April 13-14 Oklahoma-Kansas Chase

This post is long overdue, but there has been no helping the time lapse between my first Great Plains chase of the year on April 13-14 and tonight, when I’m finally setting the highlights of those days briefly in print. The reason is that, upon my return home, I immediately succumbed to the worst case of acute bronchitis I’ve ever experienced. It was characterized by constant, deep, wrenching, non-productive coughing; a chronic sore throat; a fever that topped 102 degrees; an ear infection; laryngitis; plugged-up sinuses; and if I’ve missed anything else, let me just sum it all up by saying that I was in neither the condition nor the mood to do any film editing or writing, or much of anything except to attach my face to a vaporizer and to suck down Jell-O, chicken soup, sports drinks, ginger tea, and enough fluids overall to qualify me as a human aquarium.

Today, though, I am definitely on the mend, and it’s high time I got this report written. Tomorrow looks to be another big day in eastern Kansas, so I need to write before anything I have to say about an event from two weeks ago gets swallowed up in the latest round of wedges.

And it does look there could be some wedges. Look at this NAM skew-T and hodograph for Chanute, Kansas, at 00Z. (Thanks, Ben Holcomb, for tipping me off to Chanute!) With 1km and 3km SRH at 290 and 461 m2/s2 respectively and a nice, fat low-level CAPE, that’s the broth for some violent

tornadoes. I expect that part of the area that the SPC has categorized as a light risk for tomorrow will be upgraded.

But I’m chasing rabbits. Getting back to the topic of this post: With conditions coming together for two or three days of severe weather in tornado alley from April 13-15, Bill Oosterbaan and I headed for Oklahoma in company with two new chaser friends. Rob Forry is a fellow chaser from the other side of Michigan who had yet to experience a Great Plains chase; and Steve Barclift is an editor friend of mine who, I discovered, shares my keen interest in severe weather and had been wanting to get a feel for storm chasing.

We arrived in Norman, Oklahoma, late in the morning on Friday the 13th. Dropping off our travel bags at the apartment of Ben Holcomb, who was graciously putting us up for the night later on, we promptly headed out for the chase.

We encountered our first storm of the day not far from Chickasha. Not being the superstitious type, I have no qualms about chasing storms on Friday the 13th; still, this storm gave us a shake when it led us back to Norman and spun a tornado within a mile of Ben’s apartment. We pulled out of chase mode long enough to make sure that Ben’s place was okay. Then we headed southwest a second time, this time plunging beyond Chickasha toward Boone and Meers, and thence into the heart of the Wichita Mountains. There, we positioned ourselves on the southeast flank of a tornadic supercell as it advanced slowly over the ragged landscape.

We may have witnessed a tornado at this point, but my video provides no conclusive evidence, just strong suggestions. Tornado or not, though, to stand in the inflow of that massive, beautifully crafted supercell and watch it spew lightning from its charcoal interior as it dragged across those prehistoric peaks was reward enough. No more need be said, nor shall be, since Friday was simply a scenic prelude to the action up in Kansas the following day.

Saturday, April 14, dawned on a large high-risk region that ranged from most of central and eastern Nebraska south through central Kansas and down into much of central Oklahoma. With impressive upper- and mid-level jets overlaying the region, bulk shear was beyond adequate, as was instability. The ingredients were all there. Today, it seemed, would be one of those days when anyone who chased–and there were lots of chasers prowling the prairies on this day–would see a tornado.

In practice, though, it wasn’t quite that easy. Our plan was to drift up I-35 and then head west toward a likely looking storm. Not a very sophisticated approach, but it seemed likely to work, and in fact it did. We weren’t far across the Kansas border when we decided to turn west, and in a while we encountered our first supercell of the day, and with it, our first tornado. The cone spun at a good distance, probably five miles or more away. Looking at my video clip, I’m satisfied that it was indeed a tornado–even at that distance, the outline is distinct and separate from the storm’s rain shaft.

