03/30/05 FCST: Upper Midwest / Great Lakes

Looks like Wednesday is the southern plains first true chance of chaseable storms. GFS forecasting plenty of moisture and plenty of upper air support to go along with it. It is much too far out to get into details so I shall leave it at that until it comes into the NAMs forecast range.

I think there is still very considerable differences between the ETA and the GFS to not be able to really say much. Both show a well defined dryline taking place in OK/TX, but not as far north as Kansas. ETA shows 2 high CAPE bullseyes of CAPES > 3500j/kg over eastern Texas (most likely what I think will be the center of storm development), and also over eastern Arkansas. What really got me on Texas is the forecast Lifted Indicies of -10 over the eastern part of the state. I see Td's getting up into the mid 60's on both models, but I will leave my discussion at this point right now.
It looks like a nice chase possible on Wednesday south of I40 in southeastern OK and eastern TX east of I35. NAM now showing excelletn moisture return making it in the nick of time Wednesday afternoon, with mid-upper 60 Tds, resulting in SBCAPEs >4000 near the I35 corridor in central and northern TX. With the low-level low progged to be somewhat near SPS, the low-level shear doesn't appear to be too bad, though the NAM isn't developing much of a surface low center. At any rate, with strong flow at all levels (save the surface), we could see a nice supercell event east of I35 on Wednesday in the southern plains. A lot remains to be seen, particularly whether or not we can really get the mid-upper 60 Tds up here given the beating that the Gulf is taking right now. I would't mind if this system slowed down a bit, however, since I'd prefer chasing west of I35 than east of that interstate. Granted, I'm also working off of the 84hr NAM forecast, so... The FWD AFD from this afternoon (Sunday) suggests that there may be more of a chance Tues and Thurs instead (based on the ECMWF), but I guess we'll have to see.
Wow........OK, where's my barf bag?

Yuck - I know it's the time of year for it - but I am SOOOO ready to stop chasing east of I-35 and get some "real" storms out west to play with.

Well - right now either the ETA doesn't have a handle on this system at all, or it does and it's going to be complete crap. First of all - by 12Z Wednesday 30th EVERYTHING is westerly at the surface unless one wants to chase eastern Arkansas. OK - that's the first thing that doesn't fill me with hope.

Thus - I'm assuming that this means we are now expecting this system to perhaps come out on Tuesday afternoon/evening - and if that's the case I just don't "see it" for moisture return, I'm afraid. The CAPE axis sets up east of I-35 for a mediocre amount of time (with maximum readings appearing around the 06Z Wed 30th timeframe), and by 0Z Thurs 31st we're blown dry again. It seems that this week's moisture return is going to be like squeezing blood out of a turnip.

I'm just going on trends right now - I don't really *know* anything. But from what I see, I think I'll be saving my gas money (and my whining to get time off work) for the big boys in May.

Unfortunately, there are mixed signals about what the next system's front will do to the Gulf. The ETA seems to currently be hanging on a bit too optimistically to 70oF dewpoints in the northern Gulf - whereas the longer-range GFS spells doom and gloom for the next few weeks - bringing 40oF and 50oF into the Gulf and looking like we're hosed for the foreseeable future. Bleh.


P.S. - Rumors abound that after this system comes through, Oklahomans might want to be digging out their thermals again. Temps in the low 50's for the back end of the week and I would imagine pretty dry.
This morning's ETA reorients Wednesday's s/w trough to a negative tilt and brings it flying through....Illinois?




These links are valid for the 12z run on Monday 3-28 showing 18z Wednesday and seem to indicate the potential for isolated supercells in the upper Mississippi Valley area. The left front entrance region of a strong jet streak is indicated above a moderately unstable airmass in central and southern Illinois, with SBCAPE progged around 2000 j/kg and ~150 m2/s2 0-1k SRH. Forcing is strong and a squall line appears inevitable but perhaps somthing can rotate before everything goes linear?

As I recall, many sections of central Illinois are pretty fair chase country.

