01/02/06: FCST: Ohio Valley and Southward

Feb 8, 2004
Detroit, MI
I believe the first significant severe weather episode of 2006 could be underway for Monday... But let's make this short... A deepening surface cyclone, ahead of an amplifying mid-level shortwave trough, will enter the Ohio valley by the afternoon. Low-level WAA and moisture advection northward (associated with a 30-40kt SW LLJ) will contribute to a swath of 1000-2000 j/kg SBCAPE across the warm sector. Given large-scale ascent impinging the area early, widespread severe thunderstorms could develop by the early afternoon (BL-6km shear is favorable for supercells) across this broad warm sector. While the event is still several days out, this setup does appears favorable for a few strong tornadoes across the lower Ohio and Tennessee vallys :)

http://www.rap.ucar.edu/weather/model/disp...&hours=hr72hr84 <-- amplifying shortwave

http://www.rap.ucar.edu/weather/model/disp...&hours=hr72hr84 <-- low-level moisture advecting northward
I'm wondering just how south the shortwave will dive. Latest 18Z NAM has it diving even further south (same trend on other models as well). A further south shortwave would mean a much deeper system (for example, the 18Z NAM is about 2MB deeper at the SFC). Depending on how far south it digs, we could really be looking at a powerhouse storm system. Given the trends, my bet is that the best chances for severe weather would be along and south of the Ohio River... Should things level out and / or trend northward, the threat will obviously shift. Either way, this system will be complex. We may be looking at a devastating ice storm here in the Great Lakes with a significant severe weather threat only a couple hundred miles south...

Definitely enough time to watch it evolve...
00z NAM continues to raise instability across my region and shear as well. It looks as if 700-850 mb will ensue an extreme dry punch into the region with nice height falls and 7.0+ lapse rates in the 500-850 range. -16 to -19 H5 temperatures will bring an extreme hail threat. Looks alot like my day Tuesday....very good hail day with some tornadoes in these supercells. Looks MDT risk.
It's not very often you'll see an SWODY3 with a MDT extending into eastern KY in Janurary.

Well, I am convinced there will be a significant outbreak of severe thunderstorms on Monday (will make it short, I am dead tired)... There has been some pretty good run-to-run consistency with timing of the shortwave and location of the surface cyclone (from both NAM and GFS). Sfc theta-e ridge nosing northward into southcentral Kentucky shortly after noon could be the focus point for a burst of convective initiation... very warm/moist boundary layer with steep 0-2km lapse rates are contributing to SBCAPE of at least 1000j/kg (closer to 2500j/kg further south) all the way into southern Indiana. This is easily gonna be the first big bang of the year, with both adequate deep-layer vertical shear and instability for widespread supercells with at least a few significant tornadoes (particularly from eastern Tennessee on southward).
Yes....it looks as if I will be chasing around my area and western GA Monday with Matt Grantham. Shear/Instability look more than sufficient for long tracks supercells with damaging tornadoes down this way. UVV fields indicate this will probably be a discrete event as pockets of deeper vertical motion are established and linear forcing isn't going to be all that wonderful. I look for the MDT to be extended back a little further west in later runs because I believe that the NAM is having feedback issues. I am in the left exit region of the LLJ and on the nose of the ULJ streaks and this model is trying to tell me no precip along the pseudo dryline? Yeah right...east of I-65 in AL is going to be a playground as you head eastward into the ATL metro. I will be planning out my heading tomorrow and will get as I prepare all of the equip. More tomorrow. :)
Are my eyes deceiving me or am I really seeing something that one could justifiably call a dryline surging into Tennessee and Alabama come Monday? :shock:

Taking a brief glance at the picture models are painting, I am pretty concerned about C/E Tennessee, extreme ERN Alabama and Georgia. It appears there will be a strong LLJ in place, very adequate CAPE for this time of year (1000+ j/kg over most of the area and higher in some locations), very strong 0-3km SRH and LI's of -2 to -4 being common over most of this area, I can definately see why the SPC decided to go with a MOD for the Day 3 period.

As far as negatives, I don't see too many. But in terms of tornadic activity, it doesn't appear LCL's will be particularly low. In addition, it now appears that much of the area will be capped, whereas previous runs showed little in the way of an inversion. One will have to carefully watch the strength of the forcing vs cap strength as we move closer, but as of right now, I don't think we can count on the cap stiffling out activity.

