Over the course of just 48 hours this week, summer-like heat hit the Northeast, heavy snow fell in the Rockies, and tornadoes touched down in the Plains, all while the lower Mississippi River remains at flood levels.

The heat wave that surged into the Northeast brought multiple days of temperatures that would have been high even for the middle of summer, much less mid-May. Boston went into the 90s during the last three days of the week, with a high of 95°F (35°C) on Thursday afternoon, smashing the old record from 1936 by 4°F (2.2°C). More striking, the low in Boston on Thursday was 71°F (22°C), which was 4°F above the normal high for the date.

 

 

New York City saw similar conditions. The low temperature on Thursday was 80°F (27°C) at LaGuardia Airport, which was the warmest low temperature on record there in the month of May. Earlier in the day, the high reached 97°F (36°C) there, which crushed the record high for the date, but also tied the record for hottest ever day in May. Record highs fell in Central Park and nearby Newark and Bridgeport that day as well, all reaching the lower 90s.

As the climate changes from the warming caused by the increase in atmospheric greenhouse gases, summers are getting longer and hotter, meaning these types of summer-like temperatures are more likely to occur earlier in the year as they did this week.

In some parts of the country, mainly in the Northeast and the Great Lakes, the shift is already evident. In Boston, that first 80° day is typically happening more than a week earlier than in the early 1970s.

When temperatures are much above normal in one half of the country, they are usually much below in the other half. That has been the case this week, as a late season storm brought 2-3 feet of snow to the northern foothills of the Colorado Rockies. Some of the totals from the storm:

  • Allenspark: 36 inches
  • Estes Park: 31 inches
  • Aspen Springs: 23 inches
  • Breckenridge: 17 inches
  • Vail: 12 inches

The snow came from a slow moving area of low pressure cut off from the main steering flow of the jet stream. Because these cutoff lows drift slowly before being caught back up in the main steering flow, they can produce long-lived heavy rain and snow over one particular area. Some research suggests that in a warming environment, these cut off lows could become more common, which potentially could lead to more extreme weather.

Immediately downstream of these cutoff lows, the winds are generally from the southwest, and in the case of the Rockies’ storm, this means those winds occur over the southern Plains. Such winds are one ingredient in the development of severe storms — those thunderstorms that contain hail, damaging winds, and tornadoes.

 

 

While it may not be considered a true outbreak of severe weather, there were 23 tornado reports and more than 200 hail reports focused from Missouri to Texas on Thursday.

On top of those weather extremes, the Mississippi River flooding that dominated headlines a couple of weeks ago has waned in Missouri and Illinois, but it has migrated downstream, with the river still at moderate flood stage from Memphis, Tenn., to Baton Rouge, La.

Despite the late season snow in the Rockies, heat looks like it will be the theme this summer. Next weekend, Memorial Day will start the summer travel season, and the summer temperature outlook from the NOAA Climate Prediction Center indicates the best chance for a hotter-than-normal summer is along the East Coast, Gulf Coast, and westward toward Arizona. The CPC has not projected a cooler than normal summer in any place in the U.S. this year.

For the year-to-date, this has been the second warmest year on record in both the U.S. and globally, even without the warming assistance of an El Niño in the Pacific. Heat will likely continue be in the news for several months to come.