I should add that I've been watching the Tuesday/Wednesday drama on the GFS and now the NAM for several days and the models vacillate on both the timing and orientation of these systems every 12 hours, so my confidence in this morning's solution is low. But it looks pretty and it's only a six hour drive for me.
Mickey Ptak:
Looks like Wednesday is the southern plains first true chance of chaseable storms

Well I might say that my foot doesn’t taste very well.

Different scenario today as too Saturdays (and Sunday for that matter) GFS and NAM runs. I am not real impressed now with tomorrow (3/29/05) or Wednesday setups.
Looks to me like this system will pass OK and TX by and be more of a southeastern ballgame now. So my interest in this one has been shot down.

I am going off of wxcaster models in which I am not use to reading so my forecast may very well be way off base. What is going on with COD? Grrrrr.

As of right now I would say there might be two areas too focus on. The first being AL and MS. The second being Great Lake states.

NAM forecasting 60 Td all the way up into TN and 70Td a little farther south in northern MS and AL by 00Z Thursday. Also IND and OH with 50-55 Tds.


Best shear however looks to be in IND and OH, but at the same time, as Amos has mentioned, I think things will be by far more linear that isolated.

That’s about all I have to offer at this point in time. I see no point in wasting any valuable $2+ a gallon gas on this system on either day IMO.

Mods if you would like to change the thread description please do so.

Central IL does look like the best area at this point. If you look at the instability compared to the forcing at 700MB, things shouldn't be too linear at the beginning - The linear forcing will be just east of the instability axis. I believe that instability in central IL is more associated with the cold core upper level low than SFC heating, as the 850MB thermal front is already through that area. Helicity in that region is good, so I can definately see supercells forming in that area...

Again, moving further northeast into IN/MI... The setup looks pretty much the same, except LI drop from -7C to -5C. Speed shear is more than impressive, especially with the 300MB jet peaking into the region... Forcing, at least up to 700MB, isn't all that linear... But, supercells do have a tendancy to morph into squall lines as they interact with each other.

Anyway, the severe weather threat does look decent from IL to MI, with the best chance for supercells being IL... IN and MI aren't really out of the woods though...
I agree that the threat may be shifting a bit further north. Shear looks to be focused well southeast of here (here being SE Wisconsin) with only 15-20 knots progged at Milwaukee, WI. However, we should see some steep mid-level lapse rates under cold upper level air advecting in with a little vort max and SBCAPE values per the 12 UTC NAM are up to 500-1000 j/kg. It even provides us with surface dewpoints around 54 F. Lots of afternoon QPF...I think there could be some small hail producers at the very minimum with perhaps a few 0.75 - 0.88 inch diameter hail reports. No supercells though...so I guess this will have to whet our appetites until then :(

Looks like the NAM is taking temps in MI up into the 70s now on Wednesday. I don't know about severe setup south of here though. Not a lot of QPF to the south of N. IN or Romeoville offices (NWS) so I'm not sure if you'd see much to chase. I'm not sold by any means on this setup.

...Alex Lamers...
As I recall, many sections of central Illinois are pretty fair chase country.

It's extremely flat country - so no concerns there. Looking at the NAM, positive vorticity advection forcing for upward motion sweeps through central IL during the morning hours - led by a potent 50 knot LLJ which appears to slip some modified gulf moisture into the Midwest. Despite strong synoptic lift, the NAM is stubborn with developing precipitation outside of the 850mb deformation zone. Main moisture transport slides into IN by mid-afternoon - leaving some doubt as to whether the limited moisture in IL won't disappear over the day owing to deep mechanical mixing given the forecast strength of winds. Only forcing remaining across IL for convection will apparently be the Pacific front. if this is sufficient to initiate convection, then there will be plenty of shear if cells aren't ripped apart by it - and cell motions of perhaps 45-50 knots will make for more of a storm intercept than a chase - but it's early in the season for here and I'll be happy if anything comes out of this.

