Need advice on sleeping bag for winter trek in north central states

[Timinator]

Hi I may or may not decide to hike the cdt during the winter this year in the wyoming and montana states and I'm kind of stuck on a bag choice. From what I understand a -10 degree bag is appropriate for those kinds of conditions at least but my budget is about $500 tops which leaves me with a quality 0 degree bag at best or some heavy synthetics. Does anyone have any ideas for me? Perhaps shine some light on the actual expected temps in those states during the winter.

[kayak karl]

this bag (http://www.golite.com/Adrenaline-800-Fill-4-Season-Mummy-Long-P46820.aspx) held true down to -10 for me

[Timinator]

interesting bag for the price but can it go below -10? if my knowledge is correct temps can go down to -40 out there so having a bag that has a starting rating of -10 would be best.

[mn_scout]

You can just google for -- average high low temperatures montana -- and see lots of data. weatherbase.com lists towns all over the state. It gets COLD in the winter in Montana, lower than -10. At East Glacier, the ave hi in Dec and Jan is 32 and the ave. low is 14. The record low there is -38 and -32.

[Timinator]

My best plan so far is to buy http://marmot.com/products/lithium_membrain on a discounted website with http://www.rei.com/product/797114/sea-to-summit-thermolite-reactor-extreme-mummy-bag-liner and turn it into a makeshift-10 degree bag. The survival rating on the bag is almost -40 so i guess it might do....just wish these low rating bags werent so freaking expensive.

[Llama Legs]

I've had good luck using two bags from my "quiver". I use a large 45 degree semi-rectangular synthetic bag on the outside with a 20 degree down bag inside. If both are too hot, you can use the outer bag as more ground insulation and padding. If you get snow blowing on you, the synthetic will be insulated enough to where it won't melt or if it does, doesn't get to the down. Add a big gore-tex bivy and you pretty much have what the current military uses.