Getting baseball size chunks of ice to drop out of the sky in New England takes a special kind of storm. That kind of storm blew up over portions of southern New Hampshire and Maine on Sunday.
Not surprisingly, it took a fairly unique environment to produce this giant hail. The most important feature was a remnant plume of elevated mixed layer air that resulted in steep mid level lapse rates across New England. What we mean by this is an unusually steep drop in temperature between about 10,000 and 25,000 feet above our heads. We can quantify this by measuring the temperature difference over certain levels.
Between 700mb and 500mb the lapse rate on the evening Gray, ME weather balloon launch was 7.2 C/km. The Chatham sounding (away from thunderstorms and probably more representative of the pre-storm environment) had a very impressive 7.6 C/km lapse rate. Research by Banacos and Ekster has shown that many significant severe weather events in the northeast occur when an elevated mixed layer is present.
The EML is quite common in the plains – not so common here. With that in place the stage was set for a pretty impressive severe weather event. CAPE on the order of 3,000 j/kg and large CAPE in the hail growth zone (the part of the atmosphere between -10c and -30c) and enough effective wind shear (30 to 35 knots in southern Maine) was enough to give us some hail beasts.
This cross section of the storm from the Gray, ME radar shows the exceptional hail core. 70+ dbz values were up to 27,000 ft AGL and a giant three body scatter spike was present down radial.
Prior to dropping baseballs – radar gave a clear indication that this storm was about to drop some big ice.
On the GYX dual pol products you can see the high reflectivity in the upper left panel (huge TBSS too), while on the upper right you can see the low CC in that hail core. CC values ranged from 0.75 to 0.9 in the lowest part of the hail core along with ZDR (bottom left) well below zero. This is a very solid signature for significant hail – and in this case baseball size hail. Below – you can see the storm at peak intensity at about 20,000 feet above the ground with a giant hail spike accompanied by an 80 dbz pixel!!
Prior to reaching peak strength the storm exhibited very impressive wet hail growth between -20 and -30c. You can see the depressed CC (indicating mixed phase hydrometeors) way above the freezing level – a clear signature for big hail growth. Also present (not shown) was a large ZDR column indicating a tremendous amount of liquid water being lofted by the storm’s updraft.
So that’s the story of the giant Maine hail. Never underestimate a sounding with fat CAPE!