1/7/08 FCST: IA, IL, WI, MN, TX, OK, MO, LA, AR

[Bill Schintler]

Chase target for Monday, January 7

Chase target:
Sallisaw, OK (along I-40, 13 miles west of Fort Smith, AR).

Timing and storm mode:
Convection will be ongoing and reach the target area at 3 PM, CST. A few low-topped supercells may be embedded within the larger convective mass, and a few weak tornadoes cannot be ruled out. Storm motion will be rapid, with individual cells lifting off to the northeast at 40 mph. Because of the rapid storm motion, poor terrain, and embedded nature of any storm structure, it will be a poor chase day.

Synopsis:
UA analysis indicates several disturbances embedded within the WRN CONUS trough, with a lead S/WV over ERN NM and a couple of disturbances lifting through CA. Upstream soundings (FWD, MAF, AMA, and EPZ) indicate steep lapse rates below 600mb. SFC dewpoints have increased to 55F in most of SERN OK, while a 100-150mb deep moist layer is indicated in ERN TX per soundings and the visible satellite loop. Models have initialized a few degrees too low on LLVL dewpoints.

Discussion:
Overnight, differential advection of the aforementioned moisture and EML should be maximized over ERN OK and SWRN AR. Convection should fire by late morning in the warm sector and well E of the significant SFC features in a zone of strong WAA in the H8-H9 layer. During the mid-day hours, a few breaks in the ST deck should allow for weak heating and a narrow axis of SFC-based instability should develop along the OK/AR border by early afternoon.

Marginal instability will be collocated with impressive shear parameters. MLCAPE’s should reach 1000J/kg with a 100mb deep moist layer and SFC dewpoints AOA 60F, despite poor lapse rates above 600mb. Most of the CAPE should be concentrated in the 900mb-600mb layer. Deep layer shear will exceed 60 kts as 70kt H5 flow overspreads the area. In ECNTRL OK, SFC winds should locally back which will enhance SFC-2km hodograph curvatures as the entrance region of a 35kt H9 LLJ overspreads the area. Low SFC dewpoint spreads in the neighborhood of 5F will contribute towards LCL levels around 700m AGL, resulting in an enhanced tornado threat given a healthy amount of directional shear in that layer.

- bill
[FONT=&quot]9:10 PM CST, 01/06/08[/FONT]

 

[Brandon Sullivan]

The 0z NAM is consistent in bringing moderate surface based CAPE over IL mainly south of I-80.. CAPE values of 300-1300 J/KG not uncommon. Also, SRH values and shear values continue to be rather impressive, with 50 Kts of Shear, and 300-400 M2/S2 Helicity.. I like this setup no doubt, especially for January! Have work and wont be out tommorow, until 8:00 PM. Good luck all who go out! I am still waiting on the 0z GFS run.. Will update when I get it.

 

[Chris Wilburn]

I agree with Bill in the post above. Just west of Fort Smith to around Sallisaw on I-40 looks to be a pretty good place to start. Moisture and CAPE appears to be more abundant in this area as opposed to places north. Td's right near 60 and SBCAPE should be between 1,000 and 1,500. Lift indices also put -4 in this area along with very nice 0-1 and 0-3 SRH values. Storm mode is forecasted to be at 30kts at 00z and increasing to 35kts by 03z which isn't too bad. What is bad is chasing storms at night in less than favorable terrain. The models do not break out precip. in this area until later in the evening. Another area would be NE TX into SE OK, which pretty much the same paramaters as the above mentioned target of along I-40 near Sallisaw, however slightly more moisture and instability should be located in the NE TX and SE OK area. I guess a good general target area would be from Sallisaw to McAlester to Ada to Paris, TX and points to the east. I know this is sort of a broad target area for now, but this really should be the best place to be based of what the models are showing now. I will probably stay in extreme NE OK where I live and hope for at least some good lightning storms. I don't really think I want to venture and chase storms at night in less than ideal terrain. Good luck if anybody chases tomorrow and be safe!