Sigh, I'm biting the bullet and making a forecast instead of sleeping before my 8:30 lab. Here goes...

Wednesday's setup looks pretty decent for March in IL/IN. It's not perfect, but it might be enough to get me out of town for the afternoon. The CAPE is progged to be around 1000J/kg with pretty good SRH, especially toward 0Z. I'm looking at central Illinois as a starting point, and racing eastward to the FWA area by nightfall. This brings up one of my two big concerns. Storm motion on the order of 40kts does not make for ideal chasing conditions. The other concern is moisture. Currently the Td in LAF is -3C. Eta (excuse me, NAM) brings it up to 13-16C by late Wednesday afternoon, while the GFS is much less generous. It will be very interesting to see if either model gets it right. I'm certainly not sold on the setup yet, but it has potential. I'll make a semi-final decision on Tuesday night.
the key will be the moisture return. Everything else, LI, cape, etc. looks good considering that it is late march in the great lakes region. The Nam brings 50-55 points up into the area by tomorrow afternoon. That would almost def. allow for storms to fire, as for the type however, i feel it will be mostly in the form of a squall line with maybe an embedded supercell.

FWIW: See DTX discussions for reasons this should not happen and see GRR for why they think it could.
It all depends on the moisture. Right now Td's are in the upper 20's to mid 30's - We need mid 50's by tomorrow evening. Right now, the 50F mark is barely making it past OK/TX... So it's gonna be tough. Other things that are concerning... The low is filling (weakining) somewhat as it moves eastward and the NAM outputs no QPF over the area of interest. The system also keeps slowing down, which may be a problem for folks such as me who are trying to catch things further eastward.

12Z NAM is pretty much showing what is suspected, each run has been getting drier and drier... Td's only making it to 45-50C in MI, and that's at 6Z, when T's will be falling.

Best potential still looks like central IL, they will get things early in the game (18Z-0Z)... Based on the NAM, Td's are in the 55F range, with T's creeping up into the mid 70's... Decent instability (LI of -4C or so) combined with decent helicity may allow for a few severe cells to pop... But again, the NAM may already be too moist with the Td's, and I am somewhat concerned about lack of QPF on the model...

So, the main problem with this setup is thermodynamics... The kinematics/wind fields appear to be excellent...
Ok, for IL/IN/MI this has March 1, 2004 written all over it, for those who went out that day. As is often the case with early season setups, and as many have pointed out already shear is NOT going to be a problem, but instability might be. Bulk deep layer shear on the order of 50-60 knots will support storm organization, provided updrafts can sustain themselves without getting sheared apart. Low level (0-1 km) shear of 30 knots with some weak low level turning (profiles fairly unidirectional above 1 km) could support supercells, but I tend to agree with SPC that the most likely storm mode is linear. Vertical acceleration will be somewhat weak, as forecast soundings yield thin cape profiles, regardless of parcel level chosen or method of lifting (surface, mixed layer, max T, etc.) The MUCAPEs to 1000 mentioned in the day 2 sounds a little optimistic, as the max instability I could yield using these soundings was about 700. However, in the presence of significant shear, as April 20th told us, a little instability is all that's needed. (I'm not suggesting another April 20th is in the works, far from it...definitely not a good warm front/enhanced SRH situation, nor will instability be as good)

I expect tonight's day one will have a 2% tor threat, if only for the magnitude of the shear, but I'm not quite so optimistic about the potential for low level rotation...mid-level rotation will be fairly easy to come by, though, with the shear. Any spinups tomorrow I would expect to be brief and weak, and most likely needing some enhanced SRH source (subtle boundary interactions, etc.) to even get going, and with expected storm mode (and motion), visibility/intercept potential will be poor. I'm not optimistic about hail threat, given poor lapse rates in the -10 to -30C hail growth zone, but the huge deep layer shear should support at least a minimal threat. Storm motion alone will yield some strong wind gusts, with a strong low level jet (50-60 knots rounding the base of the 850 trough) adding to that potential. There is some question about the potential for that to mix down to the surface given less than favorable low level temp profiles (I'd prefer to see a nice near dry adiabatic layer through the lowest couple of km). I'd peg it around 25%, owing purely to the dynamic strength of the system alone.
Corn Growing Yet?

