Following a short stretch of dry days centered around mid-month, an abrupt transition to a very wet and stormy 24-hour period commenced in North Central Kansas during the early morning hours of Thursday the 19th, followed by a separate, more significant event focused from the evening of the 19th into the early morning hours of the 20th. Although heavy rainfall and flooding was the main story, a brief EF0 tornado touched down on the edge of the Natoma city limits in Osborne County during the evening, with minor damage reported.
The initial wave of strong storms early on the 19th blossomed shortly after midnight CDT, lifting north across the six-county area before moving out or weakening by 5 AM CDT. These storms formed within a classic nocturnal low level jet axis, in an environment featuring up to around 1500 J/kg most-unstable CAPE. Locally brief, but heavy downpours were the main result of these storms, along with a lone report of penny size hail in Osborne.
Following a break in the action that lasted most of the day, the mid-afternoon through overnight hours featured more significant rounds of strong to severe storms, which formed along and just north of a well-defined east-west oriented surface warm front. By mid afternoon, the mesoscale environment along the warm front had become quite supportive of severe weather, featuring around 1500 J/kg mixed-layer CAPE, 50-60 knots of deep-layer vertical wind shear, and 0-1 kilometer low-level shear of 20-30 knots. The first round of afternoon and evening storms affected locations mainly along and east of Highway 281 during the 4 PM to 730 PM CDT time frame. Despite the favorable proximity of the warm front, no tornadoes occurred with this initial round of afternoon storms despite the presence of an organized supercell in southern Osborne County.
The second round of strong to severe storms affected the area primarily between 8 PM and 1 AM CDT, before finally starting to exit east out of Jewell and Mitchell Counties.  Other than the brief tornado at Natoma, additional heavy rainfall was the primary impact during this time. By daylight on the 20th, 24-hour rainfall totals of 2-4 inches were common across Smith, Osborne, Jewell and Mitchell Counties. A few of the highest measured rainfall amounts included 4.17 inches in southern Mitchell County, and 3.33 inches in Smith Center. Extensive lowland and small creek flooding resulted from this soaking, along with river flooding on the North Fork Solomon at Portis, and White Rock Creek near Burr Oak. The gauge at Portis crested 5.37 feet above flood stage on the evening of the 20th.

Hail in OSBORNE, KANSAS
From 19-MAY-11 00:58:00 to 19-MAY-11 00:58:00 (CST-6)
Location: OSBORNE
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Hail in OSBORNE, KANSAS
From 19-MAY-11 15:25:00 to 19-MAY-11 15:25:00 (CST-6)
Location: NATOMA
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Hail in OSBORNE, KANSAS
From 19-MAY-11 15:30:00 to 19-MAY-11 15:30:00 (CST-6)
Location: NATOMA
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Heavy Rain in SMITH, KANSAS
From 20-MAY-11 04:22:00 to 20-MAY-11 04:22:00 (CST-6)
Location: LEBANON
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Storm total rainfall of 3.10 inches was reported.

Heavy Rain in MITCHELL, KANSAS
From 19-MAY-11 06:00:00 to 20-MAY-11 06:00:00 (CST-6)
Location: BELOIT
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Storm total rainfall of 4.17 inches was reported by a CoCoRaHs observer.

Heavy Rain in MITCHELL, KANSAS
From 19-MAY-11 06:00:00 to 20-MAY-11 06:00:00 (CST-6)
Location: BELOIT
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Storm total rainfall of 3.17 inches was reported by a CoCoRaHs observer.

Heavy Rain in MITCHELL, KANSAS
From 19-MAY-11 06:00:00 to 20-MAY-11 06:00:00 (CST-6)
Location: SCOTTSVILLE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Storm total rainfall of 3.10 inches was reported by a CoCoRaHs observer.

Flood in SMITH, KANSAS
From 19-MAY-11 22:00:00 to 20-MAY-11 11:00:00 (CST-6)
Location: WOMER
Flood cause: Heavy Rain
Property damage: 15.00K
Crop damage: 250.00K
Reported by: Law Enforcement

Storm total rainfall accumulations of 2 to 4 inches were reported across the area. Water covered a few county roads and lowland flooding was also reported.

Flood in JEWELL, KANSAS
From 19-MAY-11 22:00:00 to 20-MAY-11 11:00:00 (CST-6)
Location: NORTH BRANCH
Flood cause: Heavy Rain
Property damage: 15.00K
Crop damage: 250.00K
Reported by: Law Enforcement

Storm total rainfall accumulations of 2 to 4 inches were reported across the area. Water covered a few county roads and lowland flooding was also reported.

Tornado in OSBORNE, KANSAS
From 19-MAY-11 19:30:00 to 19-MAY-11 19:31:00 (CST-6)
Location: NATOMA
Tornado F-scale: EF0
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Emergency Manager

The path of this weak tornado affected two farmsteads. Damage reported included a few broken trees, mangled cattle panels, feed bunks overturned, a hay shed moved 100 yards from its original location, and hay bales moved.  A garage had some tin ripped from the roof and a light pole was broken in the yard.