Atmospheric River Bringing Heavy Rain to Southern California and Heavy Snow to the Sierra Nevadas

A strong atmospheric river will continue heavy rain over southern California through Friday. The heaviest rainfall is ongoing today in the Los Angeles Basin. Flash and urban flooding is possible. A prolonged heavy snowfall has begun over the Sierra Nevada Mountains and will continue through Friday. Travel will become increasingly difficult over the passes due to snow and strong winds. Read More >

Overview

A strong storm system led to several rounds of strong to severe storms across the forecast area and the eastern U.S. as a whole. Widespread damaging winds were the most common occurrence locally, but the event also produced more than a dozen hail reports of quarter to in excess of golf ball size, a fairly uncommon event in our region.

Wind & Hail
Radar
Storm Reports
Environment

Wind & Hail

Nearly 50 reports of wind and hail were received on the day of the event with the wind reports being most widespread. Over one dozen reports of hail were received with sizes ranging from 1" to nearly 2".

Wind

Observational Data from the Automated Station at the Knoxville McGhee Tyson Airport Showing Wind Gusts in Excess of 60 mph


German Creek Marina, Bean Station, TN (Courtesy Trained Spotter)	Downed Tree in Greeneville (Courtesy Christopher Starnes)	Dorsey Street on Chattanooga's Southside (Courtesy Viewer Photo to WTVC-TV)	Lenoir City (Courtesy Josh Marler)

Hail


Golf Ball to Lime Sized Hail (1.75" to 2") in Loudon County (Courtesy Tim and Kelly Cutshaw)	Golf Ball to Lime Sized Hail (1.75" to 2") in Loudon County (Courtesy Tim and Kelly Cutshaw)	Hail to 1" or More in Diameter in Chestnut Hill, TN

Radar


KMRX Radar of Reflectivity (left) and Velocity (right) at 2130 UTC (530 PM ET) across Grainger County, Near the Time of Damage at the German Creek Marina	KMRX Radar of Reflectivity (left) and Velocity (right) at 2028 UTC (428 PM ET) centered across the McGhee Tyson Airport, Knoxville


KMRX Radar of Reflectivity (top left), Velocity (top right), Maximum Estimated Hail (MESH), and Correlation Coefficient at 2130 UTC (530 PM ET) across Loudon County. MESH estimated 2+ inch hail	Cross-Section from KMRX radar at 2130 UTC (530 PM ET) across Loudon County. High reflectivity core near 30kft+ above the ground.

Storm Reports



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

0712 PM     TSTM WND DMG     1 WSW HILANDER PARK     36.77N 82.10W
05/06/2022                   WASHINGTON         VA   PUBLIC

            A FEW TREES DOWN.

0700 PM     TSTM WND DMG     3 SSW HARR              36.54N 82.01W
05/06/2022                   SULLIVAN           TN   PUBLIC

            SOME TREES AND POWER LINES DOWN.

0640 PM     TSTM WND DMG     5 S COLLINGWOOD         36.67N 82.32W
05/06/2022                   WASHINGTON         VA   PUBLIC

            SEVERAL TREES DOWN.

0625 PM     TSTM WND DMG     1 NNE JOHNSON CITY      36.35N 82.35W
05/06/2022                   WASHINGTON         TN   LAW ENFORCEMENT

            TREES AND POWER LINES DOWN ACROSS THE ENTIRE
            COUNTY.

0612 PM     TSTM WND DMG     1 WNW CHURCH HILL       36.53N 82.73W
05/06/2022                   HAWKINS            TN   TRAINED SPOTTER

            TWO TREES BLOWN DOWN AND 58 MPH WIND GUST
            RECORDED ON HOME WEATHER STATION.

0612 PM     HAIL             1 WNW CHURCH HILL       36.53N 82.73W
05/06/2022  M1.00 INCH       HAWKINS            TN   TRAINED SPOTTER

            QUARTER SIZE HAIL REPORTED.

0608 PM     TSTM WND DMG     2 SW ROGERSVILLE        36.39N 83.03W
05/06/2022                   HAWKINS            TN   LAW ENFORCEMENT

            TREES AND POWER LINES DOWN SEVERAL LOCATIONS
            ACROSS THE COUNTY.

0604 PM     TSTM WND DMG     6 NNE TAZEWELL          36.53N 83.53W
05/06/2022                   CLAIBORNE          TN   PUBLIC

            SEVERAL TREES AND POWER LINES DOWN.

0542 PM     HAIL             1 S GREENEVILLE         36.16N 82.82W
05/06/2022  E1.00 INCH       GREENE             TN   PUBLIC

            QUARTER SIZE HAIL REPORTED 1 MILE SOUTH OF
            GREENVILLE.

0510 PM     HAIL             3 SE BLOOMINGDALE       36.54N 82.46W
05/06/2022  E1.25 INCH       SULLIVAN           TN   PUBLIC



0505 PM     TSTM WND DMG     LUTTRELL                36.21N 83.75W
05/06/2022                   UNION              TN   LAW ENFORCEMENT

            TREES AND POWER LINES DOWN.

0505 PM     TSTM WND DMG     SHARPS CHAPEL           36.34N 83.81W
05/06/2022                   UNION              TN   LAW ENFORCEMENT

            TREES AND POWER LINES DOWN.

0505 PM     TSTM WND DMG     MAYNARDVILLE            36.25N 83.81W
05/06/2022                   UNION              TN   LAW ENFORCEMENT

            TREES AND POWER LINES DOWN.

