7/18/06 FCST: NY/NJ/MA/Northeast

[HAltschule]

The stage is set once again for an explosive day thunderstorm-wise in the U.S. Today the Northeast is under the gun. Temperatures are forecast to be in the Upper 80's to Mid 90's across most of New York and Dew Points will be near 70 again. CAPE values are forecast to be in the 2500-4000 J/KG range this afternoon and a front is sliding south into the region. Latest analysis shows 45-55kts of effective shear to support organized thunderstorms and supercells. There is a mid level cap that can either bust the forecast or cause it to become highly severe. With a trigger moving into the area and slightly lowering heights, I would expect the cap to break this afternoon across Upstate NY and New England. This is why I think the explosive Severe Thunderstorms will occur. Also, any thunderstorm that forms will be able to tap the extreme CAPE that is present enhancing the downburst wind and large hail potential. (Some local NWSFO's are mentioning a very severe outbreak with 75mph+ winds and Golf Ball Hail or larger with the cells). They should also form into bows and lines so wind damage should be enhanced. SPC IS NOW CONSIDERING AN UPGRADE TO MODERATE RISK FOR MUCH OF THE NORTHEAST LATER THIS MORNING.

There is one red flag that has me concerned...The models do not really develop much of any convection this afternoon (ETA/GFS/MM5). This is concerning becuase it is more difficult to break the cap here in the NE than it is in the Plains. It takes a lot of ingredients to come together whereas it happens more quickly in the Central US. So, while I am not sure whether we will have a widespread event this afternoon based on the Models, it seems that widely scattered storms should fire at the very least. It will be interesting to see if the models are right or wrong. If they are underplaying the development, then the Northeast is in for one hell of a severe weather day.

 

[HAltschule]

Welcome to the Plains of the Northeast!! Numerous Supercells are underway over Maine and New Hampshire will 3 severe cells in NE Pennsylvania. The storms in PA have tops of 35-40k and 1.00-1.75" hail with them. More impressively, the supercells in Maine...particularly the cell just East of Bangor, has a hail size of 3.00-3.75"!!!! WOW. This kind of hail rarely happens in the Northeast...let alone Northeastern Maine.

On a separate note...the combination of a pre-frontal trof, wind shift and a cap has limited convection in New York State, Southern VT & MA. When we get a west wind here in New York it just kills the chances of convection. So we'll have to see if the cpnvective temp. alone can generate TRW's. Southeastern NY near Poughkeepsie and into the White Plains and Northern NJ areas look under the gun for some big storms in the next 2-5 hours.

EDIT: At 2:33pm EDT, the cells in Northeastern PA have had a hail spike to 2.25".

 

[Dave Kaplow]

I'm sitting in New Haven where there's 3500 CAPE, with an LI of -10! Those are pretty high numbers for this area... But shear is weak, and backing with height. Worse, I was outside a little while ago and it looked capped, capped, capped. When you have dewpoints in the mid 70s and not a cloud in the sky other than a wisp of high cirrus, it's not a good sign. But maybe if enough convection gets going upstream it'll roll right on through. I hope so, we need the relief from the heat.

 

[HAltschule]

It feels like a Plains type Bust day. Severe convection in NE PA 2 hours ago has fizzled to a few showers. TCU keep falling apart in the Hudson Valley and Upstate NY. Despite LI's in the -5 to -10, CAPE of 1000-2000 J/KG and a 30-40kt shear, we can't buy a strong storm. Special 18z sounding at OKX on Long Island shows a 3.5 degree Cap!! Here's hoping that something happens to erode that cap in the next few hours.