8/9/2004 FCST: MIDWEST/GREAT LAKES/NORTHERN OHIO VALLEY

Still kind of early, but there appears to be a threat of severe weather Monday, as an unseasonably strong trough swings through a warm/humid and possibly unstable airmass. Not going to get into real details since its a few days away (and things can change in a matter of a day, like the busted forecast a few days ago), but I am starting a thread just to discuss any future model runs or opinions...
 
I've been watching it on the GFS and now the 12Z Eta looks good as well... Fortunately this is not even close to the same set-up (bust-up) of the past week, it's a "real" storm system (but still not one that looks like Mid-August!)

- Rob
 
I noticed both Monday and Sunday have some prospects. Guess I should open a forecast topic for the 8th but seeing how little success chasers have had in the Upper Midwest here lately, I'm inclined to wait for another run or two.
 
Latest 00Z ETA is starting to roll in, and its 00Z analysis is stronger with the 500MB low over the northwest (now that is ashore) compared to the 12Z 12HR ETA. Still quite a ways out, but as Rob said, this will be an actual "storm", not a developing SFC reflection along a cold front, so models should have somewhat of a better handle on it.

Still too early in my book to determine instability/cloud cover/etc., but the potential is still there for some decent storms Monday afternoon.

BTW Rob: The LDM is pretty much back up, I had to bypass the router (that was the ultimate problem, the router kept crashing - couldn't handle the data load). So, I now have the direct IP address into the server. There maybe a few restarts here and there, since I am switching from CONDUIT back to my old FTP scripts (they seemed to do better, and have more grids), on a seperate machine. Please PM me as to whether or not Garry replied to your L2 request...
 
Still an evolving situation for the beginning of this upcoming week. Am a little concerned about SFC moisture return, but looking at the lastest METAR data, there are widespread >65F Td's all the way into northern SD.

Another concern is the timing of the front. From the 12Z models, it looks like a late afternoon or evening event (at least to me), along the pre-frontal trough.

DTX:
A NIGHTTIME PASSAGE WILL REDUCE THE SEVERE POTENTIAL ON THE FRONT...

Seems like the NWSFO are not too concerned with a severe weather, at least as of now...

ETA has been lowering low and mid level wind speeds with each run, as well as back instability off somewhat (CAPE was originally forecasted to be >2500J/KG, now AFD from GRR says 1500J/KG, which doesn't thrill me). Latest 18Z ETA is coming in, and its analysis is yet again stronger than the previous 6HR/12HR, so we shall see...
 
I don't see anything terribly anti-severe quite yet... While winds are weaker on the 12Z they still easily support a nice line, and the CAPE values range from 1500-2100 depending on what sort of warming we get in the day. Not bad for a 48hr event just yet.

- Rob
 
Originally posted by rdale
I don't see anything terribly anti-severe quite yet... While winds are weaker on the 12Z they still easily support a nice line, and the CAPE values range from 1500-2100 depending on what sort of warming we get in the day. Not bad for a 48hr event just yet.

- Rob

Okay, good... Just need some re-assurance :eek:
 
Originally posted by Jason Hetzel
well i guess it all depends on sundays overnight activity then huh?

Yep... Right now, it looks like its going to be a squall line event, but that all depends on the exact "shape" of the low and associated SFC wind fields...

I decided to bring up some forecast soundings in NSHARP (using the 18Z ETA), and by 21Z, a parcel of 83/66F would yield close to 2500J/KG or greater...
 
Originally posted by nickgrillo
I think the winds are too weak for good stuff. Does anybody else agree?

I have been watching the shortwave on the WV loop, and it looks like is spinning pretty fast, perhaps its going to be a bit stronger than forecast? Anyway, I am not too excited about the wind fields either, but if we were to ramp up CAPEs to >2500-3000J/KG, then we may get some good action (squall line at the moment)...
 
Latest 00Z ETA is in, and I have more confidence that a severe weather scenario may pan out. Latest data shows the 500mb shortwave fo be stronger than what the 18Z ETA had predicted, and looking at the WV loop, this looks probable. Low and mid level winds are also slightly better this go around, probably due to the stronger shortwave, with 30-40knts at 700mb. Given the better wind field, shear is better, with 0-3KM shear of 35knts, and effective SRH of 170M2/S2 (at LAN). Moisture return is still my main concern... However, modifying the ETA sounding for LAN with a parcel of 81F/63F creates just over 2500J/KG, and if the dewpoints can really get pooled to 65F (wow!), CAPE jumps to 3200J/KG - Which would certainly support severe thunderstorms.

Expect the main storm type to be a squall line given the strong forcing along the pre-frontal trough, but with BRN numbers in the mid 20's and effective SRH of 170M2/S2, I could imagine a few supercells popping up...

The severe weather season so far across MI has really been weak, with most forecasts becoming busts. At this point, I will take any form of severe weather I can get - Be it an outflow dominate squall line or a pulse severe storm...
 
