11/08/05 FCST: Great Lakes

[nickgrillo]

Large-scale warm air advection will strengthen during the evening TUE from central IN/IL into southern WI/MI as LLJ intensifies in response to both diurnal cycle and eastward progress of shortwave trough moving into the region. I would expect severe thunderstorms to develop across central IN and IL in the mid-afternoon... With steep mid-level lapse rates and insolation allowing for sufficiant (1000-2000 sbCAPE) instability to develop. Combination of increasing mass inflow and steep mid-level lapse rates -- ahead of the negatively-tilted shortwave trough -- suggests a favorable environment for supercells. Backing surface flow and gradually veering profiles (and strong speed) yields sufficiant deep vertical shear and 0-3km SRH favorable for a few isolated tornadoes associated with any discrete cells.

Further north/northeast across southern MI... NAM shows the warm front pulling northward into the region, with surface-based instability increasing (to >1000J/KG) by late-night in response to increasing moisture advecting northward. Surface-based activity in the form of supercells and bow echos are likely to develop/continue near the warm front... Significant vertical shear and low-level shear profiles indicates the potential for long-lived mesocyclones and isolated tornadoes with any storms across this area.

 

[Brett Adair]

Found this interesting and quite true from Fred Gossage of NEMAS. They issue there own outlook discussions.

Great Lakes and Ohio Valley
***A Moderate Risk of Severe Thunderstorms has been forecast for Most of Illinois, Indiana, Western and Central Ohio, Northern Kenctucky, Southern Lower Michigan, and Southern Wisconsin for Tuesday and Tuesday Night***

Moisture return will once again start across the MS Valley as southerly flow around the west side of the Gulf Coast ridge pumps mid 60 to low 70 degree dewpoints into the MS and OH Valleys during the period. Thunderstorms may start early, on nose of LLJ, as the warm/moist advection establishes itself over the forecast area....and thunderstorm clusters will spread northeastward through the day. Airmass over the area will grow increasingly unstable through the day tomorrow with mid/upper 60 sfc dewpoints and temps into the 70s helping to contribute to SBCAPE of 1500-2000 j/kg by the early evening over the Mid MS/Ohio Valley area.

Strong shortwave currently over the Northwest will move rapidly eastward and take on a strong negative tilt as it approaches the Great Lakes. Strongly diffluent 130 kt 250-mb flow will overspread the area, helping the large scale ascent for thunderstorm formation. The approach of strong winds aloft and favorable diurnal factors will cause the SW 850-mb LLJ to strengthen to over 55 kts during the evening from MO through IL and into IN/MI. This will cause very favorable deep layer and low-level shear profiles for supercell development.

Expect several clusters of supercells and bowing segments from eastern MO across the OH Valley and Lower Great Lakes....both in the warm sector and along and north of the warm front. Due to the expected instability, very rich boundary layer moisture, and strong wind fields, any supercells may produce large hail and strong tornadoes. Wind damage will also be a big threat due to rapid storm motion, mid-level dry intrusion, and formation of bowing segments.

Severe weather threat will be further assessed over the next 24 to 36 hours and an upgrade to High Risk or Greatest Threat is possible over parts of the area. This is potentially a dangerous weather situation, and all residents in the area need to pay close attention to weather information, and get a plan of action ready incase warnings are needed.

GOSSAGE

 

[Skip Talbot]

2000 JKg SBCAPE, 300 SRH, and 40-50 knots 6km sheer over Champaign on the 0z nam. Favorable parameters and more than sufficient for supercells, but the real question is if anything will go up in the warm sector before dark. The nam has the CINH eroding by 0z but no qpf until afterwards, further east in Indiana.

 

[nickgrillo]

Originally posted by Skip Talbot
2000 JKg SBCAPE, 300 SRH, and 40-50 knots 6km sheer over Champaign on the 0z nam. Favorable parameters and more than sufficient for supercells, but the real question is if anything will go up in the warm sector before dark. The nam has the CINH eroding by 0z but no qpf until afterwards, further east in Indiana.

I would expect initiation to occur across central IN/IL shortly before dark... Then, activity should spread northeast...

Latest 0z NAM still paints a simuler picture... This would be a severe threat across central IN and IL during the mid-late afternoon... Then spreading into the great lakes by late evening and early morning hours (as the warm front pushes northward).

