11/08/05 FCST: Great Lakes

[tom hanlon]

Parked under the dayton OH cell right now. Some pea size hail but it seems like this one has just become outflow dominate. Had some promise and will wait for further development.

SPC has a MD out for OH and Indiana.

So surprisingly things are firing a bit early. We will see what the next few cells bring.

Crazy day.

Tom Hanlon

 

[nickgrillo]

Parked under the dayton OH cell right now. Some pea size hail but it seems like this one has just become outflow dominate. Had some promise and will wait for further development.

SPC has a MD out for OH and Indiana.

So surprisingly things are firing a bit early. We will see what the next few cells bring.

Crazy day.

Tom Hanlon

I wouldn't worry about any of that activity... There is virtually no surface-based instability and there is a relatively strong inversion around the 850mb layer. This would mean any storms would be rooted above the capping inversion, and have no way in becoming surface-based (i.e. some marginally severe hail at best). However, elevated instability has obviously been sufficiant enough to sustain erected updrafts... So large hail could become a increasing threat through the afternoon.

 

[Kiel Ortega]

Well, the 18Z ILX sounding just came up and I'm more convinced now of today's event turning into tomorrow morning's event.

The bndry I talked about earlier looks like it turned into the warm front (confused me with the orientation). Still watching it in WC IL to see if it can set off some surface based convection, though I think after the 18Z ILX sounding, looks more like elevated will be the way to go. Further, it looks like the model soundings were consistent in stabilizing the surface right after dark. LLJ sets up best in the west part of the TA, which only enhances my interest in WC IL.

 

[nickgrillo]

Storms continue to grow in coverage across central OH along developing warm frontal zone in association with small wave moving through IN as of 19z. They are tapping into some pretty decent elevated instability, which will let them carry a good severe hail threat through the evening (as instability continues to increase). I would imagine SPC would consider giving this area a blue box...

 

[Robert Dewey]

I know posting NWS bulletins is against the TOS, by my GOD! Check out IWX:

THIS IS A PARTICULARLY DANGEROUS SITUATION GIVEN THE STORM
TYPE...TIME OF DAY AND RAPID STORM MOVEMENT. CONDITIONS WILL BECOME
FAVORABLE FOR EVEN TORNADOES AS THUNDERSTORMS FORM WHERE THERE IS A
LARGE AREA OF WIND SHEAR NEAR THE GROUND. ENERGY HELICITY INDEX FROM
2.0 TO 3.5 INDICATES A FAVORABLE TORNADO POTENTIAL AS MOST UNSTABLE
CAPES REACH BETWEEN 1200 AND 1800 J/KG.

That sounds more like high risk wording than SLGT... I'll probably update a forecast in a bit after reviewing SFC data and 18Z models...

 

[nickgrillo]

Latest 18z NAM continues the trend of the shortwave becoming massively neg-tilted when entering the western great lakes by 6z (with surface low rapidly deepening and increasing in baroclinicity). I completely agree with NWSWFOs mentioning the possibility of tornadoes... Given the very strong low-level shear, I have been questioning the possibility for a couple long-track tornadoes coming out of this -- particularly near triple point in southern WI/northern IL.

--> http://www.weather.cod.edu/forecast/ETA/GL...L_0_prec_12.gif (0z) http://www.weather.cod.edu/forecast/ETA/GL...L_0_prec_18.gif (06z) <-- Watch the massive explosion of precip with the approach of the shortwave by 6z

 

[David Draun]

I know posting NWS bulletins is against the TOS, by my GOD! Check out IWX:

THIS IS A PARTICULARLY DANGEROUS SITUATION GIVEN THE STORM
TYPE...TIME OF DAY AND RAPID STORM MOVEMENT. CONDITIONS WILL BECOME
FAVORABLE FOR EVEN TORNADOES AS THUNDERSTORMS FORM WHERE THERE IS A
LARGE AREA OF WIND SHEAR NEAR THE GROUND. ENERGY HELICITY INDEX FROM
2.0 TO 3.5 INDICATES A FAVORABLE TORNADO POTENTIAL AS MOST UNSTABLE
CAPES REACH BETWEEN 1200 AND 1800 J/KG.

