austin in Jarrell.

The scene from Channelview after one of the twisters. (Kerwin Plevka/Chronicle)

Houston has never recorded an EF-5 tornado — the closest call came back in 1992, when a cluster of six tornadoes struck Harris County, including an F4 tornado that developed in Channelview on Houston’s east side.

Area most likely to see tornadoes today. (NOAA)

According to forecasters, daytime heating has eroded the capping inversion over northeastern Texas, southern Arkansas and northern Louisiana, and creating a very unstable atmosphere south of an outflow boundary.

“Conditions are favorable for tornadoes, perhaps even strong, south of the boundary” the forecasters wrote.

As for Houston, the chance of strongest storms is highest north of a line from College Station to Crockett, later this afternoon and mid-evening, the National Weather Service says.

I’ll update later today as the rain and storm chances become more clear for the greater Houston area.

And although damage reports are just now coming in, by looking at the track of the two tornadoes it appears possible that today’s storm may have caused more damage and death.

A comparison between today’s tornado and that from May 3, 1999. (National Weather Service)

Based upon the track shown above it is likely today’s tornado was even wider than the 1999 Moore tornado, perhaps as wide as two miles across, as it moved through the most heavily populated areas south of Oklahoma City.

That’s sobering because, at the time it occurred, the May 3, 1999 tornado was the costliest one that had occurred to date in the United States. It has since been eclipsed by the devastating tornado that hit Joplin, Mo. in 2011.

The 1999 tornado caused $1.4 billion damage in present-day dollars, and directly killed 36 people. It also spawned countless personal tragedies, such as the six-year-old boy who lost his mom.

Without question the area around Moore where the tornado hit today has grown in both population and wealth. So there is more to destroy in 2013.

CNN is reporting there were 75 kids in Plaza Towers Elementary School hit by the tornado, and they’re pulling them out of the rubble now.

5:00 p.m. UPDATE: The National Weather Service says the preliminary rating for the Moore tornado today is at least an EF-4. EF-5 is the highest possible rating on the Enhanced-Fujita scale. This means winds were at least 166 mph, and likely much higher.

4:00 p.m.UPDATE: It’s way too early for damage or casualty estimates, but the pictures that continue to come out of Moore can tell us that both will be bad.

A bird’s eye view of Moore, Okla. (MikeFrancisWx)

3:50 p.m. UPDATE: Some of the early damage reports from Moore, Okla. are pretty horrifying. A television news helicopter pilot identified the wreckage shown below as a school in Moore.

(WFOR TV)

And here’s another picture as people in Moore begin to grapple with the carnage in the tornado’s wake.

(KWTV-9)

3:40 p.m. UPDATE: Looks like the massive tornado that ripped through Moore is now rapidly weakening as a cold front pulls it eastward. But for Moore and other areas south of Oklahoma City, the damage has been done.

A view from Moore, Okla. in the tornado’s wake. (@basehunters)

Reports are coming in of completely leveled structures across the area. Schools, shopping centers, medical centers were all in the path of the tornado. 3:20 p.m. UPDATE: A very large tornado, in excess of 1 mile across, is now moving through Moore, Okla. just to the south of Oklahoma City. This massive tornado is going to cause an incredible amount of damage.

Tornado is moving east-northeast. (NOAA)

ORIGINAL ENTRY: As forecasters expected, severe storms are again pounding Oklahoma today, and there’s a chance the activity will sag southward into Texas later this afternoon and tomorrow. There are presently tornado warnings in effect for Oklahoma, near Oklahoma City, and the area of greatest risk this afternoon and evening is in northern Oklahoma and southern Kansas.

Tornado threat later today. (NOAA)

A large and dangerous tornado was on the ground south of Oklahoma City as of about 3 p.m. today, the first of likely several twisters coming. There is no ambiguity in the radar being reflected by this tornado.

