May 7, 2011

Running from an EF-5: Part Two

Filed under: Severe — Erin @ 3:54 pm

This is Part Two of a series of three about my experience with the EF-5 tornado that went through four counties in Mississippi on April 27, 2011. Part One can be found here, and Part Three, an account of the aftermath, will be forthcoming.

Wednesday, April 27, 2011.

Bzzzzzzz! My cell phone is still in vibrate mode.  I’ve forgotten to turn the ringtone on.  I pull my eyes away from the TV and answer it.  It is my father, who is at work.  “Are you—”

“I know,” I say.  “I’m going to take cover.”

“I’ll call after it passes,” he says.  His voice is clearly nervous.  We hang up.

I take another look at the radar that the weatherman is talking about.  That sure looks like a debris ball, I think, as the menacing supercell enters southwestern Noxubee County.  Then bzzzzz! The phone buzzes again.  This time it is one of my sisters.

“Erin, do you know what’s going on?”  Of course.  I have been following it on the local news, which, unfortunately, is swamped at this point with several simultaneous tornadic supercells, and have just checked the Internet to see if anyone has reported a tornado with this one.  “Well, they are saying in the tornado warning that they’ve got a confirmed tornado—a big one.”

“Does that look like a debris ball on radar to you?”  She says that it does.  “All right,” I say, arriving at a decision instantly, as the crawl-space foundation of this old house flashes before my mind’s eye.  “I’m getting the cat and getting out of here.”  She agrees.

The tornado safety guidelines put out by the National Weather Service do not endorse leaving a house in a vehicle.  I understand why.  In general, a house can be regarded as a comparatively safe place to be in a tornado, whereas a vehicle cannot.  Moreover, it’s possible to get on the road and drive directly into a different tornado or an area of high winds.  When I tell my sister that I’m planning to leave, I know full well that I am going against this advice, and for all these reasons, I don’t recommend that to people in general—certainly not when there is not even a confirmed tornado, and in most cases, not even when there is one.  However, as a meteorology student, I have closely monitored the extreme atmospheric conditions that would be in play for this event.  I am aware that, under these circumstances, tornadoes that form are far more likely than normal to become “violent”—to reach an intensity at which even well-constructed homes are definitely not safe to be in because every wall in them is blown down.  I am aware of what to expect if I choose to drive through the precipitating part of a supercell.  (I was close to the wall cloud of one a week ago, after all!)  I am aware that there is a clear spot north of Noxubee County, and there is nothing that will enter that area in the immediate future.  And, most importantly, I have enough time to get away.

But only just enough.  There is no time to lose.  The storm is moving quickly, and at the angle it’s coming, it will be upon me in 20 minutes.  I grab my laptop, leaving behind even the power cords.  I reflect for a moment on the irony of this; I had recently seen my first AC adapter go out and had to get this one over the Internet.  Well, there is no time to waste by crawling under my desk and unplugging the cord.  I grab my purse.  I shove my protesting cat into the cat carrier.  Carrying only these things, I run into the vehicle, hoping that the lightly falling rain does not penetrate the laptop case, and apparently (so I discover later) leave a rut in the yard in my rush to get out of there.  I head north.

I would not leave my cat at home, but the delay in grabbing up these things has cost me a few more minutes.  Meanwhile, the tornado has not waited.  It’s best not to say what speed I am driving, but no one else heading north is driving any differently.  I wonder how many of them are on the road for the same reason that I am.  The rain slacks off.  I never run into any hail on this trip.

It is between Macon and Brooksville that I start seeing small pieces of branches fall from the sky.  They are not large enough to slam to Earth with violence, so there is something almost graceful in it.  I’ve never seen anything like this before.  These are not being blown about horizontally by winds; they are falling like soft rain from the storm itself.  The movement is vertical.  The branches have been sucked into the mesocyclone, which tilts southwest to northeast; the part of the storm that I am under is nowhere close to the tornado!  Seeing debris brings everything to mind that I have pushed out in my single-minded focus on getting away.  It occurs to me that people somewhere may see debris from my house later on.  Well, I’m safe, and the cat is safe, I think to myself.  There’s nothing more I can do.

