Morristown, TN

Weather Forecast Office

Event Summary of the June 21, 2021 Severe Storms

Overview

A strong cold front approached the Tennessee Valley and southern Appalachians during the late afternoon and evening hours of Monday June 21. A warm and humid airmass ahead of the front led to the development of numerous clusters of strong to severe thunderstorms. The main impact from these storms was damaging winds with two dozen reports of wind damage in the form of down trees and power lines, as well as a barn destroyed in Roane County. However, a couple of pockets of hail occurred in northern portions of the region.

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Radar
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Environment

Photos

Storm Damage in Speedwell, TN


Storm Damage in Speedwell (Mike Stanley)	Storm Damage in Speedwell (Mike Stanley)	Storm Damage in Speedwell (Mike Stanley)	Storm Damage in Speedwell (Mike Stanley)

Radar

A severe thunderstorm that developed in Campbell County moved E-NE across Claiborne County between 5:15 and 6 pm. The storm blew down numerous trees and powerlines across the county, and damaged a building near Speedwell. Peak winds measured by radar were around 61 mph just north of Speedwell.

Speedwell, TN Base Reflectivity and Base Velocity

A storm ripped through Anderson County and northern Knox County between 5 and 6 pm EDT. Numerous trees and powerlines were blown down along its path. Wind speeds measured by radar peaked at 74 mph near Corryton.

Northern Knox County Base Reflectivity and Base Velocity

Storm Reports

For a national map and detailed storm report listing, follow this link.

Radar Image

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE MORRISTOWN TN
709 PM EDT WED JUN 23 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0445 PM     TSTM WND DMG     5 WNW WARTBURG          36.12N 84.67W
06/21/2021                   MORGAN             TN   LAW ENFORCEMENT

            A FEW TREES DOWN.

0508 PM     HAIL             3 N TREADWAY            36.46N 83.24W
06/21/2021  M1.50 INCH       HANCOCK            TN   PUBLIC



0509 PM     TSTM WND DMG     2 NNW WARTBURG          36.13N 84.60W
06/21/2021                   MORGAN             TN   LAW ENFORCEMENT

            A FEW TREES DOWN.

0515 PM     TSTM WND DMG     3 SSW ROSEDALE          36.13N 84.37W
06/21/2021                   ANDERSON           TN   LAW ENFORCEMENT

            A FEW TREES DOWN.

0524 PM     TSTM WND DMG     4 WNW TREADWAY          36.43N 83.30W
06/21/2021                   HANCOCK            TN   PUBLIC

            COUPLE TREES DOWN.

0525 PM     TSTM WND DMG     SPEEDWELL               36.46N 83.88W
06/21/2021                   CLAIBORNE          TN   EMERGENCY MNGR

            SCATTERED TO NUMEROUS TREES DOWN THROUGHOUT
            THE COUNTY IN ADDITION TO DOWNED POWERLINES.

0528 PM     TSTM WND DMG     5 W HUNTSVILLE          36.43N 84.58W
06/21/2021                   SCOTT              TN   LAW ENFORCEMENT

            SEVERAL TREES DOWN ACROSS THE SOUTH END OF
            THE COUNTY.

0529 PM     TSTM WND DMG     3 SE CLAIRFIELD         36.51N 83.92W
06/21/2021                   CLAIBORNE          TN   PUBLIC

            FEW TREES DOWN.

0550 PM     TSTM WND DMG     3 NNE HALLS             36.12N 83.92W
06/21/2021                   KNOX               TN   PUBLIC

            NUMEROUS TREES DOWN ACROSS NORTH KNOX
            COUNTY.

0551 PM     TSTM WND DMG     2 ESE HALLS             36.07N 83.90W
06/21/2021                   KNOX               TN   LAW ENFORCEMENT

            A FEW TREES DOWN.

0551 PM     TSTM WND DMG     MOUNT CARMEL            36.56N 82.66W
06/21/2021                   HAWKINS            TN   PUBLIC

            REPORT FROM MPING: 1-INCH TREE LIMBS BROKEN;
            SHINGLES BLOWN OFF.

0607 PM     TSTM WND DMG     2 SW NORRIS LAKE        36.27N 83.94W
06/21/2021                   UNION              TN   LAW ENFORCEMENT

            A FEW TREES DOWN.

0612 PM     TSTM WND DMG     2 NE RUTLEDGE           36.29N 83.50W
06/21/2021                   GRAINGER           TN   LAW ENFORCEMENT

            SEVERE TREES DOWN.

0617 PM     TSTM WND DMG     6 NW HOWARD QUARTER     36.54N 83.48W
06/21/2021                   CLAIBORNE          TN   LAW ENFORCEMENT

            SEVERAL TREES DOWN ACROSS THE COUNTY.

0618 PM     TSTM WND DMG     3 ESE CLAIRFIELD        36.53N 83.91W
06/21/2021                   CLAIBORNE          TN   PUBLIC

            SEVERAL TREES DOWN NEAR THE CLAIRFIELD AREA.

0630 PM     TSTM WND DMG     3 SSE ROSE HILL         36.65N 83.26W
06/21/2021                   LEE                VA   PUBLIC

            A FEW TREES DOWN.

0635 PM     TSTM WND DMG     4 WNW VONORE            35.63N 84.30W
06/21/2021                   MONROE             TN   LAW ENFORCEMENT

            SEVERAL TREES DOWN ACROSS NORTHERN MONROE
            COUNTY.

