Hail, gusty winds, and torrential rain lashed the Two Virginias this past Saturday. What initially looked like a relatively benign day from a severe weather perspective quickly turned much more active as the early afternoon rolled around.
The first couple of thunderstorms began to appear around Tazewell County around 2 PM. These cells tracked northwestward throughout the afternoon, producing quarter sized hail in Montcalm in Mercer County, and pea sized hail elsewhere as they tracked through Summers County. These cells eventually weakened in Greenbrier County as they moved into a colder environment.
As those thunderstorms rolled on, other storms formed and dropped hail in McDowell and Monroe Counties. Pea sized hail was reported in Union and quarter sized hail was reported elsewhere in Monroe. Maury Johnson, a Monroe County resident, emailed WVVA Weather and told us that it was the "worst hail storm I have seen in 20 years".
Later on in the afternoon around 5 PM, a larger line of storms developed in Western McDowell and Tazewell counties. This intense line of storms spent the evening barreling through the entire area, finally exiting Monroe and Greenbrier County around 9:30 PM. This line of storms produced half-dollar sized hail in Summers County and downed trees in Greenbrier County.
The torrential rainfall caused minor flooding in some areas, especially along the border of Summers and Monroe County. Flood warnings are still in affect for Indian Creek in that area.
A massive thank you goes out to everybody that shared storm reports, information, and pictures! Your reports help us meteorologists out immensely and we appreciate the support.
So what caused the severe weather? A relatively small but potent upper level low pressure system sparked the stormy conditions yesterday. An upper level low (ULL) is an upper level disturbance that is typically cut off from the jet stream, which is where most upper level disturbances are located. Thus, ULLs are notoriously hard to predict and usually feature a couple of surprises. Yesterday's surprise was producing an environment that was unusually supportive of hail-bearing storms.
Typically, a severe weather set-up this time of year in the Two Virginias requires a warm, sunny morning and afternoon and temperatures in at least the 70s. This "destabilizes" the atmosphere. An unstable environment (an environment with warm temperatures at the surface and colder temperatures aloft) is an essential ingredient in thunderstorms. In contrast, yesterday featured a stubborn cloud deck and temperatures in the mid 60s, an environment typically too stable for thunderstorms.
Yesterday was different. Another defining feature of upper level lows are very cold temperatures aloft, and yesterday's environment featured that. The mild temperatures at the surfaced paired with the frigid temperatures aloft provided enough instability, thunderstorms were able to develop and thrive. Furthermore, because it was so cold in the upper atmosphere, hail had a much easier time forming than in typical thunderstorms.
The last ingredient that made the storms so potent was wind shear, or how wind speed and direction change with elevation. Yesterday, winds at the surface were blowing from the east, while winds 5 miles up in the atmosphere were blowing from the northwest! This change in direction provided enough wind shear to turn some thunderstorms into "supercells", which feature long lasting updrafts feeding into the storm. When you have long lasting updrafts, you can grow hail into half-dollar sized stones and even larger, and that was realized in Mercer and Summers County yesterday.
Yesterday was a unique event that impacted the entire region. After such a quiet spring severe weather-wise, it served as an important reminder that we are in the thick of severe weather season. Keep up with the Precision Weather Team and we'll keep you updated as the severe weather season unfolds.