World: Greatest One-Minute Rainfall

World: Greatest One-Minute Rainfall

Record Value 31.2mm (1.23")
Date of Record 4 / 7 [July] /1956
Formal WMO Review No
Length of Record 1948-present
Instrumentation Recording Rain Gauge "in satisfactory exposure"
Geospatial Location Unionville, MD [38°48'N, 76°08'W, elevation: 152.18m (499ft)]


Engelbrecht, H.H. and G.N. Brancato, 1959: "World Record One-Minute Rainfall at Unionville, Maryland." Monthly Weather Review 87(8):303-306; Krause and Flood, 1997: Weather and Climate Extremes, US Army Corps of Engineers Topographic Engineering Center pp. 89;


Krause and Flood (1997) note that the total precipitation during the storm was 91.0 mm (3.6 inches) of which 72 mm (2.84 in) fell during a 50-minute period from 2:50 to 3:40 P.M. Rainfall was masured with a recording raingauge located in satisfactory exposure. Some 13 points pertaining to functioning of the gauge were considered in evaluating this record by H.H. Engelbrecht, then State Climatologist for Maryland and T.E. Hostrander, who was Substation Insprector. It was concluded that "... 1.23 inches of precipitation occurred in an estimated period of one-minute or less." The recording rain gauge chart (shown below) indicates that at chart time 3:23+ the pen was at 2.47 inches on the chart scale and at chart time 3:32- it was 3.70 inches.

Additional Images

Unionville 1-min Data

Data from Engelbrecht and Brancato (1959)
Unionville, MD, USA

Closeup Satellite Image of Modern Unionville, MD, USA

Unionville, MD, USA

Regional Satellite Image of Modern Unionville, MD, USA