3 - 4 years since I graduated, how should I time asking for recommendations? Since I graduated as an undergrad three years ago, I've been planning to go back into graduate school, so I saved all my assignments and heavily kept up on studying and research. My transcript looks good and I've had a lot of time to focus on GREs.  

The most uncertain and anxious part is getting letter of recommendations from my former professors. Due to my nature, I haven't maintained contact with the three professors I have in mind, especially given the job I have. I'm confident that they'll remember me if I send them a quick e-mail, but I'm hesitant about the timing. It seems a bit awkward to re-establish contact out of nowhere without letting them know my intention, but at the same time, I feel it's a bit too early to let them know I would like to start looking into graduate school. 

I was thinking of sending them e-mails stating my intention to apply to graduate schools, be able to provide documents/statements so they have something to remember and write about me, and ask if they were interested on writing the recommendation. If so, I would follow up and provide them the application details several months ahead. 

Is this better than asking them out of the blue when graduate application crunch time starts? 

Also, for professors and those who wrote letter of recommendations, what are your experiences of writing recommendations for former students reaching back 3 - 4 years later? 

Edit: Update on this below
My recommendation is similar to those posted in comments. I worked for several years before applying to graduate school and did not stay in touch with my professors during that time. Approximately 4 months before I applied to graduate school, I sent each professor a brief (1 paragraph) email explaining my graduate education plans and career interests, and asking if they would be willing to write letters of recommendation, which would be due in November. I also indicated that if they were willing, I would send them my CV and a summary sheet of my college activities for their reference. I contacted them via email, as I lived in a different state than the college, and face-to-face meetings were impractical.

When they agreed to write the letters I sent them:


A summary sheet listing each program I was applying to. For each program I listed the address and contact person (so the letter could be properly addressed), 1 line about why the program interested me, the names of faculty I was interested in, the application deadline, and specific application letter forms or links to online applications, if relevant. 
My CV
A summary sheet highlighting specific grades in major-related courses; research projects and activities I engaged in during college; a 1 paragraph narrative explaining what I had done since graduating and why I was interested in pursuing another degree; and a list of courses I took with that particular professor/letter writer, along with the grade for the course and any special projects completed in those courses. Try to keep this to 1 page.


Although this sounds like a lot of information, work to keep it as brief as possible, while ensuring the professor has the information they need to write a strong letter.

You may choose to time this differently, but the four month window ensured that I had committed to applying and gave me time to identify alternative writers if they had declined. I'm not sure it would be useful to ask your professors a year in advance, as 1) your plans may change, and 2) they may not recall a commitment they make that far in advance. That said, I would make initial contact in the summer before you apply; if you wait until the school year kicks into full gear, your email might get lost in the shuffle. When I was applying I was advised by multiple people to provide all materials to my letter-writers a minimum of 2 months prior to the deadline. Many schools require letters to be written on specific forms, have surveys your letter writers are asked to complete, or even ask the letters be submitted online; it's unlikely the most recent application will be available more than a few months prior to the application deadline.

A few final notes: 


Be sure to ask if they feel they can write you a strong letter, not just a letter of recommendation. Most faculty will be honest about this. 
Send your letter writers an email two weeks prior to the application deadline to thank them and remind them of the approaching deadline. Many online applications will indicate when your letters of recommendation have been uploaded. 
Be sure to thank them, both when they agree to write the letter and when the letter is submitted. Consider writing and mailing a formal thank you note, once the application is submitted. Also, contact them once you're accepted and have decided on a school; they like to know how it's worked out!