When Will It Get Cold?

Temperatures in Fairbanks have returned to the "significantly above normal" category in the past couple of weeks, with a mean temperature so far this month of more than 5°F above normal.  Only 3 days this season have seen sub-zero temperatures at the airport, which is right on track with the past 3 years but well behind the usual pace.  Snowfall has been extremely meager, only 2.9" in total so far, and the second lowest on record for this point in the season; but at least now the ground is snow-covered and the scene looks somewhat wintry.

The latest long-range forecasts show no sign that significantly colder weather will develop any time soon for interior Alaska.  For example, here are the 8-14 day and 3-4 week forecasts from the Climate Prediction Center.

The raw computer model forecasts are similar, with nothing but warmth expected right through the next couple of months.  However, a look at the current behavior of the Madden-Julian Oscillation (MJO) provides a hint that cooler weather might be on the horizon for later this month.

For those who are unfamiliar, the MJO is a cycle of enhanced and suppressed rainfall that propagates eastward in the tropics, typically completing a circuit around the globe in about 30-60 days.  The latest MJO phase diagram, shown below, indicates that the MJO has moved into a period of strong activity (blue line moving farther away from the origin; the small "10" denotes the latest observation from yesterday, November 10), with the enhanced rainfall now moving across the Pacific.

The MJO is known to have significant impacts on weather patterns in extra-tropical regions, and so a period of strong and predictable MJO activity can provide useful long-range forecast information.  I looked at the impacts on Fairbanks conditions at this time of year by finding all days with significant MJO activity during November in each phase (1-8) and then looking up the subsequent temperature in Fairbanks out to 60 days in the future.  The figure below shows the results.

Notice the pattern when the MJO is in phase 7, as it currently is.  At about 8-15 days after the occurrence of phase 7, colder than normal temperatures are favored in Fairbanks, but warmer than normal conditions tend to return about 25-35 days later.  If the historical pattern holds true this year, then Fairbanks has a fair chance of turning significantly colder about 8-10 days from now.  Let's see if it works out.