That sounds more like high risk wording than SLGT... I'll probably update a forecast in a bit after reviewing SFC data and 18Z models...

WTF????

That is some excellent instability for this time of year. Looks like some low-topped sups could get going. Too bad I am in Iraq! :evil: Any Chicago chasers out there? Get out there and get me a tornado pic. I'm looking at the temps right now over there in the mid 60's. I'd like to see it a little warmer.

 

[Kevin Bowman]

I know posting NWS bulletins is against the TOS, by my GOD! Check out IWX:

THIS IS A PARTICULARLY DANGEROUS SITUATION GIVEN THE STORM
TYPE...TIME OF DAY AND RAPID STORM MOVEMENT. CONDITIONS WILL BECOME
FAVORABLE FOR EVEN TORNADOES AS THUNDERSTORMS FORM WHERE THERE IS A
LARGE AREA OF WIND SHEAR NEAR THE GROUND. ENERGY HELICITY INDEX FROM
2.0 TO 3.5 INDICATES A FAVORABLE TORNADO POTENTIAL AS MOST UNSTABLE
CAPES REACH BETWEEN 1200 AND 1800 J/KG.

That sounds more like high risk wording than SLGT... I'll probably update a forecast in a bit after reviewing SFC data and 18Z models...

WTF????

That is some excellent instability for this time of year. Looks like some low-topped sups could get going. Too bad I am in Iraq! :evil: Any Chicago chasers out there? Get out there and get me a tornado pic. I'm looking at the temps right now over there in the mid 60's. I'd like to see it a little warmer.

Depends on where you are in Chicago, on the far nw side near ohare the temps are only in the mid 50's, you have to head to bloomington to get mid 60 degree temps.

 

[Jeff Snyder]

We need to moisten the northern IL/IN and points north before we worry too much about surface-based supercells. I do find it odd that the latest 18z RUC run shows higher surface Tds in southern WI than the 18z NAM, and similar surface temperatures, yet the RUC shows no surface-based CAPE in northeastern IL/IN and points north by 6z, while the 18z NAM shows 1500-2000 j/kg SB-CAPE. I assume this comes down to a convective parameterization difference between the operational RUC and the NAM, but it's interesting nonetheless.

I also think that the strong wording used by whatever NWSFO quoted above is heavily influenced by the Evansville tornado of a couple of days ago. It's a good reminder to never let our guards down, but I certainly don't look at the 6-12 hour forecast and say "Wow, tornado outbreak!". Again, strong shear and fast forward motion argue for tornadic potential for a surface-based supercell (owing to the shear) that has the possilibity to affect many people (owing to the fast foward motion). Of course, this depends entirely on the presence of a "surface-based supercell". I'd have to look at RUC and NAM forecast soundings (or at least the 0z soundings in an hour or two) before I get too confident about the development of surface-based instability in northern IL/IN, and southern WI/MI. I haven't spent much time looking at the situation, but those were just my original thoughts.

 

[Kiel Ortega]

I think the forecast discussion language might be in response to Sunday morning's event. Surface temperatures are already starting to drop from the sun setting around the TA; and in an area where the surface is already stable (via RUC analysis), doesn't help out the chances for sfc based convection. Further, not going to see the LLJ speeds similar to Sunday morning's in a broad area, so the surface will decouple over the next couple of hours over much of the TA. Checked out the 18Z isentropic forecasts and looks like big time isentropic lift over the entire GL area. Given the shear, probably have a good bit of elevated convection with embedded severe cells.

 

[Mike Johnston]

Not sure whether that southern jet is enhancing or deterring upper level support for a severe breakout. Contrasted with last Saturday's setup, where base of negatively-tilted upper trough dug all the way down through central plains, creating massive environment of ascent downstream, we have a more-or-less zonal jet undercutting the northern jet trough along the northern tier. With the hint of some erosion of CIN over IN, IL, and MO, possibile the upper diffluence/exit region of the southern jet may yet set the stage for initiation over this area, where severe parameters have been building over the last few hours. RUC keeps wanting to break out precip, very tentatively, across E MO and IL. Deep-layer shear is supportive of supercells across the region also. Now, despite hopes for the consolidation of a warm front and development of a "triple point", note that surface convergence remains very ill-defined. In summary, fairly nasty November weather over the Great Lakes looks like a given, but initiation of supercells across the heartland looks very touch and go at this point.

