I got out today(7F and 20mph) with my 22 shooting Winchester Xpert22. I initially called 1/2 value, but impacts said anywhere from 0 to 1/4 value. Is there any tricks to calling wind when vegetation is leafless?

Wind VALUE and SPEED can be estimated at the shooting position by feel or meter.  Downrange/Midrange and at the target- if you can't see the effects of wind, you simply can't make a call.  Solution... stakes with ribbon or flags... if there is no vegetation, smoke, or mirage to read, you have to make something to read.  Other than that... I have nothing... sorry.

I ended up correcting off splash off the backstop. I know that's no good for hunting, though.

Well... at least you tried to use what you could.  My suggestion reference flags and ribbons are useless in hunting unless you are stand hunting and can put them out ahead of time.  No different than yardage stakes for bowhunting.

At what range were you shooting?  Typically, a 10mph full value wind will blow a centerfire round about 1 MOA per 100 yards (1 inch at 100, 2 inches at 200, etc.).  It varies some with different rounds, but 1 MOA / 100 yds is a good rule of thumb, or at least somewhere to start.  I'm not sure about a 22lr, but at shorter ranges (25-50 yards), it could get tough to determine how much the point of impact was changed by the wind.

As for reading the wind, I've used a long knife with a streamer as a flag.  You can also use the following:

3-5 mph:  You can feel it on your face.
5-8 mph:  leaves on any plants are blown continuously.
8-12mph: blows around lose paper, wrappers, larger leaves, raises dust.
12-15mph:  small trees sway.

I know you said you didn't have any vegetation, so the above may not be that helpful.  I put it out there just so you'll know a 20 mph wind is a pretty strong wind.  I'm wondering if you over estimated it?

Isn't the easiest way to do it to use a wind meter and a ballistic calculator app?

Yes... but that only provides limited information AT THE SHOOTER'S POSITION.  If shooting at distance, it's a good idea to get a reading at mid range and at the target... what wind is doing AT the shooter's position may or may not be the same at mid range or at the target.  

In the OP's case, a lack of anything down range to read off of was his concern...

My phone said 22 mph, and I could hear the wind constantly.  I misjudged the angle, hence my question about tips for the wintertime.

Trick you can use,

Purchase a battery operated remote or wireless weather station that has wind speed and direction.
http://www.weathershack.com/listing/complete-home-weather-stations.html
(just make sure you check the transmission distance on the system, get the longest distance that you can)

Place this station at the halfway point between your shooting position and your target, and it will give you the wind speed and direction values at the mid point, which you can then use in conjunction with the readings at your firing point.

Depending on the distances and directions that you are shooting, you can use multiple stations. You can use this with target shooting or hunting, you obviously just have to make sure that your setup for hunting will not spook your game.

This can be a regular system that you use with your shooting, but if you practice calling the wind and then looking at the actual readings from the station, then it will help you build your wind reading skills over time.

Winter time is a real bitch, but you just have to use anything that you can to try and get a read on the wind.

Best of Luck,
M Richardson