Step 1.Your elevation is key in solving this problem with barometric pressure. Let's tackle your elevation first.
Your CWOP registration says that you submitted that your barometric sensor is at 27 meters (89 ft).
I see that you are at 84 ft using USGS data:
https://viewer.nationalmap.gov/theme/elevation/Alternative elevation map for those outside of the US (Edit - I'm liking this site a bit better lately than the USGS topo site):
https://www.freemaptools.com/elevation-finder.htmGood Latitude / Longitude converter in case you need that:
https://www.directionsmag.com/site/latlong-converter/Forget what the phone says. That is not the most accurate information to use. It is best to use map survey data like the source I linked from USGS or from FreeMapTools.
But your barometric sensor (in your station's console) is not on the ground. We need to account for its elevation above the ground so that height needs to be included to total elevation. I'm gong to assume your WS-2902A weather station is on the first floor. Let's suppose it is at 5 ft above the ground on a kitchen counter or a shelf in the family room on the 1st floor. Perhaps it something else but I need some numbers to at least do some sample calculations. If these assumptions are wrong you can tell me what you are at and we can then make adjustments in these calculations. This would even be more important if you have this console on the 2nd floor. Your anemometer height is irrelevant for barometric calibration. Some people assume that the barometer is outside and it isn't.
Turns out that by using 89 ft (84 ft + 5 ft off the ground) matches your registration with CWOP of 89 ft or 27 meters. Good, we don't need to make any changes with your CWOP registration by using these numbers. If these numbers are wrong it is still an easy fix to email NOAA to adjust your station's barometric sensor elevation to be correct. But I'm going to assume this is right so that we can do the next calculations.
The next step is to find out what the difference between your Relative and Absolute pressure should be. This different is determined by the elevation of your barometric sensor (89 ft or 27 meters). This difference will be static (it doesn't ever change). Meaning it doesn't matter what the pressure is at any given moment as the difference between Absolute and Relative will always be the same (temperature affects this a bit but we are going to use standard temperature of 15°C or 59°F in this calculation which is the way to calculate and set configure this).
The difference between your Absolute and Relative pressure should be: 3.25 hPa or 0.096 inHg for an elevation of 89 ft or 27 meters.
Unfortunately with your weather station you can't dial in a calibration difference of that level of precision. But we can get closer by switching your console to temporarily use hPa. Then after we are done entering in this difference between Absolute and Relative you can then switch back to inHg and the calibration is still there but it was entered with the higher precision of hPa. So you enter in a difference of 3.3 hPa between Absolute and Relative. You can if you want use the less precise inHg and enter in a difference of 0.10 inHg between Absolute and Relative pressure.
Basically what we have done with this last step is tell the console that you are at 89 ft (27 meters) of elevation above sea level where the barometric sensor is. Telling the console that the difference is 3.3 hPa or 0.10 inHg says that you are at that elevation.
How I got to that number? I used the following online calculator (more details on follow-up post on how to use this site):
https://keisan.casio.com/exec/system/1224579725Then I then see the difference between Absolute and Relative which corresponds to Atmospheric pressure and Sea Level Pressure on the online calculator (Absolute and Relative mean the same thing as those things). The result I'm giving you is the difference of both numbers after you enter in your elevation (in meters for this online calculator).
Then to convert the difference in hPa to give you a difference in inHg I used this converter:
https://www.convertunits.com/from/hpa/to/inhgWhat you'll notice from the numbers you gave me before....your console is not configured for the proper elevation.
The difference between your current Absolute and Relative pressure is 0.19 inHg.
That is 6.43 hPa of difference.
Which corresponds to 54 meters or 177 ft which is way wrong. Your console thinks it is at 177 ft with your current settings.
Your difference between Absolute and Relative is about 3.1 hPa too high or 0.09 inHg too high.
After you have fixed the difference between Absolute and Relative you never touch this offset again. It remains that way to indicate that you are at 89 ft.
Step 2.The last step is to calibrate your barometer to match your Relative to the nearest Metar.
Use this map to find nearby Metars:
https://aviationweather.gov/metarThen below the map enter in the ID of the local Metar, and be sure to select "
Decoded" and then
Get METAR Data [ You are not allowed to view attachments ]
There are 3 METARs close-by to you:
KRNT
https://aviationweather.gov/metar/data?ids=KRNT&format=decoded&date=&hours=0KBFI
https://aviationweather.gov/metar/data?ids=KBFI&format=decoded&date=&hours=0KSEA
https://aviationweather.gov/metar/data?ids=KSEA&format=decoded&date=&hours=0When looking at Metar data mb is millibars which is the same units as saying hPa. So mb = hPa (HectoPascal)
This is another reason why switching your console to use hPa makes it easier and more accurate. Then when done calibrating you can switch to show inHg and everything is still calibrated.
Use those on a good clear day around noon to calibrate against. (you can do it now to get closer but then double check the next day at noon on a fair day)
To set your Relative pressure to match the Metar you'll actually be adjusting your Absolute up or down to affect a change up or down on your Relative pressure.
That last sentence I know is confusing to understand at first. So let me say it again further spelled out.
You look at the Metar from those links I provided and then you look at your current Relative Pressure before adjusting anything.
You then determine how far off you are. Meaning how much up or down is your Relative pressure compared to the Metar?
Suppose your Relative is 6.4 hPa or 0.19 inHg too high compared to Metar.
Then you need to look at the Absolute value and whatever it shows you need to lower by 6.4 hPa or 0.19 inHg.
This is because when you bump up or down the Absolute value in your console what you are actually doing is affecting the same change in the Relative value. Because the difference between Absolute and Relative is constant (since we set that before as representative of your elevation)
That is the biggest thing to realize when adjusting the barometer on these stations. Two steps are required. First you set the difference which corresponds to your elevation. Then you calibrate Relative by adjusting up or down your Absolute value, and then checking back that Relative now is calibrated. You can't change Relative directly or what you will be doing is changing your elevation. So never adjust Relative directly after you have set your difference offset value to your elevation.
Monitor your Relative pressure over a few days compared to the Metar. Make minor adjustments till you are happy. Don't go crazy though. It is impossible to always expect your barometric pressure to be exactly equal to the Metar. This can be further explained by the fact that the Metar is some distance away and the barometric pressure isobars may be not in line with your current location. There are going to be times when a given Metar is on the same isobar as you and there are going to be times when the isobars are not going to be the same as your location. That is the purpose (to use Sea Level Pressure) of comparing neighboring stations that are at different elevation. If you want to further understand isobars and how to take barometric calibration to the next level then I suggest reading this other post that I wrote. But don't jump on this other stuff just yet. First just take is simple and really grasp the content in this post before you go looking at this next advanced topic of isobars. All you need to know for this fist step is that when you are done with this that your station will be pretty well calibrated and you'll know that things are okay even on days where you seem to drift a bit from these local Metar.
https://www.wxforum.net/index.php?topic=36579.0