Basic Weather 101: Forecasting

Author’s Note

One thing that is often overlooked by preppers is the ability to read the skies. There may come a day where you no longer have access to that convenient weather app or Accuweather forecasts. Understanding the basics of meteorology can help you understand what the weather forecast may be for the near future. We first need to understand some of the common terms and phenomenon before we can use that knowledge to predict the weather. There are several aspects of weather that I will get into:

• Clouds
• Wind
• Pressure and Fronts
• Weather Instruments
• Forecasting from Observations

Please note that I am not a meteorologist and not an expert of weather. As a little kid, I wanted to grow up and be a weatherman, but that changed shortly before I entered my undergraduate studies. Still, I have always been interested in the subject.

I am drawing very heavily on Weather: A Golden Guide. I have two versions of the book – a 1965 print that was discarded from the local library, and a 1987 version. Each of these copies have been in my possession for 30 years, and are well worn. The good news is that there is a newer version from 2001! It can be found on Amazon here, and it costs $6.95 new as of this article. I highly recommend picking up a copy. Are there more detailed books out there? Sure! But I have found none that are as good as this tiny little field book, and the price point makes it well worth it.

This post in particular is going to quote the book above a lot, so as a general citation the information is found on pages 143 to 145 of the 1987 version.

General Forecasts Without Instruments

If you don’t have the instruments laid out in the previous points, there are still ways to make educated guesses about the weather. Again, I highly encourage you purchase the book above – it is inexpensive and it has a wealth of information that is relevant for the prepared citizen.

I encourage you all to talk to some of the “old-timers” in your area about the weather. As we see in the comments of the previous articles, there is a lot of field level observations that can be useful based on local climates and patterns. Generally speaking, the following weather can be expected:

Weather will remain fair:

• Gentle winds from west or northwest
• Cumulus clouds in afternoon summer sky
• Morning fog burns off by noon.

Rainy or snowy weather:

• Clouds cause ring around the moon
• Cumulus clouds begin developing upward
• Dark sky to the west
• Increasing southern wind; clouds moving from west
• Wind shifts in a counterclockwise motion (i.e. north, west, south)

Weather is generally clear:

• Cloud bases increase from ow clouds (stratus) to high clouds (cirrus)
• East wind shifts to west

Temperature will fall:

• Wind from north or northwest
• Clear night sky; light wind

Temperature will rise:

• South wind; clear skies during the day or cloudy skies at night

 

General Forecasts With Instruments

The direction of the pressure indicates a lot about the weather. If the barometer stays steady or rises, you can expect fair weather. If the barometer falls steadily, expect rainy or snowy weather. If the barometer rises rapidly, the weather will be clearing – and, if this occurs in the winter, expect falling temperatures.

The table below is pulled directly from page 145 of the 1987 versions of the book above. A few notes:

•  The pressures in the table are in inches of mercury, not millibars. To convert inches of mercury to millibars, multiply the inches value by 33.8637526. To convert millibars to inches of mercury, multiply the millibar value by 0.0295301.
• A “rapid rise or fall” in pressure is a change of 0.05 to 0.09 inches or more in three hours (adjusted to sea level).

Wind Direction	Barometric Pressure (in Hg)	General Forecast
SW to NW	30.10 to 30.20 – barometer steady	Fair, with little temperature change for 1 to 2 days.
SW to NW	30.10 to 30.20 – rising rapidly	Fair, with warmer weather and rain within 2 days.
SW to NW	30.20 or above – barometer steady	Remaining fair with little temperature change.
SW to NW	30.20 or higher – falling slowly	Fair and slowly rising temperatures for about 2 days.
S to SE	30.10 to 30.20 – falling slowly	Rain within 24 hours.
S to SE	30.10 to 30.20 – falling rapidly	Rain within 12 to 24 hours. Wind will rise.
SE to NE	30.10 to 30.20 – falling slowly	Rain within 12 to 18 hours. Wind will rise.
SE to NE	30.10 to 30.20 – falling rapidly	Rain within 12 hours. Wind will rise.
SE to NE	30.00 or below – falling slowly	Rain will continue for 1 or more days.
SE to NE	30.00 or below – falling rapidly	Rain with high winds in few hours. Clearing within 36 hours – colder in winter.
E to NE	30.10 or above – falling slowly	Summer, with light winds – rain  in 2 to 4 days; Winter – rain or snow within 24 hours.
E to NE	30.10 or above – falling rapidly	Summer – probably rain in 12 to 24 hours; winter – rain or snow within 12 hours.
S to SW	30.00 or below – rising slowly	Clearing with a few hours. Then, fair for several days
S to E	29.80 or below – falling rapidly	Severe storm within few hours. Then clearing within 24 hours – colder in winter.
E to N	29.80 or below – falling rapidly	Severe store (a “nor’easter” gale) in few hours. Heavy rains or snowstorm. In winter, followed by cold wave.
Swinging to W	29.80 or below – rising rapidly	End of storm – clearing and colder.

Conclusion

I hope you found this series enlightening. I hope to have a review soon about the weather station I purchased. It arrived today and I will assemble it over the week and put it into the field ASAP. Again, I encourage you to grab the Weather: A Golden Guide book at $7 on Amazon. The information in the past few articles are only a fraction of the information contained in this field book.