A closed upper level low over the central Rockies was deepening as a surface low developed over southeastern Colorado. Strong 700mb warm air advection over-ran cold air at the surface. The atmosphere over northeastern Wyoming and western South Dakota was saturated, with additional moisture being advected in. 300mb Jet streaks were producing strong divergence aloft and robust 500mb omega set up along the deformation zone. These features combined to produce heavy snowfall over much of southwestern and southern South Dakota for several hours. The precipitation began as rain in the warm over-running air. This rain quickly changed to snow and accumulated rapidly. The area of snowfall with this system extended in a 300 mile wide path from northern Colorado to eastern South Dakota. The path was defined by sharp edges as seen in satellite images. The heaviest snow fell over the eastern foothills and eastern Black Hills where local upslope effects dramatically affected snowfall amounts. The area of maximum snowfall extended from southern Meade County westward to the central and southern Black Hills where 12 to 22 inches covered the ground. Rapid City, in the eastern foothills, recorded a daily snowfall record of 20 inches. Elsewhere across the plains of southwestern and south-central South Dakota 6 to 12 inches of snow were reported.

Winter Storm in CENTRAL FOOT HILLS / C PENNINGTON / PART OF E CUSTER, SOUTH DAKOTA
From 22-APR-01 03:39:00 to 22-APR-01 18:15:00 (MST)
Reported by: OFFICIAL NWS OBS.

Winter Storm in SOUTHERN BLACK HILLS / CUSTER EXCEPT E / NC FALL RIVER, SOUTH DAKOTA
From 22-APR-01 00:35:00 to 22-APR-01 21:00:00 (MST)
Reported by: TRAINED SPOTTER

Winter Storm in CUSTER PLAINS / X E CUSTER, SOUTH DAKOTA
From 22-APR-01 00:00:00 to 22-APR-01 18:15:00 (MST)
Reported by: TRAINED SPOTTER

Winter Storm in MEADE CO. PLAINS / EXCEPT X SW MEADE, SOUTH DAKOTA
From 22-APR-01 03:39:00 to 22-APR-01 18:15:00 (MST)
Reported by: METEOROLOGIST(NON NWS)

Winter Storm in TODD, SOUTH DAKOTA
From 22-APR-01 08:00:00 to 23-APR-01 04:30:00 (MST)
Reported by: LAW ENFORCEMENT

Winter Storm in OGLALA LAKOTA, SOUTH DAKOTA
From 22-APR-01 08:20:00 to 22-APR-01 23:36:00 (MST)
Reported by: LAW ENFORCEMENT

Winter Storm in JACKSON, SOUTH DAKOTA
From 22-APR-01 08:00:00 to 23-APR-01 04:30:00 (MST)
Reported by: TRAINED SPOTTER

Winter Storm in HAAKON, SOUTH DAKOTA
From 22-APR-01 08:50:00 to 22-APR-01 23:26:00 (MST)
Reported by: TRAINED SPOTTER

Winter Storm in MELLETTE, SOUTH DAKOTA
From 22-APR-01 08:00:00 to 23-APR-01 04:30:00 (MST)
Reported by: LAW ENFORCEMENT

Winter Storm in BENNETT, SOUTH DAKOTA
From 22-APR-01 08:00:00 to 23-APR-01 04:30:00 (MST)
Reported by: LAW ENFORCEMENT

Winter Storm in SOUTHERN FOOT HILLS / PART OF N FALL RIVER, SOUTH DAKOTA
From 22-APR-01 00:35:00 to 22-APR-01 21:00:00 (MST)
Reported by: TRAINED SPOTTER

Winter Storm in NORTHERN FOOT HILLS / N LAWRENCE / X SW BUTTE / PART OF SW MEADE, SOUTH DAKOTA
From 22-APR-01 06:30:00 to 22-APR-01 18:15:00 (MST)
Reported by: TRAINED SPOTTER

Winter Storm in NORTHERN BLACK HILLS / LAWRENCE EXCEPT N / LAWRENCE EXCEPT SW MEADE, SOUTH DAKOTA
From 22-APR-01 06:30:00 to 22-APR-01 18:15:00 (MST)
Reported by: TRAINED SPOTTER

Winter Storm in FALL RIVER CO. / FALL RIVER EXCEPT N, SOUTH DAKOTA
From 22-APR-01 00:35:00 to 22-APR-01 21:00:00 (MST)
Reported by: TRAINED SPOTTER

Winter Storm in PENNINGTON PLAINS / E PENNINGTON, SOUTH DAKOTA
From 22-APR-01 03:00:00 to 22-APR-01 18:15:00 (MST)
Reported by: OFFICIAL NWS OBS.

Winter Storm in CENTRAL BLACK HILLS / W PENNINGTON / PENNINGTON, SOUTH DAKOTA
From 22-APR-01 00:35:00 to 22-APR-01 18:15:00 (MST)
Reported by: TRAINED SPOTTER

Winter Storm in TRIPP, SOUTH DAKOTA
From 22-APR-01 08:00:00 to 23-APR-01 04:30:00 (MST)
Reported by: TRAINED SPOTTER