• Mobile App For Android Now Online!

    Download it here. The app is searchable in the Google Play Store under Sailboat Owners.

    Sorry iPhone/iPad users, we are still waiting on Apple. :(

    Click the X in the upper right corner to make this go away
  • Sailing is all about the Weather.

    Big into the exploration of Atlantic Hurricanes since Katrina came uninvited into his world, James (Jim) Gurley (JamesG161) has followed every Tropical Storm birthed in Atlantic, Gulf and Caribbean waters since. Being a boater, he knows that we often need more time to prepare than we get from the TV weather folk. Jim relies on the science of storm development to share early warning info with friends and fellow boaters.

    Early in 2018, Jim and John Shepard, (JSSailem) started to chat about the weather data available. John asked Jim to help forecast Pacific NW storms, and this morphed into discussions on weather forecasting.

    For John, sailing in the PNW is sometimes hit and miss. One day is ugly, then a string of beautiful days but no wind, followed by a series of blue-sky days and 12 knot breezes. Being ready for those great sailing days means you need to look to the Pacific Ocean and what is brewing. John has been into Pacific NW Weather since the 1970’s when his first PNW November storm hit bringing more than 40 days and 40 nights of continual rain.

    Together we want to share information, new APPs, safety, and thoughts about letting the weather help you. Identify some of the resources for sailors and help prepare you for your next sailboat outing.

    It is far better to go out on the water knowing what to expect in weather terms, than to be out on the water and see dark ominous clouds suddenly appear, unprepared.

Barometer vs temperature

Jan 1, 2006
5,140
Slickcraft 26 Greenport, NY
My question is should I expect an inside barometer, which is an air conditioned area set at 77 degrees, to conform with barometric readings that I see on weather sites such as my Storm app?
 
Jan 11, 2014
6,099
Sabre 362 113 Fair Haven, NY
Assuming the weather app is reading a nearby station, the barometer settings should be identical. Elevation in Florida isn't a factor. The temp difference between the inside of your house and the outdoors shouldn't be a factor unless you live in a hermetically sealed house or the house is intentionally pressurized or depressurized. (Surgical suites are often pressurized to reduce the threat of air borne pathogens from entering.)
 
Jan 1, 2006
5,140
Slickcraft 26 Greenport, NY
Problem here has been the media barometric pressure has been pretty steady for the last 6 weeks i.e. 29.98" to 30.03. So I wasn't sure if it is even working. And if it changes during the day as the air heats. Thanks for the responses.
 
  • Like
Likes: jssailem
Feb 14, 2014
4,899
Hunter 430 Waveland, MS
And if it changes during the day as the air heats.
It does vary with temperature, but Jensen Beach has been in a HIGH pressure, good weather situation, like most of the Gulf States.

Perhaps you should change your units[ inch of Hg] to Milli Bars or HectoPascals. Then you can see the minor changes from Temperature.
Jim...
 
  • Like
Likes: jssailem
Jan 11, 2014
6,099
Sabre 362 113 Fair Haven, NY
Problem here has been the media barometric pressure has been pretty steady for the last 6 weeks i.e. 29.98" to 30.03. So I wasn't sure if it is even working. And if it changes during the day as the air heats. Thanks for the responses.
Good aneroid barometers should be temperature compensated, however, the ones designed for household use may not be as they are in a relatively controlled temperature environment.
 
  • Like
Likes: jssailem
Nov 6, 2006
8,812
Hunter 34 Mandeville Louisiana
Andrew, if ya go to "Weather Underground" and enter your nearest station, then go to "10 Day Forecast", it'll (or it can) show a time plot of the baro pressure that you can use to check on your meter.. (but ya prolly know that already)
 
Jan 1, 2006
5,140
Slickcraft 26 Greenport, NY
Don't assume I know anything.
I haven't understood the difference in millibars v inches. Metric v Imperial? But if millibars will allow me to better track my home barometer with the weather forecast's readings I can use millibars.
Storm app shows inches. I'll checkout Weather Underground.
 
  • Like
Likes: jssailem
Jan 22, 2008
291
Islander Freeport, 41 Ketch Longmont, CO
Also be aware that your Barometer is probably not calibrated with the other barometers in the ares (think synchronizing a watch). So your reading may not be the same. However, you should see similar movement up/down as others in your area.

Inches vs millibars is just a scale, mbar = inHg/0.029530. The measurement is the weight of the column of air above a specific point on the ground. At ground level it is the heaviest. Go up in altitude and it will change dramatically thus the need for altitude corrections. There is also probably a conversion factor for temperature to pressure since air has different densities at different temperatures as well.

The air pressure at any given time is a static reading and nice to know but doesn't tell the real story. To "predict" the weather you want to watch the CHANGE in pressure over time. The little movable hand on the barometer is used to set your reference point and then you watch to see if the pressure goes up/down. of particular interest is when it changes quickly like when a storm or low/high pressure system arrives.

Predicting the weather is always a fun game.

Fair winds
 
  • Ha
Likes: jssailem
Oct 22, 2014
13,057
CAL 35 Cruiser moored EVERETT WA
Oh the fun.
The answer is Yes Temperature affects the barometric reading you are seeing.

The more important question is it a relevant impact. Can you tell a difference in the house with a barometer at 70 degrees and outside the house with a barometer at 50 degrees.

You would need to be sure that both measuring tools were calibrated exactly the same both temperature and the barometer gauges. Then you would need the barometer to be able to report readings in .01 or .001. Additionally, the units would need to be fixed at the same elevation.

Here is a report about temperature affect on altitude readings. Altitude readings use a barometer to identify altitude by calculating the difference between a set barometric reading at a specific altitude and the barometric reading at the identified altitude.

My guess is that the difference in temp from inside and outside the house will not be evident on most barometers.

"How much does temperature affect altimeter readings?

As mentioned earlier, we can easily calibrate the altimeter for non-standard pressure settings, but we don’t have a similar mechanical calibration for non-standard temperature settings. There is a somewhat simple calculation to roughly estimate the variance, and it is 4 feet per degree Celsius of difference from standard temperature for every 1,000 feet above the reporting altitude.
In other words, you need two inputs:
  • Difference between actual air temperature and standard temperature
  • Altitude above the reporting location (for example, your destination airport)"
1602798717830.png



 
  • Like
Likes: JamesG161