How to Read a Surface Weather Map (opens in new tab)

(outsideonline.com)

67 pointssmir5y ago7 comments

7 comments

With regards to air pressure and isobars, if you want to do some basic forecasting as well, then the 500-millibar chart is something that should be examined. Historically (pre-satellite downloading via Iridium and Predict Wind) sailors/mariners would use them to help see what's coming for voyage planning:

* https://www.vos.noaa.gov/MWL/dec_08/milibar_chart.shtml

* https://www.oceannavigator.com/basics-of-the-500-millibar-ch...

* http://familygonesailing.com/2018/01/18/using-500mb-charts-o...

* PDF: https://ocean.weather.gov/articles/mariners_guide_500mb_char...

* https://www.amazon.com/Weather-Avoidance-Concepts-Applicatio...

lllr_finger5y ago

As a follow-up, if you're wondering why, 500mb is roughly 5700m/18kft above ground level in the US - not quite jet stream level (200-300mb) - but high enough to give insight into large scale patterns that drive surface patterns.

Where surface features are more localized and near-term, 500mb analysis gives you insight into whether there is broad zonal flow, a deepening upper trough, and all sorts of important information about how things on a larger scale can play out in the longer term. They're sometimes called "steering winds", because they're the primary component that dictates direction and speed of storms.

StringyBob5y ago

A bit more of detail of all the numbers on Wikipedia https://en.wikipedia.org/wiki/Station_model

red_admiral5y ago

This is a good start in understanding what the individual symbols mean - I hope at some point there's a follow-up to how to interpret the higher-level situation to make a forecast.

beckerdo5y ago

Be careful of the source of your station report. In the US, station report pressures related to aviation are in units of "inches mercury" ("Hg) with the preceding 2 or 3 omitted. Here is a resource: https://aviationweather.gov/metar

In the grand scheme of weather, it does not make much difference, as the change in pressure in time or location is more important than the units.

politelemon5y ago

That was a fun and interesting read, thanks for sharing.

Does anyone know of any EU-region surface weather maps, or are these notations specific to NA based weather maps?

chipsa5y ago

Notation is standard across the world. I think it's set by the World Meteorological Organization.

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