Focusing on the MI area... Low-level convergance along/north of warm front will be sufficiant enough for convective development by late evening in northern IL/southern WI and northern IN... Then spreading east/northeast into the great lakes well afterdark (03z-12z timeframe). As nose of strong mid-upper jet digs into the region... Covergance along/north of the warm front will strengthen and support deep moist convective initiation across this region around sunset. Strong deep-layer vertical shear, in a moistening low-level airmass (with steep mid-level lapse rates yielding moderate sfc-based instability) will support a few sustained supercells and forecasted 200-400m2/s2 0-3km SRH will support isolated tornadoes. Overall, the threat for tornadoes exists across central/northern IL and then spreading into northern IN and southern MI as the evening/night progresses.

 

[Jim Bishop]

I hate to see great shear, moisture and sufficient instability go to waste. But this will be another daylight bust because of yours truly - The CAP. But after dark things will get cooking.

850mb temps are going to be near 15C. 500mb temps and heights will actually be increasing through much of the day as large scale ridging occurs. The nose of the shortwave won't reach the vicinity of Illinois until nearly 00Z. Warm advection and convergence along the warm front will not be enough to erode this very strong CAP.

However, near or just after 00z (near dark) when the upper shortwave trough reaches the area, upper support may be enough to produce surface based convection. Shear will be incredible and CAPE near 1000 j/kg to possibly 1500 will be sufficient to support tornadic supercells. However, warm air advection will continue from 850mb to 500mb. So despite some midlevel cooling from large scale ascent, there will be strong WAA in the midlevels battling rather weak cooling. That CAP is going to be strong even when the storms are ongoing. This means updrafts are going to be fighting the CAP for the first several hours until cold air advection takes over.

By midnight the NAM shows zero CIN near the warm front over North Central Illinois and convection. I would expect the bulk of the convection to fire well after dark, or by then any isolated storms that have already fired won't be fighting the CAP anymore. So say by around 9pm to midnight there will probably be a few tornadic supercell along the warm front over North Central Illinois and Northern Indiana depending upon how much instability is left after the boundary layer cools. This looks like another potential nightime tornado event. The convection will probably form into an mcs as the night progresses and the low level jet cranks up.

 

[Fred Gossage]

Here's my Day 1 at NEMAS....updated to reflect the doubt of any daytime initiation.......

Day 1 Severe Weather Outlook for Tuesday, November 8, 2005
Valid 1200Z 11/8 - 1200Z 11/9

National Synopsis

General zonal flow continues over much of the country as New England Shortwave departs and ridge builds in across the Eastern Gulf Coast. Meanwhile, strong shortwave now entering the Northwest will shift rapidly eastward toward the Western Great Lakes through the period, taking on a strong negative tilt by overnight as jet stream energy moves into the Great Lakes and Ohio Valley.

Ohio Valley
***A Moderate Risk of Severe Thunderstorms has been forecast for Northern and Central Illinois and North Central Indiana for late today and tonight***

***Surrounding the Moderate Risk, a Slight Risk of Severe Thunderstorms has been forecast for much of the Mid Mississippi and Ohio Valleys and the Lower Great Lakes***

Moisture channel imagery early this morning shows shortwave entering the Idaho/Montana area with northern branch of the jet stream from Oregon into Montana and eastward to the Great Lakes. Meanwhile, southern branch is blasting east-northeastward from Arizona, across the Central Plains to the Mid Mississippi Valley. This pattern will continue through the day, as the shortwave takes on a negative tilt and moves from the Northwest toward the Great Lakes by the end of the period. Meanwhile, the high across the eastern Gulf will be in a favorable position to pump uncontaminated tropical boundary layer air northeastward with mid 60 F sfc dewpoints reaching central IL/IN by 09/00Z. This, combined with afternoon temps into the mid and upper 70s near and south of the warm front will contribute to SBCAPE of 2000-2500 j/kg and LIs of -4 to -7 right along the warm front by early evening.

Shortwave ridging over the Ohio Valley from the Gulf Coast high, combined with the elevated mixed layer plume advecting into the mid-levels from the west, will help to cap the warm sector for much of the day. Lack of strong forcing will keep the cap in place until near or just after 00Z, when height falls from the approaching shortwave start to overspread the region. Animation of 08/18Z-09/06Z CMI and IND forecast soundings from the 00Z NAM show a classic profile for onset of deep-layer ascent removing large amounts of convective inhibition, and this process should occur up and down the warm front near and just after dusk, allowing for rapid development of severe thunderstorms.