 

[nickgrillo]

NAM SFC Td forecast:
http://www.rap.ucar.edu/weather/model/disp...rs=hr12hr18hr24

Current surface obs:
http://www.spc.noaa.gov/exper/mesoanalysis...s/s2/bigsfc.gif

NAM forecasted sbCAPE:
http://www.rap.ucar.edu/weather/model/disp...rs=hr12hr18hr24

The NAM isn't really over moistening the surface layer... With sfc-based instability forecasted to dramatically increase with the approach of the shortwave and the development of the triple point over southern WI around 06z. I don't think any of the NWSWFOs are "playing it safe" because of SUNs tornado - they are being completely realistic based on model forecasts and current analysis. This, would be strong shear/moderate instability invof triple point setup in NOV in the great lakes... It is very wise for them to mention the possibility for something big to occur should storms become surface-based (and feeding off a moderately unstable and strongly sheared low-level airmass).

 

[Jarrod Cook]

The warm front is roughly along the I-80 corridor in IL. It appears to be moving north very slowly. If this is the case, then the s. WI/n.IL area won't be too favorable for surface based supercells. However, I'll be keeping a close eye on things here in Peoria, since we are in the warm sector. Now its just dependant on the cap. We'll see what happens.

But for now, temps and Td's in N. IL and S. WI don't look too great for strong tornadoes.

 

[Robert Dewey]

Jeff... Here is a forecast sounding out of extreme northern IN:

http://www.waveformpc.com/pics/sounding.gif

There is a very strong but shallow inversion... The question is; will that inversion be enough to stop storms from becoming SFC based? That inversion is awefully close to the SFC - yet it's pretty strong. Lift a parcel from that inversion, and you wind up with 1K to 2K J/KG of ever-so-slightly elevated CAPE.

 

[Mike Umscheid]

User beware regarding nocturnal CAPE forecasts from the NAM. The current code in the NAM model is *not* actually from a surface (2m AGL) based parcel. It is, in reality, a 70mb AGL most unstable cape. You may notice strange advection of CAPE during the overnight hours with very little diurnal decline in the maxima of "sb" CAPE from the NAM. If you pull up forecast soundings along the warm front across the ORD area and far northern IN... you'll notice a pretty significant 925mb cap at 06z. The NAM is actually calculating CAPE from the level of maximum Theta-E within this 70mb layer... which at 06z is not the surface.

I've been in e-mail conversation with someone at EMC about this very problem. Ideally, if a field is labelled "surface-based CAPE" in the model, then it should reflect a surface-based parcel ascent...and the surface only. They are looking to reduce this "surface" layer from 70mb to 20mb... which would improve the nocturnal SB-CAPE... but it still isn't technically surface-based.

Something to keep in mind when looking at sb-CAPE fields on the UCAR page and COD.

Mike U

NAM SFC Td forecast:
http://www.rap.ucar.edu/weather/model/disp...rs=hr12hr18hr24

Current surface obs:
http://www.spc.noaa.gov/exper/mesoanalysis...s/s2/bigsfc.gif

NAM forecasted sbCAPE:
http://www.rap.ucar.edu/weather/model/disp...rs=hr12hr18hr24

The NAM isn't really over moistening the surface layer... With sfc-based instability forecasted to dramatically increase with the approach of the shortwave and the development of the triple point over southern WI around 06z. I don't think any of the NWSWFOs are "playing it safe" because of SUNs tornado - they are being completely realistic based on model forecasts and current analysis. This, would be strong shear/moderate instability invof triple point setup in NOV in the great lakes... It is very wise for them to mention the possibility for something big to occur should storms become surface-based (and feeding off a moderately unstable and strongly sheared low-level airmass).