From Ice Sheet to Heat Dome
July 19, 2016
Back just in time.
As we descend into the depths of summer, some of the year’s hottest temperatures may be soon upon us. Forecasters expect a high pressure ridge and extreme temperatures to combine to create what is referred to as a “heat dome” over large portions of the United States.
A heat dome occurs when high pressure in the upper atmosphere acts as a lid, preventing hot air from escaping. The air is forced to sink back to the surface, warming even further on the way. This phenomenon will result in dangerously hot temperatures that will envelop the nation throughout the week. Heat index values for parts of the U.S. are expected to reach 110 degrees or higher. In response, the National Weather Service has issued heat alerts for more than a dozen states across the U.S.
This map, based on data from NOAA’s HRRR Model shows the predicted high temperatures on July 18, 2016 at 5 p.m. EDT. These temperatures reflect the beginning of the scorching heat wave that is expected to last throughout the week.
The culprit for the sultry weather is an unusually intense and expansive area of high pressure, also referred to as a “heat dome,” that is parking itself over the South Central U.S.
The clockwise circulation of air around this high is dragging moisture from the Gulf of Mexico and pumping it northward, all the way to Canada, which is resulting in the high humidity levels.
In addition, evapotranspiration from crops in agricultural states such as Nebraska, Kansas, Iowa and Minnesota is also adding to the moisture content of the atmosphere.
The high pressure area itself will be strong enough to put it on a list of strongest such weather systems observed in that part of the country.
Meteorologists often look to a metric known as geopotential height to gauge the intensity or unusualness of a heat dome like this. Geopotential height measures the elevation of an air pressure surface.Hot air masses expand, and elevate pressure surfaces, while cold air masses are more dense and compact, which lowers them.
According to the National Weather Service in Minneapolis, the height of the 500 millibar pressure level may be near 6,000 meters, “which is very rare and considered an extreme event.”
Citing computer model data as of Sunday morning, the Weather Service stated: “…This is expected to be the hottest atmosphere for this time of year compared to 1985-2012! As a result, this may be one of the worst heat waves in the last few decades.”
Strong heat gave rise to intense T-storms on the east coast, which accounts for me getting stranded in Newark, and not getting home till 4 am this morning.
Strongest heat wave since 2012. Welcome to the Rest of Our lives.