7/1/06 FCST: WI / MI

[Tim Gonyo]

Possible significant severe weather event to unfold Saturday in the upper midwest. If we can get Friday nights MCS up and out of here to provide ample surface heating, things could get interesting Saturday afternoon/evening.

There will be a east-west oriented warm front draped across southern Wisconsin.

ETA paints ~3000 j/kg SFC cape, 200 m2/s2 of helicity and an EHI around 2.5 to 3.0. Also there will be around 30 kts 0-1 KM deep layer shear, low LCLs, dew points pooling 65-70F, LI's to -8, and the LID erodes rapidly during the afternoon.

Tornado frenzy? We shall see. I'm charging my batteries.

 

[Jason McIntosh]

More worried about one of these rounds of storms (Fri Ngt/Sat Mrn, Sat Aftn/Eve, Sun) bringing a severe MCS with widespread damaging winds. We shall see.
[/b]

I guess i'm on the fence myself. The morning convection will be the ultimate player in this senario. I want to go back to last week(6/20/06); when SPC was almost certain that a severe MCS would form in SW MN/N IA and move into the area. Everything looked great for some severe weather outbreak whether it be tornadoes or wind damage. The reality was it was a bust! Nothing happened that day. The player was the morning convection. It capped the atmosphere over IA and stabilized WI all day. Fridays convection will determine what happens on Saturday. I think all the ingrediants are there for the taking, but will they be robbed early on is the real question.

I will be watching.

 

[Tim Gonyo]

A lot of Wisconsin's tornado outbreaks happen after morning convection. If we can get it to exit the region by noon, we'll be alright for a 4-5 PM SVR outbreak IMO.

 

[Robert Dewey]

Best combination of instability and directional shear appears to be over MI - where DTX says 0-3km helicity will be on the order of 500m2/s2. This helicity will begin to spread out of WI at around 15z and make it into MI by 18z or so...

It appears as though a very nice looking shortwave will be moving ESE creating good height falls, and dragging a trough through MI between 18z/SAT and 00z/SUN. Wind fields are beyond excellent, with the core windspeeds slamming into central MI where +1500j/kg of CAPE is available ... We're talking a +50knt low level 850mb jet, and 60-70knts at 500mb - which is quite a bit more impressive than the wind fields associated with our last MDT risk. A nice dry punch is also evident at 700-500mb. If an MCS is ongoing across WI in the morning, that will likely expand and become a rather intense squall line (more likely a derecho), spreading across much of lower MI. If that activity weakens and the associated cloud cover is able to thin out, we'd probably be looking at a significant supercell setup (given the slight degree of CINH to keep storms more isolated). This, of course, is all based on the 06z NAM.

I *REALLY* hope that we can get a large, intense, and long lived squall line (more correctly, a derecho) with a few supercells scattered around. <strike>I am going up north tomorrow towards the Traverse City area, but if things look like they will go crazy, I might have to consider delaying.</strike> Correction, I've now postponed the trip until Sunday.

 

[Jeremy Lemanski]

Best combination of instability and directional shear appears to be over MI - where DTX says 0-3km helicity will be on the order of 500m2/s2. This helicity will begin to spread out of WI at around 15z and make it into MI by 18z or so...

It appears as though a very nice looking shortwave will be moving ESE creating good height falls, and dragging a trough through MI between 18z/SAT and 00z/SUN. Wind fields are beyond excellent, with the core windspeeds slamming into central MI where +1500j/kg of CAPE is available ... We're talking a +50knt low level 850mb jet, and 60-70knts at 500mb - which is quite a bit more impressive than the wind fields associated with our last MDT risk. A nice dry punch is also evident at 700-500mb. If an MCS is ongoing across WI in the morning, that will likely expand and become a rather intense squall line (more likely a derecho), spreading across much of lower MI. If that activity weakens and the associated cloud cover is able to thin out, we'd probably be looking at a significant supercell setup (given the slight degree of CINH to keep storms more isolated). This, of course, is all based on the 06z NAM.

I *REALLY* hope that we can get a large, intense, and long lived squall line (more correctly, a derecho) with a few supercells scattered around. <strike>I am going up north tomorrow towards the Traverse City area, but if things look like they will go crazy, I might have to consider delaying.</strike> Correction, I've now postponed the trip until Sunday.
[/b]

Timing looks good, wind field is amazing, and there is moderate cape. If the MCS does not bring clouds and rain in the morning, then you can increase the temps and inturn the cape for the afternoon hours. It will all depend on sunshine again. I fear this might be another cloud cover bust, but we won't know until tomorrow morning when the MCS position is known.

