Flying into a record Nor'easter

Blizzard of 2006: a Category 3 storm
Before we talk about flying into one of the most severe Nor'easters of all time, lets mention the Blizzard of 2006 once more. NOAA has classified the storm as a Category 3 storm on the new NESIS storm scale, two notches down from the most severe kind of blizzard. While the Blizzard of 2006 set snowfall records in New York City and Hartford, the overall size of the area affected was lower than in mega-blizzards like the Superstorm of 1993 that earned Category 5 rankings.

Tale of a record-breaking Nor'easter
If you're wondering what the NOAA Hurricane Hunters do in the winter when they're not flying hurricanes, the answer is simple--they're somewhere else where the weather is bad! During my four years with the Hurricane Hunters, I regularly spent my summers in the tropics and winters in the Arctic. I logged over 25 missions into intense winter storms as part of field projects based in Norway, Alaska, and the U.S. During the winter of 1989, we were stationed at Brunswick, Maine for three months as part of the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA). This project utilized the two NOAA P-3 research aircraft and the another aircraft with Doppler radar, the NCAR Electra, to provide an unparalleled data set documenting the life cycle of ten North Atlantic extratropical cyclones. During one of these flights, we caught the central Atlantic's most intense winter storm on record.


Figure 1. The ground crew de-ices NOAA's P-3 winter storm hunter aircraft in preparation for chasing a Nor'easter that buried the Brunswick, Maine operations base with a foot of snow.

On January 3, 1989, a strong extratropical cyclone moved off the coast of North Carolina, and pulled a large mass of Arctic air over the ocean behind it. As the cyclone crossed the warm waters of the Gulf Stream, where water temperatures were over 70 degrees, the storm "bombed". It's central pressure fell 66 mb in 18 hours to an astounding 936 mb--a pressure typical of a Category 3 or 4 hurricane! Post-analysis of the data suggested that the pressure fell even further, to 928 mb. This was the lowest pressure ever observed in an Atlantic extratropical cyclone south of 40 degrees latitude in the 20th century. But since the storm never affected land, few people outside of the research community have ever heard of it, and it doesn't even get a ranking on the NESIS scale.

I was tasked to be flight director on the daytime January 4 mission into this storm, dubbed Intensive Operating Period 4 (IOP 4). As I drove to work that morning on treacherously icy roads, I reflected on the fact that this part of my day would probably the most dangerous part--not this afternoon's flight at low altitude into a hurricane-strength winter storm! Although I had had a few rough flights on my 20 or so missions into winter storms, none had ever compared to flying into a hurricane. There isn't much deep convection in a winter storm out over the ocean, since the water is usually too cold to support intense thunderstorms. Deep convection creates sudden updraft and downdrafts--the kind of turbulence that is a bane to aircraft.


Figure 2.Visible satellite image of the ERICA IOP 4 January 4, 1989 cyclone--the most intense winter cyclone ever measured in the central Atlantic.

At our pre-flight briefing, though, I began to wonder if maybe the most dangerous part of the day lay ahead! The flight crew from the just-returned midnight flight reported that the storm was entering a rapid deepening cycle. They encountered intense lightning and moderate turbulence in some of the rain bands. The morning satellite imagery confirmed that we were dealing with a true monster--none of us could ever remember seeing such huge storm over the Atlantic.

We took off and droned southeastwards towards the storm. As we neared the storm, we noticed that it's far-flung rain and snow bands painted our radar displays with bright patches of color we were unused to seeing in a winter storm. The nose radar, which had a special algorithm to plot turbulent areas in a bright purple color, was showing the the first purple I had ever seen in an extratropical cyclone. As we approached the north side, we descended to 350 meters (1150 feet) in altitude and prepared to penetrate the center of the storm.

"SET CONDITION ONE!" crackled pilot Ron Phillipsborn's voice over the aircraft's loudspeakers and intercom. When announced by the Aircraft Commander, Condition One requires all hands to return to their seats and prepare for turbulence. Throughout the airplane, the crew stashed away flight bags, clip boards, and other loose items that could turn into dangerous missiles in severe turbulence, and buckled up their heavy-duty seat belts.