We stuck with our storm as it sailed north-northeastward, but it seemed to be having a hard time establishing itself beyond its first tornadic salvo. Still we stayed with it, hoping it would organize into a rumbling monster. But it continued to attenuate into a skinny, sorry-looking mongrel, so we finally dropped it for a more promising-looking storm to its south.

I remember saying at the time, “Dropping this storm [which I was in favor of doing] could be a really good decision. Then again, the storm could reorganize in half an hour and start putting down hoses.” Of course, the latter is what happened. Half an hour or forty-five minutes later, the storm we had put behind us had morphed into a supercell that, from the looks of it on radar, clearly wasn’t fooling around, and it went on to produce a string of tornadoes.

But by then we were committed to the storm to its south, a deceptively imposing-looking beast that washed out on us as we tangled with it and ultimately disappeared completely from the radar screen. Long before that happened, we wisely abandoned it for the next storm down the line, and as the saying goes, the third time was a charm. Just drawing closer to the storm environment, we could tell that this storm was of a different caliber. There was more lightning. The inflow was strong. The thing just felt tornadic. And it was.

From here on, I’ll let my video clip tell the story. It chronicles our chase from near Pretty Prairie, where we encountered our first tornado with this storm at close range with rain bands wrapping toward us, on north-northeastward toward Lost Springs and Delavan. The latter, night-time portion of the video is best viewed in dim light.

On a side note, the SPC did a great job of forecasting this widespread outbreak, as you can see from this verification of the outlooked areas with confirmed tornadoes. One thing that puzzles me is why they showed a 45 percent hatched area for Nebraska, when from what I recall, the NAM and RUC didn’t appear at all bullish for a northern play. At the time, I figured that those SPC guys must have known something that the models weren’t revealing, but in fact the majority of tornadoes occurred southward in Kansas. If anyone from the SPC happens to read this, I’d welcome your comments on the thinking behind the enhanced focus on Nebraska over regions southward.

We overnighted east of Kansas City, and the following day found us chasing a warm-front scenario in south central Minnesota. The setup this day was utterly unlike the previous day. In fact, with the surface low nearly collocated with a closed 500 mb low to our west, we were dealing with what seemed like a quasi-cold-core setup. The storms, low-topped supercells, formed in convective “streets” that moved nearly straight northward, each street progressively kicking off new convection to its east where outflow presumably converged with strong southeasterly surface winds. Tornado reports occurred to the north, along or just past the warm front, where winds backed strongly.

The setup was an interesting one particularly in that tornadoes were reported on the cold side of the front, which cooled markedly within a matter of a few miles. This seemed counterintuitive: what kind of surface instability was available in such an environment? I recalled my chase with Kurt Hulst and Dave Diehl back in February, 2006, when we watched a storm on the far eastern side of a cold core drop a tornado several miles to our south. Where we stood, the air was so cold that I could see my breath; yet across the distant treeline, an unmistakable tornado was spinning and doing damage in a small town east of Kansas City.

As for this present date, while the four of us didn’t see a tornado on April 15, we did see the most wildly circulating wall cloud I’ve ever laid eyes on. The motion in the thing was unreal, something I attribute to the storm’s crossing the warm front and encountering a radical backing of winds.

Inevitably, we found ourselves in Minneapolis, at which point we left chase mode and headed for home. The first few coughs that would rapidly blossom into the debilitating bronchitis I mentioned at the start of this post were just getting hold of me. The following day would mark the beginning of a miserable two weeks. I’m just glad the virus held off till I got home.

Now I’m almost recovered–not in enough time for what looks to be a lively day in Kansas tomorrow, but certainly for the next round after.

For another perspective and some absolutely stunning videos of the Kansas outbreak of April 14, visit my friend Kurt Hulst’s blogsite, Midwest Chasers.

Stormy Monday in Michigan?

