Quincy

Cap winning out via TOP 00z sounding. Limited instability/poor low-level thermal profile at OAX:

Not surprised that the SPC toned up the wording a bit for day 2. Still some mixed signals, but a few signs are there for a potentially enhanced severe weather threat. Both the NAM and GFS show enlarged hodographs and considerable shear, including in the low levels, from far eastern Nebraska into west-central/southwestern Iowa, coinciding with strong instability. Some red flags/uncertainties arise from the high PW values forecast, some warming in the mid-levels, attributing to initially modest mid-level lapse rates and storm mode. While the 4km NAM is actually late with renewed storm development, the GFS shows more of a mass of convection developing over Iowa. I would suspect that the storm model will be fairly messy and if any semi-discrete or discrete storms do fire, they would be HP and merge relatively quickly. Nonetheless, a tornado threat may exist, especially if any storms can fire in the vicinity of strong low-level shear, perhaps near any lingering outflow boundaries from early-day convection.

A series of supercell thunderstorms moved through central and eastern Massachusetts this afternoon. Some of the storms prompted tornado warnings and there were multiple significant severe weather reports as a result. Some of the thunderstorms originated as far west as eastern New York and later reached peak intensity as they moved into portions of central and southern New England. Even the coastal community of Boston was hit with some regionally impressive severe weather. The prelude to these afternoon storms actually came in the form of early-day severe storms this morning. A line of severe wind-producing thunderstorms affected portions of southeastern Connecticut, Rhode Island and Cape Cod. An area that does not often see severe weather, especially during the morning hours. Once those storms moved out, there was some clearing, which led to plenty of daytime heating to fuel another round of thunderstorms. By early afternoon, there was an area of moderate to strong instability developing across the eastern half of Massachusetts, coinciding with seasonably strong wind shear. The mesoanalysis showed a corridor of moderate buoyancy coinciding with more than adequate wind shear for supercell thunderstorms. Bulk wind shear was in excess of 50 knots across the region. With clusters of thunderstorms ongoing across portions of the area, the storm mode was going to be critical in the evolution of the event. If storms merged, lines would form, suggesting more of a damaging wind threat. If the storm mode was messy, the inflow region and overall environment could be disrupted, resulting in mainly sub-severe storms. However, if any storm could remain discrete and from on the southeastern fringe of the activity, in order to take better advantage of stronger instability, then things would become a bit more interesting. Two thunderstorms began to split in northern Worcester County shortly before 2 p.m. The northern most storm tracked east-northeast into far southern New Hampshire. This storm merged with surrounding storms and did not strengthen much. The southern storm took a bit of a right turn and continued in a generally eastward direction. This cell moved through northern Worcester County, organizing quickly into a robust supercell. Velocity and hail signatures increased, indicating the likelihood of 1-2″ diameter hail. This storm further organized with rotation becoming more focused. A hook was noted on radar and a Tornado Warning was issued. The storm continued into northern Middlesex County, dropping more large to significant hail, but the velocity signature was marginal at best for tornadic development. The main story was hail. Speaking of hail, a second supercell developed on in west-central Worcester County a short time later. This storm was semi-discrete, but remained that way for quite some time. It also dropped large hail and continued for two more hours, moving right through downtown Boston. Large hail was reported throughout portions of the city and surrounding areas. Overall, there were numerous reports of golf ball or larger hail across Massachusetts, with at least three confirmed reports of hail at least two inches in diameter. A few additional discrete storms developed later in the afternoon, but earlier storms had overturned the atmosphere a bit. These storms were generally strong to only marginally severe in nature. No tornadoes have been confirmed as of 10:00 p.m. Although there was some localized backing of low-level wind fields, the lack of favorable low level helicity was a limiting factor in the tornado potential. Nonetheless, a fairly uncommon significant hail event affected the eastern half Massachusetts, an area that based on a 1980-2006 average, only reports significant hail once every 6.75 years. This is based on four reports across all of eastern Massachusetts, during the time. While there were four significant hail reports in that 27 year span, there were three such reports this afternoon alone. Keep in mind that the time of record is relatively short, as reports from 2007 to this year were also not included. A look at the 2 p.m. mesoanalysis showing 1000-1500+ J/kg MLCAPE and locally backed near-surface winds in the vicinity of the most robust supercells:

Tomorrow's setup isn't all that much different from today. If anything, somewhat stronger instability, but forcing may be slightly weaker. I'd expect a similar outcome, although the storm mode and motion may be more on the messy side. Same area too, with storms firing over northeastern New Mexico and moving toward/into the Texas panhandle.

Currently have a trio of intense supercells ongoing across the Texas panhandle. All are producing large to very large hail. The storm that passed over Channing dropped baseball sized-hail.

I find it a bit odd that the panhandle watch has <5% probs for 2+ tornadoes. I can't say I expect a bunch, but the environment looks increasingly favorable between AMA and LBB by 00-02z, IF storms can remain discrete. Dew-points are well into the 60s with backing low-level flow and moderate instability. Further north, the storms have already formed a line segment and may only pose a marginally severe hail risk with a higher likelihood of damaging winds.

A bit of a localized, conditional severe risk tomorrow - most notably around the TX/OK panhandles. A subtle vorticity lobe is progged to move from NE NM/SE CO through the southern High Plains with lee surface cyclogenesis late in the day/evening. Although boundary layer dew-points are rather low at the moment, in the mid-40s to mid-50s across the area, southerly flow beneath a retreating warm front should result in modest to moderate instability reaching the TX panhandle by 00z Thursday. Upper level flow is fairly anemic, but 0-6km shear should be sufficient for supercells and backing of low-level winds should result in sizable hodographs by early evening. A rather modest setup, but one that could result in a few robust supercells. I can see an isolated tornado threat developing, assuming moisture return is considerable enough and shear reaches the levels currently forecast. Storms may merge into a small complex into the evening, posing a marginal damaging wind threat eastward across the panhandles. The way this year has gone, marginal/modest setups like this have been fairly common, although the results have generally been below expectations. I'm not an expert on climo for the panhandles, but I would venture to assume this is rather late in the season for a setup this far south?

I thought it was odd given the S to SSE flow ahead of the cold front, strong instability and modest deep layer shear. It wasn't like the setup didn't have at least a marginal tornado threat signal. It wasn't until an MD after the damage that a brief tornado threat was mentioned. We've seen 2% tor probs for weaker signals.

Could see some isolated severe storms on either side of the SD/NE border this afternoon. At least based on mesoanalysis, conditions seem more unstable than most progs. Large to very large hail appears to be the most likely hazard. Tomorrow looks messy (#2015ing) with respect to storm mode/evolution. Perhaps the most probable significant threat will be damaging winds/hail via MCS in the evening. The focus is in SD and areas to the immediate east/southeast.