seattle to oklahoma city

I have been caught in foul weather .
Right now there is enough of it everywhere .
I refilled my propane tanks at every opportunity .
I carried chains and used them .
Cold wether clothing and carried Slumberjack down sleeping bags .
Extra fleece blankets .
And lots of food .
I carry a tow strap .
Wool socks , good underwear , a couple of gore-tex jackets , extra stocking cap for when mine gets wet , good gloves .
In the end you are best to get the weather conditions at your frequent fuel stops .
The interstates will be first priority for plowing .
I have spent some nights alongside the freeway .
Good thing I had propane and warm dry clothes .

Wait and see how long it takes for this mess between Salem and Eugene Oregon to clear up, then head south. We got a foot of snow in Albany over the last 2 days and now sleet/freezing rain on top. I-5 has been closed multiple times and I saw a photo of what looked like a 30+ foot TT or 5er with the entire passenger side ripped out by a car. peeled back like a sardine can.

I would definitely go south as far as possible - even down to I-10 if the weather across New Mexico and the panhandle of Texas is bad when you get to I-40.

Play it safe.

You can't get there without going over passes and through some nasty weather, at least right now!
South on I-5 No snow and then there is the Siskiyou mountains
East anyway you go is cold and snow. Cascades over I-90 snow chains for vehicles over 10,000 pounds.
Blue mountains chains required over 10,000 pounds.
Chains mean tow vehicle and last braking axle.

"First time pulling an RV" probably without chains or 4X4. Do you want that much salt on your rigs? Go way south or fly.

I just did this (Tulsa-Seattle). As I was 40 Westbound, I looked at cutting North at each and every logical point. From chain requirements to fast moving lows to below freezing temps... I chickened out and ending going all the way to CA-99 before heading north. Just call me a chicken.

The Blue mountains east of Pendleton to Ontario Or will be hard go. You will need to keep an eye on weather.
When you get to the Iron Horse Casino east of Pendleton, pull into lot or get fuel at truck stop, then look if the trucks are going up Cabbage Hill go for it. If they are sitting in parking lot and along I-84, go gamble for a while until they go as it is a good chance chains are required.
Go to ODOT Tripcheck for better information.
Trip check

Based on what we have right now, i personally would postpone the trip a week look at the weather and then decide. Right now in the Portland area chains are required, meaning you also must chain up the trailer. And more snow is predicted for tonight. If you must go on the 11th then consider flying. If you can wait it out, do it.

Done that route many times, Houston and back, and that time of year your 1st concern would be the RV killer,mostly summer months...and that would be Cabbage just east of Pendleton. Then, again my concern, would be I-80 from Green River to Laramie...a vast stretch of nothing. There are many areas you could have weather issues that time of year but there is almost always ways to deal with it.

But given that I prefer that route than doing the get south then east thing. So do your do diligence on Cabbage in regards to the ability of your tow vehicle.

Look at the 7day NOAA weather forecasts at various points along the possible route. For Seattle they are talking about another cold day then warming, with a chance of snow in then transition, followed by a wet, possibly heavy, week. And potentially heavy snow in the mountains.

http://graphical.weather.gov/sectors/conus.php?element=Wx
NOAA forecast map for the next week. The 'weather' loop is particularly instructive. A lots going on in the west right now, though by next Thursday it looks a lot more settled - the exception of the Idaho/MT/WY border mountains.