Radar Reflectivity: March 1, 2017 Severe Weather Event

March 1, 2017 Severe Weather Event

Strong linear storms, sparked by an incoming cold front, swept across most of the eastern united states. There was also strong forcing along the impending cold front, as shown in figure 1. Due to the very warm temperatures prior to the cold front with steep mid-level lapse rates and some wind shear, that encouraged the storms to become severe. However, the Georgia area had enough instability for convective development which gave way to the watches and warnings which were issued throughout the day from 11:50 AM to about 9:00 PM, as you can see in figure 2. Strong winds downed many trees and power lines, leaving roughly 32,000 people without power. Meanwhile, further north, the great smoky mountains national park, straddling Tennessee and North Carolina, closed all roads due to the high wind danger. Many reports of hail were also recorded and even one brief tornado in northern Georgia. The QLCS (quasi-linear convective system) tornado had 90 MPH winds, the EF-1 tornado touched down near Chatsworth, GA, tracking three miles west of Chatsworth. As you can see in figure 3, the cell to the northeast of the red point (Chatsworth, GA) seems to be the one from which produced a tornado. Unfortunately, the closest radar, KHTC in Hunstville/Hytop, AL, was down due to the power outages thus the next closest radar was used, KFFC in Atlanta, GA. The NWS (national weather service), from KFFC, provided figure 4 which shows the storm when it produced the EF-1 tornado over Chatsworth, GA at about 4:30 PM. This system also produced up to golfball sized hail and peeled back roofs. However, as the system continued to move southeast into central Georgia, the storms weakened substantially. Nonetheless, before dying out, this system produced roughly five dozen tornadoes, over 600 high wind reports, and over 100 large hail reports as it tore through parts of the Midwest, South and East United Stated from February 28 to March 1, 2017, making it the largest severe weather outbreak since late spring 2011.

Figure 1

Figure 2

Figure 3

Figure 4

Velocity Radar: November 5, 2017 KBUF

November 6, 2017—Buffalo, NY

A storm system moved through the area of Buffalo, New York on November 6, 2017 between 0029Z and 0200Z. A cold front was prominent near Saint Catharines, Ontario, Canada to Erie, Pennsylvania and crossed the region from west to east between 0100Z and sunrise. In advance of this cold front, there was moderately strong south-southwest low-level flow with surface gusts up to 30 MPH (fig.1). In radar imagery from GIF1 and GIF2, there seems to be a mesoscale convective vortex (MCV) present over northwest Pennsylvania. Towards the beginning of GIF1, there was actually an EF-1 tornado reported at 23:22 UTC (6:05 PM EST) by the National Weather Service (NWS) storm survey team, just four miles southwest of the town of Erie in the Millcreek Township. The tornado track was roughly 2.4 miles in length by 100 yards in width, with maximum winds estimated to be 90 MPH. Fortunately, no one was killed or injured during this event that brought nearly three inches of rain to the area. However, there was not really any indication on radar that there was a tornado. Next to the green inbound winds, there was no red outbound winds near the area, instead there was purple haze, indicating that the radar was unable to determine the wind’s velocity, which is referred to as range folding (RF) or velocity folding. Depending on the radar’s operation mode and PRF (pulse repetition frequency), the range folded data may occasionally obscure large portions of the radar’s image. As you may notice in GIF3, there seems to be a decent amount of range folding near the southern end of this storm system. At any rate, another reason I would not have thought there was a tornado just from radar alone was due to the lack of intensity of the inbound winds. Generally, intense circulations with diameter of one mile or less are tornadic, while large couplets are associated with mesocyclones. There is no specific value of diameter and magnitude that differentiates between the two due to the variety of circulations that may occur and due to gates having a variety of volumes and height, which depend on range and beam width. However, in this case, I suspect that the radar probably overshot the tornado circulation completely, given that the tornado occurred roughly 8,351 feet from the radar.

Figure 1

GIF 1

GIF 2

Figure 2

GIF 3