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West-Central Semi-Arid Prairies

Last updated: November 24th, 2025

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Name	†	Color on Map	CEC Code‡
Northwestern Glaciated Plains	✓		9.3.1
Northwestern Great Plains	○		9.3.3
Nebraska Sand Hills	○		9.3.4

† Status: ✓ = Complete ○ = Needs Image … = Incomplete ∅ = Stub Only

‡ This code refers to the CEC's Level 3 ecoregion codes for North America, see here.

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↑About the West-Central Semi-Arid Prairies

The West-Central Semi-Arid Prairies are a large region in the northwestern part of the Great Plains. It extends roughly northwest-southeast, and occupies most of Montana, the western portion of the Dakotas, northeastern Wyoming, and much of northern Nebraska.

The region has a semi-arid continental climate. Precipitation is seasonal, with dry winters and a wet season peaking in May in much of the region, and in June in the north. Late summer is slightly drier. Locally-originating streams are mostly seasonal or intermittent, but there are also perennial streams originating in mountains, mostly those to the west. Seasons are well-defined, with hot summers and cold winters. Rainfall increases with elevation, but at areas of similar elevation, decreases to the west. Winter lows also decrease to the west due to increased distance from the cold air masses that often penetrate farther south in the center of the continent. The effect of east-west distance can be greater than considerable elevation changes, with some areas being warmer and drier in the west than areas in the east that are over 1,500 feet in elevation lower. So even though this region tends to slope upwards to the west, it still becomes warmer and drier in the west.

The topography is fairly diverse, ranging from flat to tablelands and badlands, with some sand dunes.

This area was historically covered by short- and mixed-grass prairie. Nowadays there is significant agriculture in the region, although less than the more fertile lands to the east. Use of land for grazing animals is more common than for cropland. Agricultural use of the grasslands in this region is expected to increase.

Most of this region is sparsely populated, and it does not contain any large cities.

In Wyoming, to the southwest, this regions transitions gradually into the Cold Deserts. To the west, and also at a few isolated regions of higher altitude, this region borders the Western Cordillera. Most of this region, however, is surrounded by more of the Great Plains. To the north and east, it transitions to the slightly moister Temperate Prairies, and to the south, the South-Central Semi-Arid Prairies.

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