2018-2019 Winter Outlook

Introduction

It is that time of the year. Days are getting shorter; temperatures are getting cooler; and, many have already seen their first freeze or snow of the season. October is an important month for climatologists and meteorologists to analyze certain trends and variables from August to present to obtain an idea of what may come during the winter season. Seasonal forecasting is difficult, and an inexact science, in which many meteorologists have varying methods to generate a seasonal forecast. There are certain areas around the world we can observe to assist in providing a ‘snapshot’ of what the winter season may look like for the United States. A handful of current or predicted teleconnections and variables around the globe can aid in providing the ‘snapshot’ of the upcoming winter. A few of these are: ENSO, QBO, snow and ice cover, NAO, AO, PDO, TNH, and solar activity. A few of these aforementioned variables will be included in the technical discussion later in the article, but first, here is the 2018-2019 Winter Outlook and Snow Outlook.

Regional Discussions

A (San Antonio, TX; Houston, TX; New Orleans, LA; Tallahassee, FL; Charleston, SC; Fayetteville, NC): This region will feature an active winter. Temperatures will be below average and precipitation will be above average. Wintry precipitation will be above average for this region outside of Florida.

B (Dallas, TX; Oklahoma City, OK; Little Rock, AR; Jackson, MS; Birmingham, AL; Atlanta, GA; Greeneville, SC; Charlotte, NC): This region will be characterized by temperatures below average and precipitation above average. This region has the opportunity for several winter storms to provide snow and ice opportunities.

C (Kansas City, KS; Omaha, NE; Rapid City, SD; Casper, WY; Billings, MT; Fargo, ND; Des Moines, IA; Chicago, IL; Columbus, OH): This region will be characterized by temperatures well below normal and snowy conditions. Several winter storms and brutal cold are possible.

D (Philadelphia, PA; New York, NY; Boston, MA; Portland, ME): This region will be characterized by temperatures below average and snow well above average. A few potent Nor’easters are possible in this region over the winter.

E (Detroit, MI; Marquette, MI; Green Bay, WI): This region will be characterized by chilly temperatures and frequent snow opportunities.

F (Denver, CO; Salt Lake City, UT; Twin Falls, ID; Spokane, WA): This region will be characterized by temperatures slightly below average and near normal precipitation. A few winter storms moving in from the Pacific Northwest are possible in this region.

G (Albuquerque, NM; Phoenix, AZ; Los Angeles, CA; San Francisco, CA; Las Vegas, NV): This region will be very bland during the winter. The “Pineapple Express” will cease to exist, thus, temperatures near to above average with precipitation below average. Far eastern areas in this region may see precipitation near average.

H (Portland, OR; Seattle, WA; Boise ID): This region will be characterized by temperatures above average and precipitation near average to slightly below average. There will be a few winter storms that move in from the northern Pacific, thus, providing beneficial snow to ski resorts in the region.

Discussion/Method

The equatorial Pacific is an important region to analyze in October. The state of this region can play one of the puzzle-pieces (an important puzzle-piece) into how the winter will shape up. There are three very important variables to analyze when looking at the equatorial Pacific: I) sea-surface temperature (SST) anomalies, II) the positioning of the anomalously warm or cool SSTs, and III) the depth of the anomalously warm or cool SSTs. As of late-October, the state of the equatorial Pacific is trending anomalously warm which is signaling El Niño conditions developing. In fact, the trade winds (normally flow from east to west) in the central and eastern equatorial Pacific have started significantly weakening. This is only reinforcing the anomalously warm temperatures that have persisted for several weeks; another sign of a developing El Niño. This is supported and is expected to continue per the majority of the models. We are currently in a neutral condition (not El Niño or La Niña); however, due to this region continuing to warm since summer, the chances of El Niño developing are increasing. The Climate Prediction Center has increased the odds of El Niño developing in the winter to 70-75%.

Current SST Anomalies

ENSO Predictions Plume

So what is El Niño? El Niño simply put a climate pattern that occurs when SSTs (in the equatorial Pacific) are above-normal for a long period of time. This climate pattern is a cycle (ENSO) in which below-normal SSTs can occur, too. When SSTs are below normal for an extended period of time in this region, the development of La Niña can occur. This climate cycle play an important role in shaping weather patterns around the entire World. Of significance, are the impacts of this cycle on the winter in the U.S. El Niño is typically associated with an extended Pacific jet stream and amplified storm track for parts of the southern United States. This can cause an increase in cloud-cover and precipitation for the southern United States In return, due to the cloud-cover and precipitation, temperatures tend to be below-average in this region. With the hyperactive storm track across the south, the chances are increased that at some point a phase between the northern and southern jet stream will occur, leading to the possibility of southern winter storms. It can also lead to above-average temperatures in northern/northwestern parts of the United States. The impacts on temperatures and precipitation, however, are dependent upon the strength of the El Niño and the positioning of the warm SSTs.

