Update #1 [Monday February 6 at 1 pm EST] - Tom Moore
A surge of colder air remains on schedule to push down into the northern U.S. on Wednesday, February 8th. The colder air mass will then move to the east and southeast on Thursday and Friday. As we indicated earlier, we are not talking about extremely cold temperatures with this surge.
The answer to the two main questions that were posed earlier have become quite clear.
- The colder temperatures will be short-lived
- Only a bit of this cold air will make it into the Southeast. Much of the southern Plains and Texas will continue to experience above average temperatures.
As we have seen through much of this winter season, the colder air in the Northern Hemisphere has been on the other side of the globe.
Since average high and low temperatures are now rising across the nation, it becomes very unlikely that we will see any significant or long-lasting cold spells. In fact, February 2017 will likely be another month with above average temperatures across most of the United States.
Since the meteorological winter began on December 1st, 2016, the temperature pattern has been in a state of flux across much of the nation. In previous articles, we alerted you to a mild spell around Christmas, followed by a cold spell to kick off January. Recently, we have seen much above average temperatures but that is in the process of changing again.
Earlier in January, a by-product of the cold spell was a winter storm that affected parts of the southeastern and eastern sections of the nation. As the jet stream retreated well to the north and the pattern transitioned toward a much warmer regime, we encountered a significant ice storm in the nation's midsection.
More recently, many locations experienced much above average temperatures resulting in an extensive "January thaw". Atlanta, Georgia, recorded a nine-day streak with a high temperature of 70 degrees or above. That shattered a previous January record of four days. As the overall pattern was set to undergo another transition, there was a major severe weather event across the Southeast that, unfortunately, featured killer tornadoes.
Short Term Changes
Once again, the overall weather pattern is in the process of changing. Those much above average, and in some cases (record high) temperatures, are being replaced by colder temperatures as the jet stream shifts father south into the U.S.. Over the next couple of weeks, it appears that temperatures will fluctuate across the northern and eastern U.S. but don't expect temperatures to reach the heights that we have seen recently.
Looking Ahead Into February
Keep in mind that when meteorologists look beyond the 7 to 10 day period, they look for general trends in computer models and they are subject to change. If we look ahead as February transitions from its first to second week, there could be a most persistent sign of a colder temperature trend for the northern and eastern sections of the U.S. The graphic below shows the jet stream forecast for February 8th from the GEFS (Global Ensemble Forecast System) model. This is a conglomeration of 21 separate forecasts (ensemble members).
In this case we see a building ridge of high pressure aloft (bulge in the jet stream) over Alaska. Farther east, we see a trough of low pressure (dip in the jet stream) moving farther south into the U.S. This allows colder air from the high latitudes to flow southward. Another branch of the jet stream is even farther south.
Although the trend is looking colder, it does not appear to be excessively cold, so temperatures would be somewhat below average but nothing extreme by February standards. Over the past couple of months, the absolute coldest air has resided on the other side of the globe.
Such a pattern shifts the storm track southward in the U.S. so the situation could be more conducive to winter storms. There is also uncertainty regarding how much of the colder air will penetrate into the South. We will look at this overall pattern more closely as we move into February (forecast guidance will be updated as needed).
It remains to be seen whether this generally colder pattern will hold on for a longer period of time, or if it will yield to milder conditions, once again, later in the month.