Tornado Outbreak: April 12/13, 2020

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Synopsis:

A deepening low pressure system tracked across the Midwest US on Easter Sunday (April 12). At the same time a 250mb jet streak was located across the Southern Coast states from Texas to North Carolina. Winds in this layer were from the west-southwest, while winds in the 850mb layer were from the south-southwest. Dewpoints in the deep south surpassed 70 degrees with the passage of a warm front moving from the Gulf Coast to the Tennessee Valley. The environment was extremeley conductive for tornadoes from Louisiana to Georgia. Throughout the day on April 12, the low pressure continued to deepen as it tracked across the midwestern states. A strong cold front was trailing across the deep south, with severe weather ahead. The warm sector reached as far inland as Kentucky. The 250mb jet streak remained potent into the morning hours of April 13. 850mb winds reached 50-70 knots out of the SSW ahead of the cold front. Effective shear was greater than 40 knots. Signifigant Tornado Paramater (mesure of the atmosphere's potential to create strong tornadoes) reached 11-12 across the interior LowCounty -off the charts-. By this time a squall line was tracking into an extreme environment. Even though it was 5-8am during the severe weather event in the LowCountry, surface CAPE (Convective Availbale Potential Energy) was approaching 2000 J/kg. Surface winds ahead of the squall line were 20-40mph.

The first mention of potential severe weather in SC came from the Storm Prediction Center on Thursday, April 9. Subsequent outlooked slowly increased the confidence in severe weather until the SPC issued an Enhanced Risk of storms on Saturday. Sunday morning, that risk area was expanded to cover all of the LowCountry and the SPC issued a hatched risk area for tornadoes (10% chance or greater of an EF2+ tornado within 25 miles of a point).

 

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Timeline of Events:

At 3:20 AM EDT, the National Weather Serivce and Storm Prediction Center issued Tornado Watch 117 for the entire LowCountry. This tornado watch would be in effect until 11 AM. At 5 AM the QLCS (Quasi-Linear Convective System) began to approach Allendale and Hampton Counties, while producing 60mph wind gusts and penny sized hail in Georgia.

The first warning of the day was issued at 5:30 AM for Millet, Allendale, Estill, and Hampton SC. This storm also featured an embedded supercell in Hampton County. At 6:13 AM the first damage was reported in the LowCountry, from a likley tornado in Estill. The tornado warning for this storm was issued at 5:55 AM, approximately 10 minutes before the tornado began causing damage in SC. At 6:00 AM another tornado warning was issued for a cell just north of the one passing Estill. This tornado warning covered Allendale and Fairfax. Around 6:10 AM it was becoming evident on radar that a signifigant tornado was developing just south of Estill, SC. At 6:15 AM, a Tornado Debris Signature became visible, indicating a large and destructive tornado was on the ground south of Estill. This tornado led to the issuance of another warning at 6:19 AM for Hampton, Cummings, and Islandton. The tornado had now been observed near hwy 601. Less than five minutes later, a Severe Thunderstorm Warning was issued for Hampton, Jasper, Beaufort, Colleton, and Dorchester Counties (60mph winds and penny sized hail). Around 6:30 AM the Estill-Varnville tornado reached its peak intensity. The tornado was tracking ENE towards Interstate 95 and Walterboro. At 6:39 AM a tornado warning was issued for Central Colleton County and Walterboro. The large tornado was the only tornado on the ground in the LowCountry, as the tornado warning to the north was cancelled.

At 6:50 AM the tornado appeared to have weakened, but was still on the ground in Colleton County. Around this time, the tornado crossed I-95 and entered Walterboro. At 6:53 AM, a Severe Thunderstorm Warning was issued for the remaineder of the LowCountry (Berkeley, Charleston, and remaining portions of Dorchester, Colleton, and Beaufort Counties). This warning was more signifigant, advising that 70mph wind gusts were possible. At 6:55 AM the tornado began crossing through the center of Walterboro and it produced large amounts of damage. The National Weather Service in Charleston issued its first ever Tornado Emergency due to the extreme threat in Walterboro. The tornado then followed hwy 17A towards Cottageville. At 7:02 AM a tornado warning was issued for Cottageville, Ridgeville, and Knightsville. The tornado produced damage along its track to the east of Cottageville. Once the supercell reached Cottageville, the radar indicated rotation signifigantly weakened. The tornado lifted off the ground from 7:10 AM to 7:25 AM. During this time the supercell crossed Summerville and Knightsville, producing wind damage and incredible lightning density.

At 7:30 AM the tornado couplet began to tighten on radar as the circulation crossed Interstate 26 nearJedburg Rd. The southern flank of the cell began to bow out across Goose Creek, Ladson, and North Charleston at 7:35 AM. Winds greater than 70mph likely occured at some point. By this time, Moncks Corner was already under a tornado warning (issued at 7:25 AM). At 7:45 AM, the tornado crossed just south of downtown Moncks Corner and began to create signifigant damage to homes. At 7:50 AM, the tornado crossed through neighborhoods as it hit its second peak. The tornado then crossed the Tail Race Canal just south of 17 A, and continued to create damage on hwy 402. At 7:54 AM, a tornado warning was issued for the remainder of the cell's track through the LowCountry (Jamestown). The tornado, although weaker now, continued to created damage across Francis Marion National Forest. Finally, around 8:00 AM the tornado crossed into Georgetown County and left the LowCountry. This circulation would unfortunatly create more damage in Georgetown and Murrells Inlet.

However, at 8:00 AM, a tornado warning was issued for a similar embedded circulation over Edisto Beach. This would become a confirmed tornado that tracked down the length of Edisto Beach from 8:10 AM to 8:20 AM. Considerable damage was reported on the island, and at 8:27 AM a tornado warning was isued for Seabrook, Kiawah, and Folly Islands. However, the tornado lifted over Seabrook Island and the circulation moved offshore.

Summary:

Since this severe weather event is less than 24 hours old, many storm reports are still coming in, the ratings of the tornadoes are unknown, and some details still are not certain. In the coming days I will have a new post with signifigant mesoscale details, tornado information, and storm reports.

This event was well forecasted by the SPC and NWS, but even so at least 5 people in the LowCountry have died from these storms. It was dark for the Estill-Varnville-Walterboro tornado, and most people were likely asleep.

This outbreak of tornadoes is the most impactful in the LowCountry since March 15, 2008. Early indications show an EF-4 tornado may have touched downm which would be unprecidented. The morning of April 13, 2020 is one for the record books!

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