Touring - Southern Tour temperatures?

Does anyone know what the nightly temps can drop down to on the Southern Tier?
I'm starting from East coast and headed west on or about the 25th or 28th
of March. I don't want to get a sleeping bag that I'll sweat to death in.
But I don't want to freeze either.
Any info would be appreciated.

Here are some of the higher locations in the western section -

Alpine, TX:
http://cdo.ncdc.noaa.gov/climatenormals/clim20/tx/410174.pdf

Silver City:
http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?nmforb

Cliffton, AZ:
http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?azclif

Thus the high country of New Mexico will be the coldest section - on average.
You can expect average lows in the low 40s in early May.
It may be warmer - it may be colder.

You can wait a day or two in the Hatch Valley before you hit the high country.
The valley is about 10 degrees warmer - probably more in a spring cold snap.
http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?nmhatc

40-degree bag
Cheap sleeping bags rated 40 degrees don't give you much warmth.
Marmot or North Face or other quality brands might do.
Remember that you can sleep in your fleece pull-over, ski liners, and headband.

32-degree bag
Only a little more weight and much better warmth.
Plus you will have more versatility in later tours.

Are you taking a fleece pull-over?
Also - super thin ski liners provide just emough warmth for your hands.
A fleece ear band makes a huge difference on windy, chilly mornings.
Both are small and lightweight.

PS - -

You also might want to think of the heat.
By late May in the Imperial Valley the highs are in the upper 90s.
Sometimes topping 100.

Thanks for the quick reply janawani
I am taking fleece pullover and a stretchy all in one head thingy.
Actually looking forward to the heat a little bit.
It's been too cold here this year.
Now I'm off to find a 32 degree sleeping bag.
Cheers

It could be cold in the mountains in New Mexico for sure and the desert crossing will be HOT by the time you get there. But those are only a couple of days out of the trip. You have chosen a reasonable time for that route. The info jamawani has provided is good stuff.