Almost mockingly, the sunlight breaks out as I leave Noxubee County.  I hear the buzzing of my phone once more.  It is my father, who has tried to call me several times since my sister called him and told him that I had decided to leave the house.

“You’re fine in that part of Lowndes County,” my father tells me over the phone.  That fits with what I had seen on the radar; I knew that there was a dangerous supercell in Monroe County (the Smithville tornado, it turned out).  I also know that, though nothing tornadic is coming for Starkville and Columbus at the time, I do not want to be stuck in one of these cities if that changed in an hour or so, as it often does during tornado outbreaks.  I also don’t like the idea of pulling off the road indefinitely.  I decide to stop at the house of friends in rural Lowndes County, and there I stay for an hour or so.

I am fully expecting that I will not have a house to go back to, or my house will be damaged beyond repair, or the town will be destroyed.  I’ve read a lot of personal accounts of extreme weather events, and now it seems that I am about to live that awful aftermath.  It is truly amazing how we are able to push thoughts like this out of our minds when we are focused on something critical, such as (possibly) survival itself.  Now that this is not an imminent concern, the ugly realities of a tornadic strike hit me.  I don’t know exactly what will be damaged, or how much, but there is absolutely nothing I can do about it.  All I can do is wait to hear some news.  It is a hideous wait, and yet, I am focusing more on the animal confined in her carrier next to me, and the fact that no one else was at home, than on the home itself.  No one wants to lose a house, but when all is said and done, it’s just a house.

Over the course of my visit, my hosts learn that Macon has not been hit.  The storm apparently passed over with rotation still apparent, but no tornado anymore.  To my astonishment, there was apparently some nonchalance about the whole event in at least some parts of Macon.  Finally I decide to return home, since I still indeed have one.  I get there in time to settle in and watch with amazed horror as live footage of the tornado in Tuscaloosa airs.  Later, I see video of the Noxubee County tornado.  I find out through the TV news and Twitter—Macon, amazingly, has power—that many people in the Southeast are not so fortunate as I have been this afternoon.  My own experience is pushed back to a different corner of my mind as the hideous extent of the destruction and suffering becomes known.  I have not suffered loss.  I focus on those who have.

May 6, 2011

Running from an EF-5: Part One

Filed under: Severe — Erin @ 4:24 pm

Note: This is something a little bit different from the usual fare for this blog. Nothing particularly notable is occurring in the South except for the river flooding, and at this point that is a matter of concern for the engineers and hydrologists more than meteorologists. (I could rant about the Corps of Engineers, but that would be better suited for my other blog.) Since this is the case, and since I have felt that I needed to write about my experience on the tornado outbreak of April 27, I’m going to do that. This will be a three-part piece about my experience involving the EF-5 tornado that went through Neshoba, Winston, Kemper, and Noxubee Counties that day. The first part does not even occur on the 27th; it is from a week earlier. I’ve come to the conclusion, though, that it is part of the same story and an important factor in why I chose what I did that dark day.

Wednesday, April 20, 2011. I sit parked on the side of Highway 45, somewhat north of Crawford, in a line of other vehicles whose drivers have made the same decision.  We are all being pelted by hail that I estimate is up to an inch in diameter, mixed in with some rain.  No one dares to drive any farther.  This is, I believe, the third time that hail in this storm has forced me to pull off the road in my drive south to Macon from Starkville that afternoon.  I’ve almost lost count, and that’s not even counting the other storm that produced some hail before I even left Starkville.

I may be in the minority these days in having a cell phone that does not have Internet capability.  Ordinarily that is not a problem for me, but right at this particular moment, I find myself really wishing that I had a radar picture in front of me.  I call my sister and ask her to pull up a radar image on the Internet.  I have some urgent questions for her.