The Storm Prediction Center’s Day Three Convective Outlook has stamped lower Michigan with a “See Text” attended by the following discussion:

A POCKET OF COLD
TEMPERATURES AT MID LEVELS…MINUS 18-20C AT 500 MB…WILL SPREAD
ACROSS LOWER MI JUST NORTH OF A FOCUSED SPEED MAX. THIS FEATURE
WILL LIKELY INDUCE DIURNALLY ENHANCED CONVECTION AS 50F+ SFC DEW
POINTS SURGE NWD WITHIN THE WARM CONVEYOR. LATEST FORECAST
SOUNDINGS SUGGEST SFC-BASED CONVECTION IS POSSIBLE WITHIN A STRONGLY
SHEARED ENVIRONMENT THAT WOULD OTHERWISE FAVOR SUPERCELL
DEVELOPMENT. GIVEN THE SOMEWHAT LIMITED BOUNDARY LAYER MOISTURE
ACROSS THIS REGION WILL NOT INTRODUCE HIGHER SEVERE PROBS ATTM.
HOWEVER ANY UNDERESTIMATION IN LOW LEVEL MOISTURE WILL LEAD TO A
MORE UNSTABLE AIR MASS THAT WOULD SUGGEST AN INCREASED RISK OF
SEVERE FROM EXTREME NRN IND/NWRN OH INTO LOWER MI.

Hmmm…okay, that’s worth looking into, and I have done so. The NAM surface map is more optimistic about moisture than the GFS and SREF, wanting to bring in mid-to-upper-50s surface dewpoints, and therein lies the possibility for severe, from what I can see.

Today’s 12z 250 mb 4km NAM also shows a 70 knot jet streak moving into the area on top of 35-40 knot 850 mb winds, and GFS is in better agreement with the shear than it is the moisture.

Earlier on, I also sampled a few 6z Bufkit NAM soundings using RAOB, and these show impressively curved hodographs–a different story from TwisterData’s point-and-click hodos–as well as dewpoints tapping on 60 degrees. That seems pretty exuberant, particularly in the light of other forecast models, but it does give me at least this take-away wisdom: Monday bears keeping an eye on. If, as the SPC states, decent moisture manages to infiltrate lower Michigan, then we could be in for some severe storms.

Just for kicks, below are the aforementioned RAOB forecast soundings for Monday evening taken from this morning’s 6z NAM run, along with the 4km NAM 250 mb map. The soundings are for Kalamazoo, Jackson, and Fort Wayne. Take them with a grain of salt, but let’s see how things shape up (or not) between now and then.

KALAMAZOO, MI

JACKSON, MI

FORT WAYNE, IN

250 MB WINDS (FCST 21Z)

Looking Down to Dixie

This bright morning sun streaming through the sliding door of my balcony is blinding. At quarter-to-ten on the day before Thanksgiving, it shines low over the southeast horizon directly onto my face, forcing me to write with my left eye shut. That is not an altogether satisfying modus operandi, but I don’t feel like closing the blinds or wearing a … well, what the hell, why not wear a hat? I’ve just put on my trusty Tilley. Problem solved, though Lisa will probably look at me oddly when she steps into the room.

Here in West Michigan, we’re moving into high pressure and a warming trend through the holiday. But “warm” is a relative word which in this case means not terribly cold–rather nice, really–but don’t plan on wearing a T-shirt.

Hundreds of miles to my south, though, warm means warm. Warm enough to get the job done for convective weather. From now through April, Dixie Alley once again becomes the star of the show. The trough moving in for the weekend offers a good example of why.

It’s a deep trough, and a surface low up in the Great Lakes looks to wick up enough moisture into the Southeast to stoke the storm machine. I’ve included a couple of the latest 00Z Euro/GFS comparisons plus Euro 850 mb relative humidity to give you a sense of what’s shaping up for 96 hours

(click on images to enlarge them). The GFS is predictably faster than the ECMWF, but both are pointing to the same overall scenario, with the trough eventually pinching off into a closed low.

Cloud cover presently looks like it will be rampant, minimizing instability. Still, given some ripping bulk shear, this system is something to keep an eye on as it evolves, particularly if you live in Dixie Alley.

