March 31st - April 1st, 2023 Historic Tornado Outbreak

NOAA National Weather Service Davenport, IA

This is a picture of the strong tornado that occurred near Keota IA on March 31st.

Overview

An historic tornado outbreak occurred on March 31st and April 1st, 2023 across the United States. There were 147 tornadoes surveyed across 16 states making it the 3rd most tornadoes in a 24-hour period in the U.S. since 1950. Locally, 29 tornadoes occurred in the NWS Davenport County Warning Area, which is the most for any given day. Nationally, there were 175 tornado warnings issued, 29 fatalities, and over 200 injured during this outbreak. An EF4 tornado was surveyed near Keota, IA, which was the strongest tornado for the NWS Davenport County Warning Area since 1995.

March 31st - April 1st Warnings Issued. Yellow = Severe Thunderstorm, Red = Tornado

This is a map of all the tornadoes that occurred on March 31st, 2023

Environment

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Pattern Recognition

There were many signs that March 31st was going to be a very busy day for the NWS Davenport, IA office. A composite of 500mb heights and 850mb winds was taken from DVN significant tornado days from the months of March through May 2008-2022. As in most cases, a strongly negatively tilted trough and strong low level winds were recognized by this composite. The NARR analysis shown below the composite shows this was definitely seen on March 31st.

This is a composite map of 500mb heights and 850mb winds from DVN significant tornado days from the months of March-May 2022.

SPC Outlooks

The Storm Prediction Center (SPC) in Norman, Oklahoma began highlighting the severe weather risk on March 26, 2023. For just the second time since SPC started issuing the Day 4-8 Outlook in 2015, the NWS Davenport county warning area (CWA) was placed in a 30% probability for severe weather on Day 5 (March 27th). On the Day 2 outlook issued March 30, 2023 much of the area was placed in a Moderate risk. An excerpt from the SPC discussion mentioned the Mid-Mississippi Valley: “...a couple strong tornadoes…QLCS tornadoes also possible.”

This is a map of all the convective outlooks issued by SPC leading up to March 31st.

On March 31, 2023, for the first time in nearly a decade a rare HIGH risk was issued by SPC for portions of the NWS Davenport CWA. SPC noted for the Mid-Mississippi Valley: “...several long-track strong to potentially violent tornadoes are forecast…”. A total of 29 tornadoes occurred in the NWS Davenport CWA, the largest on record since 1950. It was one of the largest, multi-state tornado outbreaks in U.S. history. There were nearly 600 reports of severe weather across portions of the Midwest, Ohio Valley, and the Mid-South.

SPC Mesoanalysis: MSLP, Temperature, Dewpoint

At the surface, a deepening low pressure system moved from western Iowa toward southern Wisconsin. A warm front lifted into the area, while a cold front trailing south of the low approached from the west. The warm, moist air surging northward set the stage for thunderstorm development ahead of these fronts. The warm front increased the low level shear aiding in an environment ripe for rotating thunderstorms. The low pressure system can be seen on the surface map to the left indicated by the black mean sea level pressure contours. While both the cold front and warm front can be seen as the regions of packed isotherms, or lines of constant temperature (red contours), and isodrosotherms or lines of constant dewpoints (blue contours). The green shading represents dewpoints of 60 degrees or greater.

This is a hand surface analysis map of weather conditions at 21z on March 31st. — 21z (4 PM CDT) surface hand analysis of strengthening warm front across southeast Iowa and central Illinois, with the parent supercell of the violent tornado beginning near this time near Ottumwa, IA.

This is a hand surface analysis map of weather conditions at 23z on March 31st. — 23Z (6 PM CDT) surface hand analysis showing the cold front along the Mississippi River and the warm front along the I-80 corridor through north central Illinois. This set the stage for the second round of widespread severe storms, as the tornadic supercells evolved into a quasi-linear convective system (QLCS) with tornadoes and severe winds.

SPC Mesoanalysis: MLCAPE

Mixed Layer Convective Available Potential Energy (MLCAPE) is the amount of energy if an air parcel is lifted in the lowest 100 mb of the troposphere. MLCAPE values on this day peaked between 1500-2000 J/kg, which was very high this early in the season.

SPC Mesoanalysis: 0-6km Shear

0-6km shear depicts the change in wind from the ground level to 6 kilometers above ground level. Thunderstorms tend to become more organized and persistent as vertical shear increases, while supercells are commonly associated with vertical shear values of 35-40 knots and greater through this depth. On this day as the outbreak began these values were 70-80 knots!

