Heavy Rainfall to Bring Flooding Threat to California; Heavy Snow in the Sierra

A strong atmospheric river will bring heavy rainfall to California through the holiday week. The heaviest rainfall is expected on Wednesday in the Los Angeles Basin. Flash and urban flooding is possible. A prolonged heavy snowfall is expected in the Sierra Nevada from the atmospheric river, raising concerns for major snow‐load impacts. Travel may be difficult to impossible over the passes. Read More >

Overview

Despite it being September, the severe weather ingredients necessary for severe weather including tornadoes came together Monday afternoon/evening: plenty of moisture (65 to 70 degree dewpoints), low cloud bases, wind shear (change of wind direction/strength with height), and just enough instability ahead of a low pressure system. The first tornadoes of the day occurred in Hamlin and Codington Counties, and several others followed in Day County a few hours later. While no injuries were reported with this activity, a couple farmsteads did sustain damage. Hail and strong straight-line winds also occurred on occasion with these storms, as did heavy rainfall. The last time tornadoes occurred in September in South Dakota was on the 15^th and 19^th in 2017, and on the 30^th in 2014.

Find an interactive map of storm reports here.

Radar Reflectivity from 4pm to 10pm CDT Monday Sept 9, 2019

Tornadoes
Rainfall, Other

Tornadoes

Tornado - near Thomas, SD
Hamlin County

Date	September 9th, 2019
Time (Local)	3:39-3:45 PM CDT
EF Rating	0
Est. Peak Winds	80
Path Length	3.2 miles
Max Width	40 yards
Injuries/Deaths	0
Summary: The tornado started around 0.75 mile south of Thomas and tracked across farm fields. Trees and outdoor lawn items were damaged after the tornado crossed Highway 22 and before crossing Clear Lake. The tornado move off the lake and crossed a cornfield and proceeded to damage several metal beams on a quonset barn. Finally, several outbuildings and a silo were damaged on a farm before additional trees were uprooted in a shelter belt.

Track Map


Destroyed Outbuilding	Tree Snapped in Half	Flipped Storage Shed	Bird House Stand Bent Over

KABR radar imagery at 3:41 PM CDT when the tornado was occurring near Thomas, SD

Tornado - Near Watertown Airport
Hamlin County

Date	September 9th, 2019
Time (Local)	3:37-3:41 PM CDT
EF Rating	0
Est. Peak Winds	70
Path Length	2.5 miles
Max Width	20 yards
Injuries/Deaths	0
Summary: The tornado tracked across farm fields and was photographed near the Watertown airport at 3:40 PM CDT.

Track Map


Photo taken at 3:40 PM CDT by Justin Arendsee at the Watertown airport.	KABR radar imagery at 3:31 PM CDT shortly before the tornado occurred. The red square on the image is the location of the Watertown airport runway.	Drone image from Alex Resel of tornado damage to cornfields at 3rd Ave NW and 42nd St NW, south of the Cattail Crossing Golf Club

Tornado - 3N Webster
Day County

Date	September 9th, 2019
Time (Local)	6:55-6:56 PM CDT
EF Rating	0
Est. Peak Winds	73
Path Length	0.1 mile
Max Width	10 yards
Injuries/Deaths	0
Summary: A witness observed and recorded the tornado touchdown over a lake then track onto a pasture land before lifting. No damage occurred.

Track Map

Screenshot from video by Elizabeth Gravley taken approximately 2.5 miles north of Webster

Tornado - 4N Bristol
Day County

Date	September 9th, 2019
Time (Local)	8:03-8:11 PM CDT
EF Rating	1
Est. Peak Winds	90
Path Length	1.6 miles
Max Width	80 yards
Injuries/Deaths	0
Summary: Many tree limbs were downed and a fiberglass shed was destroyed and tossed about 70 yards. In addition, another outbuilding was lifted off its foundation and set about 30 yards away.

Track Map


Photo Courtesy of Bryan Anderson	Photo Courtesy of Bryan Anderson		Tree Snapped in Half by the Tornado


KABR radar imagery at 8:02 PM CDT as the tornado was developing	KABR radar imagery at 8:06 PM CDT during the tornado

Tornado - 7 NNE Bristol
Day County

Date	September 9th, 2019
Time (Local)	8:14-8:15 PM CDT
EF Rating	0
Est. Peak Winds	73 mph
Path Length	0.2 mile
Max Width	10 yards
Injuries/Deaths	0
Summary: Witnesses observed a tornado and the only additional evidence of the touchdown was an area where cattails were flattened in a convergent pattern.

Track Map


Photo courtesy of Karen Johnson	Photo courtesy of Karen Johnson

The Enhanced Fujita (EF) Scale classifies tornadoes into the following categories:

EF0 Weak 65-85 mph	EF1 Moderate 86-110 mph	EF2 Significant 111-135 mph	EF3 Severe 136-165 mph	EF4 Extreme 166-200 mph	EF5 Catastrophic 200+ mph

Rain Reports

24 hour rainfall reports listed as well as estimated in map-form below.

September South Dakota Tornadoes in Perspective

September 2019 was very active compared to normal. Preliminary data through September 28th, from the National Centers for Environmental Information's Storm Data

Map of all confirmed September tornadoes since records began in 1950, minus 2019, from the MRCC's Tornado Tracks page

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Heavy Rainfall to Bring Flooding Threat to California; Heavy Snow in the Sierra

September 9th, 2019 Severe Weather Summary