That’s all for now. The sun has moved and is no longer blinding me. Time to get on with the rest of this day. May you and yours enjoy a happy and blessed Thanksgiving!

Storm Chasing in Illinois on Wednesday

The formidable system that ground out large, violent tornadoes in Kansas, Oklahoma, and Texas on Tuesday will move east on Wednesday to bring another round of severe weather to southeast

Missouri, Illinois, and Indiana. And finally–finally!–I’m in a position to do some storm chasing. Financial constraints have majorly crimped my expeditions so far this season, but no way am I missing tomorrow.

Based on Tuesday morning’s NAM run, I’d been eyeballing Effingham, Illinois, as a preliminary target for trolling the I-70 corridor. The sounding for that area looked mighty pretty, as you can plainly see.

Now, however, with the 00Z runs in, I’m inclined to shift farther east near Terre Haute. Here’s another model sounding, courtesy of TwisterData, for near Oblong, Illinois. Maybe not quite as sexily backed at the surface as the Effingham sounding, but with stronger low-level winds and definitely quite functional. Maps of 500 mb winds and SBCAPE (see below) paint in a little more detail and suggest that near the Illinois/Indiana border is a good choice.

Tomorrow morning’s data will tell all. Meanwhile, it’s time for me to get my ugly-rest. I am so excited about the prospect of finally getting out and feeling the moisture, watching cumulus towers erupt and organize into glowering supercells, and hopefully videotaping some tornadoes out on the flat, wide-open Illinois prairie! A good night’s sleep and then I’m off in the morning.

How It Feels to Not Be Chasing

Right now my buddies are out west chasing this latest storm system. I’m not with them because I can’t afford it. Money has been extremely tight and what I take in has got to go toward paying the bills and putting food on the table for Lisa and me. That’s the reality of life. I’ve been on a couple of unproductive chases so far this year, and now that a decent system is finally in play out west, I’ve got to pass it up. I can’t even chase what promises to be a fabulous day today in Illinois. Once again I’ll be picking over the scraps later on here in Michigan. It’ll be nice to get some lightning, but it just isn’t the same.

Armchair chasers are typically regarded as off on the sidelines of storm chasing. But there’s a difference when you’ve been in the game and find yourself benched. You know what you’re missing. You’ve been looking forward to it all year with intense eagerness, like a kid looks forward to Christmas. So when you can’t do a thing about it unless it lands right in your lap–which in Michigan, land of cold fronts and veered surface winds, doesn’t happen often–it is extremely frustrating. SDS is one thing, but this is something else.

Armchair chasing? Nuts. I get to where I don’t even want to go near a radar. But I do anyway. I can’t seem to help myself. I want to see what’s happening with my friends, what storms they’re on. I look at the forecast models, too, hoping against hope that they’ll stop sticking their stupid tongues out at me and smile at me for once.

Today the RUC actually seems to do so. Here’s the 10Z KGRR sounding for 23Z this evening. Not bad. I just wish I believed that those surface winds and helicities were accurate, but I don’t, not with other models (NAM, GFS, and SREF) shouting them down. Besides, the HRRR composite reflectivity hates me. I can’t stand looking at it. Again, though, as with the radar, I do anyway. Storms progged to fire in northern Illinois and even south along the Michigan border…all I’d have to do is hop in my car, head west along I-80 and maybe down toward Peoria, or even just 80 miles south down US 131 toward the state line as a compensation prize, and I’d be in the sweet zone. But it ain’t gonna happen.

Rant, rant, rant. On this date last year I was on the most unforgettable chase of my life in northern South Dakota. Today, I wish this present system would just get on with it and get it over with so I can forget about weather, forget about the fact that I call myself a storm chaser when I’m not chasing storms. What a laugh. True, I’ll be chasing this evening locally for the first time for WOOD TV8. That I can at least afford, and it’s a nice way to work with the storms that we do get and possibly provide a bit of public service. But I don’t have high expectations. That’s a good thing here in populous West Michigan, but it doesn’t satisfy a convective jones. I just hope this season doesn’t drift into the summer pattern before I can get out and see at least one good tornadic supercell.