The area of greatest interest for me Monday will be along and extending about 80 miles E of a line running from Oak Ridge, TN to Chattanooga, TN down to Gadsden, AL. Some major cities included in this area include Knoxville and Atlanta. Considering that temps are forecast to reach the mid to upper 60's for my area Monday, I might even have to expand my "greatest interest" area farther N pending future model runs.

While I won't mention the "O" word just yet, Monday very much looks conducive to a widely scattered outbreak of strong to severe storms capable of producing the full array of severe weather threats.


PS...... if Oklahoma and Texas really are becoming a desert, perhaps KY, TN, MS, AL and GA will become the new Tornado Alley as storms fire off the new SRN Plains generated drylines! Of course I am kidding, so please don't shoot me! :wink:
"Fly in the ointment": lack of backed winds

Very impressive setup for January (and chaseable for many since Jan 2 is a holiday) There will be a nice band of instability shooting northward through AL and TN, then GA and eastern TN.
CAPES 1000 to 1500 with storm relative helicities ranging from 150 to 300 m2s-2. There's upper level support with a strong lower level jet. 60 degree dewpoints to the border of Indiana.

Although some are concerned about the cap, I am more concerned about the lack of backed surface winds over most of the area. Per the 12Z Dec 31 Eta, the only are of SE winds are extreme western NC by 12Z Jan 2. This vanishes except for parts of WVa by 00Z Jan 3.


The GFS is similar.

There will definitely be strong storms and I think this forecast justifies a MDT risk, but there may be less chance of tornadoes. If I lived nearby and had WXWorx turned on, I would definitely chase this event. I live in Richmond and would have to be back at work Tuesday at 7:30AM, therefore a chase is unlikely. Good luck to those who go out!

**EDIT: I changed the links to the 12 Z model runs for Dec 31, but the lack of backing winds is still present!**

Bill Hark
There were I think at least one maybe two times this year where a MDT was issued on the day three. I also believe this is the first year where they changed the rule where MDT's can be issued on Day 3 and High's on Day 2.

I got thinking about Bill's comment about the backed winds as I noted the same thing. Im sure S winds would suffice from a moisture standpoint, based on the location to the GoM but that low level directional shear is a key ingrident in a lot of SE tornado outbreaks. I went backed and looked at a couple and you do have backed winds, in some cases extremely backed (SSE or E). I would think that would be tough on moisture, after all it's pulling it's air from the Atlantic, but they did produce tornadoes. The farther north/slightly less amplified solution isn't helping any. Georgia appears to be looking the best to me despite the backed winds with 40+kts of Effective SRH, decent CAPE. Enough Instability/Lift/Shear to make for an interesting day.
Yeah, I'm not liking this weaker / further north solution on the NAM in terms of severe weather... I also don't like how the system is weakening as it tracks eastward - that's never a good sign.

I agree with Bill and Scott about the backed winds... TN looks like it gets in on the action around 12Z MON - most likely linear stuff... Then later in the day areas further southeast get in on the action. By that time, NAM shows WSW SFC winds, though helicity is still high due to the strong speed shear. In cases like this, helicity can be misleading - you have enormous speed shear, but little directional shear... Unless something changes, I am thinking more of a broken squall line with isolated supercells...

Hopefully the models will start showing some sort of southward digging / intensification so that it holds on to its strength a little longer - but that's just wishcasting at this point.
LOL... I'm really not seeing how a slight lack in backed winds will prevent an outbreak in this case. Heck, we had way weaker of a system a few days ago and that did not prevent the 9 reports of tornadoes and widespread damaging winds and large hail all the way into the Ohio Valley. In that case, flow was mostly unidirectional, with only slight veering flow in the boundary layer (but strong speed throughout the column), which helped yield very strong helicity with mostly southwest flow at the sfc.

NAM forecast soundings show pretty decent CAPE profiles across KY at 12z, with a KPAH sounding at 12z showing over 800 j/kg of CAPE by lifting a SB parcel. Despite absolute crap for low-level lapse rates (around moist adiabatic)... Mid-level lapse rates of 7.2c/km and low-level WAA/moist advection will help continue to destabilize boundary layer, with the development of at least moderate instability (>1500 j/kg SBCAPE) by the early afternoon from the Ohio Valley well into the south. Forecast soundings from scross the region show a very favorable environment for tornadic supercells, with a strongly sheared/moist boundary layer by the late morning (at least 50kts of BL-6km vertical shear available). The persistant >40kt SW LLJ will continue the northward advection of deeper moisture, with the sfc 60F isodrosotherm all the way into Indiana by 12z. Still, an outbreak of supercells and tornadoes appears likely from southern Indiana/Ohio well into the south, with early initiation expected, with an increase in storm converage by the mid-afternoon as stronger mid-level ascent sweeps into the region associated with the amplifying shortwave.
Nick, let me clarify...

