La Crosse WS2813u barometric pressure way off

[kufuu]

I just purchased an old but never used La Crosse WS2813u-it weather station with weewx 4.10.2 and the Barometric pressure is much higher on weewx than on the console, any thoughts ?

[vince]

Uncertain how 'way' it is off....is it high ?  low ?  how different ?

Does https://github.com/weewx/weewx/wiki/Barometer,-pressure,-and-altimeter help any ?

[kufuu]

The console shows 30.02 which is right with my other stations and weewx shows 32.03

[kufuu]

I found this on WXForum.net but have no idea how to correct it,    
https://www.wxforum.net/index.php?topic=41276.0

[Tom Keffer]

See the wiki article on atmospheric pressure. It's possible that your station is reporting "gauge" temperature. WeeWX reports pressure corrected to sea level.

If you're convinced that you're comparing the same type of pressure, then check the entry for altitude.

-tk

On Fri, Jul 25, 2025 at 11:21 AM kufuu <toef...@gmail.com> wrote:

I just purchased an old but never used La Crosse WS2813u-it weather station with weewx 4.10.2 and the Barometric pressure is much higher on weewx than on the console, any thoughts ?

--
You received this message because you are subscribed to the Google Groups "weewx-user" group.
To unsubscribe from this group and stop receiving emails from it, send an email to weewx-user+...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/weewx-user/fde00adc-8b99-4294-8cea-939e97b5a8a2n%40googlegroups.com.

[kufuu]

weewx script

Jul 25 15:55:47 weewx-weather weewx[2911] DEBUG user.mqtt: data: {'dateTime': '1753473300.0', 'inTemp_F': '73.58000000000001', 'inHumidity': '54.0', 'outTemp_F': '87.07999999999998', 'outHumidity': '66.0', 'pressure_inHg': '29.99951430125', 'rain_in': '0.0', 'windSpeed_mph': '0.44738837038786095', 'windDir': '22.5', 'windGust_mph': '1.3421651111635826', 'windGustDir': '22.5', 'interval_minute': '5.0', 'usUnits': '1.0', 'altimeter_inHg': '32.08486850330134', 'appTemp_F': '96.78463511145246', 'barometer_inHg': '31.986219029757965', 'cloudbase_foot': '4771.9496637540215', 'dewpoint_F': '74.31142147948229', 'heatindex_F': '95.85380134124786', 'humidex_F': '106.47314915297711', 'inDewpoint_F': '55.89516079858936', 'rainRate_inch_per_hour': '0.0', 'windchill_F': '87.07999999999998', 'windrun_mile': '0.037282364198988414', 'hourRain_in': '0.0', 'rain24_in': '0.050787401574803145', 'dayRain_in': '0.04062992125984252'}

[Tom Keffer]

You didn't mention that you have an MQTT intermediary. 

Most likely whatever is receiving the MQTT packets is mapping type "barometer_inHg" to the WeeWX observation type "barometer." They both have roughly the same value.

So, either your console is, in fact, reading gauge pressure (not sea-level pressure), which would explain why it's lower, or whatever is generating your MQTT packets is mapping values to the wrong MQTT types. 

Are you POSITIVE that the console is showing sea-level pressure? Unless the LaCrosse knows something about altitude, it's probably showing gauge pressure (possibly with a correction value).

If you are positive, then look at whatever is generating the MQTT packets. It's getting the values wrong.

-tk

[kufuu]

Weewx must have picked that up from a previous weather station, reinstalling weewx without all the mqtt stuff and it is still

Outside Temperature 85.9°F
Heat Index 93.8°F
Wind Chill 85.9°F
Dew Point 73.9°F
Outside Humidity 68%
Barometer 31.878 inHg ( N/A)
Wind 0 mph N/A ( N/A)
Rain Today 0.00 in
Rain Rate 0.00 in/h
Inside Temperature 71.6°F
Inside Humidity 56%

Log

Jul 26 10:50:02 raspberrypi weewx[554] DEBUG weewx.drivers.ws28xx: handleHistoryData: appending history record 1: {'dateTime': 1753541400, 'inTemp': 22.0, 'inHumidity': 56, 'outTemp': 29.799999999999997, 'outHumidity': 69, 'pressure': 1012.5, 'rain': 0.0, 'windSpeed': 0.0, 'windDir': None, 'windGust': 0.0, 'windGustDir': None}

And the console shows 29.90inHg

Will let it run a while to see if anything changes.

