6:18 p.m. on November 27, 2011 (EST)
Hey Mike, It’s 6:00 am and I'm up all night without being able to sleep due to my restless leg syndrome. It's a drag and can be really un-fun esp. when your out in the back country and cant sleep because of it spending all-night hour after hour laying on your back in a un-hooped bivy. The same can be said for ending up being up all night long for any reason in an un-hooped due to , injury, insomnia, not having the right sleeping bag and your way to cold to sleep, pick your reason, etc. I've done this and it's just plain miserable. Here are my suggestions regarding the matter of which you speak in your original post and it will be wordy but I’ve spent many years thinking about this and buying all my tents based upon these ideas, thoughts and decisions.
First of all traditional Bivouacs are different than traditional Bivys. The traditional Bivy in a number of was designed to be a small tent. The tradition Bivouac was designed as a system for people on the move. It was mostly designed for military forces on the move. It was designed to be a single system that incorporated a number of different layers of sleeping bags for changing conditions. It also has and is used in different forms for people who feel it's necessary under any and all conditions to summit mountains. Many Bivouacs do not close completely at the top I just bought a As New Military Mummy shaped Gore-Tex Bivouac shell the does not close at the top it’s made fo fold over so water drips of of the top which over hands the bottom. Not so good if you have swirling winds blowing raind in on your head,
The bivouac was designed to keep marching men and or men on the move warm and dry while they slept. They were usually so busy and tired form tactical moment and fighting that they did not have the time or energy in regards to being uncomfortable. They were designed to sleep in in your clothing in the bags utilizing which ever layers that came with the sleep system. They were designed to get in and out of as fast as possible so as to be able to be on the move in seconds. They were designed to get in and out of so fast that no matter what the weather you could keep it dry inside. I just bought a Military Gore-Tex Bivouac sack and will be using it for the same purposes as I just discussed but . it will only be used in my motorcycle journeys. And not backpacking.
From the Bivouac came the bivy. The bive comes in two main types, the hoop(s), and the hoopless bivy. Where the bivouac was designed to be a combined sleeping bag/shell system that was usually hoopless, the bivy was/is desigend to be a bivouac like tent that has nothing to do with the sleeping system itself and in fact is jsut mini tent. Of cource they come in double wall and single wall. When it comes to tents I like bot , but when it comes to bivys I only go with single wall. They are much, much quicker to set up a single wall bivy than a double wall bivy.
I have used single wall, double wall, hoopless, hooped and double hooped.. The hoopless bivy in my IMHO is only good for emergency situations in which your life depends on getting in as fast as possible, staying alive, and then getting out of the situation as fast a possible. For a few more ounces you can have a hooped bivy with either one or more hoops. I've used both. I like both. I feel in is not necessary to have a hoop at the end of the bivy in relation to how well the bivy works and or breaths under normal conditions esp. if you are not using it in sub freezing conditions. If you are using it in sub freezing conditions then you will not only want it to be made out of breathable fabrics but you will want it to have cross ventilation. Having a hoop at the end of the bivy does aid in being able to store the many items you will have to remove from your backpack and will aid in the drying of your wet gear. When one has a double or triple hooped bivy it should have a vent ant the end if possible. If it does not I find this to be a not as efficient in it's design as on that does have a vent a the foot of the bivy With that being said my very first Bivy was/is a Mamrot Gort-Tex called the Burrow that has a tree piece pole fpr a small amont of head roon and no hoop at the foot area. This bivy has never leadked nor has it ever had any condensation problems.
There are two ways to maintain structural integrity in regards to wind, rain, snow. A properly designed bivy will take care of all that nature has to offer with no problems including snow load,. that does not mean you will not have to get out of your bivy to unload the snow that has piled up on your bivy. If your bivy collapses under the load of snow it is not even a tent I would consider unless you are buying the tent for certain circumstances such as the tent I bought to go to Thailand. Where I’m pretty sure I will not encounter snow.
One of the first things I learned about a bivy style tent is to figure out how much sq ft you will need when you need to use your bivy. This is one of the most important starting points when dealing with small tents. As I said above with a military bivy you get in-sleep-get out- continue on with your mission. not so with the bivy, you may have to sleep in it, stay into it for days on end and (yes I know, not recommended) cook in it. Having power bars along is a great thing but if all you brought was food that needs to be cooked then you must do what you must do to eat.
If you are stuck out in the rain as we are prone for days on end in the PNW you know that you will need a place to stay dry and keep all your gear dry. If you take a guy that’s say 6 ft by 2.5ft (30in)wide, you have a square ft measurement of 15 sq ft. minimum Now measure your pack. lets round of again 4 ft tall by 30 in wide. 10 sq ft.. minimum . Now lets say you want to not have your gear touching the sides of the bivy so that you don’t get condensation. Ad a few more sq ft. So rounding out were lookng at 25 sq ft. minimum. I have a Garuda Atman which is basically like a large bivy with 21 sq ft and a few more feet in th open floored vestibule. This is an assault tent that is designed be used in high altitude where there is no rain, but only snow so that the small floor less vestibule. If I were to use this tent in the rain the vestibule would be useless as far as keeping anything dry. It could be used as a place to cook however in only in the worst of circumstances. But think about using the tent for any lent of time when you need 15 sq ft laying in a mummy position. Do you really want to store you pack out in the rain and have to go out in the rain everytime you need something. I don't, I've done this and it sucks.
One of the things you will need to think more about if your in a bivy type tent is ventilation. It's one thing if you climb in a bivy for 7-8 hours for a good nights sleep it's another thing if your waiting out a storm for days on end and even then cooking in your vestibule. As you hail in th PNW if it's raining all day everyday and your in your bivy you will have to have superior ventilation which most of all the tents made today do not contain. Since you would most likely not be in freezing weather you will not have to worry about breathable fabric freezing with ice so that it cannot breath.
It seems to me and it’s just my opinion of course that your be really happy with what I feel I have found as the perfect two man tent(s). The are all based and including the Marmot Taku and the Garuda & Dana/Design Garuda’s tents. Most weigh in at around 5 lbs., with some in the 3.5 lb range. They either have two or three polls that are really easy to set up. They are all incredibly stable in any and all weather I’ve had them in. There are a couple of other here on Trailsapce that agree with me and I can mail them and see if it's ok if I give you there name. The two problems with these tents is that no one makes such an animal any more and they sure do cost a lot for 20+ year old tents. But I have a thought. It would-be really easy to adapt a Bibler Tripod Bivy to be much like the a one man Taly or in fact not like the Garuda Atman thereby being much like the rest of Garuda line of tents. Since the Bibler Tripod has poles to hold the material up over your head and it has a hoop at the foot section you could add if more material to the rear piece that’s already attached to the rear tie down (see the Bibler link bellow) if necessary. A rear hood just like the Taku and Garuda’s would then allow you ot ad a vent at the foot section. Leaving the zipper up front would very likely give you enough cross ventilation so that with the Todd-Tex fabric you should never have any condensation. I own and have used a Bibler Tripod bivy without any adaptations to in regards to ventilation and have never had any condensation problems. The tripod bivy only weighs in at 2lb 10 oz.
Here is the Black diamond site to show you and tell you more about it.
http://www.blackdiamondequipment.com/en-us/shop/mountain/shelters/tripod-bivy/
Here is a picture of what mine looks like. It is the old school Bibler before Black Diamond bought them.