I'm not saying there won't be an outbreak of severe thunderstorms. What I am trying to say is that I don't think this will be a huge event if the 12Z NAM has its way (meaning we will likely only see isolated tornadoes, most probably F2 or less)... Take a look at the forecast sounding for BHM a F54... There is absolutely NO directional shear to speak of... In fact, the hodograph shows 160 m2/s2 of positive helicitity in the 0-3KM layer, while at PAH at F51 the hodograph shows 120 m2/s2 with -26 m2/s2 of negative helicity - a bit better than further south). Both soundings also show very steep lapse rates, nearly moist adiabatic all the way up, and NO CAP.

Even with a weakening shortwave, that's enough to touch of severe thunderstorms, possibly an outbreak... What I am questioning is the mode. Yes there is a significant amount of speed shear, and supercells will likely be present... But with little in the way of a CAP and a unidirectional profile (again, checkout BHM at F57 and ATL at F57 / F60), I can't help but think squall line.

I am not trying to be a naysayer or underplay the event... I really think there is some potential here, but I think it might be in the form of a broken squall line with isolated supercells. Still a good event in my eyes - I don't need a whole plate full of F4's and F5's to consider it an outbreak.
I agree with rdewey here as this morning's model runs show weak directional shear in the sfc-700 mb layer. What concerns me the most is the ETA's handling of the development of the surface low, and if the winds have turned to WSWly by the early evening, there is not going to be enough low level shear to support organized storms. Furthermore, the strength of the midlevel vorticity advection will weaken the cap substantially by early afternoon. Gotta go with a squall line on this one, though I wouldn't rule out the possibility of embedded supercell structures given the substantial magnitude of the deep shear vector. I'm visiting my fiancee's family near Atlanta, and though the sight lines are awful in this area, I still will make every attempt to find a high point and get some decent shots.
I agree on the chance for more linear activity... But, heck, the prior system (12/28 ) that slammed into the south looked strikingly simular (except this wave is way stronger). A mostly unidirectional profile, with little inhibition... So, I had said to another chaser at the time lines were most likely, with embedded low-level mesocyclones given strong 0-1km helicity. But, what happened? Everything did go off at one time... But, they were mostly discrete, productive tornadic supercells across GA. Lapse rates were quite a bit steeper in the low-levels (sfc-2km lapse rate nearly cooled dry adiabatically) then in the upcoming event, but the two are still pretty simuler.

It could indeed get messy given a weak inversion, but I was just commenting that the lack in backed sfc flow will NOT prevent an outbreak in this case... No biggie :wink:
Okay, I see now :)

The 18Z NAM is slightly weaker yet again... Though the strength / depth of the 500MB shortwave does hold on, rather than slowly collapsing as the 12Z run showed. I don't think that would make or break the case, but it's still interesting... But for some reason, I can't get over weakening SFC lows... They just always seem like bad news to me (I've seen a few events get screwed over by a "lame low").

I'm not going to go in depth and waste my time with an 18Z run... The shortwave is just now coming on shore and the 00Z models should have it sampled pretty well, at which point I might post additional thoughts.
Don't let a weakening surface low fool you though. The main surface low associated with the Super Outbreak filled 6 millibars during the severe weather event.
You're probably right Fred...

Just looking over the latest 00Z NAM (out to 18 HRS) and I don't know what is with these 00Z runs. We are again looking at a shortwave MUCH stronger than what even yesterdays 00Z run showed... Hopefully this is the trend, and not the exception.

Once all of the data is in, I will likely update

I'm starting to get the idea of a focus for strong low-level shear over the area in question again.

