8/8/07: FCST: GREAT LAKES/NY/NEW ENGLAND (DERECHO/MCS)

[HAltschule]

The weather parameters and models seem to be suggesting a rare overnight MCS will move across New York State and Western New England Tuesday night and early Wednesday morning. All of the different models including the MM5/NAM/WRF/GFS show the potent shortwave plowing across NYS with excellent wind shear on the order of 30-50 knots. LI's will be between -1 and -3 and CAPE values should be between 500-1000 J/KG. The SUNY Stony Brook MM5 shows a nice broken, linear line of severe thunderstorms moving into Eastern NY around 5-8am Wednesday. The 6z NAM run forecast soundings suggest that winds of 50-60 knots will be present from 400mb all the way down to 950mb. 0-3km Helicity forecasts are 491 with 0-1km helicity of 379. Impressive wind shear and Bulk shear will not be lacking.

The only thing that may hinder the development of a Derecho would be the time of night and the lack of strong instability at the surface. I am concerned that the storms will not be surface-based and if this is the case, it will cut down on the wind damage/derecho potential. IF we can manage to hang on to more surface instability/surface based storms, then a widespread wind damage event appears likely for much of NYS and Western New England. The 12z, 18z and 00z models will be interesting to see later today.

 

[Andrew Ryan]

When you say much of NY, are you including the NYC metro area under the threat of the derecho/mcs?

Thanks,
Andrew

 

[HAltschule]

No. I'm thinking the main activity will be between Poughkeepsie up through Lake Placid.

 

[Dustin Wilcox]

I would consider the possibility of including the plains States in the title on Wednesday once again as well, the last couple of days have been let downs in terms of significant severe weather, and while Wednesday may be no different, I think there is the possibility for at least some severe weather in localized areas. While the numerous boundaries in place and left over convection debris will make forecasting difficult, the NAM has pointed towards favorable conditions for severe weather setting up across Extreme SE NE and SW IA maybe even NE KS and NW MO for the last couple of runs. If clearing can be realized instability will certainly be extreme, per the 0Z run a 35kt 500mb wave works into the area during the early evening. Effective shear values approach 40kts and Helicity values creep up enough during the evening to allow EHI's of 5+ given the high CAPE values. The NAM places the area on the nose of a 25kt LLJ and points towards the possibility of slightly cooler midlevels. While certainly not expecting a whole lot but more of the heavy rain as experienced the last couple of days, IMO with the possibility of extreme instability and numerous boundaries in the area its at least worth monitoring for those relatively close.

 

[Dustin Wilcox]

Appears the models may not have been to far off, substantial clearing has taken place in the SE NE area and CAPE is approaching the Extreme Category just south of the boarder, a decent 35kt H5 wave is over the area, really things are lining up just as it appeared they would last night, SPC has new MD and upgraded to 5% in latest outlook, still primarilly a heavy rain threat but worth monitoring.

 

[Mike Hollingshead]

Saw the md and was pondering heading down there. Glancing around at a few things and noticed the lovely -2 to -3c at 500mb. Screw that. I'm still waiting to see something worth a darn in that stuff. The other day it was painful to see updrafts trying and trying, then they seem to be taking off, but fuz out quite a ways up there...surely thanks to the warm mid-levels. Shear is pretty crappy as well. All in all it doesn't look any better than the 6th did to me, and is in some ways pretty similar with the boundary orientations. The spin you can see with that low on the sbcape loop from mesoanalysis is different though and has me thinking something could go earlier than it was able to on the 6th. Still, the 35knots at 500mb and looking to lessen from there, combined with the warm mid-levels, pretty weak low level flow....I ask myself why I'm so concerned about missing anything. Sigh. Will probably drop south no matter what I see that says stay home.

Yeah crap, something is going to pop pretty soon in se NE by the looks of the satellite loop. I'd prefer to be out west by Hastings, but am a bit late for that I think. May go to Nebraska City and shoot for the other stuff looking to maybe pop east of there(Hastings stuff).

Dustin...is I80 from Omaha to Lincoln still closed from that semi tipping over? That would pretty much dictate if I go to Lincoln or Nebraska City. Sucks there is no Altell data from Council Bluffs till Nebraska City too. Plus stupid traffic this time of day. Man I hate chasing around this local area.

 

[Dustin Wilcox]

Dustin...is I80 from Omaha to Lincoln still closed from that semi tipping over? That would pretty much dictate if I go to Lincoln or Nebraska City.

Last I heard it was but that was about 1 hour ago. I share many similar concerns as you do that are telling me to stay home and enjoy the wonderful weather , obviously the warm air aloft, as well as the fact that the core of the 500mb wave is pushing to the East of the area and looks to lessen from here on out, but much like you I will probably drop at least a little south. I'm thinking you may want to avoid I-80 even if it is reopend as I am sure with all the trucks backed up it will still be a mess, I'll probably just drop south on hwy 77 from fremont to Lincoln and use hwy 2 should I need to get E, I'll give it a little while and see what can happen, I figure at least if anything forms it will be moving this way.

 

[Mike Hollingshead]

Hmm, couple new returns north of Beatrice. Guess I'm heading to Nebraska City.