It’s been a long time since I offered up rankings of the Colorado state senate races most likely to switch party hands this fall. Now that the latest voter registration numbers are available, campaign finance reports are in and the legislature is out of session, it’s time to take a fresh look.

Just for review, there are 35 seats in the Colorado state senate, and Democrats possess a decisive 21-14 advantage. State senators serve four-year terms and only come up for election every other cycle, unless there was a vacancy filled and a special election is needed. Nineteen of the 35 seats are up for grabs in 2010: 11 held by Democrats and 8 held by Republicans. Five of the Democrat-held seats and all but one of the Republican-held seats are not competitive, leaving four Democrat incumbents, two Democrat open seats and one Republican open seat in play.

In late January I forecast based on trends that Republicans would pick up 2 or 3 seats in the November election — putting them close to the majority, but just out of reach. This time trends look even more favorable for the GOP, putting as many as 4 seats (and the majority) in the balance. Races are rated in order of probability that the outside party will wrest control:

1. Senate District 6 (Archuleta, Dolores, La Plata, Montezuma, Montrose, Ouray, San Juan, San Miguel) – DEM Prev rank: 1 Republican state representative Ellen Roberts now has a primary opponent from the Right in Dean Boehler, who shocked southwestern Colorado with a 2-to-1 victory at the April assembly. But appointed Democrat Bruce Whitehead has less than half the cash on hand as Roberts, and active voter registrations favor the GOP by a margin of 40 to 29. Likely GOP pick-up

2. Senate District 16 (Boulder, Clear Creek, Gilpin, Grand, Jefferson, Summit) – DEM Prev rank: 2 Conservative Republican businessman Tim Leonard made quite a dramatic statement by raking in $39,000 in the past quarter to reach $52,000 cash on hand — leaving both his Republican primary rival Mark Hurlbert and Democrat Jeanne Nicholson in the dust. Keep an eye on the Republican SD 16 assembly on May 21. Likely GOP pick-up

3. Senate District 20 (Jefferson) – DEM Prev rank: 3 Last month’s Democratic assembly highlighted the deep divisions between the two candidates seeking to replace Moe Keller: moderate former representative Cheri Jahn edged liberal Dave Ruchman by a very narrow margin, 91-89, despite heavy establishment support. Ruchman has $18,600 and Jahn $10,200 to wage a heated primary while Republican John Odom is all alone sitting on $50,000 in a district with a small Democratic edge but a lot of unaffiliated voters up for grabs. Leans GOP pick-up

4. Senate District 11 (El Paso) – DEM Prev rank: 5 Young rising GOP star Owen Hill has a clear field and nearly $30,000 after a strong fundraising quarter in a very closely divided district — one third Democrat, one third Republican, one third unaffiliated. The challenge? Facing Democratic majority leader John Morse, who is only $10,000 behind in cash on hand at the end of session but who recently decided to rip into Amazon on a now infamous video. Tossup: slight edge GOP pick-up

5. Senate District 5 (Alamosa, Chaffee, Conejos, Costilla, Delta, Gunnison, Hinsdale, Mineral, Pitkin, Rio Grande, Saguache) – DEM Prev rank: 4 The GOP actually has a small registration edge in this large mountain district, but incumbent Democrat Gail Schwartz cast some savvy votes, has more money than any other state legislative candidate ($82,700), and has two Republicans battling it out in Bob Rankin and Wayne Wolf. Tossup: slight edge Dem hold

6. Senate District 24 (Adams) Prev rank: N/A Any other year I doubt this race would break the list, as incumbent Democrat Lois Tochtrop gets a 2006 rematch from Luis Alvarez. But keep it on the outer edges of your radar screen. Likely Dem hold

7. Senate District 2 (Baca, Bent, Crowley, Custer, Fremont, Huerfano, Las Animas, Otero, Pueblo) – REP Prev rank: 7 A field of three Republicans — Kevin Grantham, Matt Heimerich and Talon Canterbury — has lined up to fill the shoes of the GOP’s retiring state senator Ken Kester. Right now, any of them looks like better odds than the two late-entry Democrats Gloria Stultz and John Webb, neither of whom has reported raising a dime. Likely GOP hold

Stay tuned, as tomorrow I plan to release the updated rankings of state house races.