[kufuu]

Still no change in BP after deletion of all mqtt components and reinstalling weewx !!

[Tom Keffer]

Let's check what's going on in weewxd.

1. Set debug=1 in weewx.conf.

2. Run weewxd directly from the command line, and post the output from startup through the first archive record. Make sure you post both LOOP and REC outputs. This will show us what values weewxd is processing.

3. For the same period of time, post the system log from the startup through the first archive record. This will show us internally what weewxd is doing.

-tk

To view this discussion visit https://groups.google.com/d/msgid/weewx-user/cdd5a7b8-f9ac-4a3c-8681-1ebbf73711b5n%40googlegroups.com.

[kufuu]

[kufuu]

Current Conditions ♦
Outside Temperature 78.6°F
Heat Index 80.3°F
Wind Chill 78.6°F
Dew Point 74.6°F
Outside Humidity 88%
Barometer 31.969 inHg (0.011)

Wind 0 mph N/A ( N/A)

Rain Today 0.12 in
Rain Rate 0.00 in/h
Inside Temperature 73.9°F
Inside Humidity 57%

[kufuu]

[matthew wall]

hi kufuu,

as i understand it, you are seeing values for 'pressure' on the console. the values for 'barometer' are around 31.94 and 'pressure' are around 29.9.

you said you are seeing values around 29.9 on the console. is this correct?

if so, then the discrepancy is simply that the console is displaying pressure (the raw sensor readings) whereas weewx is displaying barometer (which is derived from pressure).

apologies in advance for slow response to this thread, but i am racing for the next few days and will not be back to a stable computer/network until next week.

m

> On Jul 31, 2025, at 08:35, kufuu <toef...@gmail.com> wrote:
>
> Finally got the LOOP- REC
> LOOP: 2025-07-31 08:31:02 EDT (1753965062) 'altimeter': '31.994965595814566', 'appTemp': '82.21392182410236', 'barometer': '31.943187567801353', 'cloudbase': '2960.322777616846', 'dateTime': '1753965062', 'dewpoint': '69.84057977848587', 'ET': 'None', 'heatindex': '75.821', 'humidex': '89.87136422415446', 'inDewpoint': '55.657507277210414', 'inHumidity': '59', 'inTemp': '70.7', 'inTempBatteryStatus': '0', 'maxSolarRad': '303.4440342696196', 'outHumidity': '85', 'outTemp': '74.66', 'outTempBatteryStatus': '0', 'pressure': '29.919783335', 'rain': '0.0', 'rainBatteryStatus': '0', 'rainRate': '0.0', 'rxCheckPercent': '100', 'usUnits': '1', 'windBatteryStatus': '0', 'windchill': '74.66', 'windDir': 'None', 'windGust': '0.0', 'windGustDir': 'None', 'windrun': 'None', 'windSpeed': '0.0'
> REC: 2025-07-31 08:30:00 EDT (1753965000) 'altimeter': '31.994965595814566', 'appTemp': '82.27412271683694', 'barometer': '31.943891983670653', 'cloudbase': '2727.7835087874173', 'dateTime': '1753965000', 'dewpoint': '70.68375256133537', 'ET': 'None', 'heatindex': '75.76400000000001', 'humidex': '90.44043121162365', 'inDewpoint': '55.657507277210414', 'inHumidity': '59.0', 'inTemp': '70.7', 'inTempBatteryStatus': '0.0', 'interval': '5.0', 'maxSolarRad': '297.0055413107822', 'outHumidity': '88.0', 'outTemp': '74.48', 'outTempBatteryStatus': '0.0', 'pressure': '29.919783335', 'rain': '0.0', 'rainBatteryStatus': '0.0', 'rainRate': '0.0', 'rxCheckPercent': '100.0', 'usUnits': '1', 'windBatteryStatus': '0.0', 'windchill': '74.48', 'windDir': '225.0', 'windGust': '1.3421651111635826', 'windGustDir': '225.0', 'windrun': '0.027961773149241306', 'windSpeed': '0.33554127779089565'
>
>
> On Tuesday, July 29, 2025 at 8:37:37 PM UTC-4 kufuu wrote:
> I set Debug to 2 and reran a start log, hope this helps !

