Signs are beginning to point towards the cold wave we’ve seen since late last week ending by President’s Day. Since the beginning of the month, upper air patterns have allowed colder Canadian air to infiltrate the Southeast, bringing an end to the warmer than normal weather we saw in January. The primary culprit has been a trough of low pressure over the Eastern seaboard.

Essentially, this is the opposite of what we had in January, when a ridge over the east coast kept temperatures warm. So far in February, we are 3.6 degrees colder, on average, than we were last month, although that’s still 1.7 degrees above normal.

Forecast models are predicting that the trough will move out by February 17th or so, allowing warmer Gulf Coast air to come back in, and raise afternoon temperatures back into the 60 degree range, and keep overnight lows above freezing. In addition, it looks like the Arctic Oscillation is moving towards the positive configuration we saw for most of January.

Of course, the models initially predicted that we would have the current cold spell sometime in late January, rather than what actually happened, and they could be wrong again. But, at least for the moment, the Climate Prediction Center says we have equal chances of above or normal temperatures from February 15th through the 21st, when our normal high should be 56 degrees.

On another note, the winter weather predicted for Monday turned out to be a bust. Forecasts of 1 to 3 inches of snow ended up with about an inch of cold rain. You had to go to Gilmer or Union Counties in North Georgia to see an inch of snow. The close in counties to metro Atlanta got just rain, while the northern metro saw a bit of sleet, but that was about it.

While it will be cold enough for snow over the next few days, the storms predicted for Wednesday night and Friday night are unlikely to have enough moisture to work with to do anything significant. As is typical, when cold blasts come out of the north, they can’t take advantage of Gulf moisture to produce any real snow.

The Weather Service’s Climate Prediction Center recently changed its home page, which normally shows a map of the US highlighting areas of drought, to display the recent history of the Arctic Oscillation. The chart is reproduced below.

The Arctic Oscillation tracks the relationship between air pressure in the Arctic and the middle latitudes (around 45 degrees North). Useful for measuring and predicting winter weather, when it’s in a positive phase, high pressure in the south and low pressure in the north tend to bring warm, dry weather to the central and southern US, while when it’s in a negative phase, the jet stream moves south, and we get colder, wetter weather.

The Arctic Oscillation is one of several relationships between pressures or temperatures called Teleconnections that can be useful in measuring and predicting weather.

As you can see, the AO has been in its negative phase since late November, just as the weather started to turn colder than normal here in Georgia. So far in December, we’re running about 5.4 degrees cooler than normal, on average, with only two days of above average temperatures. The normal temperatures for the beginning of the month are a high of 58 and a low of 39, and at the end of the month, a high of 51 and a low of 32. The normal average temperature is 44.5 for the entire month, to date, the average is 40.5 degrees.

The news isn’t good for people that enjoy moderate temperatures. Below the large historical chart of the AO is the most recent 14 day prediction for future activity, and as you can see, it’s predicted to stay negative for the period.

The Weather Service released its monthly long range forecast for January, which calls for equal chances of above or below normal temperature and precipitation in Georgia, except for South Georgia, which is predicted to have a 33% greater than normal chance of dry weather. The medium range forecast through January 1st calls for colder than normal temperatures through the period, with precipitation tending from wetter than normal the early part of Christmas week, and dryer than normal New Year’s weekend.