The jumper was startet with provisional cast on for sleeves The cast on was choosen to match a circumference in between the widest and narrowest part of the arms. This makes it possible to choose the tightness after knitting a couple of rounds: just move the knitted tube up on the arm for tighter fit or down for more loose fit and continue from this point in both directions.
Works the same for the body.

Sleeves:
Provisional Cast on 30sts in round with 5,5mm needles. Knit to shoulder with following increases:
(k 9rd, k1 rd with 2 inc at start and end of rd) x7
Total=44sts now
(k 5rd, k1 rd with 2 inc at start and end of rd) x5
Total=52sts now
k 10rd straight stockinette.

Body:
Provisional cast on 126sts, 5,5mm needles.
Knit 1 rd.

Yoke:
Join Body & Arms on one needle:
Put 8 sts on hold under each arm/body side.
Knit 1 rd.
Add short rows on the back: +6 rows extra.
Knit 1 rd.
Follow colorwork pattern. Follow decreases of the Alafoss-Pattern.
Add +4 short rows in back after last colorwork-round.
Knit on with Dec Rounds according to Alafoss Pattern.
Bind off with 6mm crochet hook. Leave rim rolling.

Neckline:
I changed the neckline after finishing the body: made it more narrow and added the same edge like the body hem.

Body knit downwards:
Take the live stitches from prov. cast on onto needle.
Knit 3 rows straight down.
Following the body shaping of Sing-Winter Pattern.
After last inc round knit xx rounds straight.
Add +6 short rows in the back.
Knit 3-4 rounds straight.
Change to contrast colour (blue).
Purl 2 rounds.
Knit 1 round.
Bind Off with crochet hook 6mm.

Finish sleeve lenght:
Put live stitches from provisional cast on onto 4,5mm needles (smaller needles used for cuff).
(k1,p1) all rounds until length is reached.
Bind off with 5mm crochet hook.