> To view this discussion visit https://groups.google.com/d/msgid/weewx-user/719b04de-3035-4161-b50c-3ce7f9e26418n%40googlegroups.com.

[kufuu]

Let me redo this and put the dates in order,

LOOP:   2025-07-31 08:45:20 EDT (1753965920) 'altimeter': '31.994965595814566', 'appTemp': '82.83203424777768', 'barometer': '31.942483641883886', 'cloudbase': '2805.6732703464695', 'dateTime': '1753965920', 'dewpoint': '70.70103761047554', 'ET': 'None', 'heatindex': '76.113', 'humidex': '90.81599237942409', 'inDewpoint': '55.52280883736111', 'inHumidity': '58', 'inTemp': '71.06', 'inTempBatteryStatus': '0', 'maxSolarRad': '357.687499228319', 'outHumidity': '87', 'outTemp': '74.84', 'outTempBatteryStatus': '0', 'pressure': '29.919783335', 'rain': '0.0', 'rainBatteryStatus': '0', 'rainRate': '0.0', 'rxCheckPercent': '100', 'usUnits': '1', 'windBatteryStatus': '0', 'windchill': '74.84', 'windDir': 'None', 'windGust': '0.0', 'windGustDir': 'None', 'windrun': 'None', 'windSpeed': '0.0'
REC:    2025-07-31 08:45:00 EDT (1753965900) 'altimeter': '31.994965595814566', 'appTemp': '82.83203424777768', 'barometer': '31.942483641883886', 'cloudbase': '2805.6732703464695', 'dateTime': '1753965900', 'dewpoint': '70.70103761047554', 'ET': 'None', 'heatindex': '76.113', 'humidex': '90.81599237942409', 'inDewpoint': '55.52280883736111', 'inHumidity': '58.0', 'inTemp': '71.06', 'inTempBatteryStatus': '0.0', 'interval': '5.0', 'maxSolarRad': '351.7781598061274', 'outHumidity': '87.0', 'outTemp': '74.84', 'outTempBatteryStatus': '0.0', 'pressure': '29.919783335', 'rain': '0.0', 'rainBatteryStatus': '0.0', 'rainRate': '0.0', 'rxCheckPercent': '97.5', 'usUnits': '1', 'windBatteryStatus': '0.0', 'windchill': '74.84', 'windDir': 'None', 'windGust': '0.0', 'windGustDir': 'None', 'windrun': '0.0', 'windSpeed': '0.0'
Traceback (most recent call last):
  File "/usr/share/weewx/weewx/reportengine.py", line 248, in run
    obj.start()
  File "/usr/share/weewx/weewx/reportengine.py", line 465, in start
    self.run()
  File "/usr/share/weewx/weewx/reportengine.py", line 621, in run
    ncopy += weeutil.weeutil.deep_copy_path(path, html_dest_dir)
  File "/usr/share/weewx/weeutil/weeutil.py", line 1811, in deep_copy_path
    shutil.copy(path, d)
  File "/usr/lib/python3.9/shutil.py", line 418, in copy
    copyfile(src, dst, follow_symlinks=follow_symlinks)
  File "/usr/lib/python3.9/shutil.py", line 264, in copyfile
    with open(src, 'rb') as fsrc, open(dst, 'wb') as fdst:
PermissionError: [Errno 13] Permission denied: '/var/www/html/weewx/seasons.css'

[kufuu]

It can wait till then and good luck, 

[kufuu]

If I put 0 altitude in weewx config then it reads what is on the display, is there any way to correct or just leave it 0 ? 

[michael.k...@gmx.at]

Which obs_type "reads what is on the display", when altitude is set to 0? pressure, altimeter or barometer or all three? (It should be all three) When setting your altitude, pressure should always "read what is on the display", altimeter and barometer will change with the altitude you configure.

