Morse Code of Weather: explaining our recent active pattern with the Pacific-North American teleconnection

BISMARCK, N.D. (KFYR) - We’ve been seeing a lot more moisture in the Northern Plains over the past month or so, but what weather pattern changed that allowed that to happen after a relatively dry start to 2022?

One major factor to look at is teleconnections all across the globe. Teleconnections are often used for longer-term weather trends to give meteorologists clues as to what could happen locally in the coming weeks and months.

Percent of average precipitation in April — Percent of average precipitation in April(NOAA)

Below is a list of notable teleconnections that meteorologists look at and all of which influence weather across the United States in various ways and capacities.

Notable teleconnections — Notable teleconnections(KFYR)

Since weather systems usually move west to east across the country, the Pacific-North American Pattern (PNA) teleconnection is one of the more important ones to look at here in the Northern Plains. The phase, positive or negative, of this teleconnection in the northeast Pacific Ocean can have big downstream impacts on our weather.

Area of the northeast Pacific Ocean we look at to assess the PNA — Area of the northeast Pacific Ocean we look at to assess the PNA(KFYR)

The positive phase usually favors above normal temperatures in the western U.S. and below normal temperatures in the east, with storm systems riding along the jet stream in a way that favors Alberta clippers to form and track through our area. This pattern also allows for bigger storms to ride up the east coast instead of through the central part of the country.

Positive PNA phase: typical orientation of the jet stream and where colder/warmer air usually are — Positive PNA phase: typical orientation of the jet stream and where colder/warmer air usually are(KFYR)

When the phase of the PNA switches to negative, the pattern is flipped with below normal temperatures favored in the western U.S. and warmer conditions in the east. This also allows for storm systems to dive south in the west and through the Rockies, before sometimes developing into larger storms, such as Colorado Lows, in the central part of the country.

Negative PNA phase: typical orientation of the jet stream and where colder/warmer air usually are — Negative PNA phase: typical orientation of the jet stream and where colder/warmer air usually are(KFYR)

Looking at how the PNA has fluctuated over the past few weeks, we can see that it lines up with how much precipitation we have seen in Bismarck. The positive phase was in place for the second half of March and the beginning of April when we didn’t see much precipitation. Then, a big flip happened for the second half of April when we saw our historic blizzards and other storms, and the PNA was negative during this time frame. We went back to the positive phase of the PNA for a short period of time to end April and start May before we’re now back on the negative PNA side of things, leading to more active weather in our area.

Pacific-North American Pattern teleconnection and precipitation over the past few months in... — Pacific-North American Pattern teleconnection and precipitation over the past few months in Bismarck(KFYR)

Looking at our current upper-level pattern, you can see how this resembles the negative phase of the PNA with a trough, or dip in the jet stream, across the western U.S. allowing for storms to strengthen and move through the central part of the country.

Upper level pattern on May 11 — Upper level pattern on May 11(KFYR)

And we can see how that translates into our active pattern that will likely be continuing with above normal precipitation favored for the May 17 to 21 period.

Precipitation trend for May 17-21 — Precipitation trend for May 17-21(KFYR)

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