Persistent rainfall from a potent, slow moving upper low pressure system led to heavy rain and isolated flooding across south central Nebraska heading into the Memorial Day Holiday weekend. The worst of the flooding occurred near the Crystal Lake Recreation Area in Adams County, but pockets of minor/brief flooding were noted in and around Kearney as well.
Rain first moved into the area during the early morning hours of Thursday, May 21st as a closed upper low pressure system slowly moved into the area. More persistent and heavier rain developed within a west to east band focused along the Highway 6 and Interstate 80 corridors around midday Thursday, and persisted through the late afternoon. Brief and minor flooding occurred in poor drainage areas in and around Kearney Thursday afternoon. Activity weakened and became somewhat disorganized during the evening hours, but pockets of light to moderate rain persisted through Thursday night and into Friday morning, May 22nd. The most persistent band of rain, with some embedded thunderstorms, developed around dawn on Friday and blossomed in coverage such that the entire area was seeing rainfall by noon as the upper low slowly inched its way into north central Kansas. Rainfall was efficient through the entire afternoon due to a persistent feed of moisture into the system from the southeast and very slow movement of the upper low. This led to increased runoff into area streams and rivers such that sandbagging was needed by Friday evening in Holstein due to rising river levels along the Little Blue River. Rainfall rates slowly decreased Friday evening and the upper low gained a little bit of eastward momentum as it moved into southeast Nebraska and northeast Kansas. New thunderstorm development in these areas began to cut off the moisture flow into south central Nebraska, with only isolated light showers persisting into Friday night. Widespread rain amounts of 3 to 6 inches resulted in flooding along the Little Blue River, as well as the Crystal Lake Recreation Area, which led to camper evacuations. Flood damages and lost revenue totaled $10,000 for the recreation area alone. Additional damage occurred to infrastructure including Highway 74 near Ayr (which was closed for a time on Saturday, May 23rd), numerous county roads, as well as a BNSF railroad bridge just north of Crystal Lake.
Meteorologically speaking, it was somewhat unusual to have such a potent, slow-moving, and cut-off upper low pressure system so late into spring. The slow moving nature of the upper low, along with nearly stationary forcing from deformation within the northwest quadrant, were the key factors that led to such heavy rain amounts as precipitable water values were not overly high, around 1.1��� to 1.4���. Persistent cloud cover, cool surface temperatures, and weak mid level lapse rates kept instability values seasonably low, generally less than 1000 J/kg, meaning this heavy rain event was largely synoptic driven, with a lesser convective component than normally seen during late May.

Flood in ADAMS, NEBRASKA
From 22-MAY-20 17:00:00 to 24-MAY-20 11:00:00 (CST-6)
Location: HOLSTEIN
Flood cause: Heavy Rain
Property damage: 200.00K
Crop damage: 1.00M
Reported by: Emergency Manager

Heavy rain around and upstream of this area resulted in flooding during the Memorial Day holiday weekend. Widespread amounts of 3 to 6 inches fell, with much of the flooding affecting areas along the Little Blue River. Sandbagging was required in Holstein on the evening of the 22nd due to rising waters. Flooding affected the Crystal Lake Recreation Area near Ayr. All campers were evacuated, with flooding causing damage and a loss of revenue for the holiday weekend, totaling approximately 10,000 dollars. Numerous rural roads were damaged, and Highway 74 near Ayr was closed for a period of time due to debris becoming jammed under a bridge, causing water to rise over the road. The highway reopened during the late evening hours of May 23rd. Major damage to a BNSF trestle bridge was reported north of the Crystal Lake campground due to clogged water drainage and undermining. Flooding subsided on the 24th.