Well, there is such a tool, the Kestrel weather meter. This little fella is small enough to carry absolutely anywhere and easy enough to operate that anyone can use it. The unit itself made of weather resistant, strong plastic and come with a protective slip-on cover. The unit weighs in at just a few onces which makes it very easy to carry for long periods, especially with the built in carry lanyard. The instruction sheet is very well written and easy to read, with detailed illustrations for us right-brainers.
I'm sure you are wondering how the Kestrel can help you as a shooter. The answer is simple, weather and atmospheric conditions have the greatest influence on rifle and ammunition performance. Being able to diagnose those conditions and make notes of them will enable you to record better shooting data and use that data accordingly. Altitude, barometric pressure, humidity, temperature, and wind speed all play a great part in affecting performance.
Let's look a little bit at the above conditions:
*Altitude- Also known as elevation. It's measured in feet above sea level (ASL). Trajectories tend to be a little flatter at higher altitudes. Shooters who travel will find this useful. You can take an altitude reading of where you normally shoot for sighting-in data, then another reading at your destination. You can then run the two elevations through a ballistics program and compare the differences.
*Barometric pressure- Barometric pressure pushes down on bullets. The higher the pressure, the more downward force the bullet will experience. If you zero you rifle on a day with low pressure and then shoot again on a day with high pressure, you see a slight change in elevation. Knowing these conditions ahead of time can help set an accurate cold bore zero adjustment for the current conditions-excellent for long range and varmint hunting where "sighters" just aren't practical.
*Humidity- Humidity is basically moisture content in the air. The moisture more moisture in the air, the thicker the air becomes. As humidity rises, so does drag on the bullet. More drag equates to more bullet drop.
*Temperature- Temperature doesn't have a whole lot to do with bullet performance except for warm air is less dense than cold air. However, it does play a key role in powder performance. Powders are sensitive to temperatures. Some powders are more sensitive than others and how sensitive your powder is going to be is good information to know. Put simply, powders create higher pressure when they are warm. The warmer they are, the higher the pressure will be. Higher pressures will make for higher velocities. The opposite is also true. Cold powder makes lower pressures and this will create lower velocities. That means that your zero will be higher or lower depending on temperature. If your powder is very sensitive to warmer temps, it could create an over pressure situation.
*Wind speed- This one most all shooters understand. I'm sure all of us have struggled with shooting in windy conditions. Knowing the wind speed will help you with "leading" or "Kentucky windage" while aiming at your target.
For this review, Kestrel sent one of their 3500 series meters. It's a fine little tool that does all the above measurements and then some. Here's what makes the Kestrel 3500 a great meter to have:
1) It measures: Current wind speed; Maximum wind gust; Average wind speed; Air, snow & water temps; Wind chill; Relative humidity; Dewpoint; Heat stress index; Barometric pressure; Altitude; and Wet bulb temperature.
2) Design: User replaceable impeller; Instruments and components are assembled in the USA; and Thermally adjusted humidity sensor.
3) Features: Clock; Protective cover; Data hold function; Easy to read display with back-light; Waterproof; Floats; Lanyard; Auto shutdown; and Batteries (CR2032) which are included.
4) Warranty: The Kestrel 3500 has a two year warranty that covers parts and labor.
The Kestrel 3500 has retail price of $249. That is not cheap but few well made precision instruments are. I believe the information that the meter can provide to a serious shooter is worth that investment.