You should calibrate your station to the real pressure provided by a reliable station near you, which is located at the same altitude. Then configure the altitude of the station in weewx, then choose the obs_types you want to have displayed in your report. Depending on what you choose, the may or may not  "read what is on the display", which is perfectly fine for altimeter and barometer.

[gszla...@gmail.com]

The three pressures on your LOOP was "altimeter", "barometer" and "pressure".

If you set station altitude = 0 then you are telling your weather station's barometer that it is located at sea level.

Therefore all three pressures shouldl read the same.

"pressure" is just your local atmospheric pressure at your location's altitude..

"altimeter" is a sea level pressure that factors in your altitude above sea level and "corrects" your local pressure (station pressure) and calculates an equivalent pressure at sea level.

"barometer" is also a sea level pressure except it factors in your station pressure "(pressure" in WeeWX) , local  temperature and humidity and "corrects" it to an equivalent pressure at sea level. 

I took a quick look at your weather station's manual and it appears that your display console reads "relative pressure" only. So in your case if you set station altitude = 0 in WeeWX, WeeWX's SLP correction will calculate a correction = 0. It makes sense because you told WeeWX you are located at sea level so there is no need to correct your "pressure" to sea level - you are already at sea level! Therefore "pressure" = "barometer" at sea level ( altitude = 0).

I am not familiar with LaCrosse barometer operations- but I'll try to help. Other LaCrosse owners can certainly jump in...

Things to check.

1. What have you entered as your station altitude in WeeWX? Did you ensure that the station altitude you entered in WeeWX is the altitude of the barometric sensor (total height above sea level?) How did you calculate your station altitude?

2. Your weather station manual makes no mention of sea level pressure calculations, entering an altitude or elevation in your display console.or using an offset. The manual implies that the console only displays relative pressure?  Can you confirm that?

3. How close are you to an official weather station at an airport? Can you provide the ICAO code for it? Or the name of the airport?

4. Your July 31 LOOP altimeter and barometer readings appear to be unseasonably high for typical summertime weather. 

5. WeeWX is calculating altimeter correctly but WeeWX  barometer seems high compared to the Starpath online SLP calculator using the same input parameters. WeeWX "barometer" should be close to be the same or less than "altimeter" at the temperatures you reported.

6. Does your weather station use PC software from the manufacturer? If so, what is it reporting currently for absolute pressure and relative pressure? Can you adjust your absolute pressure?

7. Can you do another LOOP and give us the three pressures (altimeter, barometer, and pressure)?

At the same time you do a LOOP ,can you obtain the altimeter setting of a close-by airport. And finally, can you obtain the elevation of that airport.

 Summing up, we need: your station altitude, your weather station's absolute pressure, relative pressure and the current WeeWX LOOP pressure values (altimeter, barometer, and pressure) and the LOOP outside temperature. In order to make some pressure comparisons and accuracy checks. We would also need , the name(s) of any close-by airport(s) and how close you are to these airports. lus we need the airport altimeter setting reading and elevation. As Tom mentioned in the wiki, you have to be careful about comparing your relative pressure on your display console with the WeeWX "barometer" calculation. They could be two different things.

Michael's advice is I think, correct. You probably need to re-calibrate or at least verify if your station pressure/absolute value is accurate.

[kufuu]

My actual elevation is 1865ft , weewx is set to 0

Using configuration file /etc/weewx/weewx.conf

REC:    2025-08-20 18:35:00 EDT (1755729300) 'altimeter': '29.856197863702114', 'appTemp': '84.16620032955495', 'barometer': '29.850973617639387', 'cloudbase': '1750.7310847902036', 'dateTime': '1755729300', 'dewpoint': '69.42478322692313', 'ET': 'None', 'heatindex': '77.86800000000002', 'humidex': '91.66911741879971', 'inDewpoint': '56.232061622715676', 'inHumidity': '56', 'inTemp': '72.86000000000001', 'interval': '5', 'maxSolarRad': '192.36417227192797', 'outHumidity': '78', 'outTemp': '76.82000000000002', 'pressure': '29.778039395', 'rain': '0.0', 'rainRate': '0.0', 'usUnits': '1', 'windchill': '76.82000000000002', 'windDir': 'None', 'windGust': '0.0', 'windGustDir': 'None', 'windrun': '0.0', 'windSpeed': '0.0'

