Where Is All That Snow?

Waking Up Thursday... You May Have Noticed Something (Or Lack There Of)

Myself, Joe as well as Alex started talking about a potential incoming snow storm starting as early as Friday of last week; that’s when our models started to agree more that a system was going to be pushing through the Plains towards the middle of that next week (now this week). However, what was still, no pun intended, “up in the air” was the exact path of this next low pressure system which would ultimately affect snow totals.

On Monday, we posted on the KDLT Weather Facebook, and Twitter, the big difference, to say the least, that two of our models were showing in possible snow accumulations. The NAM (North American Model) and the GFS (Global Forecasting System), at 2:30pm on Thursday, suggested two different scenarios: one was suggesting a major snow storm going into the weekend the other suggested a fresh blanket of snow before the weekend with northwestern Iowa potentially picking up over a half a foot of snow. Because of that big difference, we wanted to make sure that you at home understood why we were holding off on putting out an official snow fall forecast until Tuesday night/Wednesday morning since there was still room for changes…

KDLT Weather Facebook Post Showing Snow Differences – Monday

Waking up Thursday morning, you probably noticed something – there was hardly any snow on the ground. Sioux Falls Airport reported a total of 1.1″ of snow at 6am while other places like Hurly and Emery only had a couple tenths of an inch. Which may have you asking, where was all that snow we were forecasting? The answer is two fold – it’s in parts of Kansas, Nebraska and Iowa there thanks to a low pressure system that stayed too far south. It’s also not here due to another low pressure system, to our north, that weakened.

As mentioned before, into late parts of last week our models started to agree that a low pressure system was going to develop, stay to our south, usher in our next round of Arctic Air as well as our next round of snow after a weekend of mild temperatures and melting. Leading up to Wednesday, when the low pressure system was forecasted to begin to move into the Plains, plenty of melting occurred which meant that there was an amble amount of moisture present in the atmosphere which supported our thoughts for a heavier snow event. Speaking of moisture needed for snow, believe it or not you do not need a lot of moisture for snow to develop; snow can develop in air with dry dew points.

Satellite Image of Sioux Empire on Jan 10th, 2018 – via NASA Rapid Response

700mb Relative Humidity Thursday Morning – Via College of Dupage Weather Models

KDLT Weather Snow Fall Forecast as of Wednesday Morning

Because we had moisture throughout the column of the atmosphere from melting, along with southerly winds, we were confident that parts of the Sioux Empire could receive a couple inches of snow. Another factor that further supported our forecast was a low pressure system that was expected to, and did, develop across southern portions of the Plains (near the Texas/Oklahoma Panhandle). Model data as early as the 9th suggested that, while the center of the low would stay south, a cold front to our east would help act as an area of lower pressure, as well as a small source of lift, to further help with snow development and guide the southern low east/northeast.

Low Pressure System Located Over Oklahoma Panhandle Thursday Morning

 

 

Evolution of Southern Lows Center at 06z on Thursday; Top Photo from 00z NAM on the 9th
Second Photo from 18z NAM on 9th, Third Photo from 18z on 10th

Unfortunately, that southerly low remain too far to our south but why does that mean the Sioux Empire missed out on snow? This low pressure system, like most, are areas of lift that usually have a decent amount of moisture associated with them. Though you do not necessarily need a lot of moisture for snow to develop, you still need some nonetheless. You also need lift; to get clouds, rain, snow, thunderstorms, etc. you need parcels of air to raise. Because the low pressure system remained too far to our south, those conditions were not as strong as previously seen in model data as this low slowly trended towards the south. However, there were still model runs that suggested the center of the southerly low would stay at a distance where the needed conditions would be there

The cold front and it’s placement also caused the Sioux Empire to not receive as much snow as previously thought. Cold air is considerably denser than warm air, because the molecules in the air are, essentially, too cold to move whereas warm air is less dense. As a cold front passes over an area that dense air extends to the surface and literally “pushes” the warm air its replacing upwards, forcing it to condense. That’s why, during the summer months, we usually expect to see a line of storms develop along/just ahead of the cold front. Not only are front, both cold and warm sources of lift, they’re also sources of rotation. Because of this, a more easterly placed cold front would mean that the Sioux Empire would see less lift as well as rotation, allowing for southerly flow to last longer over an area before the cold front completely changed the wind direction.

The Evolution of the MSLP with the Cold Front In Central Iowa; Top Photo from the 00z NAM on Friday
The Bottom Photo from the 18z NAM on Wednesday

The last factor that played a role was a smaller, weaker low pressure system that was forecasted to move eastward, while remaining north of the Sioux Empire. While the center of that low was well off to our north was well, the same principle applies to this low as the one off to our south – it would have been close enough to provide moisture as well as lift to help create a better environment for snow to develop then fall.

In the days leading up to this latest snow fall event, myself, Joe and Alex tried our best to be transparent with our latest forecast. Unfortunately, while we made changes based on the latest data we saw and based on our own meteorological intuition, the snow fall forecast didn’t pan out exactly how we had thought. A busted forecast, as they say in the meteorological community. Sometimes forecasts do that, even if we look at as many factors as we can because meteorology isn’t an exact science. It’s us, looking at data taken a certain point in time and seeing how one model interprets it changing moving forward through time and hoping that the data isn’t bad… because we’ll have to wait until the next time the data is collected to try forecasting all over again. And because of that, we want to thank you for understanding why our forecasts aren’t always right but that we try very hard to make sure they are as accurate as possible.

Blaise Keller
KDLT Morning Meteorologist
Twitter: @blaisekellerr

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