Published: 2018-11-19 17:54:00
Updated: 2018-11-19 18:47:26
By Greg Fishel, WRAL Chief Meteorologist
Raleigh, N.C. — There’s a special ingredient that could play tricks on the temperatures and snowfall amounts this winter in the Triangle, according to WRAL Chief Meteorologist Greg Fishel.
Predicting weather several days in advance is tricky business, and predicting the forecast several months out is even harder.
Last year, the O-Fishel winter forecast came pretty close. Fishel predicted five to six days of temperatures above 70 degrees, two to three days of temperatures below 10 degrees and 3 to 6 inches of snow.
What actually happened was a whopping 13 days above 70 degrees, two days below 10 degrees and 7.3 inches of snow.
The reality included more warm days and more snow than expected, but this year El Niño will add another ingredient to consider in the forecast.
Every few years, El Niño develops in the Pacific Ocean, and it affects weather across the world.
Normally, trade winds in the tropical Pacific blow from east to west, pushing warmer water to the western side of the Pacific, around Asia. During El Niño years, the trade winds are weaker, allowing waters to warm along Central and South America.
When this happens, the Western Pacific has cooler waters, drought and even fish shortages.
Closer to home, El Niño typically means cooler than normal winters for the south and southeast and wetter than average conditions from Southern California to North Carolina. In the northern part of the U.S., El Niño triggers warmer and drier weather.
This year, meteorologists are forecasting a weak El Niño, making it more challenging to come up with a local forecast.
Looking back over all records at Raleigh-Durham International Airport, weak, moderate and even strong El Niños suggest the Triangle is going to be in for a colder winter.
In the past, a weak El Niño was associated with the record-breaking cold winter of 1976-77, as well as the very mild winters from 1952-53 and 2006-07. Fishel, however, says history shows the Triangle will be on the colder side of normal this year.
In regard to snowfall, weak and moderate El Niños both typically produce about the same amount of snow as the overall average for the region. The ranges are huge, from winters with absolutely no measurable snow to winters with more than a foot of snow.
The weak El Niño category has an historical range of anywhere between 2 and 8 inches of snow.
The National Oceanic and Atmospheric Administration’s winter outlook forecasts above-normal temperatures for a good part of the country.
North Carolina is included in NOAA’s “equal chances” category, meaning it’s hard to predict what the temperatures will be like across the southeast during weak El Niño years.
NOAA’s precipitation outlook paints a clearer picture. While parts of the northern U.S. could be drier than normal, the southern part of the country could be wetter than average.
With all of the uncertainty, Fishel said he supports NOAA’s overall outlook when it comes to temperatures. It’s really a guessing game as to whether temperatures in the Triangle will be hotter or colder than usual, he said.
Fishel said there is also no clear signal on snowfall, but the overall outlook does indicate a higher probability of warmer than average temperatures in the western United States as opposed to the east.
That would suggest an upper air ridge in the western part of the country and at least an occasional trough in the east, Fishel said. El Niños tend to produce a split in the jet stream with a northern branch and a southern branch.
Fishel said he is going to count on the northern branch delivering a couple of shots of cold air while the southern branch delivers moisture. Therefore, he predicts about 5 to 8 inches of snow at RDU, which is slightly above normal.