1. Base Case Building Update For TRANSAC 10/21/10

2. assumptions… • Load levels • Linked to 1-in-10 forecast of System Load • For all cases (2010, 2015, 2020, and 2025): • Summer has 37 MW adder over 1-in-2 forecast • Winter has 59 MW adder over 1-in-2 forecast • Heavy Summer/Winter loads (2010) • 1500-1600 MW range (NWE only) • Light Spring/Autumn loads (2010) • 800-900 MW range (NWE only) • Bus loads used individual growth projections • Used for 2015, 2020, and 2025 cases • Default growth rates of W=1.1%, S=0.8% used when individual projections not available • Bus loads are then scrunched to ‘fit’ System Load

3. assumptions… • Topology • All cases: • Existing wind dispatched at 35% for LA & LSP • Existing wind dispatched at 50% for HS & HW • 2010 cases • Smurfit-Stone load gone • MCGS included, but off-line • Great Falls 115/100 kV transformer upgrade • Hardin Auto 230/115 kV transformer upgrade • Missoula #4 100/69 kV transformer upgrades • Laurel Auto capacitors • Laurel 50 kV configuration

4. assumptions… • Topology • 2015 cases • New generation: signed contracts included • MATL • Crooked Falls • New Billings area capacitors • Morony & Black Eagle GSU upgrades • Jackrabbit – Big Sky 161 kV line upgrade • Great Falls 230/100 kV transformer upgrades • Great Falls 230/161 kV transformer upgrade (WAPA) • Great Falls 230 kV Swyd – City Tap 100 kV reconductor • South Butte 230/161 kV transformer upgrade • 2020 & 2025 cases • 2015 cases with load growth