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

[Mickey Ptak]

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.

Mick

 

[Ben Prusia]

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.

 

[Jeff Snyder]

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.

 

[Karen Politte]

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.

KR

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.

 

[Amos Magliocco]

This morning's ETA reorients Wednesday's s/w trough to a negative tilt and brings it flying through....Illinois?

http://www.wxcaster.com/CONUS_ETA_250_GPHT...TMPSPD_54HR.gif

http://www.wxcaster.com/CONUS_ETA_500_GPHD...DIFGPH_54HR.gif

http://www.wxcaster.com/CONUS_ETA_SVR_CAPE...HSWEAT_54HR.gif

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]

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.

http://www.wxcaster.com/CONUS_ETA_SFC_SLPT...PTSBLI_60HR.gif

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.

Mick

 

[Robert Dewey]

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...

 

[Alex Lamers]

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...

 

[Glen Romine]

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.

Glen

 

[Ben Cotton]

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.

 

[Jeremy Lemanski]

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.

 

[Robert Dewey]

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...

 

[Joe Nield]

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.

 

[rdale]

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

 

[Mike Hollingshead]

http://www.rap.ucar.edu/weather/model/eta1...hr_sfc_mslp.gif

http://www.rap.ucar.edu/weather/model/ruc1...hr_sfc_mslp.gif

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.

http://www.rap.ucar.edu/weather/model/eta1...hr_sfc_dewp.gif
http://www.rap.ucar.edu/weather/model/ruc1...hr_sfc_dewp.gif

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.