I just checked out the GFS and it breaks out precip. in extreme Eastern Oklahoma by 18z and keeps it in the same area until 06z so who knows. The NAM barely had any precip. breaking out before say 9pm. I believe that storms should be ongoing in the afternoon and some low topped supercells could be imbedded in all of that junk. Less than an ideal chase situation, but I guess it is better than nothing.

 

[Brett Roberts]

12z NAM just rolling in appears to hold back the dryline substantially farther west than previously indicated, and is also printing out some awfully impressive forecast soundings for this time of year across eastern OK. A peek at the KDUA (Durant, OK) sounding valid at 03z shows 2100 SBCAPE and ~300 0-3km SRH, making for an EHI of 4.1! Of course, this is just one run, and the RUC doesn't seem quite as bullish at the moment.

 

[Karen Politte]

Today's severe risk is still considerable although I'm not all that impressed for chasing chances. The more-reliable GFS still has this system mis-timed, with the majority of the upper energy holding back until well overnight into Tuesday morning. I think insta-squall with some imbedded "interesting" storms with transient tornadic features could be more of a realistic scenario - and all that will be after dark for the most part.

Tornado watches will more than likely be hoisted for several states, I have no doubt. The system is active and has tremendous speed shear, if only fair-middling directional shear (which could tank further if winds veer and stay that way). Moisture is already in place and will continue to pump into the risk area for today. I mostly agree with SPC's outlooked risk area on the Day 1 this morning.

If I were to have a target, it would likely be bounded by Alma AR - Fayetteville AR - Sallisaw OK. At least in this area I have some freeways on which to wait for my passing train - even if it's just a linear piece of sausage. The RUC keeps winds southerly or veered across most of the outlook area all day until after dark when it begins to try and back them.

We'll see,

KL

 

[Jim Bishop]

An interesting setup is beginning to show itself over Central Oklahoma. Surface dewpoints are already in the upper 50s and lower 60s. Cloud cover is an issue right now, but a look at the visible loop shows a cirrus deck that becomes thinner and less widespread the further southwest you go, so most of the cloud cover issues will be resolved by this afternoon.

At any rate the GFS & WRF forecast pressure falls over the Texas Panhandle this afternoon and evening in response to a large upper trough and persistent vorticity advection. A pseudo dryline could be a focus for convection across Central portions of OKlahoma where good low-level moisture combined with cold air aloft will contribute to more than 1000j/kg CAPE. Shear profiles support supercells. And given the 30-40 knot southerly 850mb jet along with very low cloud bases, the tornado threat is there too.

The RUC is fires discrete convection just ahead of the dryline by 3pm. While the WRF doesn't actually fire convection, it does show a completely broken cap in that region.

For early January this is not a bad setup! We'll see if Central Okahoma surprises people today..

I didn't mention the areas further east do too poor chase terrain and it's already been talked about on this board.

 

[Chris C Sanner]

Looking around here in Norman outside of my house I would be shocked if storms don't form in C/NE Oklahoma this afternoon. Mesoanalysis shows SBCape of 1000+ already in place and NWS OUN is jumping on the bandwagon of getting storms to form here due to a very weak cap among other things. Fly in the ointment is the weaker (and veered) 850 winds the further N and W you go. I'll be keeping a close eye on things today, it'd be nice to knock January out and be able to have chased a severe storm all 12 months of the year.

 

[Jeff Snyder]

I agree about a central OK threat, but the continued veered sfc flow doesn't get me excited. The 12z NAM and GFS both agree on backing the sfc winds to southerly by 0z, but we'll have to see if that actually happens. Surface dewpoints have mixed out a bit across central OK (into the mid-50s), and I expect this will continue to happen until the sfc winds can back a bit more. However, I've seen many more cases in which winds remain veered than otherwise. In fact, while sunshine will help increase sfc temperatures, full sun may not be desired... As insolation warms sfc Ts, it will deepen the boundary layer, which will likely continue to force veered sfc flow (winds are typically homogeneous in direction through the boundary layer, except in cases of strong isallobaric forcing that can help force backed sfc flow). Given that temps may be running a bit above the 12z NAMs 6hr 2m T forecast across parts of OK, I wouldn't mind us keeping some cirrus to stave off further deepening of the boundary layer.