0505 PM     HAIL             CHESTNUT HILL           35.93N 83.34W
05/06/2022  M1.00 INCH       JEFFERSON          TN   PUBLIC



0455 PM     HAIL             2 ESE BENHAMS           36.66N 82.18W
05/06/2022  E1.25 INCH       WASHINGTON         VA   LAW ENFORCEMENT

            SEVERAL TREES AND POWER LINES DOWN AS WELL.

0448 PM     HAIL             3 NNW GREENEVILLE       36.20N 82.84W
05/06/2022  E1.25 INCH       GREENE             TN   PUBLIC



0430 PM     TSTM WND DMG     2 NNW PIGEON FORGE      35.82N 83.58W
05/06/2022                   SEVIER             TN   EMERGENCY MNGR

            TREES AND POWER LINES DOWN BETWEEN PIGEON
            FORGE AND SEVIERVILLE.

0330 PM     HAIL             1 NNW PIONEER           36.44N 84.32W
05/06/2022  E1.25 INCH       CAMPBELL           TN   PUBLIC

            CORRECTS PREVIOUS HAIL REPORT FROM 1 NNW
            PIONEER. TREES AND POWER LINES DOWN.

0250 PM     HAIL             1 WNW TARIFFVILLE       35.49N 84.19W
05/06/2022  E1.50 INCH       MONROE             TN   PUBLIC

            SEVERAL TREES DOWN.

0214 PM     TSTM WND DMG     1 NE WHITWELL           35.21N 85.51W
05/06/2022                   MARION             TN   LAW ENFORCEMENT

            A FEW TREES DOWN.

Environment

A strong upper trough moved across the midsection of the Ohio and Tennessee Valleys into the central and southern Appalachians from mid-afternoon through early Friday evening. The strongest part of the jet was over the southern Appalachians where 300mb winds exceeded 90 knots. This placed East Tennessee, southwest Virginia, and southwest North Carolina under strong upper forcing during the afternoon and evening of Friday, May 6th 2022.

A thermal trough of colder air pulled eastward into the southern Appalachians late Friday. The 500mb temperature map depicted temperatures dropping below -16 degrees Celsius. The colder air helped to increase the instability over the area as well as enhanced the potential for large hail.

The strong upper jet structure produced a relatively deep trough of low pressure system over the Ohio and Tennessee Valleys. This deep low pressure system strengthened the boundary layer jet over the southern Appalachians and southeast United States pulling abundant moisture and instability into the region.


Figure 1: 300mb Heights, Divergence, and Winds at 2300 UTC, 06 May 2022	Figure 2: 500mb Heights, Winds, and Temperatures at 2000 UTC, 6 May 2022	Figure 3: 850mb Heights, Temperatures, and Winds at 2000 UTC, 6 May 2022

The strong low-level jet pulled abundant moisture into the East Tennessee Valley and the southern Appalachian region. Unseasonably warm air was also pulled north into East Tennessee, southwest Virginia, and southwest North Carolina with temperatures climbing into the 70s over much of the area. The increased moisture and unseasonably warm temperatures produced an unstable air-mass over the Tennessee Valley and southern Appalachians.


Figure 4: 850mb Moisture Transport at 1800 UTC, 6 May 2022	Figure 5: Surface Temperature, Dewpoints, Winds, and Isobars at 1800 UTC, 6 May 2022	Figure 6: Surface Station Plot at 1900 UTC, 6 May 2022


Figure 7: Surface Analysis of Isobars, Temperatures, Dewpoints, Fronts, and Low Pressure Centers at 1900 UTC, 6 May 2022	Figure 8: MLCAPE and CIN at 2000 UTC, 6 May 2022	Figure 9: Mid-Level Lapse Rates (700-500mb) at 1900 UTC, 6 May 2022

Numerous storms produced large hail of 1 inch or greater with several reports up to golf ball size. The main contributors to the numerous hail was the cold air aloft and the sustained updrafts with the storms. The cold air produced high mid-level lapse rates and favorable values of Hail CAPE. The Significant Hail Parameter (SHIP) depicted values of 1 or greater across much of the area, which indicated the potential of large hail.


Figure 10: Hail CAPE (-10 to -30 Celsius) at 2000 UTC, 6 May 2022	Figure 11: Significant Hail Parameter (SHIP) at 2000 UTC, 6 May 2022	Figure 12: 0-1km Shear at 2000 UTC, 6 May 2022

Several of the storms late Friday exhibited mid-level and low-level rotation, but no confirmed tornadoes were reported. Effective and 0-1km shear were favorable for tornado development, but speed shear contributed to most of the available shear. The more favorable low-level environments occur with some directional shear when the low-level winds are southerly. The lack of low-level directional shear limited the Significant Tornado Parameter due the event.


Figure 13: Effective Shear at 2000 UTC, 6 May 2022	Figure 14: Supercell Composite Parameter (SCP) at 2000 UTC, 6 May 2022	Figure 15: Significant Tornado Parameter (STP) at 2000 UTC, 6 May 2022

The main severe weather threat from the line of showers and thunderstorms were damaging straight-line winds. The main reason why these storms produced high winds was due to the availability of mid-level dry air and the strong pressure rises behind the frontal boundary. The Derecho Composite Parameter depicted values between 2 and 4 across much of the area. Typically, values of 2 or greater indicate an environment favorable for damaging winds.