NAM has dew points this morning of 50+ into southern Illinois - the closest 50+ dew points are in the northern Texas. Tomorrows Td's are progged to be > 60*F across Indiana with the 50 line well into northern Michigan / Wisconsin - but a 60 is only found around Houston right now. Just seems to be WAY too much moisture blossoming up for me to believe any sort of meaningful instability will be around.

Tonight's 00Z Td's are forecast to be 60+ into Oklahoma City, so I guess we'll take a look then and get a good idea on how advection is coming.

- Rob


Interesting trends already on the speed of this system. Continues its slowing trend each run. RUC holds the sfc low in western KS by midnight tonight while 12z eta had it nc KS. The further sw this stays for tomorrow the better ops imo.


Can see the difference in the dry push already with that as well. Man I hope the ruc is onto this and it continues to slow. Guessing at a new target of Ft. Dodge to Des Moines for tomorrow. 18z runs should be interesting as well as tonights 0z.
FWIW, the points in eastern ok. are in the mid to upper 50s mostly, so there appers to be some moisture return, but as for the amount we can only wait and see. If there is a good return and points can get to around 60 give or take a degree watch out

As for chase areas, its a lose-lose type of setup for me. A faster moving storm will mean storms firing further east, but also less time for moisture to return and thus less coverage of the storms, poss. none at all? A slower moving storm means more moisture, better chance at severe storms, but also the storms would be further west and would weaken by the time they get within my very limited chase range for tomorrow. :(
NAM still on track with the slowing trend... Approx. 6 hours slower than the 12Z run. I really wish this thing would speed up some - As I'm not chasing half-way across the country on such a low risk. Instability still remains, decent even up until 12Z THU through the Great Lakes region, which would likely support a strongly forced squall line. Helicity values are also pretty impressive through 12Z as well.

All in all, IN/MI appear to have the threat for a squall line, most likely between 0Z and 6Z (from far western IN to far eastern MI, respectively) - Probably broken and strongly forced. I'm really diggin' the 100knt 500mb speed max moving in from the WSW combined with ESE SFC winds (which could be a moisture killer for OH/far eastern MI). The 500mb jet will likely enhance damaging wind potential...

Best supercell and tornado potential still appears to be central IL, possible extending into the far western reaches of IN, even with the slowing trend. The center of the low is located in southern IA/WI, so they are under a "lull" in the low/mid level kinematics - causing a significant drop-off in helicity. I would put my target area in central IL, just east of the IA border, where initiation will probably occur (should it occur at all)... Upper level winds will be increasing through the day, hitting nearly 80knts at 500mb... So you better have your racing gear ready...

I really wish COD would start working, so I have more fields then just the basic 5 maps...
I just don't see anything that would get storms going in MI during the day - and anything at night won't have the instability needed.
I just don't see anything that would get storms going in MI during the day - and anything at night won't have the instability needed.

Well, if the NAM had it's way, it maintains LI down to -4C and CAPES between 1000J/KG-1500J/KG (via COD) through 12Z THU. Forcing is strongest at 500mb, as shown on the VV fields. Looking at RelH fields, the NAM appears to develop a nice dry slot around 6Z across MI, with a nice band of higher RelH's just to the east... Which may indicate that the model is developing some sort of convection. Maybe severe, maybe not... But I do agree that it would be pretty hard since a tight inversion may develop just off the SFC. Ever since December 6th (1999 I believe), I never ignore very strong low level jets, even when it looks like a strong inversion may be in place... SFC temps during that event were in the mid 40's... I can't imagine any instability being present in such an environment.
looks like all the parameters are coming together today for a possible outbreak in IL, and IN. With Dewpoints >55 as far north as Keokuk, IA, looks like moisture return during the day will be no problem. Also the Wind fields appear to be great. IF I were to chase today, I would make a initial target of the Quad Cities, but that might have to be changed eastward as the day progresses and local conditions warrant. Sadly to say, I highly doubt I will be able to chase today:( So to those that do, Bag one for me! I think you will have good luck!
I'm actually a bit suprised to see the 1300Z SWODY1 still MDT. The current Tds are lower than I would like, but there's still time. I'm going to stick with my current target of BMI. I plan on leaving around 11am (skipping Dynamics and Political Science for this), so I might end up with a lot of time to kill. If that's the case, I'll find a free wifi location and check back in.