 

[Tim Gonyo]

If its a cloud cover bust, it will be over Michigan. WI will clear out easily by afternoon.

 

[Robert Dewey]

I'm really only seeing one round of convection per the latest 12z NAM, and it looks like that "morning junk". After that stuff blows through WI, the NAM shows a massive amount of subsidence (and rapidly decreasing helicity values as the best jet max moves east). In addition, the front/trough will become aligned with the mean flow, so convergence will slacken. Still, the WI/IL border (and a bit further south) would be primed for isolated supercells given the inreasing instability, outflow boundaries, and the frontal boundary hanging around, but the threat will be slowly decreasing through the day (again, as best low and mid level winds move eastward).

Further east, MI will likely become unstable before that "morning junk" reaches the western shores. I'm guessing an existing MCS would likely intensify given the combination of +250m2/s2 (0-1km helicity), >2500j/kg SBCAPE, and a 55-60knt 850mb LLJ. I also wouldn't throw out the possibility that we might be dealing with an MCV. If this activity does hold off until +18z, we'd be looking at a large scale bow echo across MI. After that blows through, the subsidence will likely choke off further development as shear decreases and instability gets cut off by the MCS/bow echo/derecho.

 

[Robert Dewey]

I wouldn't be discouraged. The NAM and GFS are showing a strong signal that there will be a pretty intense MCS crossing the region (ramping up a LLJ during the daytime, massive precipitation output near the area, strong VV's, etc). Even if WI doesn't have time to heat up before the MCS rolls through, the dynamics should be enough to compensate (yes, I'm not taking convective feedback into account so the models are probably overdone).

Like I said though, while everyone is hoping that the "morning convection" moves out as soon as possible, it's that "morning convection" that has the highest risk of turning into a damaging MCS. After that passes, I don't really see a trigger other than the frontal boundary (but that starts to lose it's punch as it orients itself parallel to the mean wind), or maybe an outflow near the IL/WI border.

 

[nickgrillo]

Like I said though, while everyone is hoping that the "morning convection" moves out as soon as possible, it's that "morning convection" that has the highest risk of turning into a damaging MCS. After that passes, I don't really see a trigger other than the frontal boundary (but that starts to lose it's punch as it orients itself parallel to the mean wind), or maybe an outflow near the IL/WI border.
[/b]

No, there is a shortwave perturbation (and weak ageostrophic divergence) that plows through northern (and central) MI by the 00z timeframe -- with much of southern MI in large-scale subsidence associated with DNVA unti the mid-late afternoon. Now, the large-scale environment certainly appears favorable for organized severe weather... For instance, the 21z forecast sounding for DTX (Detroit/Pontiac) is quite georgous -- with near-extreme CAPE (for a surface parcel) and strong cyclonic curvature in the hodograph (favoring supercells being the main convective mode). Now, the weak low-level CAPE is due to the moderate CINH, which will hopefully erode with solar radiation through the afternoon. The WRF shows the MCS weakening over MN late tonight, so supposing we get full-day insolation on Saturday -- then I could see redevelopment as the shortwave induces ascent (mainly north of I-96) -- with the background thermodynamic/kinematic setup being favorable for both supercells and bow echoes.

 

[Robert Dewey]

I suppose it could go either way... Weakening MCS generates an MCV, which in turn re-generates as it crosses MI in the 18z-00z timeframe... Or it dies out completely and we get scattered supercells. I'm not sure how much convective feedback is occuring with the NAM, but some of the fields (in particular the VV fields and wind fields) might be contaminated.

BTW... Nick - that sounding you posted has to be one of the best DTX soundings I've ever seen. MI soundings rarely get better than that, especially this far east! :lol:

 

[nickgrillo]

I suppose it could go either way... Weakening MCS generates an MCV, which in turn re-generates as it crosses MI in the 18z-00z timeframe... Or it dies out completely and we get scattered supercells. I'm not sure how much convective feedback is occuring with the NAM, but some of the fields (in particular the VV fields and wind fields) might be contaminated.

BTW... Nick - that sounding you posted has to be one of the best DTX soundings I've ever seen. MI soundings rarely get better than that, especially this far east! :lol:
[/b]

Yes, indeed it is. Heck, take a look at the FNT (Flint MI) forecast sounding and hodograph for the same timeframe (even stronger low-level cyclonic curvature in the hodo). At any rate, looking at the latest SWODY2, it appears Dan McCarthy also sees the potential across the area --with a 30% hatched with wording for supercells and bow echoes firing by the late afternoon. If we do get surface-based initiation during the 21-00z timeframe, then a storm will be able to take advantage of the very rich streamwise vorticity and potentially become quite intense (with deep-layer shear profiles favorable for strong supercells). This almost looks like a stronger (in terms of both thermodynamics and kinematics) version of the setup we had last week which resulted in the fast-moving supercells near the state line (which featured large-scale ascent provided by weak boundary layer convergence and WAA). The rich low-level shear (with more than >250m2/s2 SRH accruing in the lowest 1-km AGL) and low LCLs would favor tornadoes, should storms indeed ingest surface-based inflow. We'll see...

