Minnesota weather: The heat is coming back, but is far from locked in

MINNEAPOLIS (FOX 9) - After a pleasant, although smoky, couple of days, temperatures will quickly soar starting this weekend and potentially extending through much of next week. But this is unlike many of our heat waves here in Minnesota as we may enter a rarely seen setup.

A surge in temperatures is expected to develop in the southern Plains on Friday. These above-average temperatures will then quickly get transported northward Friday night and Saturday, thanks to gusty southerly breezes. This is likely the start of what could be a large "heat dome" that will develop and wobble over the Central Plains for several straight days. 

The animated map above shows the likely development of this dome of heat going into next week. Now, it doesn't show temperatures exactly though. It's called geopotential height with the red shaded colors indicating a higher height value when compared to what's considered normal. One of the basic principles of the atmosphere is that air expands and contracts based on its temperature. The warmer the objects, the more they can expand. As temperatures rise, the overall depth of the atmosphere actually expands. This means the height of the atmosphere in warmer locations, like near the equator for example, are actually taller (farther away from the ground) than at the poles. Now, it's not a HUGE difference in the grand scheme of things, but can vary by a few thousand feet. 

Because of this natural feature though, computer models can estimate the depth of the atmosphere in the days ahead just like they would temperatures, precipitation, or wind speeds. That can give meteorologists an indication of the potential peak temperature for the days and weeks ahead. This doesn't necessarily indicate temperatures down to the degree, as there are dozens of other factors that determine just how hot each location will be. But it often indicates whether there is a larger or smaller potential range for daily highs and lows. Think of it like a probability meter for us hitting 100 degrees here in Minnesota. The taller the atmosphere, the more likely it will be for us to get to the triple digits. So, the above-animated graphic shows the expanding atmosphere in the central U.S. essentially creating a dome of warmth, with the reds indicating the height of the atmosphere is significantly higher than average.

With this higher height, it gives us a higher likelihood of very warm temperatures and possible extremes in some cases. Those extreme temperatures can often show up in computer model data that many of us consume on our weather apps in the seven-, 10- and 14-day forecasts. This is well known in the weather community and adjusted for in our forecasts, but the average Joe rarely understands why this occurs. You can find out more about why your weather app forecast changes so much from hour to hour and is seemingly unreliable, by heading here. 

A more simplistic reason for the very hot temperatures is often the sheer lack of rain or even cloud cover underneath the dome. This dry weather can be easily seen on the rainfall forecast for the U.S.

Any color on the map above indicates at least a trace of rainfall possible over the next seven days. Notice that a large portion of the central and eastern U.S. escapes any sort of rain into next week. This is all thanks to the high pressure associated with that dome that more or less circulates clockwise. This sends moisture around the periphery of this very hot air mass but keeps the hottest areas dry, further exacerbating the contrast in temperatures from inside and outside the dome. 

But here's where the forecast enters uncharted waters. A hurricane in the eastern Pacific is strengthening and moving northward along the coast of Mexico. The current forecast from the National Hurricane Center has it potentially ending up in or around southern California late in the weekend. 

While remnant tropical moisture is pretty common in the Desert Southwest this time of year, a full-blown organized tropical system of any kind is not. In fact, if this were to make landfall as any kind of tropical system in southern California, it would be the first to do so in the better part of a century. 

This is the wildcard to our heat. 

Tropical systems bring with them plenty of heat and moisture and can exacerbate the current overall weather pattern for areas near or around them. While it doesn't sound like we're close enough to be impacted, because of the overall lack of anything other than a heat dome for much of the U.S., the dome itself will be influenced by where this system goes and therefore would affect temperatures for those experiencing the dome. 

Think of it like sitting next to a bonfire. It's hot regardless of wind direction or wind speed. But say a person ran by the fire and changed the wind direction for even a brief period of time. That would change the amount of heat coming toward you one way or another, giving surrounding areas a "wobble" in temperatures. Something similar could happen in our atmosphere as the hurricane "runs" by, leading to varying degrees of heat depending on just how the dome wobbles, which can't be forecasted before the tropical system makes landfall. 

Because of this, while temperatures are likely to be hot and well above average, exactly how warm we are on each day remains to be seen. Not to mention, exactly when the heat winds down is in flux as well. Stay tuned!