We plowed through an intense band of snow and rain that rocked the aircraft. The winds jumped to 60 mph. Glimpses of the ocean below revealed a maelstrom of white-capped, wind-whipped 20-foot waves.

"Whoa, that was a pretty intense band!" I remarked over the intercom as we emerged from the band and the turbulence subsided. "Ron, are you happy at 1200 feet?" I asked the pilot, who had just joined the Hurricane Hunters, and had yet to fly a mission into a hurricane.

"No problem!" Ron replied. He held us on course for a penetration straight through the center of the cyclone. When we reached the calm center, there was no spectacular view like one sees in a hurricane--the center of this storm was surrounded by clouds. But there was plenty of excitement among the science team, headed by Dr. Mel Shapiro of NOAA.

"Did you see that pressure?" Mel exclaimed. "941 millibars! And what a temperature jump--we've got an incredible amount of warm air at the core of this storm. And check out out those SST's--70 degree water. No wonder we're seeing such impressive convection!" Indeed, the radars showed an impressive amount of intense echoes on all sides of us.

We continued southward, then cut across the cold front. As we crossed the cold front, we hit a remarkable updraft of 7.5 m/s (17 mph). All around us, huge cumulonimbus clouds pushed upwards by the tremendous lift along the front lit up with impressive lightning displays. As we crashed through the front, the surface winds picked up to 100 mph, and some hard, jolting bumps of turbulence rocked the airplane. This was like flying through a Category 2 hurricane! An awesome parade of 35-foot high waves whipped into a green-white froth rolled beneath us.

"Hey Ron!" I exclaimed as we emerged into the clear beyond the cold front. "How does it feel to fly through a Category 2 hurricane?"

"No problem!" Ron replied. He was handling the turbulence like a veteran.

We turned back towards the center again. It was time to take another reading of the storm's central pressure to see how much it had deepened. As we approached the center, once more we encountered bands of showers with strong turbulence. This storm was getting to be a bit of a pain! Finally, we punched into the center again.

"Whoo-eee!" I exclaimed, as winds went calm and the lowest pressure flashed onto the monitors. "936 millibars! That's got to be a record!"

"Fantastic!" agreed Mel. "Let's go check out the triple point now." The triple point is where an extratropical cyclone's cold front, warm front, and occluded front all meet, and is often the most turbulent portion of the storm.

We turned east towards the triple point, and our ride steadily grew rougher and rougher. Frequent intense bands of showers rocked the aircraft, and the ominous purple color of turbulence grew more and more concentrated on the nose radar. Ron did his best to sneak through gaps in the clouds to avoid the worst of the turbulence, but it was still a rough, uncomfortable ride. Finally, the radar showed no more soft spots--we were surrounded on three sides by thunderstorm cells showing some very nasty-looking purple radar echoes.

"Uh, Jeff, what do you think we should do here?" Ron asked, sounding uneasy about the mass of purple directly in front of us.

I took a moment to study the radar display before replying. "Let's get out of here! U-turn, back the way we came!"

"You got it!" agreed Ron happily, immediately banking the the big plane over into a 180-degree turn.

"Ron, Jeff, I think its time to do some high-altitude work!" agreed Mel. We were more than happy to oblige, and climbed to 18,000 feet to study the upper-level structure of the cyclone for a while.

Postscript
The January 4, 1989 flight into the IOP 4 storm marked the only flight I'd ever been on where we performed a U-turn to escape severe turbulence. Despite not directly measuring the most interesting part of the storm, we were able to capture the best data set ever of an extratropical cyclone tapping the warm waters of the Gulf Stream to become a hybrid warm-core system.


Figure 2. Sea Surface Temperature in degrees C on January 4, 1989, and the track of the IOP 4 cyclone. Numbers in parentheses are the saturation water vapor mixing ratio in g/kg. Image credit: Neiman, P.J., and M.A. Shapiro, "The Life Cycle of an Extratropical Marine Cyclone. Part I: Frontal-Cyclone Evolution and Thermodynamic Air-Sea Interaction", Monthly Weather Review: Vol. 121, No. 8, pp. 2153-2176, doi: 10.1175/1520-0493(1993)1212.0.CO;2.

My next update will be on Friday, when I'll probably talk about hurricanes and global warming again.

Jeff Masters