 

[Robert Dewey]

NAM develops precipitation over far eastern WI at 18z, growing as it heads into MI through 00z. It is weak, but that's enough of a signal since the model can't resolve stormscale features (such as rainfall from one or two supercells). The GFS shows even less, but again - I think that has to do with the model resolution. If there was NO precipitation around, then I'd be real hesitant and say that things might be capped off. I'm gonna continue thinking that tomorrow will feature a significant event (for the Great Lakes anyway), just what and how is the unclear part.

EDIT: Check out these images from July 2, 1997 across MI (they depict how the model handles the precipitation):

http://meted.ucar.edu/convectn/w41/jul02case/fig9a.htm (many supercells were ongoing at this time)
http://meted.ucar.edu/convectn/w41/jul02case/fig9b.htm

That's almost 10 years ago, and models have finer resolution... But I think the same cautions still exist.

 

[nickgrillo]

The problem is that nothing is over a tenth, which is precisely what happened on June 20 when a bunch of people trekked out to Iowa only to be extremely angered when nothing developed. Sure, models do make mistakes sometimes as huge as that but I don't think a case from 9 years ago can be comparable to the models we have today especially since they went from the ETA to NAM to now WRF. If there were a lot of scattered thunderstorms around it would probably be at least a tenth of an inch, but it isn't which has be worried. And its not like theres a long continuous region of precip along the front, its very blippy and barely a couple of hundreths of an inch.[/b]

I don't understand why you would be comparing tomorrow to the 20th in IA. First off, there was a shortwave aloft that pushed through the region by the early afternoon (which weakened CINH in northeast MO and southeast IA, yet didn't induce lift) and left the entire open warm sector in large-scale DNVA and resultant subsidence through the rest of the evening. For that matter, the previous runs prior (to the 20th) showed an additional shortwave trough pushing into southern MN by the 00z timeframe, which made me think that could help storms initiate on the cool side of the warm front and ingest the strong low-level shear (assuming the cool side of the boundary destabilized some). Yet, models began to differ from this solution (which made me stay home) and weakened the evening shortwave even further (and reduced QPF). I thought there would be enough PVA (and low-level WAA) in southern MN (which would have pushed southward into the I-80 region by the late evening) to help induce ascent on both the cool side and warm sides of the front, with the large-scale background conditions being favorable for supercells -- yet the large-scale CINH kept killing storms (blocking buoyant inflow -- as mentioned by the few posts I made on the day).

In this case, you have a strong upper-level low (with a strong WNWerly jet aloft -- with divergence in the right-exit region of the jetstreak nosing into the area) with a sfc cold front dragging into MI by the evening (with a strong boundary layer WAA regime across much of the region) and large-scale lift provided by the shortwave by 21-00z.

 

[Tim Gonyo]

http://grib2.wxcaster.com/wxcaster4/CONUS_...SIGSVR_36HR.gif

Looks like a good severe weather probability is shaping up.

 

[Tim Gonyo]

I just spent ample time analyzing tomorrow's setup. Here are the facts:

CAPE: 2000-3500 j/kg (axis of highest cape over WI)
HELICITY: 120-280 m2/s2 (axis of highest helicity over Lower MI)
EHI: 1.5-3.5 (axis of highest EHI over extreme N IL)
SHEAR (BOUNDARY TO 6KM): 30-50 KTS (axis of highest shear over southern WI)
RAPIDLY WEAKENING CAP OVER SOUTHERN WI AND LOWER MI BY 00Z SUNDAY.
LCL HEIGHT: 400-1000m (axis of lowest LCL's over WI)

Lastly some other info:

Significant Tornado Index: 3.0 (bullseye over southern WI)
Significant Severe Index: 60-90 (bullseye over WI)
Supercell Compositve: 10-20 (highest over WI and MI)

Based on my personal analysis of past southern WI severe events (especially if we have morning convection to lay out some nice outflow boundaries), I STRONGLY BELIEVE this event will be SIGNIFICANT if... and I say if all these parameters come together. I do believe they will and here are my following maps regarding this situation.

NOW FOLKS

Before you blow the horn and make fun of my outlooks, try to see the potential in it. Remember as much as you think the "glass is half empty" some of us believe it to be "half full".

Discuss away.