The “Never-Ending” Winter of 2017/2018

When Will Spring Finally Get Here?

Spring officially started on March 20th with snow moving across the Sioux Empire only to return a couple days later. It seems like this Winter has overstayed its welcome, to say the least… but why? Why does it seem like the Winter of 2017 and 2018 has lasted longer than previous Winters, especially the below normal temperatures? The answer is found thousands of miles away in the Pacific as well as off to our northeast and there’s good news on the horizon.

Starting in the Fall of 2017, the Pacific Ocean began to see cooler than normal sea surface temperatures appear across eastern portions of the Equatorial region. Caused by a pressure difference between an area of higher pressure to the east and an area of lower pressure to the west, westerly winds pushed the surface water east all while, upwelling was occurring. Upwelling is the replacement of warmer surface water with cooler, more nutrient rich water. You can see the process in the image below, provided by NOAA.

The process continues until the area of higher pressure breaks down and the Pacific settles into a neutral-phase. Once in a neutral-phase, climatologists and meteorologists will begin to forecast ahead to see if the Pacific will transition to El Nino, back to La Nina or stay neutral.

But how does the Pacific being in La Nina affected our weather here in the Northern Plains? If you were to take a snapshot of the atmosphere over the Pacific and the United States, you’d see the jet stream ridging over the west coast, like in the image below.  That means that there’s warmer air underneath that ridge or along the west coast. Low pressure systems out of the Pacific will ride along the jet stream, following the overall path of the jet unless they’re particularly strong.

As these low pressure systems lift northwards, they interact with cooler air found across portions of Canada and, in doing so, the make up of their airmass changes. From maritime polar (or maritime tropical if it’s origins are further south in the Pacific) to continental polar, the air with the incoming low will become more dry and cooler. This process occurs as the low moves towards the top of the ridge and as it moves down into the trough, the airmass has almost completely changed over.
As the low moves southeast it’ll most likely (especially during this Winter season) pass through the KDLT forecast area. As it does, we may see temperatures warm just slightly due to the warm front then we’ll see (or feel) our temperatures cool down once the cold front passes. Based on the temperatures, we’ll most likely see either rain, snow or a mix of both. Following the passing of the cold front, an area of higher pressure will move in, reinforce the cooler air overhead then move out and the process begins all over again. You can see that perfectly in the video below of a low pressure system expected to move into the forecast area starting Friday, March 30th, and exiting going into Saturday. Now, we’ll move our attention to our north to discuss another factor contributing to our longer feeling Winter

Another contributing factor to our long lasting cooler temperatures is located over the Hudson Bay area. Formed by the temperature difference between the water and surround land, the Hudson Bay Low forms beginning in the Fall and is a major determining factor to the winter weather across central and eastern portions of the United States. And is part of a bigger climatological pattern called the Tropical/Northern Hemisphere Pattern (TNH). You can see the counter-clockwise movement of the Hudson Bay Low below.

The definition of this pattern, taken directly from NOAA states, “The TNH pattern reflects large-scale changes in both the location and eastward extent of the Pacific jet stream, and also in the strength and position of the climatological mean Hudson Bay Low, and is dominant in the winter months. The pattern significantly modulates the flow of marine air into North America, as well as the southward transport of cold Canadian air into the north-central United States”. During a positive TNH phase (which it was in December of 2017 and February of 2018), surface temperatures are usually cooler than normal across western and central portions of the United States and is usually accompanied by cooler than normal temperatures in the Pacific aka a La Nina event. That’s because during a La Nina, the Aleutian Low is weaker resulting in a stronger Hudson Bay Low. To the left, you can see the approximate locatation of the Aleutian Low provided by NASA Rapid Response.

At this point in the blog, you may be saying, “all of this information is great, Blaise, but you said there’s good news so…” and there is! According to meteorologists that specialize in ENSO (La Nina/El Nino), during the month of  February La Nina weakened. Even though temperatures are still below normal, the weakening of the La Nina resulted in weather related anomalies weakening “considerably”, to quote the ENSO discussion posted in early March. The weakening of La Nina is expected to take place throughout March, April and May resulting in a neutral phase ENSO for the summer months and the second half of the year. At least, there’s a ~55% chance (good odds I’d say) of ENSO staying neutral. As a result, long range models suggest that the Sioux Empire has a EC (equal chance) of seeing cooler than normal temperatures or warmer than normal temperatures from April through June. We’ll just have to keep our fingers crossed and hope that Old Man Winter will finally loosen his hold and we’ll start to feel like Spring sooner rather than later!

Blaise Keller
KDLT New Morning Meteorologist
Twitter – @blaisekellerr

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