GFS 500mb geopotential height and anomaly (dam) over the eastern seaboard of the U.S., 21 February 2018. The spectacularly strong upper-level high centered just off the southeast U.S. coast at 12Z (7 am EDT) Wednesday, 21 February 2018. Colors show the departure in decameters (tens of meters) from the average height of the 500-millibar pressure surface at this time of year. Graphic:

Dr. Jeff Masters
22 February 2018

(Weather Underground) – Astonishing summer-like heat cooked the Eastern U.S. on Wednesday, smashing all-time records for February warmth in cities in at least ten states, from Georgia to Maine. At least 24 cities recorded their hottest February temperature on record on Wednesday, including New York City (78°), Hartford, CT (74°) and Concord, NH (74°). According to Weather Underground weather historian Christopher C. Burt, February 20 - 21 marked the most extraordinary heat event to ever affect the Northeastern quadrant of the U.S. during the month of February, since official records began in the late 1800s. He catalogued the following eight states that tied or beat all-time February state heat records over the past two days, noting that in the case of Maine and Vermont, “It is simply amazing to beat a state temperature record by some 8°F!”:

  • Pennsylvania: 83° at Capitol City (ties old record for the state)
  • New York: 79° at La Guardia Airport (old state record 78°)
  • Vermont: 77° at Bennington (old state record 68°)
  • New Hampshire: 77° at Manchester (old state record 72°)
  • Maine: 77° at Wells (old state record 69°)
  • New Jersey: 83° at Teterboro (old state record 80°)
  • Massachusetts: 80° at Fitchburg (old state record 73°)
  • Ohio: 80° at Cincinnati Lunken Airport (ties old record for the state) […]

A ridge to remember

The record February heat was caused by an unusually pronounced kink in the jet stream that brought a big trough of low pressure over the Western U.S. (accompanied by very cold temperatures) and a record-strength ridge of high pressure that locked in over the eastern half of the U.S. This ridge brought exceptional warmth miles above the eastern U.S. and northwest Atlantic. All else being equal, warmer air is less dense than cooler air, so a deep, warm air mass raises the heights of various benchmark heights such as 500 mb (roughly the midpoint of the atmosphere’s density, almost four miles up). As shown in Figure 2 below, the 500-mb map at 12Z Wednesday (7 am EDT) was simply mind-blowing for mid-February.

To verify just how unusual this ridge was, Lance Bosart (University at Albany, State University of New York) dug through the radiosonde climatology compiled by the NOAA/NWS Storm Prediction Center. The dataset goes back to the start of routine radiosonde launches in the late 1940s. At nearly every site along the U.S. East Coast, the weather balloons launched at 12Z Wednesday found a 500-mb surface higher than anything on record for January or February—and in some cases across even longer seasonal spans, as shown below. [more]

Summer in February! 80° in Massachusetts, 78° in NYC


  1. Anonymous said...

    The link goes to an article about flooding.  

  2. Jim said...

    Thanks, fixed!  

  3. Anonymous said...

    It's been -2 here (at night). Washington. The state.

    Our turn for cold weather. About ten days back, all the snow had melted in any place with sunshine, it even got into the mid 50's. Then we got two heavy storms packing tons of snow. Back to full-on winter here.  

  4. messtime said...

    Here in New Zealand we just had the hottest year in recorded history 2017 (For NZ).
    The weather is messed up in NZ also as it is in many parts of the world or all of the world.
    Lots of flooding events.  


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