Are you crazy Rob? LOL. :lol:

MI had over 25 tornadoes so far this year! :lol:

My perspective on chasing:
Supercells/Rotating Storm: YES.
Anything Outflow Dominant: NO
 
Originally posted by nickgrillo
Are you crazy Rob? LOL. :lol:

MI had over 25 tornadoes so far this year! :lol:

My perspective on chasing:
Supercells/Rotating Storm: YES.
Anything Outflow Dominant: NO

Yeah, but when those 25 tornadoes happened over a long period ot time (i.e. 2 tornadoes a month), then you can see the "lack" that I was talking about. I havn't checked on this, but I don't think there has even been an F2 or higher tornado this year in MI... The best event I recall was the lone supercell in central lower (the one that you were on earlier).

Anyway, hope you arn't too disappointed, because Monday is looking to be linear (hopefully I am wrong).

Anything Outflow Dominant: NO

You mean to tell me you would rather seen nothing at all than a derecho with +80MPH winds? I like tornadoes too, but I take what I can get (in MI, beggers can't be choosers :lol:)

To me, thi s summer has been relatively cold and severe weather free...
 
Sun 12Z

Don't see anything from today's runs that scares me... Still looking at CAPEs in the vicinity of 2000, with nice wind structure and good timing for Mid-Michigan.

As SPC noted, lapse rates are still a little on the weak side but not enough to make me go no-severe.

Yet.

- Rob
 
The 12Z data is in, and things still look on track as far as the large scale synoptics. I orignally had some concern when it comes low level moisture, but current OBS show numerous reports of +65F Td's (even creeping into WI), with several +70F reports across eastern IA/MN. Current ETA suggests that this moisture will move eastward into lower MI tomorrow afternoon, with Td's in the low to mid 60's... Given the current OBS, I wouldn't be surprised to see some upper 60's to near 70F dewpoints.

I decided to extrapolate the 500mb shortwave track based on the WV loop and RUC analysis for the past 24HRs... Which would put the "center" of the 500mb low (or trough axis) near eastern Lake Superior by 00Z TUE (mean speed of the shortwave was found to be 20KNTS). ETA and GFS show a nice dry air intrusion at 700mb pushing into MI between 21Z-03Z, which would suggest a line of thunderstorms beneath the highest RELH.

Wind fields are decent, with a 40-50knt jet developing just behind the dry air intrusion. Modifying soundings across the region for a parcel of 80F/65F yields >2500J/KG across much of the region (I believe 65F is possible given upstream dewpoints). Of course max temps will be based strongly on how much cloud cover is present, but 80F shouldn't be too hard to hit.

My guess is that a squall line will likely develop and track eastward across the region given the linear linear look to all of the forcing mechanisms (dry air intrusion, convergence, etc.). Looking at the derecho "check-list", there are a few parameters missing, such as monster CAPE values and conditions extending downstream for 250nm (since a derecho is defined as having a long track). However, a local "derecho" (AKA squall line) still seems like a pretty good bet...
 
"Current ETA suggests that this moisture will move eastward into lower MI tomorrow afternoon, with Td's in the low to mid 60's... Given the current OBS, I wouldn't be surprised to see some upper 60's to near 70F dewpoints."

I considered that though initially but wonder if that's more of Iowa corn helping the high DPs as opposed to synoptics?
 
Originally posted by rdale
\"Current ETA suggests that this moisture will move eastward into lower MI tomorrow afternoon, with Td's in the low to mid 60's... Given the current OBS, I wouldn't be surprised to see some upper 60's to near 70F dewpoints.\"

I considered that though initially but wonder if that's more of Iowa corn helping the high DPs as opposed to synoptics?

I am thinking that the IA corn is the cause for the 68-70F dewpoints (I now see a few 72F readings in extreme southern MN!), but the mid 60's (~65F-67F) look more synoptic, given the greater coverage (into northern/western WI)...

The
 
Originally posted by Jason Hetzel
well sadly it looks to be an all linear event for tomorrow as lapse rates and winds will not be great. :(

Lapse rates are generally weak, but I don't see how this would have a large effect on storm type. As for wind fields, they are relatively decent, especially for early August.

Rob: I am looking at soundings in NSHARP, and I have a question - When I click on "hodograph" to view a hodograph, I see a section on the bottom right called "environmental shear"... It then has a column labled "TOT SHEAR", are those units in m/s or knts?
 
Originally posted by Jeremy Lemanski
rdewey, How do you get to the NSHARP data? Is it software or a pay site?
thanks.

You can just call me Robert :D (Rob doesn't work, because there is already another Rob)

Anyway, its software from Unidata http://www.unidata.ucar.edu . You need to know a bit about Linux or Unix based operating systems and some programming (to write scripts to get the data through FTP). Its all free though :D, and you can make all kinds of weather maps, and overlay data on top of satellite/radar to get a better idea of whats going on in the atmosphere...
 
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