As you can see the rear of the bivy already has material attached to the tiedown so it would not take much to add material to cover the needed area that would protect a vent in at the foot of the bag as pictured in my next picture.
If you do decide on something like the Bibler tripod bivey I would go with the older yellow one rather than the newer Black Diamond one for tow reasons. They are much more plesant of a color to spend time in than any other color I have had to spend time in.
This is the tail section of off the Marmot Taku. One could easily sew on a tail section to the back of the Bibler Tripod Bivy

If you could find on of these. This is the Marmon Burrow, Marmot's first Gore-Tex bivy and this fits into your original weight parameters. Of all th bivy's I have ever woned this one is the lighest and the smalest weighing jsut over 1 lb. I will still sue this as my backpacking backup but am swithing to the Bivouac style bag cover in other situations is that if it's raining, buy the time I get the pole put together and in place and then get in the bivy I'm then wet thereby defeating the whole idea of the bivy for me in the first place.

Showing the over hang of the zippered door so tha tthe bive can be ventented. As this is a Gore-Tex bivy in which the Gore-tex works as it should I have slept with the Bivy completely closed without condensation nor asphyxiation occurring. *Note do not try this at home as some would consider this "Risky Behavior"

Last but not least is the picture of what you originally asked for in the opening post. This is a US military Gore-Tex Bivouac bag designed for a military sleeping system that I picked up of of EBay the other day for $22. It does not have a way to close it off completely and it does not have any bugnetting. It is mearly to throw your bag into and and pul over yor head. It has a zipper on th side that goes half way down the bag as well as snaps that werr designed for the military sleeping system. Just as you could pull your teeth to save some weight you could take out the snaps and use some patches to cover the snapholes save a bit (a very small bit) of weight.

Here we ahve the bivy open at the head. Notice that there is a set of patche that hold the top to the bottom. Tha is the entire closure system with the excepton of a elastic drwstring on the bottom to pull the bottom around the hood of yur sleeping bag so that the top overhangs the bottom and the rain runs of off the bivy. The problem iwht this set up is if the wind changes direction ti will blow rian directly inot the bag. One oculd of cource ad more velcro so that this does not happen.

I can take more detailed pictures if yu wish but it was pouring and not much fun outside today.
leadbelly2550 said:
"it won't surprise anyone that the tent is really the beginning of how to deal with high wind. tent placement, tent orientation, the stakes you use and the way you use guylines to secure your tent all play a very significant role in how it performs in high wind. example - a tent that might get hammered and destroyed in a hard winter storm when pitched at ground level, out in the open, can do fine if you pitch the tent in a depression, near some kind of natural rock outcropping or barrier that deflects the wind, or if you dig into snow and make a platform that's a few feet under the snow surface. having secure, well-anchored guylines for a tent fly substantially reduces the risk of a tent getting blown away.
a bivouac bag will keep your sleeping bag dry, but it's not a great option in a windy storm. leaves you and your gear more prone to getting blown around. really hard to effectively anchor a bivy."
That is so very true but quite often one ends up pitching in an area of changing wind conditions as on just has to pitch where one has to pitch due to rapidly changing weather conditions or oncoming darkness. If you put some stakes in the ground running up each side of the Bivouac (4 on each side is plenty) and run cord/webbing across the the Bivouac bag(sack) that will hold your gear in place. I've done this and it works. All the Bivy's I have/had will have their own tieouts, at least all of mine do. The Bivouac pictured does not have tie downs.