Last year the National Center for Environmental Information (NCEI) updated its website and launched two new tools for researching historical temperature and precipitation data. The good news is that the website is now more user-friendly; the bad news is that my older tutorial, posted in March 2021, is obsolete, so it’s time for a new one.
The value of historical temperature and precipitation data
Climate normals are extremely useful in predicting likely weather months in advance — and therefore the gear, supplies, and skills that will likely be required on a backpacking trip. Temperatures and precipitation influence most my choice of clothing, shelter, and sleep system, as well as when I schedule the trip.
Tutorial: Finding US climate normals
Start by going to this page on the NCEI website. It’s worth reading the introductory text before you jump into the data.
NCEI offers two ways to access its data:
- Start with Quick Access, which is easier to use and generates faster results.
- If you can’t find the data you want with Quick Access, use Full Access.
Click here to launch.
Enter the name of towns or other significant geographic places near your route, then select the “Monthly” or “Daily” tab.
- Monthly: Best for long itineraries, or trips centered around the middle of the month (e.g. July 10-17).
- Daily: Best for shorter itineraries that are towards the beginning or end of the month.
In addition to the chart and graph, you can “Get this data as .pdf,” which you could save for your records and which sometimes provides a daily chance of precipitation.
I usually start this process by using the “Find location using map” feature, to display weather stations near my route that I may not have known about.
Weather stations are rarely located where we like to backpack — they’re difficult to install, power, and maintain; and data from more populated areas has more relevance.
Because mountains make their own weather, adjustments often must be made to the climate normal data. For temperatures, assume 3 to 5 degrees F per 1,000 vertical feet of change (less in humid locales, more in dry locales). There’s no similar rule of thumb for precipitation, other than it’s more likely at higher elevations and on the windward sides of major mountains and rides.