- Increased # of tornadoes during strong El Niño years in Alabama (fall, winter & spring)
- Above normal precipitation (usually rainfall)
- Cooler than normal temperatures (due to increased cloud cover, not necessarily due to cold outbreaks)
- Some of the top snowiest winters during moderate to strong El Niño years in Alabama
- Correlation between snowiest winters & strong El Niño & NAO
Studies have been conducted comparing severe weather in Alabama with El Niño cycles, like the one back in 1987. That study, by Chuck Terrell of the National Weather Service Forecast Office in Birmingham found a good correlation with strong El Niño years and the increased number of tornadoes in Alabama.
A possible explanation for this correlation is that a stronger jet stream pattern develops over the United States during El Niño years. With the added jet stream energy, storms over the southeastern US that develop from the collision of the warm Gulf of Mexico air and the cool continental air dropping down from the plains, are enhanced.
PREVIOUS VERY STRONG El Niño YEARS: 1997/1998 AND 1982/1983
So here is some analysis of the weather that occurred during very strong El Niño years:
- There is some correlation between an increased amount of tornadoes in Alabama during very strong El Niño years, both in the late fall, winter and spring.
- There were normal to slightly higher than normal tornado occurences between October-December of 1997.
- In April of 1998, killer tornadoes impacted Alabama. Remember the one in Tuscaloosa and Jefferson counties that impacted places like Brookwood to Pratt City.
EARLY WINTER FORECAST:
- Below normal temperatures
- Above normal precipitation
- Higher chance for above normal snowfall
During strong El Niño years, we tend to see below normal temperatures and above normal precipitation especially rainfall. There are some studies that show mild temperatures during the late fall and early winter and then cooler than normal temperatures due to increased cloud cover. Cooler than normal doesn't always mean cold outbreaks during El Niño years.
Some of the top snowiest seasons have occurred either during strong or moderate El Niño years: http://www.srh.noaa.gov/bmx/?n=snowfacts
MODERATE El Niño Years vs Snowiest Seasons:
1963-64: BIRMINGHAM: 8.4" ANNISTON: 6.6" TUSCALOOSA: 2.7"
1986-87: BIRMINGHAM: 7.6" ANNISTON: 7.8"
1991-92: ANNISTON: 4.3"
2009-10: TUSCALOOSA: 1.0"
STRONG El Niño Years vs Snowiest Seasons:
1957-58: ANNISTON: 3.6"
1972-73: MONTGOMERY: 3.1"
VERY STRONG El Niño Years vs Snowiest Seasons:
1997-98: ANNISTON: 4.5"
There is a greater chance based on climatological records for a top snowy season during an El Niño pattern. 7 snowiest seasons out of 11 (moderate, strong & very strong) El Niño years. Basically a 64% chance for higher than normal snowfall amounts.
El Niño isn't the only oscillation that impacts the weather patterns. The AO and especially the NAO (North Atlantic Oscillation) impacts the weather greatly each winter depending on what phase it is in and when it is in that phase.
NAO depends on the strength of two pressure systems. A low pressure system across Iceland and a high pressure system located near the Azores.
Positive NAO is when the pressure systems are strong, resulting in a strong westerly flow across the U.S. and that can mean and increase in wetness.
Negative NAO is when the pressure systems are weaker and cold air is allowed to plunge southward which can result in enhanced snowfall across the eastern United States.
M./S./V.S. El Niño YEARS: SNOWIEST YEARS: NAO:
1957-58 YES STRONG -
1963-64 YES STRONG -
1965-66 NO STRONG -
1972-73 YES STRONG +
1982-83* NO + TO -
1986-87 YES WEAK + TO - TO + TO -
1987-88 NO WEAK - TO + TO - TO +
1991-92 YES STRONG +
1997-98* YES +-+-+STRONG-
2002-03 NO + TO -
2009-10 YES -+-+STRONG-
The convergent patterns of El Nino and negative NAO during the winter has been studied for years. Studies found that when these two combine that statistically Mid-Atlantic seasonal snowfall is higher during ENSO/-NAO winters. You can kind of see that correlation in the chart above for even Alabama. It is probably more pronounced though for the Mid-Atlantic region rather than The South.
WHAT HAPPENED DURING THE LAST El Niño in 1998?
- Above normal precipitation in Alabama
- Cooler than normal temperatures in Alabama
- Top snowiest season in Anniston with 4.5"
- Ice Storm in New England
- California flooding
Overall, ENSO & NAO are examined for potential effects on the jet stream, storm activity, temperature and precipitation patterns and regional snowfall.
It's a perfect time to prepare for any potential weather disaster so that if one strikes, you will be ready.
Jill Gilardi Fox 6 Meteorologist