00Z NAM starting to get a good idea of a wedge creeping down into northern Georgia. This is probably gonna help to setup a mesoscale boundary.....sort of warm frontal or stationary in nature.....and the low-level winds may get a chance to locally back near this thing. This could also prove as a focus for mesolow development. If this occurs, we may still be looking at a chance for a few significant tornadoes....probably very close to the I-20 corridor of GA.
New NAM has really grabbed my attention. It's showing -4 to -6 LI's over Kentucky on Monday, SBCAPE of 1000-1500, 0-3 km SREH 150-200 and sfc dewpoints possibly exceeding 60 degrees F. My interest level has now shot up tremendously from this morning, since it appears my area may be much more favorable than previously thought. This is getting very interesting and taking me back to the year 2000 when an F3 tornado struck Owensboro, KY on Jan 3 of that year. However, conditions for that event were far more marginal than with this system (minus the crazy shear that was present that day). I just hope people will be paying attention and remember that severe weather outbreaks can and do occur in January.
Considerable run-to-run consistency continues to help me have strong confidence in a significant severe weather outbreak on Monday (and looks to be a HIGH risk from KY southward).

Some supercells could develop by late night tomorrow just south of the warm front, before a more significant episode develops shortly around noon, from southern IN and OH southward into the Gulf. At 18z MON, lifting a SB parcel on the KLVX (Louisville) fcst sounding yields nearly 1900 j/kg of CAPE, with no inversion to prevent a surface parcel ascent (LVX at 18z is on the northern fringe of low-level WAA / on the nose of sfc theta-e ridge). A very favorable wind/thermodynamic (BL-6km deep shear +60kts / very moist boundary layer) setup across the warm sector should be supportive of long-lived tornadic supercells and a few bowing structures. KLVX fcst sounding showed a very low CAPE profile, with nearly 75% of CAPE below 500mb with a very low LFC height given no negative buoyancy on the sounding.

My area of interest would be from southern IN and southwest OH into eastern KY and TN through 16-21z... Current thinking is for at least a few significant tornadoes to develop across this region through that timeframe (however, I expect a widespread outbreak, from this northern focus area all the way into the gulf).
All indications per the newest NAM cycle soundings indicate a very slim window for tornadic supercells, between 20Z and 0Z east of Atlanta. Low-level lapse rates in excess of 8K/km will contribute to significant surface-based instability in an uncapped environment. The deep shear is incredible, with 0-6 km vector differences in excess of 60 knots, oriented nearly perpendicular to the forecasted position of the surface dryline. However, once the 500 millibar impulse overspreads the region with intense midlevel cooling (~2 C/hr from the MCN forecast profile) the storms will rapidly transition to a quasilinear mode. I would not be surprised to see the SPC decrease the areal coverage of the moderate risk on the upcoming Day 2 outloook, encompassing the northern third of Georgia and perhaps a small sliver of South Carolina.
Well, I think this stronger trend in the models might be what actually happens. The 03Z RUC is actually a touch stronger than the 00Z NAM in regards to the 850MB shortwave. The GFS and Canadian GEM are also getting in on the act of a stronger system. It almost appears as though the 500MB shortwave wants to take on a negative tilt, but lack up upper level support should put a stop to that.

I still think a rather widespread severe thunderstorm event is in store, but I agree with Michael Morris in regards to the overall tornado threat. This setup looks kind of like a very early season (or late season?) squall line / derecho.
Just finished checking out the models. Looking like anwhere from KY through southern AL and GA could be seeing some interesting weather tomorrow night through Monday night and I'm wondering if it will actually come through in two rounds.
CAPE doesn't look that high, only up to about 1500-2000J/kg, but this time of year in the south, even 500J/kg will get severe weather going. Speed and directional shear look more than adequate for supercells and tornadoes. Looks like most of the strongest upper level dynamics will be in southern TN and southward into GA and southern AL. The dryline really caught my attention...the only other time I've seen a similar feature in that part of the country was with a tornado outbreak in Feb 1993...three weeks before the Superstorm. (That outbreak dropped an F3 in my backyard in E TN).
I'm thinking a warm front should set up in central to northern KY with the dryline trailing back through AL. Should be isolated supercells to start with, then a squall line will form in association with the dryline passage. I'm getting the feeling that GA will see the brunt of the tornadic storms given the deeper moisture (Td's in the mid-upper 60s) and stronger upper dynamics, but tornadoes will be possible from KY south. Looking like round one will come through overnight tomorrow, then round two Monday afternoon-evening (maybe even go through the night into SC). As usual for this time of year in the south, these things will be speed racers...forward speeds 40-60mph. I'm not nailing down a specific target at this time, but instincts are saying from Atlanta south may see the worst of it.
I hope the TV mets are already emphasizing the possibilities of the seriousness of this. Too many people don't understand that tornadoes can, do, and will occur when conditions are right...regardless of what the calendar says.
Update and finalize in the morning.