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Chicago o’hare Late season Winter storm Sun 4/14/2019

What
happened

A rare and unexpected late winter storm hit Chicago city and its international airport (ORD) on Sunday, April 14. For the first time since 1982, more than 5″ of accumulated snow fell on ORD on a single day in April, causing significant disruption to both airport and airline operations.

Climacell provided accurate warning more than 30 hours before the snowstorm occured.

Micro Weather

ClimaCell’s weather forecast correctly predicted 5″ of snow accumulation, while the City of Chicago (AccuWeather), the National Weather Service, and WSI erred regarding snow accumulation amount, intensity, and timing.

Micro Decision

Most airlines were caught off guard before and even during the event, and missed the chance to prepare together with Airport Authorities and take down the flight schedule in advance.

Macro Impact

For one of the major airlines, this lack of preparation resulted in 230 realtime cancellations and 40 diversions, translating into $5-15M costs — only for this single event.

ClimaCell forecast

ClimaCell’s forecast remained consistent in the 24 hours prior to the storm, indicating moderate/heavy snow on Sunday, April 14, with snow accumulation of up to 6″.

  • The Saturday, April 13, 5am forecast highlighted 3-6″ of snow accumulation with heavy to moderate snowfall between mid-morning to mid-afternoon on Sunday, April 14.
  • The Saturday, April 13, 1pm forecast predicted heavy snowfall on Sunday morning through about 12pm, then light to moderate snow in the afternoon with a total accumulation of 3-5″.
  • The Sunday, April 14, 5am forecast indicated heavy snowfall to start at 9am reaching/exceeding 1″ per hour and overall accumulation of 3-5″.
  • ClimaCell provided short-term weather alerts Sunday morning (4am and 8am), predicting the upcoming snowstorm as well as the snowstorm’s downtrend around 2:30pm.

Traditional forecast

Traditional forecast: Light snow with no accumulation on pavement and 1-3″ accumulation on the grass.

“If this was a storm system a month or two ago, it would probably be a major storm but since it’s mid-April, we may see a couple of inches in grassy areas.”

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NWS Chicago:
Actual snow accumulation report

Accumulated Precipitation Comparison
for Chicago O’Hare Airport