As strongly diffluent, 130 kt 250-mb flow approaches from the west, in response to approaching shortwave, 0-6 km shear values across the warm front will increase to over 55 kts, which will be very supportive of supercell thunderstorms with large hail and damaging winds. Normally, with a general pattern like this, a tornado outbreak would be a huge concern, but due to the timing of convective initiation and boundary layer decoupling, it appears that the tornado threat will be fairly low, as most thunderstorms will form after the boundary layer nocturnally decouples, and the sfc significantly cools. With storms right on the warm front, tapping into 0-3 km SRH of 400-600 m2/s2, there may still be a few isolated tornadoes, but no widespread tornadic activity is expected. HOWEVER....if convective initiation is a couple hours earlier, when things would be more surface-based, this may drastically change.

As cold front approaches the region after midnight, strong upward forcing and the presence of low-to-mid 60 dewpoints may allow a line of strong to severe storms to develop and race east-southeastward. The main threat with this would be damaging winds due to rapid storm motion, 700-mb winds in excess of 60 kts, mid-level dry air entrainment, and the line crossing the 50kt SW 850-mb LLJ.

GOSSAGE

My earlier forecast you saw was based on the assumption that storms would be able to fire before the boundary layer decouples after dark...... now I really don't see that happening...

***BTW, our Moderate Risk is different from that of the Storm Prediction Center. Our MDT would be equivalent to a mid/upper end SLGT Risk from them.***

 

[Robert Dewey]

NAM is showing decent CAPE across MI at 12Z tomorrow, which made me a little bit suspicious (1500J/KG SFC and 1000J/KG ML) considering the SFC parcels of 55F/50F T/Td. I'm gonna have to pull this sounding up in some program to find out just what's going on and at which layers the best CAPE is located (I am guessing that most of it's within the first 100MB, given the decent MLCAPE)...

If that is in fact correct, and MLCAPE hits 1000J/KG while the low level jet and associated shear is maximized, the threat for severe thunderstorms with large hail would seem pretty high over that area. But, if there is only a small and/or weak inversion, then the threat for damaging winds and tornadoes would probably increase...

 

[rdale]

It's a long skinny cape, and the inversion is quite significant until 12Z so I don't think winds/tor will be that much of a worry. Hail and a nice light show should be our primary mode of fun, but no chance of anything happening on the 8th (at least around MI/IN/OH.)

- Rob

 

[Kiel Ortega]

I think the 12Z RUC did okay with the set up...looks like the surface towards the warm front won't be able to keep up with the levels just above the surface (in terms of temperature)...especially with these clouds still hanging around. If some elevated supercells get going, probably would see HPs as the constant veering through the atmosphere should keep them seeded well. I would keep my eye on that boundary setting up from PPQ (whatever that is) through C IL to around West Lafayette, IN...the RUC is still destabilizing this area nicely (especially towards MO). Storm motions will be maximizing the low level helicity, which might provide a surprise.

 

[Brett Adair]

NAM is showing decent CAPE across MI at 12Z tomorrow, which made me a little bit suspicious (1500J/KG SFC and 1000J/KG ML) considering the SFC parcels of 55F/50F T/Td. I'm gonna have to pull this sounding up in some program to find out just what's going on and at which layers the best CAPE is located (I am guessing that most of it's within the first 100MB, given the decent MLCAPE)...

If that is in fact correct, and MLCAPE hits 1000J/KG while the low level jet and associated shear is maximized, the threat for severe thunderstorms with large hail would seem pretty high over that area. But, if there is only a small and/or weak inversion, then the threat for damaging winds and tornadoes would probably increase...

That is the only place that I can see an isloated tornado risk now....along that warm frontal boundary where some CAPE will possibly still be intact and be surface based. There will be great speed/directional shear across the region, but it seems that this lid will be of great strength and hard to break with the extreme mixed layer plume in tact through about 12z/WED and maybe even beyond that. Seems as if the inversion strengthens as time goes as well...

