Milwaukee – Wow, it is sunny and hot across most of the United States. That is not a surprise in early August. Most of the United States is now starting to experience a slight drop in average temperature now that we are inching towards late summer. June was quite warm and July has been very similar. And that makes it a perfect time to talk about this winter, right? For some of us it is always too early to discuss winter. And for others, they never stop talking about winter.
La Nina or El Nino?
If you follow the weather more than just watching the 7 Day Forecast on the news or your favorite weather app, you have probably heard about El Nino. In fact, you can call yourself an avid weather fanatic if you have also heard of La Nina and ENSO Neutral conditions and know what they mean. I bring up ENSO because it is a large scale circulation in the Pacific Ocean that can impact North America. Specifically, it can impact our winter weather. Are you interested now? ENSO and the specific phase – warm (El Nino), cold (La Nina) and neutral – are very important drivers in the type of winter North America can experience. Let’s discuss figure 1 and 2 below.
Figure 1 depicts a generalization of global impacts when La Nina occurs during the northern hemisphere winter. In the United States, the Pacific Northwest and Northern Plains experience cooler than average temperatures and the southern United States is dry and warm. The Pacific Northwest and Ohio River Valley can expect wetter than normal conditions. Figure 2 represents winter during El Nino. Much of the Pacific Northwest and Northern Plains experience above average temperatures while the southern United States is wetter and cooler than average. Okay, that was a lot of information, but did you catch all of that?
So, where are we right now and what can we expect going into fall and winter? Good question!
Figure 3 shows the four Niño regions and how much the sea surface temperatures are departing from long term averages. Niño 3.4 is the standard for tracking the ENSO phase. Note there is no departure from the long term average. This means we are in a neutral phase of ENSO. Figure 4 is the latest forecast and goes out to April 2018 in three month periods. The green bar is neutral. The forecast calls for a 48 to 52% chance of neutral through January, February and March 2018. These probabilities are much higher than the red bar (El Niño at 32 to 36% chance) even though climatology favors an El Niño or La Niño during these winter months.
Neutral Phase during a U.S. Winter…
So, if the ENSO forecast verifies and we are neutral during the winter, what does that mean for the United States? Well, we can use an analog method and look backwards using data. What do I mean? Well, we have ENSO phase records for every winter, specifically December through March, back to 1950. I am going to isolate neutral winters since 1950 for the United States. I will plot temperature and precipitation anomalies over the entire country and compare the findings to the 1981 to 2010 long term average.
The above maps plot temperature and precipitation from December through April for all neutral years noted at the top of each map. Figure 5 plots temperature anomalies for these winters. Note that most of the country is in green and blue – below average temperatures of -1.0 to -3.0F. That is a strong signal. Figure 6 plots precipitation and shows below average precipitation (yellow and red) in the southwest. Above average precipitation (blue) is scattered in the northwest and southeast. If you just look at these two maps, you would conclude that most of the country will see average to below average temperatures and near average precipitation. How does this compare to the official NOAA outlook? Let’s check it out.
Note the stark difference in the temperature and precipitation forecasts. NOAA is calling for most of the United States to experience average to above average temperatures from December through February and nearly average precipitation.
Winter 2017/18 Conclusions
Let me preface that weather is not simplistic and there are many variables that impact weather. ENSO is not the sole driving factor that will impact our winter. However, it has been shown to have a significant impact. Coming off of two mild winters, expect temperatures to return to normal for most of the United States. Precipitation should be more evenly distributed this winter with most of the United States experiencing average precipitation. For the northern United States, this means most of us experience more snow than the winters of 2015 and 2016. These are long term outlooks and do not try to pinpoint cold air intrusions or specific storms. Those types of forecasts are only accurate within a week, or less, of occurring. The takeaway as of August 1st, this winter will look more like a typical winter for most of us. In the meantime, enjoy the sunshine and wear the sunscreen!