Okay, enough of this self-indulgent, babyish whining. I just had to get it out of my system, because in all seriousness, missing out on the action bothers me a lot, an awful lot, more than I can describe. It’s an absolutely miserable feeling. But it’s how things are, and life goes on.

Good luck out there in the Plains, Bill, Tom, and Mike–and Ben and Nick, though I know you guys are chasing separately. I hope you bag some great tornadoes today and over the next few days. As for me, it’s time to shower up, head to church, and remind myself that there’s more to life than this.

First Great Plains Chase of 2011 This Wednesday

At last, the setup I’ve been waiting for–one that warrants dipping into my tight finances in order to make the 1,000-mile drive to the Southern Plains. To date, this present system has been a miserable disconnect between upper-level support and instability, with a nasty cap clamping down on the whole shebang. Last night it managed to cough up a solitary tornado in South Dakota. That was it. I’m not sure what today holds, but I haven’t seen anything to excite me about it or tomorrow.

But Wednesday…ah, now we’re talking! The SPC places a large section of the Great Plains under a slight risk, and their discussions have been fairly bullish about the potential for a wide-scale event. At first I couldn’t see why. My mistake–I was looking at the NAM, which with straight southerly H5 winds has not provided the best PR for Wednesday’s setup. But once I glommed the GFS, I got a whole ‘nother picture, one which the SREF and Euro corroborated.

That was last night. I haven’t looked at today’s SREF, and the new ECMWF gives me a slight pause as its now somewhat negative tilt has slightly backed the mid-levels from the previous run. But only slightly. The H5 winds still have a nice southwesterly flow, and taking the three models together, everything you could ask for is lining up beautifully for tornadoes in the plains.

The event promises to be widespread, with a robust dryline stretching from a triple point in southwest Kansas south through Oklahoma and Texas. Positioned near a dryline bulge, Enid, Oklahoma has drawn my attention for the last couple of GFS runs. Check out this model sounding for 00Z and tell me what’s not to like about it. Everything is there, including a voluptuous hodograph and 1 km SRH in excess of 300 m^2/s^2.

Other places in the region also look good, though. Farther south in Texas, Wichita Falls shows potential. Helicity isn’t as persuasive as Enid, but the CAPE tops 3,000 J/kg and there’s less

convective inhibition. Here’s the sounding for you to compare with Enid.

I haven’t been as drawn to Kansas so far, but with the triple point perched there, storms are bound to fire up just fine in the Sunflower State. The details will work themselves out between now and Wednesday evening. Significantly, the tyrannical cap of the previous few days no longer appears to be an issue.

The bottom line is–it’s time to head West! This evening I’m taking off for the plains with my long-time chase buddy Bill. At last! Time to sample what the dryline has to offer, and–now that I’m equipped with a great HD camcorder–finally get some quality footage of a tornado or two.

There’s no place like the Great Plains! YeeeeHAW!!!!!

April 10, 2011, Upper Midwest Chase Shaping Up

Tomorrow looks to be a big severe weather day in the upper Midwest and Great Lakes. It will also be my first storm chase of 2011, and with departure time less than 24 hours away, I’ve been scrutinizing the forecast maps, mainly the SREF and NAM.

Whew! There are some formidable parameters coming into place for southeast Minnesota, northeast Iowa, much of Wisconsin, and northern Illinois. The SPC has outlooked this area for a moderate risk, with a mentioned of strong, long-lived tornadoes, and it’s not hard to see why. The one thing that bothers me is the marginally veered ambient surface winds overlaid by 500 mb winds from the southwest. Backing shows up way to the north in Wisconsin, in horrible territory for chasing.

