Understanding the Difference Between Zonal and Amplified Jet Streams

The coming week is going to bring a significant shift in the weather across much of the U.S. thanks to what meteorologists refer to as a transition to an amplified jet stream. Here is what you need to know about this pattern and how it will impact the weather as the calendar says goodbye to October and hello to November.

Shift in Jet Stream Flow to Drive Weather This Week

The weather pattern this week is going to take on characteristics of an amplified jet stream, as opposed to the zonal flow that was anchored over the U.S. last week. A zonal flow means that the weather is moving from the west to the east across the nation.

This zonal flow has dissipated, leaving the jet stream in an amplified flow. This flow means that the jet stream is stretched out across the U.S. in a wavy north to south pattern.

So how does the change in the jet stream flow impact the overall weather patterns? In short, amplified weather patterns generally support stormier conditions. This happens as a result the meaningful temperatures contrasts on either side of the curvy jet stream. In contrast, zonal flow patterns tend to bring calmer weather that is more predictable.

The jet stream is forecast to dip to the south this week across the western half of the U.S. This drop will usher in cooler than average temperatures for the West by Tuesday or Wednesday.

It will be the opposite situation for the central and eastern states on the other side of the wavy jet stream. This half of the country is expected to see the potential of new record high temperatures as the jet stream hitches up to the north in this region. The northward bulge will support a southerly wind flow, bringing unseasonably warm temperatures well into the northern tier.

How warm will it be? Some areas of the Great Lakes may eclipse the 80-degree mark by the middle of the week, well over the historical average for the end of October. For instance, Detroit will see a high in the upper 70s on Wednesday as the morning clouds give way to afternoon sun.

Western and Central U.S. Experiencing Unsettled Weather Thanks to Amplified Flow

Meanwhile, the western and central states will be dealing with a host of weather impacts in the form of rain and snow. The first impacts showed up on Sunday in the Pacific Northwest. Sporadic bouts of heavy rain hammered the Seattle area at times with winds also whipping up across the Emerald City.

Significantly colder temperatures in the higher elevations of the Northwest resulted in snow showers for the area mountain passes. For example, motorists using Snoqualmie Pass along Interstate 90 in Washington state encountered light snow showers Monday morning with more flurries in the forecast when the temperatures drop again overnight. This rain and snow pattern will continue for this heavily traveled pass for the balance of the week.

This snow will begin to spread to the mountainous terrain and Northern California to start the work week. You can expect the snow to expand to the east and into the Rockies by the end of the day Monday and into Tuesday. Ski resorts in Utah, Colorado, and Wyoming will welcome the arrival of significant accumulation thanks to the shift to the amplified jet stream pattern.

This amplified jet stream will then raise the chances of rain for the central U.S. starting on Wednesday. The arrival of a cold front will pair with a southward dip in the jet stream to create widespread rain showers that impact the Midwest and the Plains.

The rain will push along with the cold front as it tracks to the east through Thursday. A large part of the Great Lakes and down through the Mississippi Valley will be under the gun for rain on Halloween. These rain showers will also be a nuisance for trick-or-treaters in some parts of the interior Northeast, the Ohio Valley, and down into eastern Texas. Cities such as Nashville and Pittsburgh will want to check the hourly forecast before heading out for the evening festivities.

This unsettled forecast is the result of the shift from the zonal flow to the amplified flow, providing meteorologists with the certainty that conditions may be dicey at times as the jet stream continues to fluctuate in direction and intensity.

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