WeatherWeather Blog


Record November Nights Ahead

The Science Behind Warm November Nights
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Posted at 2:20 PM, Nov 08, 2022

You don't need to take a meteorology course to know that the sun heats the Earth during the day, hence why it gets warmer during the day. At night, when the sun sets below the horizon, the Earth slowly cools, meaning it's colder at night. However, there are rare cases where temperatures either fail to cool off at night, or in some cases we actually warm overnight. Although rare, this process can happen occasionally here in the Midwest. One prime example is overnight tonight into Wednesday, where the temperatures will slowly rise through the overnight into Wednesday.

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Temperatures overnight warming through the entire night.

Our forecasted low of 59 overnight tonight will shatter the old record warmest night of 50 set back in 1917! Likewise, our forecasted low of 60 Wednesday night into Thursday will also break the warmest night record that night is 53 set back in 1909! Doing one better, the warmest November night ever was on November 1, 1938. If we manage to remain above 61 degrees either night (which is possible), we have a chance of either night becoming the warmest November night on record.

You might be curious; how can this happen if we don't have sunshine at night?

If you ever stood outside at night and watched small clouds zoom northward at very fast speeds. These clouds are low, and they are moving fast. If you ever experienced that, you witnessed the low-level jet in action which is a major factor in overnight warming.

The Jet Stream, more commonly known and is generally responsible for moving weather systems, is also referred to as the upper-level jet. The upper-level jet is around the height planes fly with wind speeds that can at times reach over 100mph. Below the upper-level jet is the mid-level jet, then finally the low-level jet. While the height can vary, the low-level jet sits around 5,000 feet.

Overnight, the airmass over the mountains cools at a faster rate than over the plains. If you remember from Earth Science, cold air is denser and likes to sink while warm air is less dense and wants to rise. Thus, the colder air on the mountains begins to transfer into the plains to balance out the density. Movement of air from one place to another is what we call wind, thus the low-level jet.

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A low-level jet that we typically see overnight. It all comes down to temperature differences.

Where it gets interesting is ahead of low-pressure systems, which disrupts the traditional balances of the atmosphere. The area of lower pressure acts as a vacuum of sorts pulling in air from all directions. Therefore, ahead of low-pressure systems the low-level jet will sometimes 1.) strengthen, with wind speeds upwards of 60-70mph at times! As well as 2.) turn more out of the south than southwest.

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A lot of times ahead of low-pressure systems the low-level jet strengthens and turns out of the south, bringing in warm air.

This brings in the second major factor into play, warm-air advection. Advection in meteorology is the transport of one airmass to another location, so warm-air advection is just the transport of warm air from one place to another. As you'll recall, the source for warm and humid air for the United States is the Gulf of Mexico. To bring that warmer air north, we need a southerly wind to do so. This is why we call a wind coming from the south the "warm-weather direction" because that is what brings in the warm air!

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Southerly winds bring in warm air from the Gulf of Mexico, a process known as Warm Air Advection

Warm-air advection tends to strengthen ahead of low-pressure systems due to the processes explained above, warm air rushes northward as cold air rushes southward to balance each other out. What helps the warm air get transported to the north? You might have already made the connection, the low-level jet!

So, now that all the science is over, how does it all work for Omaha?

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An example of the low-level jet in action with the strong winds blowing in the warm air towards Omaha ahead of our next low-pressure system

To our west we have a low-pressure system, which turns that low-level jet towards the south bringing in the warm air. This process for tonight and tomorrow will be so intense that it will overcome the traditional methods to cool the atmosphere. Hence the record-breaking warmth for the next few days!