LOOP:   2025-08-20 18:35:44 EDT (1755729344) 'altimeter': '29.856197863702114', 'appTemp': '84.16620032955495', 'barometer': '29.850973617639387', 'cloudbase': '1750.7310847902036', 'dateTime': '1755729344', 'dewpoint': '69.42478322692313', 'ET': 'None', 'heatindex': '77.86800000000002', 'humidex': '91.66911741879971', 'inDewpoint': '56.232061622715676', 'inHumidity': '56', 'inTemp': '72.86000000000001', 'inTempBatteryStatus': '0', 'maxSolarRad': '189.6877965534115', 'outHumidity': '78', 'outTemp': '76.82000000000002', 'outTempBatteryStatus': '0', 'pressure': '29.778039395', 'rain': 'None', 'rainBatteryStatus': '0', 'rainRate': '0.0', 'rxCheckPercent': '100', 'usUnits': '1', 'windBatteryStatus': '0', 'windchill': '76.82000000000002', 'windDir': 'None', 'windGust': '0.0', 'windGustDir': 'None', 'windrun': 'None', 'windSpeed': '0.0'

KPSK dublin VA

Current conditions at Dublin / New River Valley (KPSK) Lat: 37.13°NLon: 80.68°WElev: 2106ft.

Mostly Cloudy

76°F

24°C

Humidity
76%
Wind Speed
E 7 mph
Barometer
29.95 in
Dewpoint
68°F (20°C)
Visibility
10.00 mi
Heat Index
77°F (25°C)
Last update
20 Aug 6:35 pm EDT

More Information:

Local Forecast OfficeMore Local Wx3 Day HistoryHourly Weather Forecast

[kufuu]

Im about 15 miles away

[kufuu]

Correction , I have weewx set at 70ft elevation to try and match another weather station, sorry about that.

[gszla...@gmail.com]

Given:

Aug 20 6:35 pm

Altitude (true) = 1865 ft
WeeWX altitude = 70 ft
WeeWX altimeter= 29.86 inHg (rounded))
WeeWX barometer = 29.85 inHg (rounded)
WeeWX pressure = 29.78 inHg (rounded)

NOTE: at altitude = 70 ft we are very close to sea level (altitude = 0). As mentioned in my previous post, all three pressures hypothetically, should be the same at sea level. We can see that clearly happening at the 70 ft altitude where the readings start getting closer together.

Aug 20 18:35 (from mesowest):

KPSK elevation = 2106 ft
KPSK pressure = 27.74
KPSK altimeter = 29.95

EXAMPLE station elevation calculation:

LaCrosse true altitude = 1865 ft
KPSK altimeter= 29.95 inHg

Solving for LaCrosse "pressure" = 27.99 inHg

As reported LaCrosse "pressure" = 29.78 inHg

It looks like your current pressure of 29.78 is much too high.

In order to calculate altimeter, at a location with a 1865 ft altitude, your relative pressure on your console should always be reading 1.96 Hg higher than your current live absolute pressure ("pressure").

To re-calibrate your display console:

1. Calculate your station pressure (follow the example above) and then add 1.96 to this number to get your corrected relative pressure. Modify the existing relative pressure in your display console.
2. Your pressure is wrong and you will have to fix it. I was unable to find a way to modify your absolute pressure from your manual. You may have to contact LaCrosse and see how this may be done.
3. Alternatively, I believe there is a way to add a pressure calibration offset in the WeeWX config file.

4. Once you fixed your absolute pressure and relative pressure,, don'forget to put back your correct station altitude of 1865 ft.

---

[gszla...@gmail.com]

EDIT: Sorry. I meant to say station pressure calculator not station elevation calculator

You can use this station pressure calculator: https://www.sensorsone.com/elevation-station-qfe-sea-level-qnh-pressure-calculator/?ab=1&v0=1865&f0=ft&f1=inHg0C&f2=inHg0C

Note: This calculator uses aviation terms. QFE = station pressure and QNH = altimeter setting. I've already entered in your elevation. All you have to do is enter in the altimeter setting of your airport in the QNH input field and the calculator will calculate your QFE (station pressure).

