05/07/10 FCST: IL/IN/OH/KY

[Jesse Risley]

Friday, May 7th has the potential to be a significant severe weather outbreak somewhere in the Great Lakes region should the current GFS and NAM forecast models verify. A deepening surface low is progged to eject out of the lee of the southern Rockies, becoming centered over the Great Lakes region by 12z Saturday at 992 mb.

Taking a look at the incoming dynamics for Friday’s setup (looking at some specifics from THUR due to the fact that the NAM isn’t out beyond 84 hrs attm), a strong upper level jet streak will eject northeastward as the low pressure system advances towards the Great Lakes region. Strong upper level dynamics will be juxtaposed with a strong LLJ at 850 mb (40-50 kt per the 12z GFS / 30-40 kt per the ECMWF), though the GFS has a similar speed on the LLJ, albeit placed further SW at 00z on Thursday. The enhanced LLJ will allow for more robust moisture advection in advance of this stolid system. These dynamics should correlate to produce effective bulk shear values on the order of 50-70 kts, along with quixotic SRH values on the order 350-450 m2**s2 at 0-1 km (450 – 600 m2**s2 at 0-3 km).

For a more detailed analysis with graphics, a full write-up is available at Convective Addiction.

 

[Dave Marshall]

I'm eager to get a good look at it in the NAM tomorrow morning, as the GFS has been trending up and down, as it's been prone to doing the last few weeks. It looked like a mid-south event again, not unlike this past weekend, then the GFS brought the low much further north across northern IN, southern MI, and into Ontario yesterday. The 06z run this morning in particular looked like a significant outbreak in Ohio. It's since calmed down again.

The 18z runs did show good cohesion up to 06z Friday morning, so I'm hoping it will keep that cohesion (and move the event back north) with subsequent runs. I will say that despite good turning with height and promising wind fields, even on its best run, the thermodynamic environment looked rather sloppy. We can hope it will perk up, but it was hinting at a considerable moisture plume and lots of morning clouds. If thats the case, I'd expect to see a whopper of a squall line given the current scenario.

 

[Chip Redmond]

As mentioned above, will examine the analysis of NAM tomorrow when it gets into the window. Looking at the 12 and 0z runs, it seems like a crapvection event, common in this region it seems when the temp and dew get respectable for severe weather. However, it is finally something to watch/perhaps get excited over a reasonable chasing terrain. Definitely wouldn't mind a good lower Great Lakes chase after taking a pass at all the past jazz the previous two weeks.


Chip

 

[Chris Hayes]

Well, looking at the latest NAM run it appears as if there's still a decent shot at severe weather on Friday, especially over Ohio. MLCAPE of 1500-2000 along with off the charts 3km helicity of 150-450, and 3km EHI peaking at over 5 seem to be painting a pretty good picture for severe weather Friday evening.

 

[Dave Marshall]

There's good model agreement here. I don't trust instability estimates 5 days out one bit, but timing and track of the low, as well as forecast high temps and dew points are all pretty similar between the NAM and GFS. I'd like to see the low move about another 100 miles north, just to get northern Ohio firmly into the warm sector. Roads in southern Ohio, south and east of I-71 are crappy for chasing.

The forecast hodographs look *very* good, especially before 00z. My only concern is that the forcing may be a bit too far to the west to get a good maximum heating event. The 12z NAM run doesn't break the cap at all really, at least not until after 00z on the 8th which is out of it's forecast window right now. Maybe the 18z run will shed some light on it.

One way or another, this looks like it could be a dandy, and the fact that it's only the first week of May and we're already seeing regular severe events up here gives me a lot of hope for a good season locally.

EDIT: Ugh, well it took my advice and pushed the low further north. It also slowed it down considerably. Here's hoping it doesn't play out like that, or I'm pretty much out of the game.

 

[Mike Kovalchick]

Per Thursday 12Z NAM at 21Z Friday, NW Ohio looks good for chasing.

For example, near Lima, Ohio at 21Z:

Surface CAPE 2000+
EHI(0-3) 3+
0-1 SRM 450 at the Warm Front, 100 South
LCL 750 meters
Bulk Shear 50+
See attached HODO:

(Note: The 12Z GFS scenario isn't nearly so nice.)

Forecast reflectivity products suggest a MCS in Michigan along the 850 mb Warm front (which should originate from the convection that fires this evening near the Kansas/Nebraska border) with convection firing in a linear fashion along the cold front in Indiana. A lone supercell printed out in front of the squall line near Lima, Ohio.

I assume an outflow boundary will sink South from the MCS. I plan on targeting just to the North of where it becomes stationary and starts to retreat. (Low or no surface based instability was shown at the Warm front and to the North.)