0706 PM     TSTM WND DMG     2 N MOUNT VERNON        35.44N 84.36W
06/21/2021                   MONROE             TN   PUBLIC

            REPORT FROM MPING: 1-INCH TREE LIMBS BROKEN;
            SHINGLES BLOWN OFF.

0712 PM     TSTM WND DMG     5 N ALCOA               35.86N 83.96W
06/21/2021                   BLOUNT             TN   LAW ENFORCEMENT

            SEVERAL TREES DOWN ACROSS THE COUNTY.

0713 PM     TSTM WND DMG     5 NNW TALASSEE          35.61N 84.10W
06/21/2021                   BLOUNT             TN   LAW ENFORCEMENT

            TREES DOWN ACROSS THE AREA.

0721 PM     TSTM WND DMG     4 NNW WISE              37.03N 82.60W
06/21/2021                   WISE               VA   LAW ENFORCEMENT

            NUMEROUS TREES DOWN ACROSS THE COUNTY.

0735 PM     TSTM WND DMG     ROCKWOOD                35.87N 84.68W
06/21/2021                   ROANE              TN   LAW ENFORCEMENT

            NUMEROUS TREES AND POWERLINES DOWN
            THROUGHOUT THE COUNTY, ROCKWOOD AREA HIT THE
            HARDEST.

0742 PM     TSTM WND DMG     2 SW ROCKWOOD           35.85N 84.71W
06/21/2021                   ROANE              TN   LAW ENFORCEMENT

            SEVERAL TREES DOWN NEAR THE ROCKWOOD AREA.

0805 PM     TSTM WND DMG     5 E OAK RIDGE           35.97N 84.21W
06/21/2021                   KNOX               TN   LAW ENFORCEMENT

            TREE DOWN ON CAMPBELL STATION RD AND
            POWERLINES DOWN ON GUINN RD.

Environment

A strong upper level trough digging into the Mississippi Valley placed the Tennessee and Ohio Valleys under increasingly strong southwesterly flow aloft during the afternoon and evening hours of Monday June 21. The strongest jet dynamics stretched from Illinois to Michigan and were associated with a 100-120 knot 300 mb jet streak. This axis of strong upper level winds progressed further east and southeast into the Ohio Valley during the evening, placing the southern Appalachians near the right entrance region of the jet streak as indicated by the contours of enhanced divergence in the 300 mb plot. This upper level divergence over the region promoted an increase in southwesterly winds in the lower levels, and resultant warm/moist advection, as seen in the 700 mb and 850 mb charts.


Figure 1: 300 mb Heights, Divergence, and Winds	Figure 2: 700 mb Heights, Winds, Temps, and Mean RH	Figure 3: 850 mb Heights, Temps, and Dew Points

The strengthening warm air advection as the aforementioned upper trough dug further into the Ohio Valley pulled very warm and moist air into the region with 850 mb temperatures increasing to around 20 C and 850 mb dew points increasing to 12 to 14 C, aided by a modest 20 to 30 knot low-level jet as seen in the 850 mb chart above. This allowed surface temperatures to rise into the upper 80s and lower 90s F during the afternoon with oppressively high dew points in the lower 70s F as seen in the surface temperature and dew point plot below. A strong surface cold front moving southeast toward the Tennessee Valley during the late afternoon and evening enhanced low-level convergence and lifting of this warm, moist airmass as seen by the strong deep layer moisture convergence up the Tennessee Valley and southern Appalachians in the chart below. This combined with forcing from the upper level divergence led to the development of widespread showers and thunderstorms.


Figure 4: Surface Temps, Dew Points, and Mean Sea Level Pressure	Figure 5: Deep Layer Moisture Flux, Convergence, and 100 mb Mean Mixing Ratio

Strong heating of the increasingly moist low-level airmass, combined with mid/upper height falls and steepening mid-level lapse rates as the upper trough approached, resulted in MLCAPE values of 1000-2000 J/Kg across the southern Appalachians from mid afternoon into the evening. This is impressively strong instability for this part of the country. The hot and humid low-level airmass caused low-level lapse rates to become very steep in the 7 to 8.5 C/Km range, and this led to strong convective downdraft potential, making damaging winds the most prevalent severe weather hazard. A punch of mid-level dry air noted in the 12Z observed sounding from Nashville further enhanced downdraft potential, and this can be seen in the DCAPE values which exceeded 1100-1200 J/Kg during the afternoon and evening. These types of environments do not require much wind shear to produce many reports of severe convective winds, but areas north of I-40 did see a modest increase in shear as the trough and associated cold front approached. Deep layer shear increased to 25-30 knots in these northern areas during the evening with effective shear increasing to 30-40 knots, and this was enough to sustain organization of stronger updrafts and downburst potential for a longer period of time compared to south of I-40 where shear was weaker. The stronger and more sustained convective cores north of I-40 also produced some hail in addition to the widespread damaging winds since they were closer to the approaching upper trough. This was likely due to slightly steeper mid-level lapse rates nearing 6 C/Km and hail CAPE values of 300-600 J/Kg, and the greater shear in that area sustaining updrafts.


Figure 6: MLCAPE and MLCIN	Figure 7: Low Level (0-3 Km) Lapse Rates	Figure 8: DCAPE


Figure 9: 12Z Observed Nashville Sounding	Figure 10: Deep Layer (0-6 Km) Shear	Figure 11: Effective Bulk Shear


Figure 12: Mid-Level (700-500 mb) Lapse Rates	Figure 13: -10 to -30 C CAPE, Freezing Levels, and 0-6 Km Shear

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Event Summary of the June 21, 2021 Severe Storms