It is that time of the year. The days are getting shorter; the temperatures are getting cooler; and, many have already seen their first freeze or snow of the season. After last winter’s lackluster performance, for most regions, many are wondering what the 2017-2018 winter season will bring. Seasonal forecasting is difficult, and an inexact science, in which many meteorologists have varying methods to generate a seasonal forecast. There are a variety of current or predicted teleconnections and features around the globe that can aid in giving a snapshot of what this winter may feature for the U.S. A few of these are: ENSO, QBO, snow and ice cover, NAO, AO, PDO, TNH, and solar activity.
I will get into a few of these later in the article, but first, here is the 2017-2018 Winter Outlook and Snow Outlook. You will notice I have a National map and two Regional maps (Southern Plains and Southeast).
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2017-2018 Winter Outlook
2017-2018 Snow Outlook
2017-2018 Winter Outlook (Southern Plains)
2017-2018 Snow Outlook (Southern Plains)
2017-2018 Winter Outlook (Southeast)
2017-2018 Snow Outlook (Southeast)
Regional Discussions For NATIONAL MAP (Image 1):
A (El Paso, TX; Albuquerque, NM; Tucson, AZ; Phoenix, AZ; Las Vegas, NV): This region will feature bland winter conditions. Temperatures and precipitation will be near average. The best chance for rain and snow in this area will come with cutoff lows that can develop southwest of California and move across the Southwest or through northern Mexico into southwestern Texas. It is possible upslope freezing drizzle may occur at times in west Texas.
B (Houston, TX; New Orleans, LA; Biloxi, MS; Montgomery, AL; Augusta, GA; Charleston, SC): This region will be characterized by temperatures above average and precipitation near to slightly below average. Do not let the above average temperatures fool you, though. Temperatures will swing from warm to cold frequently. During these temperature swings, it is possible that severe weather will occur. It is possible the northern parts of this region will see one significant winter weather event.
C (Dallas, TX; Shreveport, LA; Jackson, MS; Birmingham, AL; Huntsville, AL; Atlanta, GA; Chattanooga, TN; Knoxville, TN; Ashville, NC; Washington D.C.): This region will be characterized by temperatures near normal and a very active storm track. Temperatures will see great variance between warm to cold, and thunderstorms possibly followed by sleet and wet snow. Western parts of this region have a higher percentage to see an ice storm, and at least two winter storms are possible in this area.
D (Lexington, KY; Pittsburgh, PA; Philadelphia, PA; New York, NY; Boston, MA; Portland, ME): This region will be characterized by temperatures near to slightly above average. Don’t let this fool you though. Snow will be above average and occur frequently in this region. 1-2 potent Nor’easters look possible for eastern parts of this region.
E (Chicago, IL; Milwaukee, WI; Minneapolis, MN; Rapid City, SD, Bismarck, ND; Billings, MT; Salt Lake City, UT; Boise, ID; Seattle, WA): This region will be characterized by cold temperatures and frequent snowstorms. The coldest temperatures will occur in the Northern Plains with the wettest conditions occurring in the Northwest.
F (Detroit, MI; Marquette, MI; Cleveland, OH; Erie, PA; Buffalo, NY): This region will be characterized by heavy lake enhanced snow and temperatures below average. Lake temperatures are anomalously warm, which will aid in heavy snowfall once cold airmasses move in from the northwest.
G (Amarillo, TX; Oklahoma City, OK, Tulsa, OK, Wichita, KS; Kansas City; St. Louis, MO; Indianapolis, IN): This region will be extremely active, and likely be the region that will see the most frequent mid-latitude storms. Temperatures will be slightly below average and snowfall will be above average.
H (Portland, OR; San Francisco, CA; Los Angeles, CA: Reno, NV; Colorado Springs, CO): This region will be characterized by its unsettled conditions. Precipitation will be above average and temperatures near to just below normal. The higher terrain will see above average snowfall.
La Niña was finally realized over the past few days. Below-average sea surface temperatures (SSTs) have been observed across much of the central and eastern equatorial Pacific, and the Niño indices are just below -0.5° C in the Niño-3.4 region and the Niño-3 region. I know this concerns winter-temperature lovers across the South because La Niñas can generate upper-level ridging across the Southeast (which brings anomalously warm temperatures), but please note, there are several more variables that play into a seasonal outlook outside of ENSO. The location of anomalously cool SSTs in the ENSO regions and strength of La Niña are important and plays a large factor in precipitation and temperature patterns in the U.S. (although it is not the only indicator of future atmospheric patterns).