I obviously don’t want the car to be damaged by the hail, but what is currently happening to me is not my primary fear.  See, I have been at Mississippi State University as a graduate student in meteorology, I am well aware that the storm I am under is a supercell thunderstorm, and most likely, I am in what is called the “core” of the storm—the area of the heaviest precipitation.  Supercell thunderstorms are the ones that are most likely to produce tornadoes, and if there is a tornado, the core of the storm is located to the northeast of it.  And the storm is moving northeast.

In this particular situation, I could easily be in far more danger after the hail ends, and that is what I want my sister to tell me about.  I give her my approximate location.  “I think you’re in the hook,” she says uneasily.  (A hook echo on radar is an indication of strong rotation and possibly a tornado.)  My nerves tense at this, but if she can see a hook, it means that there is a slot of low to no precipitation, which I am most definitely not in.  “No, I’m not in the hook,” I say.  “I’m in the core.  I’m getting hammered.  But you are saying there is a hook with this storm?  Is there a tornado warning?”  It turns out that there is, and it is radar- rather than sighting-based.  That’s no surprise, and it certainly doesn’t mean that there isn’t a tornado.  The perils of high-precipitation supercells strike again.  I ask some more questions.  It seems that I am on the north edge of the core, and that based on the motion of the storm, I would be best off staying put until the whole thing is east of me.  The hook should pass south of me if I do that.  I just want to get out of this.  I’m not opposed at all to storm chasing, but it’s really not something I’m inclined to do without another person in the car or live radar available.

Once I am on the road again, I get a glimpse of the wall cloud off to my east with the aid of the nearly constant cloud-top positive lightning flashes that the storm would put out as it intensified.  I recall from my thesis reading that intensifying supercells often do produce a great deal of positive lightning.  This particular supercell would go on to produce larger hail and threaten Columbus.  I take several hours to come down from the adrenaline rush.  One week later, I would be very glad I had this experience.

Part Two of this will be about what happened to me personally on April 27. Part Three will be the aftermath of that event.

April 26, 2011

Dangerous Severe Weather Situation for Tennessee Valley

Filed under: Forecasting,Mid-latitude cyclones,Severe — Erin @ 9:57 pm

So far the severe weather outbreak of late April 2011 has brought devastation to many different areas in the southern Plains and Southeast. A tornado that was probably of a violent intensity hit a small town in Arkansas last night, reportedly removing pavement from the ground, and tornadoes have touched down from Texas through Arkansas and Louisiana into Mississippi, Tennessee, and Kentucky today. The severe weather is going to continue through Wednesday as the second of two low pressure centers intensifies over the mid-South.

A powerful mid-level jet has formed, with winds screaming at 70 knots or more:


Winds and pressure at 700 mb

This will provide powerful upward forcing. Additionally, strong thermal advection feeding into the developing low pressure center (which has become quite strong today, checking in at 989 mb as of this writing) will promote instability as well as additional vertical uplift:


Temperature and wind at 850 mb

For specific tornado threat regions, the NAM model has been fixing on an area centered over the Tennessee Valley. Yesterday the bull’s eye appeared to be right over the state of Tennessee, but today, it has shifted somewhat south.

The 18 UTC run of the NAM had CAPE over 4000 J/kg in central Mississippi at peak (mid-afternoon Wednesday), with a local maximum roughly over the Golden Triangle region and Tupelo, MS:

This run also had 3 km energy helicity values literally off the charts over the same area:

The 00 UTC run has CAPE peaking around the same value as before.

It has, however, moved, the helicity indices to extreme northwest Alabama:

Bottom line? I think that at this stage, such deviations are just model noise. Observations will be needed to determine exactly what area will have the highest risk of severe weather tomorrow. However, it is important to note that the model has been very consistent with an elevated tornado threat Wednesday afternoon in the Tennessee Valley area. With that in mind, I offer up my own subjective severe weather threat map for this event. I am not assigning probabilities to any of the color regions of this map; they are present only to indicate the areas that I think are in increasingly higher danger of seeing powerful severe weather, including long-tracked tornadoes.

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