---

[kufuu]

Thanks

[gszla...@gmail.com]

Unfortunately your LaCrosse model has been "retired" and from looking at a number of posts at wxforum.net it appears that your absolute pressure value is not user adjustable. Therefore, we can try using WeeWX to modify/re-calibrate your absolute pressure/pressure.

Restore the station altitude back to 1865 ft  Try putting in a calibration offset of -1.79 inHg. in your weewx.conf file (see below). Restart WeeWX then run another LOOP to obtain the three pressures; "pressure", "altimeter" and "barometer" to see iif barometer and altimeter seem to be more accurate.  When you are comparing pressure values from your weather station  to an airport you must ensure tht both you and the airport  you are comparing with is in the same pressure system, i.e, the same high pressure or low pressure system, KPSK is considered to be a close-by airport 15 miles/25 km so chances are you should be in the same pressure system. Any other airport farther away gets a bit trickier.

If you wish to read a bit more about barometer set-up, configuration and troubleshooting, check out the barometer wiki at www.barometer-wiki.ca/barometer. 

Good luck!

[StdCalibrate]       
    [[Corrections]]  
      pressure = pressure - 1.79

[kufuu]

REC:    2025-08-24 08:50:00 EDT (1756039800) 'altimeter': '30.029532326429237', 'appTemp': '72.57562147734592', 'barometer': '29.981221699640386', 'cloudbase': '2929.6889799923492', 'dateTime': '1756039800', 'dewpoint': '63.31536848803366', 'ET': 'None', 'heatindex': '68.495', 'humidex': '78.03578397157159', 'inDewpoint': '54.71694388930514', 'inHumidity': '61', 'inTemp': '68.72', 'interval': '5', 'maxSolarRad': '315.9994602721425', 'outHumidity': '85', 'outTemp': '68.0', 'pressure': '28.058911365', 'rain': '0.0', 'rainRate': '0.0', 'usUnits': '1', 'windchill': '68.0', 'windDir': 'None', 'windGust': '0.0', 'windGustDir': 'None', 'windrun': '0.0', 'windSpeed': '0.0'
LOOP:   2025-08-24 08:51:41 EDT (1756039901) 'altimeter': '30.029532326429237', 'appTemp': '72.82860931324616', 'barometer': '29.98054422916703', 'cloudbase': '2930.511265697056', 'dateTime': '1756039901', 'dewpoint': '63.49175043093296', 'ET': 'None', 'heatindex': '68.69300000000001', 'humidex': '78.34213268284668', 'inDewpoint': '54.71694388930514', 'inHumidity': '61', 'inTemp': '68.72', 'inTempBatteryStatus': '0', 'maxSolarRad': '322.44979536500733', 'outHumidity': '85', 'outTemp': '68.18', 'outTempBatteryStatus': '0', 'pressure': '28.058911365', 'rain': 'None', 'rainBatteryStatus': '0', 'rainRate': '0.0', 'rxCheckPercent': '100', 'usUnits': '1', 'windBatteryStatus': '0', 'windchill': '68.18', 'windDir': 'None', 'windGust': '0.0', 'windGustDir': 'None', 'windrun': 'None', 'windSpeed': '0.0'

[kufuu]

Current conditions at Dublin / New River Valley (KPSK) Lat: 37.13°NLon: 80.68°WElev: 2106ft.

Overcast

67°F

19°C

Humidity
88%
Wind Speed
SW 3 mph
Barometer
30.02 in
Dewpoint
64°F (18°C)
Visibility
10.00 mi
Last update
24 Aug 8:35 am EDT

[gszla...@gmail.com]

WeeWX:
altimeter': '30.029
barometer': '29.98
pressure': '28.058

KPSK 2025-08-24 08:35:00 altimeter = 30.02 inHg

KPSK 2025-08-24 08:35:00 SLP =1014.22 = 29.95 inHg

You are spot on with altimeter!

KPSK does not publish SLP in its METAR so I had to hunt around for it. You can us your NWS Time series Viewer to get SLP.. WeeWX refers to SLP as "barometer".

I'd say you are now calibrated.

[kufuu]

Thank You very much !!