There are two important factors to evaluate with the current La Niña. I) The current and and forecasted intensity of La Niña, and II) the ENSO regions with the most anomalously cool SSTs. The current La Niña is weak and should remain weak through the winter. The dynamical and statistical models for SSTs in the Nino 3.4 region shows this to be the case through the winter months (DJF). The current La Niña is more of an eastern Pacific based event. The eastern based La Niña is evident when looking at the current sea surface temperature anomalies (SSTAs). The SSTAs are very cool across the equatorial parts of the eastern Pacific down through just off the West Coast of South America.
This type of La Niña, when weak, can aid in more volatile weather for southern parts of the mid-latitudes by allowing the Polar Jet to not stay fixed over higher latitudes throughout the winter season–especially when paired with specific phases of other teleconnections, which is discussed below. This year’s La Niña will feature frequent, but not prolonged, periods between anomalously cold and warm conditions for areas closer to the Gulf. Overall, the temperatures will average out just above average, but several bouts of cold are likely throughout parts of the winter. The weak La Niña should aid in enhanced storminess through the Arklatex, Tennessee Valley, and Ohio Valley due to surface lows digging into the mean trough axis.
Current SST Anomalies (Pacific)
ENSO Predictions Plume
The North Atlantic Oscillation (NAO), the Artic Oscillation (AO), are also 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. Currently, the NAO appears to take a negative phase dip for the second half of November–and I believe a more neutral to slightly negative phase is likely for parts of the winter. This is due to the SSTs across the northwestern Atlantic. SSTs are anomalously warm in this region, which again, increases the likelihood of the NAO dipping to a negative phase, and increases the chance of Mid-Atlantic/New England systems tapping into the warm/moist air leading to intensification. The positive phase of NAO tends to bring warm temperatures to eastern parts of the U.S. while the negative phase of NAO tends to bring cool temperatures to eastern parts of the U.S.
Current SSTAs (NW Atlantic)
The AO has been trending towards negative values in mid-to-late November and should remain in this phase during parts of the winter–similar to the NAO. The negative phase of AO can usher in chilly air into eastern and southern parts of the U.S. This is because the circulation around the North Pole becomes weak, and chilly air can more readily ooze southward. When these two teleconnections dip to negative values, the atmosphere will eventually respond, and very active weather (likely winter storms) will establish across parts of the South and the Mid-Atlantic/New England.
The Pacific Decadal Oscillation (PDO) is important to analyze, too. The PDO has two phases (negative and positive) like the aforementioned ENSO, NAO, and AO. What is unique about the PDO is that the positive and negative 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. When the PDO is positive, 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 U.S. The PDO has been positive for a while, but the values have recently dropped from moderately positive to just slightly positive values. The positive phase of the PDO can cause lower heights across the eastern U.S, which equivocates to unsettled weather for this region in the U.S.
Negative AO Pattern
Negative NAO Pattern
Positive PDO Pattern
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. The snowcover is well above average and much more impressive this year compared to last year. Very cold air has already begun to establish itself across Siberia. This is promising for those who love cold because the above average snowcover will allow cold airmasses to become well established over this region and move equatorially at times during the winter. This will extend the below average temperatures further south and east outside of the Pacific NW in the U.S. due to the possibility that the polar vortex will break down later in the winter. This would usher in cold air into the U.S., especially northern and eastern regions, according to recent research.
Current Snow and Ice Cover
Taking into consideration some of the aforementioned teleconnections and global features, I picked a few analog years to try to get a good snapshot of what this winter may feature. (Please note, no two years exactly parallel one another.) I chose weak La Niña years to generate temperature and precipitation anomaly composites to help form the framework of the winter outlook. This is what the analog years chosen showed:
2017-2018 Winter Outlook and Snow Outlook Conclusion:
So, to wrap it all up, I believe the 2017-2018 winter will feature great temperature variance across the Southern Plains, South, and Mid Atlantic. Snowfall will be above average in the Mid-Atlantic and for the rest of the Northeast, while the northern parts of the South and the Southern Plains will see a few winter storm threats (including ice). The Northwest, Northern Plains, and Great Lakes will see cold temperatures and above average snowfall. The immediate Gulf Coast and parts of the Southwest will see precipitation near normal and warm temperatures, with a severe thunderstorm threat at times for the Gulf Coast regions.
Bonus: here is MATTHEW’S Winter Outlook.