From the 6Z NAM, I can see the reasoning for the shift in the tornado outlook. More SRH would be nice, but I think there's enough to work with, assuming sufficient low-level moisture. Otherwise, things still look to be in good shape. This might be another of those good-setup-busts. We shall see.
I would still say the best threat is in central IL, somewhat near the IA border, as depicted here: http://www.waveformpc.com/outlook.JPG

WV loop shows a strong dry punch slowly working through central MO as of 14Z, which may help get things going a little later today. RUC advects Td's of 55F into southern IL by 21Z (60F on the NAM)... This will result in SFC based CAPE of 1000J/KG or 1500J/KG, with LI down to -5C. At the same time, the 500mb jet max will be entering the region from the southwest, while SFC winds remain SSE. Speed shear is quite impressive for 0-3KM and 0-6KM, and directional is decent. Helicity (0-3KM) reaches 200-300m2/s2 all the way into central IL at 21Z, increasing the further east you go, as winds will be more backed. Forcing doesn't actually appear to be all that strong in the beginning, so supercells definately a possibility before shear allows things to evolve into short lines, or a single "broken" line. Instability and shear persist well into the night time, remaining around 1000J/KG... So any linear stuff should persist well into the night across IN/MI and possibly northwest OH. The 700mb jet really starts cranking by 6Z, at 60-70knts, so I could very well imagine a low topped and/or thunderless line persisting.

I am somewhat concerned about moisture, NAM returns things very fast, so it's kind of suspect, but, 14Z SFC obs do indicate Td's as high as 57F already in southern IL, and a very narrow toungue of +54/55F Td's extending through MO, getting ready to head into IL - The one hour RUC forecast (valid 14Z) is quite low with these readings, only showing upper 40's across those areas.

RUC initiates convection around 21Z near the red "target" area, which is where I think the greatest potential for any tornadic activity will be. This also coincides with the dry slot moving through... Given the speed of winds aloft, these storms will be moving fast, possibly in excess of 50mph.
Morning soundings revealing a far better than expected environment. Topeka sounding in particular showed very little CIN and steep lapse rates through a good depth. Convection fired early this morning - and could be surface based by late morning. Near the sfc low, the deep shear may be weak enough to slow the motion of storms to chaseable speeds, but will hopefully be adequate to suppport storm rotation. I'd be most interested in tracking ~ 75 miles SE of the surface low along weak trough axis. RUC maintains convergence along this most of the day. Further east - potential is less certain. Perhaps a better idea for that region's potential can be assessed later today.

Chase target for today, March 30

Chase Target:
Cedar Rapids, IA

Storms will reach the area around 3 PM

Storm type:
Isolated severe winds to 70 mph. There is also a small possibility of a weak tornado although the tornado threat is small today.

A strong surface and upper level system tracking west to east through IA, and an associated front/trough will serve as the focus for severe weather today. Ongoing convection in SW IA will continue to develop to the east through the early afternoon. An E/W oriented boundary was noted on visible satellite at 15:30Z, while the front/trough in SW IA and WRN MO was surging to the east. Expect the triple point to line up in East Central IA by 21Z. MLCAPE’s to 1000 J/kg, coupled with BL-6km shear values of 50 kts and 0-3km SRH’s to 200 m^2/s^2 will create an environment favorable for severe weather.

- bill