Messy overnight convection could shift everything North/South or just plan out ruin the setup completely. Won't have to make a chase call on until noon since I live only a couple of hours to the North. In this case, the chase corridor is rather narrow as the storms will quickly move towards the population center around Toldeo/Lake Erie.

Overall, nice to have a decent setup close to home!

 

[Mike Smith]

I just looked at SPC's 1730Z outlook, www.spc.noaa.gov/products/outlook/day2otlk.html , and given the 45% probabilities, I don't understand why it is not "moderate" risk in that area.

Seems SPC has been awfully coy about moderate risks this season.

The turning and instability both seem sufficient for a concentrated area of severe weather and there are decent dynamics. I believe a "moderate" risk is warranted.

 

[Chip Redmond]

Looked and thought the same thing. Oh well, it doesn't bother me.

Right now best instability should be from C-bus to Dayton. Hodographs in that region, as SPC points out are good right turning with height. However, the only problem I have is that there could be alot of morning convection that may take a while to move through and bring cloud cover. Should things clear out early and several clusters move through, there could be some nice boundaries for storms to latch onto later in the day. Will wait and make a final decision in the morning but I am liking the Dayton area and north.

Target: Vandailia, OH


Chip

 

[Kevin Cramer]

I just looked at SPC's 1730Z outlook, www.spc.noaa.gov/products/outlook/day2otlk.html , and given the 45% probabilities, I don't understand why it is not "moderate" risk in that area.

Seems SPC has been awfully coy about moderate risks this season.

I'm not sure if you've seen it but this would explain why: http://www.spc.noaa.gov/misc/SPC_probotlk_info.html It would have to be a significant area to be a moderate.

Being about 15 minutes from Lima, I'm keeping a close eye on how things are shaping up (but unfortunately don't have awesome forecasting skills yet, so thanks to everyone who has commented so far in this thread).

 

[Mike Smith]

I'm not sure if you've seen it but this would explain why: http://www.spc.noaa.gov/misc/SPC_probotlk_info.html It would have to be a significant area to be a medium.

The way I read that table 45% (hatched or unhatched) = moderate risk if it pertains to wind. Maybe one of our SPC gurus can chime in.

I MISREAD THE DAY ONE TABLE FOR THE DAY TWO TABLE AND WITHDRAW THE ABOVE COMMENT.

That said, the difference makes no sense to me: Why is a 45% probability of wind a "moderate" risk on day 1 and a "slight" risk on day 2? The "risk" to the public is the same.

 

[Kevin Cramer]

The way I read that table 45% (hatched or unhatched) = moderate risk if it pertains to wind. Maybe one of our SPC gurus can chime in.

You gotta look at the Day 2 table

 

[Mike Kovalchick]

Looking at the HPC model preference discussion:

http://www.hpc.ncep.noaa.gov/discussions/pmdhmd.html

Looks like they really don't like the GFS/NAM solution for tomorrow.

GFS moves things through too fast..NAM little too slow.

 

[Mike Smith]

Kevin,

You are correct.

If you will look, you will see I had already withdrawn the comment when you posted yours.

Mike

 

[Dave Gore]

I like the chances of possible tornado development in any of the pre frontal storms that can get going while helicity still remains relatively high in west central and northwestern Ohio. I know that instability will be higher south, but shear will be better the farther north you go. Hopefully the warm front can stick around long enough to add to the environment, and we can see some supercells tomorrow.

Anywhere from Lima north to Findlay, and south to Dayton looks good, as does points east towards Marysville, Marion, and Columbus.

Should be a fun day....

 

[Dave Marshall]

I've been going off the NAM most of the week, and hoping it would turn out to just be a bit slow. It would appear thats the case, and that makes me rather optimistic about the scenario tomorrow. The GFS seems to be completely ignoring any vorticity/helicity associated with the low tracking across northern Ohio, so I've mostly been ignoring it's assessment of the kinematic environment. It's instability forecast has in the last two runs started to come more in line with the NAM, which is cause for even more optimism.

I don't see the potential for too much early morning convection occurring south of Akron, though given the presence of the EML, at least some cloud cover is a pretty fair bet. I would point out though, some good early morning convection would certainly help bolster the marginal dewps in the region, so long as the cloud shield broke by about noon. In that case, the similarities to May 31st, 1985 would start to be a little eerie.

Here's hoping that the fun happens north of I-70, as the area south of that can be a real bear to chase in. Roads tend to be sparse, and the terrain is rough and heavily forested (really, anything south and east of I-71 can be described that way).

My initial target will be Columbus, and I hope to be in the area no later than 16z. Looks like this one should let me chase all the way home by 1am.

EDIT: I think PA could be safely added to the topic. It would appear that the event is likely to go on well into the night, carrying activity into the I-79 corridor while dynamics for tornadoes and high wind will still be present.