 

[tom hanlon]

Complex setup today for sure. Prepared myself for the chance of some daytime severe weather but it is looking more and more like a night time event. I guess I knew that all along, just hoping things would change for the better.

Also as the day develops the focus of potential activity is moving North and a bit west from me. I would say the area around Southern lake Michigan including IN, IL and MI has the best chance for severe this evening. From my location in Columbus OH a chase into a potential nightime event is not warranted.

I will see how the days heating goes and how far north the warm air from the south can get. But... in general I am not hopeful for a chaseable event today.

These short days really make chasing dificult.



--
Tom Hanlon

 

[nickgrillo]

Surface obs currently showing surface Tds into the 55-64F across IL, with the 50F isodrosotherm slowly pushing towards WI as of 16z. These observations are in complete agreement on NAMs solution of moisture -- with the 60F isodrosotherm up into Springfield at 18z -- where it's currently 59F at 16z. Surface-based instability is also increasing across the region... Mesoanalysis shows sbCAPE 500-1000J/KG as of 16z across eastern MO/southern IL and slowly increasing as boundary layer deepens/moistens. NAM shows the trough taking on a significant negative-tilt as it pushes through the region around sunset and then pushing through the great lakes by latenight/early morning. Assuming storms can become rooted in boundary layer across northern IL/southern WI near the warm front (which shouod become more defined by mid-afternoon) and can sustain themselves and feed off surface-layer parcels through the night... Low-level shear will be highly supportive of tornadogenesis. I would say the chance for a few sustained surface-based supercells afterdark is pretty good... With the greatest chance for isolated tornadoes over northern IL and then into southern WI. Further northeast into MI... If we can get a surface-based storm in the 6z-12z timeframe - the threat for tornadoes and very large hail remain likely. Assuming the boundary layer can remain nearly well-mixed due to the deepening surface low would further enhance any potential across MI... Otherwise, large hail would be main threat.

 

[J West]

I wasn't ready for this when I looked at the MKX page a few minutes ago:

THUNDERSTORMS ARE LIKELY TONIGHT. THERE IS A SLIGHT CHANCE THAT
SOME OF THESE THUNDERSTORMS MAY BECOME SEVERE. THE MAIN SEVERE
WEATHER RISKS WILL BE LARGE HAIL AND DAMAGING WIND GUSTS. AN
ISOLATED TORNADO CAN NOT BE RULED OUT.

:shock:

I couldn't have paid the SPC for a 5% 'nader risk for most of the summer, but now I get it on the 8th of November?! Deer hunting is 2 weeks away and I might get a tube tonight?

From the info here, and the quick poking around I just did, it seems like Nothern IL and Southern WI are good for a show later tonight, so I guess we'll see what sundown brings.

 

[Robert Dewey]

I really think the heart of this event will be late this evening/tonight through tomorrow morning...

12Z NAM continues to show a combination of 0-1KM CAPE of nearly 1000J/KG and 0-1KM helicity of 400-500M2/S2 overlapped between 12Z and 15Z tomorrow morning over portions of lower MI, which is concerning... The NAM also shows a relatively strong inversion from 950MB to 850MB, which could be the event killer in terms of damaging winds and tornadoes.

There's just something about a 55-60F BL temperature with a strong inversion that has me second guessing any severe weather threats, but with the parameters involved, I definitely be watching.

 

[nickgrillo]

I really think the heart of this event will be late this evening/tonight through tomorrow morning...

12Z NAM continues to show a combination of 0-1KM CAPE of nearly 1000J/KG and 0-1KM helicity of 400-500M2/S2 overlapped between 12Z and 15Z tomorrow morning over portions of lower MI, which is concerning... The NAM also shows a relatively strong inversion from 950MB to 850MB, which could be the event killer in terms of damaging winds and tornadoes.

There's just something about a 55-60F BL temperature with a strong inversion that has me second guessing any severe weather threats, but with the parameters involved, I definitely be watching.

Yeah, it's concerning... Just hoping the strong surface low and weak WAA can keep the boundary layer from decoupling and keep it semi well-mixed through sunset (so surface-based severe storms can occur across northern IL/southern WI). If this can occur, and storms can feed off surface parcels (and not become rooted above the 850mb inversion) then obviously tornadoes and damaging winds will be a very good threat as frontogenesis occurs across the great lakes area as the massively neg-tilted shortwave trough approaches around 0z.