S'not difficult to see some issues here... I'm not experienced with Hail teams, but I can see some things that need fixin'.
-Froslass
I'm not sure why you're LEADING with Froslass, especially since she's packin' Blizzard, and at this point, you have no Hail, not to mention, she's Scarfed, and yet she's packing Confuse Ray. Besides that, she's TIMID (Attack reducing nature), and packing a physical Ice attack with 40 power? Ice Shard's not going to do her much good. DBond with Scarf isn't too terrible, but I would definitely consider swapping out Confuse Ray and Ice Shard for Shadow Ball and T-Bolt if you're gonna keep her Scarfed. If not, I'd probably invest in Taunt. I'd take a look at T-Wave, too, since paralysis is just so darn useful. As for item, if you don't go with Scarf, I'd consider Wise Glasses, Leftovers, or a good ole' Sash.
-Abomasnow
THIS is what you oughta be leading with, since you wanna get Hail up as quick as possible. Besides that, I'm not sure it's a good idea to pack Blizzard AND Ice Shard, especially considering you're apparently investing everything in both Atk AND Sp.Atk- is there really a point to investing so much in Atk when your only physical move is a 40 power Ice priority? Protect is good for scouting, but if you're going to bother with Leech Seed, invest more in his defenses for some bulk. Besides that, I'd probably pack either Life Orb or Leftovers, and try mixing it with Blizzard and Wood Hammer- Life Orb will boost the power of both attacks, and Leftovers will help soften that Wood Hammer recoil. You might get some interesting results with the proper spread. If you give him Leftovers, try investing enough HP EVs that his HP is divisible by 16, so he'll get max Leftovers recovery.
-Weavile
Brick Break, Fake Out, and Ice Shard are pretty standard, but I worry as to the usefulness of Double Hit, not to mention you don't have a Dark STAB. Night Slash is WORTH investing in, and you might wanna play around with trying Ice Punch and/or Swords Dance over Fake Out and Ice Shard. Weavile's a tough Pokemon to fuck up, so it really comes down to experimentation- I'll note that I have a SubPunching Sneasel set on the UU Discussion thread in the UU Dojo which works REALLY well, and may be worth looking into for Weavile, as well.
-PorygonZ
PorygonZ is pretty easily one of my favorite Pokemon, but I'm not sure how this one would fair... The usual set tends to involve BoltBeam, Nasty Plot, and Tri-Attack, but I personally like a Hasty or Naive PZ with 252 Atk, 252 Spd, and 6 Sp.Atk to abuse the Adaptability boost to Return- Blissey pisses herself when PZ comes at her with a 204 power Return. Blizzard makes sense over Ice Beam, thanks to Hail, and T-Bolt completes the combo, but Dark Pulse isn't all that useful, and HP Fire doesn't seem to have too much purpose here. If you were gonna Scarf anything, this would be it.
-Charizard
I can tell you right now that BellyZard cannot and will not function well here. Consider this- you switch in after your Pokemon faints. You Sub, losing 25% HP, and then Hail hits, losing you another 12%. 37% gone. You BellyDrum, losing 50%, and Hail hits you again. Salac triggers. 99% HP gone, assuming the opposing Pokemon hadn't broken your Sub. Because of Hail, you'd only have time for ONE attack. BellyZard does NOT work on Hail teams. If you chose Charizard for the convenient Fighting and Fire resistances, go with Moltres instead, unless you've got something different planned for Charizard.
-Mamoswine
Mamo can scare off a lot of opponents... Once again, Double Hit doesn't belong here. I'd replace it with, say, Curse, or Stone Edge/Rock Slide. Also, I'd train it in Atk and Spd instead of HP and Atk. 259 can outrun walls easily enough, and that's where Mamoswine shines- Banded, with max Atk and Spd to break walls.
-Team as a Whole
I can say right off the bat that you may want to invest in a Spinner, since Stealth Rock will destroy you otherwise- PorygonZ is the only Pokemon on this team that won't take 25%+ from Stealth Rock alone. Remember, with Magic Guard, Clefable doesn't take damage from Rocks OR Hail, so I'd consider that, and while Moltres is 4x weak against Rocks, It DOES pack those nifty Fighting and Fire resistances. Starmie and Tentacruel ALSO resist Fire and Fighting attacks, and both learn Rapid Spin.
Just giving an idea for each Pokemon.
Abomasnow @Life Orb/Leftovers
-Blizzard/Ice Shard
-Wood Hammer
-Focus Punch/Earthquake
-Protect/Substitute
Snow Warning, Naughty
124 HP, 252 Atk, 132 Sp.Atk
Life Orb/Leftovers Mixer.
Froslass @Bright Powder
-Blizzard
-Shadow Ball
-Thunderwave
-Taunt
Snow Cloak, Timid
252 Sp.Atk, 252 Spd, 6 HP
Snow Cloak hax Sp.Sweeper with Taunt and Paralysis support.
Weavile @Leftovers/Liechi/Salac
-Substitute
-Focus Punch
-Ice Punch
-Night Slash
Pressure, Jolly
252 Atk, 252 Spd, 6 HP
SubPunch Weavile with Liechi or Salac options.
PorygonZ @Choice Scarf
-Return
-Blizzard
-Thunderbolt
-Trick
Adaptability, Hasty
252 Atk, 252 Spd, 6 Sp.Atk
TrickScarf Mixer PZ.
Charizard @Leftovers
-WilloWisp
-Dragon Dance
-Flare Blitz
-Earthquake
Blaze, Jolly
252 Atk, 252 Spd, 6 HP
DDZard with WilloWisp support.
Mamoswine @Choice Band
-Ice Shard
-Avalanche
-Earthquake
-Stone Edge
Snow Cloak, Adamant
252 Atk, 252 Spd, 6 HP
Banded WallBreaker.
Clefable, Starmie, Tentacruel, and Moltres would all make fine additions to the team, considering Clefable's got Magic Guard, Starmie and Tentacruel pack good resistances as well as Rapid Spin, and Moltres just has good resistances. Good luck. ^^