Welcome to our final Electoral College update. Every Monday since Labor Day, we have analyzed the latest poll results from the 12 most competitive states. This week, we’ve added Minnesota, where Mitt Romney has made a heavy last-week investment, to our analysis and have dropped New Mexico, which Romney has abandoned.

The big picture:

President Obama has taken a small lead in polling conducted after Superstorm Sandy with an average poll margin of one-half of one percentage point. Obama is ahead in three of the five nationwide polls conducted after the storm hit, while two were tied.

Obama’s small lead reflects an important change in the dynamics of the race. Last Monday, Romney led in six of the ten previous polls. Now, Obama is ahead in states (and the District of Columbia) with 281 electoral votes — more than enough to win if he just hangs on. Colorado is the only toss-up left on our national map.

Romney has the edge in the southern swing states (Virginia, North Carolina and Florida). Obama is clinging to his campaign-long lead in the industrial heartland (Ohio, Wisconsin, Michigan and Pennsylvania), along with Iowa, New Hampshire and Nevada. To win, Romney needs to move one of the Midwestern Obama states — Ohio, Wisconsin or Minnesota are his best shots — into his column, or score a major upset in Pennsylvania, which hasn’t voted Republican since 1988.

Romney’s best hope for victory: that all of the polls are wrong and that Republican enthusiasm trumps the pollsters’ turnout models.

National average: Obama +0.5
Electoral College advantage: Obama
Trend: Obama

The battlegrounds:

Colorado Lead: Obama +0.6
Compared to national average: Obama +0.1
Momentum over past week: None
Rick Dunham rating: Toss-up

Florida
Lead: Romney +1.4
Compared to national average: Romney +1.9
Momentum over past week: None
Rick Dunham rating: Lean Romney

Iowa Lead: Obama +2.5
Compared to national average: Obama +2.0
Momentum over past week: None
Rick Dunham rating: Lean Obama

Michigan
Lead: Obama +3.8
Compared to national average: Obama +3.3
Momentum over past week: Romney
Rick Dunham rating: Lean Obama

Minnesota
Lead: Obama +5.8
Compared to national average: Obama +5.3
Momentum over past week: None
Rick Dunham rating: Lean Obama

Nevada
Lead: Obama +2.8
Compared to national average: Obama +2.3
Momentum over past week: None
Rick Dunham rating: Lean Obama

New Hampshire
Lead: Obama +1.5
Compared to national average: Obama +1.0
Momentum over past week: Obama
Rick Dunham rating: Lean Obama

North Carolina
Lead: Romney +3.8
Compared to national average: Romney +4.3
Momentum over past week: None
Rick Dunham rating: Lean Romney

Ohio
Lead: Obama +2.8
Compared to national average: Obama +2.3
Momentum over past week: None
Rick Dunham rating: Lean Obama

Pennsylvania
Lead: Obama +3.9
Compared to national average: Obama +3.4
Momentum over past week: Romney
Rick Dunham rating: Lean Obama

Virginia
Lead: Romney +0.3
Compared to national average: Romney +0.8
Momentum over past week: None
Rick Dunham rating: Lean Romney

Wisconsin
Lead: Obama +4.2
Compared to national average: Obama +3.7
Momentum over past week: None
Rick Dunham rating: Lean Obama

Longshots to watch:
For Obama: Arizona
For Romney: Wisconsin

Spotlight state: Colorado

Numbers based on RealClearPolitics poll data compiled by Max Kranl of the Hearst Newspapers Washington bureau and analyzed by Rick Dunham. Our thanks to RealClearPolitics for the timelines.