So my present choice for a target is Dubuque, Iowa. According to the NAM, the jet core is aimed in that direction. CINH wants to erode there, MLCAPE looks great, there’s a nearby 3 km MLCAPE max of 75 J/kg (forecast soundings may show better than that–haven’t looked yet), and…well, look down below at the maps I’ve been perusing and judge for yourself. There are a lot of them. In many cases, I’ve shown both 21Z and 00Z so you can see the progression of dynamics.

With height falls and vorticity moving in from the northwest, it may take a bit of will power not to get lured in that direction where the first storms will likely fire in Minnesota and start putting down tornadoes. They’ll be rocketing northeast along the warm front into rough territory, and patience will be the key to remaining in an area where the roads are decent and the prospects of seeing tornadoes instead of trees is better. I think our best play will be from northeast Iowa through northern Illinois. But I’ve got three other team mates with a vote, and I’m not the guy who’s driving. Plus, the best dynamics may have changed by tomorrow. This post just lays out what I’m seeing right now.

And now I give you the maps I’ve been looking at. Click on them to enlarge them. Please forgive the lack of organization. I added the 12Z F5 NAM maps to the gallery after I processed the others,  which makes for a lot of maps. I just don’t want to take the time to get them all in order. The SREF maps are no doubt already dated as I hit the publish button, and I think it’s important for me to keep the data as current as I can. I figure that if you’re savvy enough to make sense of these models, then you’re smart enough to know how to compare them!

Good luck and safe chasing to all of you who head out tomorrow.

Backing Winds: Really Necessary for Tornadoes?

That’s right, fellow storm chasers, you read my headline right. I’m about to raise a few eyebrows by tossing out the possibility that backing winds–or, more precisely, what we normally consider to be backing winds as depicted on forecast maps–aren’t always vital to tornadic storms.* This isn’t speculation as much as it is observation. Over the years I’ve seen a number of tornadic events develop in the midst of southwest surface flow, enough to think that the absence of southeasterly winds on the forecast map isn’t always a deal breaker.

What is indispensable are the conditions that southeasterly boundary layer winds tend to create. I’m thinking of ample deep-layer moisture and sufficient low-level storm-relative helicity. Those are what count. If they are present, it doesn’t much matter which way the wind blows from our perspective. The atmosphere sees things differently and doesn’t care what we think. It just does what it does.

Let me quickly say, I’m a huge fan of southeasterly surface winds. I love to see them on forecast maps. And I’m aware that winds can back locally in ways that the maps don’t portray. What I’m really talking about here is forecasting using the tools we have to work with, which continue to improve. Until last year, for instance, I’d never heard of the HRRR. It’s a marvel. But generally speaking, in contemplating the prospects for a chase day we’re still dealing with pretty broad brush strokes, and the farther we live from Tornado Alley, the better we need to be at determining how those strokes will play out.

A Regional Thing?

In writing about forecasting matters, I still feel very much like a neophyte who may be getting into matters that are over my head. I’m no Jon Davies or Chuck Doswell. I’m not even a meteorology student. But you know the old saying about fools, angels, and where they tread.

My sense of things is that as we move east of the Mississippi, southeasterly surface winds become less important for moisture fetch–and, I might add, southwesterly 850s aren’t such a terrible thing. Why? For one thing, moisture sources in the Gulf of Mexico no longer lie to the southeast, but to the south, and even to the southwest in eastern parts of the CONUS. Also important, the desert southwest isn’t nearly so proximate an influence. Thus, H85 winds that would kill a setup with dry air advection in Oklahoma can carry moisture up into Illinois and Indiana. Moreover, that moisture is apt to follow a curvy path–one that can, for instance, take it first northwest from the Gulf, then north, then northeast up into the Great Lakes.

All that to say that the trajectory of moisture transport can look different in different parts of the country.