SPC Mesoanalysis: Effective SRH

Effective Storm Relative Helicity (ESRH) is a measure of the vertical wind shear that takes the thermodynamic profile of the troposphere into consideration, and is useful in discriminating between significant tornadic and non-tornadic supercells. Essentially larger values are associated with a higher potential for tornadoes. On this day ESRH values were quite high at 300-400 m2/s2.

SPC Mesoanalysis: STP

The Significant Tornado Parameter (STP) is a composite index that includes parameters of instability and wind shear. A majority of significant tornadoes (EF2 or greater) have been associated with STP values greater than 1. Values during the outbreak peaked between 2 to 4. While strong tornadoes did occur on this day, it should be noted that may not always be the case when the STP is so high.

Upper Air Soundings

Weather balloons are typically launched twice a day (12z/00z) at various NWS offices. If severe weather is forecast, balloons may be launched at various times ahead of the storms. Data is collected from the instrumentation and plotted on a Skew-T diagram, which allows forecasters to evaluate the vertical distribution of temperature, wind, and humidity which is all critical to forecasting severe thunderstorms and tornadoes.

The sounding from 12z or 7 a.m. on the morning of March 31, 2023 already showed the presence of strong deep layer shear (0-6km at 65 knots) and strong low level shear (0-1 km at 49 knots).

The special sounding at 18z or 1 p.m. on the afternoon of March 31, 2023 showed a slight decrease in the deep layer and low level shear, although it was still more than sufficient to support the threat for organized severe weather. The thermodynamic profile was changing with a marked increase in instability.

Timeline

Storms were moving northeast at a very fast pace throughout the event (average speed between 45 and 65 mph). The radar loop to the right shows severe thunderstorm warnings (yellow) and tornado warnings (red) from 3:20 pm to 7:30 pm CDT on March 31st, 2023

GOES-16 "mid-level" water vapor imagery between approximately 3:00 and 9:30 PM CDT March 31, 2023 (courtesy of NWS Chicago). This imagery shows the pronounced counterclockwise circulation over Nebraska as it moved into Iowa, and this is the center of the anomalously deep weather system. Ahead of this center was where very warm and moist air were drawn northward, and supported the development of robust severe thunderstorms, shown here in the brighter yellow and red colors.

This is a water vapor satellite loop from approx. 3pm to 930pm CDT on March 31st.

List of all tornadoes in chronological order

Tornadoes

Total: 29 Injuries: 11 Fatalities: 0 EF-U: 2 | EF-0: 3 | EF-1: 9 | EF-2: 13 | EF-3: 1 | EF-4: 1 Weak: EF0 65-85 mph | EF1 86-110 mph Strong: EF2 111-135 mph | EF3 136-165 mph Violent: EF4 166-200 mph | EF5 >200 mph

Click on the tornado of interest to zoom to location. Click on tornado track or points for more information. To zoom back out, click .

1) | 2) | 3) | 4) 5) | 6) | 7) 8) | 9) | 10) 11) | 12) | 13) 14) | 15) | 16) 17) | 18) | 19) 20) | 21) 22) | 23) 24) | 25) | 26) 27) | 28) |

EF3 / EF4 Tornadoes

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Martinsburg Tornado

Time: 3:53 - 4:15 PM CDT Rating: EF-3 Estimated Peak Wind: 150 mph Path Length /statute/: 17.3 miles Path Width /maximum/: 1000 yards Fatalities / Injuries: 0 / 0 Survey Summary: A large, very strong tornado developed in Wapello county and tracked into Keokuk County about 1 mile southeast of Martinsburg. The tornado continued to the northeast before lifting just north of Highway 92, southwest of Keota. The tornado produced EF-3 damage to a house northeast of Martinsburg, and caused additional significant damage to farmsteads and outbuildings.

This image shows a feature following radar loop of the 2 strong / violent tornadoes

Keota-Wellman Tornado

Time: 4:12 - 4:37 PM CDT Rating: EF-4 Estimated Peak Wind: 170 mph Path Length /statute/: 20.3 miles Path Width /maximum/: 700 yards Fatalities / Injuries: 0 / 3 Survey Summary: A large, violent tornado developed in eastern Keokuk County as another tornado was weakening southwest of Keota. This tornado tracked to the northeast, on the western fringe of Keota, and continued through northwest Washington county, into far southwest Johnson County. The tornado severely damaged several homes near Keota, wiping out one house completely off its foundation, resulting in EF-4 level damage. A car was lofted in the air and tossed about 1000 feet into a nearby field and trees were completely debarked with only stubs of the largest branches remaining. As the tornado tracked west of Wellman, Iowa it knocked over a 325 ft cell phone tower. The tornado began to dissipate as it tracked into southwest Johnson county.