Classic hook feature of a tornado just to the southwest of Oklahoma City. (RadarScope)

Here’s a visible radar loop from just before noon into the early afternoon hours that shows the storm blowing up — it’s worth a click. Forecasters also anticipate that storm activity will increase further south along the front, and much of central Texas is under a tornado watch until 10 p.m. CT. Here’s a map of the watch area:

Area under a tornado watch until 10 p.m. CT. (NOAA)

These storms are expected to steer clear of the eastern half of Texas today, but tomorrow the threat moves closer to Houston. Here’s a map showing the probability of severe thunderstorms across the United States tomorrow:

Convective outlook for Tuesday into Wednesday morning. (NOAA)

As you can see in the map above, Dallas, Austin and San Antonio all face a slight moderate risk of severe weather on Tuesday. I’m not anticipating that severe weather will work its way down to Houston on Tuesday, but it’s possible. The highest likelihood for our region, however, is scattered showers.

Most airlines have canceled flights into Boston, New York and other northeastern United States cities. Trucks are rolling over on freeways. It’s begun snowing throughout Manhattan.

Harlem at 1:30 p.m. CT. (Erik Pindrock, Twitter)

And in the parlance of Boston forecasters, bombogenesis is imminent. Look that one up, non-weather nerds. It’s a real word.

Let’s start with the big picture. Earlier today NASA released a satellite image showing how two low-pressure systems were coming together to form this powerful Nor’easter.

How the massive winter storm is coming together. (NASA)

In this image there are two distinct storms, a western frontal system stretching across the United States and a coastal low pressure system.

The two systems can also be seen in the infrared satellite image below, upon which the fronts have been superimposed. Note the frontal system is generally linear and moving east-southeast, while the coastal low is a more of a cyclonic feature, rotating about a point of the Maryland coast.

Infrared satellite with surface observations and fronts superimposed. (NOAA HPC)

To see both of these systems in motion, check out this really cool loop of visible satellite images.

What’s now happening is that the coastal low is swallowing the frontal system and becoming a still more powerful storm. And it’s going to move northward, up the New England coast.

A foot of snow is possible in New York City, and much more — in excess of 2 feet — is likely in Connecticut and Massachusetts. The map below shows the probability of at least 1 foot of snowfall according to the Boston office of the National Weather Service.

Probability of at least 1 foot of snow. (National Weather Service)

As you can see the probability in Boston is 100 percent. Yep, that’s a big storm. It’s going to be a long, cold night up there.

Be safe, y’all.

Here’s a look at the current radar, which shows the storm moving north, and a rain-into-snow transition occurring as the storm moves into New York.

Radar as of 7 a.m. CT. (chron.com)

There are two reasons to think (hope may be the better word) the storm won’t be quite as significant for parts of the Northeast.

For one, several models now bring the storm on a slightly more easterly track, which would keep some of the storm’s heaviest snowfall offshore. One of the models with the most aggressively eastward track is the Global Forecast System. The image below shows accumulated precipitation (in inches, in liquid) for the next five days.

Five-day precipitation accumulation forecast from the GFS model. (IPS MeteoStar)

Now 2 inches of rain is still significant snowfall — about 20 inches — but as you can see the very heavy amounts of snowfall are along a corridor to the east of land.

Other models, such as the European forecast model, are still following a more westward track, and this remains entirely possible if not likely. Under this scenario, portrayed below, in excess of 2 feet of snow should still falls across parts of Connecticut and Massachusetts.

Two-day snowfall accumulation map, ECMWF, 12 model. (Weather Bell)

Another reason for southern areas of the affected region, including New York City, to feel slightly better about this storm is that the initial precipitation from it will be coming in liquid form this morning. As the New York City National Weather Service suggested this morning, that could knock as much as six inches of snow accumulation in parts of the city.

With that said, this remains a severe storm, and its effects this afternoon, evening and tonight will be substantial. Find somewhere safe to hunker down beginning this afternoon.