El Niño winter pattern in North America (CPC)

Based on the current trends and available data, it appears a weak to moderate Modoki El Niño may develop this winter. I am sure you’re wondering what differences, if any, are there between Modoki El Niño and El Niño. And yes, there are differences. An Modoki El Niño is slightly different than the conventional El Niño. Modoki El Niño features stronger warming, and at a great depth, of the central equatorial Pacific and cooling in the eastern and western tropical Pacific. This is what is occurring based on the latest SST anomalies. Also, notice the cooler temperatures along the West Coast of South America. This is a signature, when paired with the central warming, of Modoki El Niño.

El Niño SST anomalies (JAMSTEC)

Modoki El Niño SST anomalies (JAMSTEC)

This type of warming and cooling pattern in the tropical Pacific alters the normal winter pattern in the United States and has different implications than the typical El Niño on temperatures and precipitation. Instead of the Southwest seeing an increase in rainfall, as expected with El Niño, Modoki El Niños can cause an increase in temperatures and lack of precipitation in this region. This is depicted in our winter outlook in which we are forecasting the Southwest to see a warm and dry winter. An increase in storminess and cool temperatures can occur for South-central and Southeastern parts of the United States during a Modoki El Niño. This active storm track from Texas across the Gulf Coast states and up the East Coast is also depicted in our winter outlook.

El Niño temperatures (JAMSTEC)

Modoki El Niño temperatures (JAMSTEC)

El Niño precipitation (JAMSTEC)

Modoki El Niño precipitation (JAMSTEC)

The North Atlantic Oscillation (NAO), the Arctic Oscillation (AO), are crucial teleconnections to take into consideration during seasonal forecasting–-especially during the cool months. The NAO, which can be hard to forecast outward more than a few weeks in advance, has large implications on winter seasonal outlooks—-especially for areas east of the Rocky Mountains. Throughout much of the year, the NAO and AO have been positive but the strong positive phase of these teleconnections has begun to relax and dipped to negative levels. A more neutral or negative phase of NAO allows a high to build near Greenland, which tends to lead to cooler temperatures for parts of the eastern United States due to a dip in the jet stream across this region. SST anomalies distribution across the North Atlantic Basin is looking increasingly favorable for the NAO to go neutral or negative during the winter. Research shows a link between SST anomalies and NAO in which a certain pattern of SST anomalies across the Atlantic Basin can increases the likelihood of the NAO dipping to a negative phase. A negative phase of the AO also aids in ushering chilly air for parts of the eastern and southern parts of the United States due to the circulation around the North Pole becoming weak, thus, can allow chilly air to move southward at times. When these two teleconnections (NAO and AO dip to negative values, the atmosphere will eventually respond, and very active weather will establish across parts of the South and the Mid-Atlantic/New England. Ensembles show the NAO and AO remaining neutral with negative dips at times during the winter, which will lead to large winter storms at times from the Southeast up the East Coast.

Current SST anomalies (North Atlantic)

Negative NAO Pattern Implications On Surface Temperatures

Negative AO Pattern Implications On Upper-Levels

The Pacific Decadal Oscillation (PDO) is important to analyze, too. The PDO has a warm and cool phase. What is unique about the PDO is that the warm and cool phases can last 20-30 years–-this is much longer than your ENSO cycles that last half a year or up to almost two years. The PDO also has an influence on the strength of ENSO. When the PDO is warm, higher heights develop over Alaska and the northwestern Pacific, which can dislodge cold air over Canada and usher it southward into central and eastern parts of the United States. The PDO is in a warm phase, which will have big impacts downstream–leading to lower heights across the eastern United States. Alaska has observed impacts from this “warm blob” so far this Fall. Many records have been broken across the state for the warmth and lack of snow that have occurred thus far. This will likely continue through the winter season.

Warm PDO SST anomalies

Another important factor to take into consideration is the snowcover across Siberia and other parts of the Eurasian continent, snowcover across western and central Canada, and the Arctic sea ice extent. While the snowcover was not abundant in parts of Siberia, it has begun to increase over the past couple of weeks, and the snow cover continues to build in eastern Canada and advance southward in central Canada. This will allow for cold air to build and become well established, followed by an eventual equatorial movement at times during the winter.

Current Snow and Ice Cover

Taking into consideration some of the phases of the aforementioned teleconnections and current global features, here are a few analog years that may give a good snapshot of what this winter could look like. Weak to moderate central based El Niño years were selected to generate temperature and precipitation anomaly composites to help form the framework of the winter outlook. Please note, no two years exactly parallel one another. This is what the analog years chosen showed for the winter:

Temperature Anomalies

Precipitation Anomalies

2018-2019 Winter Outlook Conclusion

The 2018-2019 winter will feature below average temperatures for southern and eastern parts of the United States. Above average temperatures are expected for the the Pacific Northwest. Precipitation will be above average for southern and eastern parts of the United States. The above average precipitation will lead to seasonal snowfall totals above average across the Southern Plains, Southeast, Mid-Atlantic and the Northeast. Please keep in mind, if your region is in an area with above average temperatures, this does not mean wintry precipitation will not occur.

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