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

[Robert Dewey]

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.

 

[Fred Gossage]

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.

 

[Robert Dewey]

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

...

 

[Fred Gossage]

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.

 

[George Tincher]

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.

 

[nickgrillo]

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).

 

[Tyler Allison]

My area of interest would be from southern IN and southwest OH into eastern KY and TN through 16-21z

That's my backyard. Care to take a stab at one of your SPC outlook type maps?

 

[Michael P. Morris]

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.

 

[Robert Dewey]

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.

 

[Angie Norris]

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.
Angie

 

[Brett Adair]

I agree. Looks like we will be setting up on the AL state line sometime around 15z Monday and run I-85 and bust south or north depending on supercell formation. Maybe we can get a nader or two tomorrow.

 

[Scott Olson]

Im betting on GFS more southern SLN but with a little bit more amplification. Even so, there is a nice amount of moisture and speed shear. An OFB could make a heckuvalot of difference here. SBCAPE of 1200 J/KG in Georgia and 1K J/KG reaching into past KY. If not for a tornado threat a good threat of wind and a decent threat of hail still seems reasonably possible.

 

[Robert Dewey]

Im betting on GFS more southern SLN but with a little bit more amplification.

That actually sounds reasonable. Latest messages from NCEP indicate that a couple of important upper air OBS are missing from the NAM and GFS intialization. That means the shortwave wasn't completely sampled, and the models may actually be underforecasting it somewhat. Judging by the WV loop over the past 18 hours, I would say that's true - This thing is really taking on a good shape as of 05Z.

The general thinking is that the system will move along a track like the GFS, or even slightly further south... With more amplification, as you suggested.

 

[SteveCarter]

I'm pretty excited about the latest forecasts coming out! This is really in my back yard...I live on the Ga/SC border, about 120 miles east ne of Atlanta. The local weather people on TV are saying to DEFINATELY keep an eye out for severe weather, with poss tubes, starting Monday afternoon. I think the best area to go will be from Athens - Macon. The topography is NOT indusive to chasing north of Athens at all. The land evens out south of I-85. It takes me 1 hour to get to Athens, and 2 hours to get to Atlanta, and slightly over 2 hours to get to Macon from here. The reason for this post is to just mention that YES, it IS being mentioned on ALL the weather reports here, and they seem to be making a pretty big deal about the possibilties....more so than earlier forecasts. If any of you will be around here, holler at me if I can help you out with side road info or anything. I lived in the Athens/Atlanta area for 10 years, and have used every side road there storm chasing during that time. My e-mail is [email protected] I'll give ya my cell number if you want it. Good luck out there on Monday!! Looking better every hour, at least up until now. SC

 

[Robert Dewey]

...Latest 06Z NAM continues the southward and more amplified trend as discussed earlier...

While that doesn't significantly change anything in the SVR department, I could imagine that a deeper system will provide slightly better mid level winds and thus an increase in shear. The threat is looking pretty good at this point.