Aside from that, forecast hodographs look a little too linear for my liking, but I can't complain too much considering the time of year. Sunset being 5:30 pm doesn't help the cause much... I need to back home before 7pm, so I'll take a wait-and-see approach this afternoon in regards to central OK convection. Even if I could stay out later, my luck in similar early-season high-shear, relatively low CAPE setups has been relatively poor.

 

[Jared Farrer]

Things are looking to me like a possible night event. But like a lot of people are saying things will probably congeal into lines/bow echos with embedded supercell structures.

I hope things get started earlier though. That seems to be the big mystery today, initiation. I wouldnt be surprized however to see things start to fire near southern AK OK border. The time though is hard to say. I guess when the upper lift arrives and or a boundry.

A few clearings are showing up on the visible. It would be nice if alot of these areas could see more sunlight, to help juice things up! All-in-all though this could make for a perfect SDS reliever, especially if a couple good lightning shows are in the works!

 

[Karen Politte]

An MCD discussing the possibility of a watch being needed shortly has been issued for central OK into northern/northeastern OK. With the development of enhanced cu on satellite oriented SW to NE across the midsection of OK, a NOW thread may need to be started. But, to be in-keeping with a FCST post...

I am not thrilled about the strong, veered sfc winds presented across OK at this hour. As Jeff has mentioned, there is very little change in the surface's homogenous appearance throughout the most of the state and into AR even. With winds this veered, and with the upper support still lagging behind, I would go out on a limb and say that worthwhile severe chances for OK during daylight are greatly diminished. Not until the true energy kicks out after dark will we likely see the needed dynamics for a focused severe threat. Any storm that forms in the regime currently in place will likely become linear very quickly with few supercellular characteristics.

The RUC continues to promise backed surface winds in spectacular fashion by 0Z whereas the GFS resists this to a certain degree. In reality - it is a wait-and-see situation and only time will tell. I would still be sitting in the FSM area - but I would be thinking of the $$$ in gas it took me to get there.

KL

 

[Karen Politte]

Can anybody join me in helping me identify whether or not there was a small impulse in the upper flow or a shortwave that moved across the areas that are currently being affected by tornadic storms (WI/IL/MO) that kicked the game off up there today?

My makeshift analysis of the present run of the RUC certainly suggests to me that there could have been a scenario like I am describing - but I'm not very certain. I'm trying to learn, too...

KL

 

[Bill Schintler]

Can anybody join me in helping me identify whether or not there was a small impulse in the upper flow or a shortwave that moved across the areas that are currently being affected by tornadic storms (WI/IL/MO) that kicked the game off up there today?

I think it shows up fairly well in the water vapor loop... Look at a 3 hour loop and note the wave and associated assent race across IA, northern MO, and IL. See also the Blue River, WI, profiler; paying particular attention to the flow at 500mb.

http://weather.cod.edu/mcprofiler/BLRW3.1hr.gif

Look at Slater, IA, in the 500-300mb layer, while paying particular attention to 19Z to the present:

http://weather.cod.edu/mcprofiler/SLAI4.1hr.gif
http://weather.cod.edu/analysis/analysis.profiler.html

Further south, in eastern OK, has been a relative bust - so far, anyway. That area has remained largely capped to surface-based convection, owing primarily to a mid-level thermal ridge across eastern OK and lack of any significant forcing mechanisms. The WV loop currently shows a band of assent moving towards that area.

- bill

 

[Karen Politte]

Bill - thank you very much for your very attentive reply. Some great links there - and I'm pleased that I identified that shortwave correctly.

Amazing. The winds DID back, there WAS a shortwave impulse that was probably largely responsible for setting off the daytime for north events, and now the most amazing tornado outbreak is in progress across many parts of the srn half of MO. Insane.

KL