I’m not very knowledgeable about weather, I’m trying to remember back to my high school science classes.
Here is my understanding of why it is so hot in the Midwest. A warm front enters from the south of the United States. Weather, except for hurricanes, travels from west to east. A very warm front traveled from the American west, heating up Denver to 108 degrees. It crossed the Rocky Mountains and since there is more water east of the Rockies, it picks up moisture. So, now there is a warm front sitting over the Midwest, waiting to be replaced by a cold front. There is no cold front coming, so it just sits over the Midwest, circulating hot steamy air for days on end.
Allowing for how simplified your explanation is… basically yes.
I will also note that both hurricanes and tropical storms (Florida just experienced TS Debbie) tend to make Midwestern weather patterns “stall”. Whatever we had when the TS or hurricane rolled ashore, that’s what we tend to have for a week (or more) and it’s frequently hot, humid, hazy weather when that occurs.
The reason has to do with the upper-air pattern, which currently has a ridge of high pressure situated over the U.S. (left shows actual values and right is anomaly, which shows that heights are abnormally high over the U.S.), which is associated with warmer temperatures. You are right about the air stagnating and just getting hotter and hotter from day to day; developing drought conditions which cover much of the country are also helping to make things even hotter (heat leads to drought, which leads to more heat, which leads to more drought and so on; what starts this in the first place, well, pretty much random weather variations).
Such a pattern can persist for a long time, sometimes not until the seasons change at the end of the summer, as was the case last summer when it was centered over Texas and Oklahoma (shifted further north this year). Note also that it isn’t so much because a warm front moves in from the south, since there isn’t any large source of hot air south of the U.S. (i.e. warm fronts bring warmer air north, but don’t bring in hotter temperatures that where they originated from, although the air can heat up as it moves north).
Also, the current pattern is more or less what we have seen for at least the past year (last summer was also very hot, followed by a warm fall, winter and spring, although at least where I live it was wetter than normal until the past couple months).
We do get enough sun that it does warm up quite rapidly during the day all on it’s own. Like for example, today we went from mid 60’s in the early morning to upper 80’s in the late afternoon (Minneapolis). From there it’s only going to cool off to the upper 60’s to about 70 at night, and then tomorrow we get low 90’s.
We are at roughly 45 degrees north latitude here in Minneapolis. Halfway between the equator and the north pole. But remember, the axial tilt of the Earth is roughly 23.5 degrees, so at summer solstice, we’re the equivalent of 21.5 degrees north latitude when you’re looking at the angle of the sun. That is the equivalent of being in central Mexico, or Saudi Arabia, or India on the equinoxes, except that we get 15 hours and 36 minutes of daylight to help warm us up!
That also means we get the other extreme, being at equivalent of 68.5 degrees north latitude at the time of the Winter solstice. We only get an 8 hour, 46 minutes of sun on that day, which isn’t a lot of daylight hours to warm things up besides the low angle of the sun.
There’s another factor here: the presence of a large body of water, especially the ocean, is a moderating factor in temperature because it acts as a heatsink in heat waves and releases heat in cold waves. That’s why coastal cities are somewhat milder in temperature, on average, compared to inland cities of similar latitudes. The Midwest, as you may have noticed, does not have a nearby ocean.
Note that due to the bigger “kinks” in the upper flows, you are also getting record “cold” temperatures in other parts of the country. When I checked the Weather Underground’s extremes page a couple days ago, record lows were being set in the upper Columbia basin, parts of Arizona and Jacksonsville, FL.
Checking for June 29th, record lows in MT, NV and FL.
This was also the situation during the spring heat wave in the upper Midwest. Cold weather behind and ahead of the dip.
The extra energy in the atmosphere makes the jet streams and such more energetic, like a river moving fast on a gentle grade, you get more meandering and cutoffs (oxbows).
Jeff Master’s regularly posts about weather extremes in his blog. Here’s one of his entries from the April heat wave. More discussion about the “why” in posts made around that time.
Remember, extra energy just doesn’t mean warmer, it means more aberrations from normal.
It started with a warm and dry spring which caused less moisture in the ground, which makes the air warm faster when the sun hits it. This warms the lower troposphere and increases “thickness”, which means the lower atmosphere actually extends higher than normal, so once it heats up, it’s harder to cool off since it’s so thick.
Then comes the subtropical ridge, an upper high pressure air mass that migrates from the tropics into the US during the summer. It helped heat everything up, then other areas of high pressure, “ridges”, came in and basically stacked on to it, adding warm dry air to the air mass that was already warm, dry and very thick and strong. Whatever air masses might have helped break it up weren’t strong enough to do it, and there haven’t been many of them.
The atmosphere became “blocked,” meaning a stationary high pressure area keeps everything stable and forces weather to go around it. The eastern part of the country is locked into what is called an “omega block” where air circulation resembles the greek letter Omega. So we’re stuck in a cycle where the air is warm, hard to cool, and nothing can break it for the forseeable future.
Is he talking about a different heat wave? The heat wave didn’t come from the west, it came from a high pressure ridge from the south. Warm air from the west may have also moved east and warmed some areas of the midwest, and may have driven the storms that have been in the news, I don’t know at the moment, but the big record breaker didn’t come from Denver.
The storms that the country has been having are not all that unusual. Derechos, big swaths of strong winds, form from storms that occur in hot summer air and often happen along the northern boundaries of a stationary front. The stationary front that was setting temp records.
As already posted, your hot weather came from the Gulf of Mexico, not from “the American west.” We here are in the prevailing westerlies, and air masses generally move from west to east. Air masses can originate in Alaska, Canada, or the Pacific. Warmer air masses with low pressures can originate in the warm waters of the Gulf or the Atlantic. If they are associated with a frontal system, they are called barometric or frontal lows; however, tropical low pressure areas are not associated with frontal systems. They will move according to steering systems, which can be westerly or northerly. If they get picked up with a front (leading edge of an air mass, which generally here moves west to east), they will move with the front and lose their tropical characteristics.
