5/31/08 FCST: NY/NJ/PA/MD

[Andrew Ryan]

I cannot believe that no one hasn't started a thread on this event!

After a round of showers and t-storms moves through in the morning, the skies should clear long enough for SBCAPE values of at least 1000 J/Kg, with pockets of 1500-2000. Around 18Z, a 90-kt H3 Jet streak moves into the Northern portion of the atlantic seaboard. Coupled with strong 0-1 km, lowl LCLs, and Tds approaching 70F, a couple of tornadoes are not out of the question. But the main focus will be supercells and mulit-cellular clusters.

Depending on how much breaking we get tomorrow, I would not be surprised if the SPC issues a MDT risk for the mid-atlantic seaboard.

 

[Geoff Manikin]

certainly a setup that bears watching. The question is how much the low level flow will veer during the afternoon. NAM shows a nice veering profile just south of NYC by early afternoon, but it becomes more unidirectional towards later in the day:
http://www.emc.ncep.noaa.gov/mmb/nammeteograms/stations/000190.html
(time increases from right to left along the y-axis)

further south in MD, the low-level flow is progged to badly veer, leading to modest low-level shear:
http://www.emc.ncep.noaa.gov/mmb/nammeteograms/images/724060.cloud.gif

The strong westerly low-level component usually works against much convection firing here in the Delmarva, and that's suggested by the meager model QPF.

The strong deep-layer shear throughout the mid-Atlantic region certainly favors organized svr for the storms that do form.

 

[HAltschule]

Saturday's severe weather setup will be very favorable for wind damage, bow echoes, hail and perhaps a tornado. I also see the potential for a well-organized MCS in Upstate Eastern New York and also one down in Northern/Central New Jersey between 12PM and 5PM. As you guys have mentioned...SBCAPE values of 1000-2000 will be common as the warm front moves north.

It actually looks to me as if there will be 3 rounds of severe weather in the Northeast. Any MCS that forms in Upstate New York around Midday Saturday (see 18z WRF) just may have enough helicity for serious tornadic potential. At 18z Saturday, Albany has a saturated sounding but will be warming with breaks of sun. 18z Saturday forecast sounding in Albany has 0-3km helicities of 438 and 0-1km helicities of 299 along with LCL's near 120 METERS/360 FEET (WHEW!!!). CAPE however is only 200-300 at that time with LI's around -2. Should more breaks and heating occur earlier and closer to the departing warm front then it could get interesting. During the afternoon the helicity values drop tremendously but the 0-6km wind speeds are 35-50 knots. It seems like the best instability will not mesh with the best dynamics...but there will still be enough of each during the afternoon for scattered severe thunderstorms.

I agree that the parts of the Northeast may be upgraded to a Moderate risk of severe storms. I note that SPC has much of NJ and NYC in the hatched area also. It should be an interesting day...and one of those types of days that won't take much to get an even bigger and more severe thunderstorm/tornado outbreak. I will be watching the models closely tonight and tomorrow morning.

PS: Today (Friday) is the 10 year anniversary of the Mechanicville, NY F3 tornado...an event that I will never forget.

 

[HAltschule]

In addition to my last post:

After reviewing 18z NAM soundings, it appears that the area from the Lower Hudson Valley of New York through Northern New Jersey will have the best chance for supercells and isolated tornadoes. 0-3km and 0-1km helicity values of 100-150 are expected around 21z-00z coinciding with CAPE values of 1500-1800 J/KG. Very low LCL's also.

In the Hudson Valley, it is very common for the models to underforecast the southerly flow up the valley so even more turning (veering with height) will likely enhance supercell/tornado potential.

 

[Andrew Ryan]

MDT risk has been issued for most of the NE corridor...

I'm looking to target somewhere around Newburgh, NY tomorrow, where the best 0-1km shear, helicity, and CAPE are. There should be at least 1000 J/Kg of SB CAPE. I get a better hold of the situation in the morning.

 

[Dave Kaplow]

Yep, looks like some interesting possibilities for our neck of the woods. If there's going to be any tornadic activity at all things would have to come together just right, with perfect timing... But if there's just a little bit more instability, forming just a bit more north than what the models are predicting... And if isolated storms develop early enough to take advantage of the relatively backed winds, say shortly after 18z when helicities are progged to be at their highest... It could certainly get interesting for Southern New England.

If I were to chase this, and I'm sure I will in some form or other, I'll likely hang out as long as I can looking at data, and then if no particular area or developing storm calls attention to itself I'll probably head up towards the Berkshires (near where NY/MA/CT all meet), if only because that's an area that seems to be historically favored by supercells and tornados.

I've seen so many of these things look really sweet the night before only to fall apart on the day of the event - for some reason the models just don't seem to handle severe weather as good here in the Northeast as they do in the Plains. But you never know, this could turn out to be The Big One, the major significant tornadic event I've long said the area is overdue for, although to be honest I think that's extremely unlikely. There should at least be a supercell or two, though.

If anyone else is thinking about chasing in the CT area and would like to compare notes and possibly coordinate efforts, send me a PM.

 

[HAltschule]

Dave,

Like you...I am sifting through data and more importnatly...looking for the junk to clear out of all Eastern New York. The models have done a poor job clearing the area in timely fashion.

I am starting to think that the mid to late afteroon might be the better severe weather event once we get the sunshine thats coming from Central NY. Had we experienced the sunshine between 10am-1pm then the tornadic supercells would have erupted at about 1pm. Not out of the question for sure...but certainly not as good as it looked before. Later today may be more of bow echo/broken squall line event more than anything else. I will watch the conditions before I go find an area to target.

PS: Given the high shear in place now over the Albany, NY area...I am watching the stronger convection that seems to be slowly organizing over Utica. Low Cape/High Shear environments can always produce tornadoes. A long shot but we'll see....

 

[HAltschule]

Anyone else notice that the 12z RUC keeps an awful lot of 0-1km and 0-3km helicity and BRN Shear over Dutchess/Ulster/Columbia/Putnam/Westchester and Rockland Counties? Maybe we will still have enough low level shear later this PM for tornadic potential yet? Awaiting SPC's 12:30pm discussion...

 

[Saul Trabal]

Looks like my area of the woods will be affected, eh? I'm at the library, checking the radar off the Weather Channel, and a line of storms seems to be moving into central New Jersey now.

New York City almost always seems to miss getting a tornado, but I never take these storms for granted. I'll keep an eye out and report when/if possible...

 

[Dave Kaplow]

As soon as I got up and looked out the window I knew this wasn't going to be the chase day I had hoped for, at least not in CT. It always seems to happen around here, the models predict great shear which always verifies, but we never get the forecasted instability to go with it. I see that SPC has moved my area out of the 10% tornado risk on the latest outlook, we're now a marginal 2%, and I can't say I'm at all surprised. I agree that if anything is going to happen now it will likely be a late in the day surprise.