As for helicity, does it really matter whether you’ve got southeasterly, or even southerly, surface winds as long as 0-1km SRH is in the neighborhood of 150 or greater? Years of reading convective outlooks leads me to believe that the SPC doesn’t think so.  What I’m saying here is no doubt old hat to them. But it may seem a bit out of the box to at least some storm chasers, particularly those whose thinking has been conditioned by setups in the southern and central Great Plains. The whole concept of storm-relative helicity suggests that the term backing is, well, relative, a matter of how winds relate to a storm as it moves, not to the compass. That’s why right-turners produce. A few days ago in Pennsylvania, overall storm motion was consistent with unidirectional winds from the west; yet a rogue supercell deviated to the right and spun up a tornado near Greensburg.

A Few Examples

Seeing is believing. Here are a few maps that show surface conditions around the time of tornado incidents east of the Mississippi.

july-13-2004-roanoke-ilThe July 12, 2004, Roanoke, Illinois, tornado is an example of a classic northwest flow event. Rated F4, the tornado was large, long-lived, and not the first violent tornado to occur in northwest flow during the warm season in Illinois. Four years earlier, the disastrous 1990 Plainfield F5 was fueled by massive CAPE amid northwest flow.

june-5-2010-elmwood-iljune-5-ilx-pm-soundingThe June 5, 2010, central Illinois outbreak was a sort of quasi northwest flow situation. Mid-level winds were predominantly westerly with just a slight northerly component to them. The surface and 850 winds were unquestionably veered. Besides the surface map, I’ve also included the ILX 00z sounding, which preceded tornadogenesis by roughly an hour.

august-24-2007-pottervillepotterville-500mb-12zFinally, the Potterville, Michigan, tornado practically dropped in my lap, but I ignored what the radar was showing me because I was too dumb to believe my eyes even when the dynamics were plainly visible in the clouds right over my head. This was not a northwest flow event; in fact, as you can see by comparing the surface and 500mb maps, it looked to be unidirectional from the southwest, with directional shear increasing as the trough moved east and mid-level winds became more westerly.

You can find plenty more examples besides these, I’m sure. My point is simply this: Don’t be too quick to write off a synoptic setup because of veered surface winds in the forecast, particularly east of the Mississippi. If moisture is in place and there’s reason to hope for adequate SRH, then it can pay to take a deeper look. Things could pop. They’ve done so before and they’ll do so again.

_______________

* ADDENDUM, March 3, 2013: The term “backing” has a couple of different applications. I used it a bit naively in the title and copy to mean southeasterly surface winds, which is the meaning by which I first came to understand the word. That becomes apparent quickly  in the article, but it bears explaining. If I were writing this  post today, I’d simply say “southeasterly” and erase any uncertainty of what I meant.

A Stormy New Years Eve in the South?

slp-gfs-123110slp-nam-123110Could be. If the GFS is right, the chance of severe weather in the Gulf states looks good. The NAM too, having leaned in with its 12Z run, also points to the possibility of a New Years Eve episode down in Dixie Alley, though it wants to nudge the ingredients slightly to the west and north.

sfc-tds_mlcape-gfs-123110sfc-tds_mlcape-nam-123110So far the SPC appears to believe that severe weather is likely in the South on Friday, but while they’ve mentioned the T-word, tornadoes, they’ve been reluctant to say anything emphatically. Of course, we’re still four days out, and hitherto the forecast models evidently haven’t jibed (I haven’t followed the trends till now). But between this 500mb-heights-gfs-123110500mb-heights-nam-123110morning’s GFS and NAM, it looks like a pretty decent intrusion of moisture will lick inland from east Texas eastward to Florida, with 500 J/kg MLCAPE overlaid by ample shear as a large mid-level trough digs into the nation’s midsection. From the looks of things, Louisiana, Arkansas, and Mississippi could be in the crosshairs, and eventually, 500mb-winds-gfs-123110500mb-winds-nam-123110perhaps Alabama and the Florida panhandle.

Here are some GFS and NAM models for you to compare. Left-click on the thumbnails to enlarge them. I’ve used the model runs available to me at this writing on F5 Data–6Z for 6km-shear-gfs-1231106km-shear-nam-123110GFS and 12Z for NAM. The valid times should read 18Z, not 17Z.

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