Say It Ain’t Snow…

Could The Sioux Empire See Significant Snow This Weekend?

After sitting underneath temperatures anywhere between 10-20 degrees warmer than usual, it’s hard to believe that the Sioux Empire could be bracing for its first real snow storm of the 2017/2018 Winter Season. A Colorado Low is expected to develop then move southeastern portions of the forecast area starting Saturday and, as it moves northeast, it could bring some significant snow to eastern/southeastern portions of the Sioux Empire… but there’s still some uncertainty as to where this low will inevitably track.

Starting Saturday, a cold front will move across the Sioux Empire and help develop a Colorado Low. What is a Colorado Low, you ask? It’s simply a low pressure system that develops off the Lee of the Rockies. Sometimes, after a front passes, particularly a cold front, over the Rockies some of it gets “stuck” due to the topography. That rotation that gets stuck may become more organized and become what we call a Colorado Low. These low pressure systems are the third most frequent synoptic systems to occur in the United States; during the winter months these low pressure system tend to bring a mix of snow and rain to portions of the Plains while, during the summer months, they can bring severe weather outbreaks. While the development of the Colorado Low looks to be certain, it’s where it’ll ultimately end up moving which is still up in the air (again, no pun intended) and there are many factors that will play a role in determining its path.

Colorado Low Developing Saturday Night

The 850 millibar layer is a very important layer for meteorologist to look at when it comes to forecasting daily weather as well as upcoming severe/winter weather. Meteorologist look at this layer of the atmosphere to see what kind of air is moving into, or out of, a forecast area, where the freezing line is as well as whether or not moist or dry air is moving in, or out, of a forecast area too. Because of the time the low is expected to move into the forecast area, meteorologists can only use the long range models to look at these factors. Currently, the 06z GFS suggests that there may be strong warm air advection (WAA) over northwestern Iowa which may take the center of this low on a more north/northeasterly track while 6 hours earlier, there was less WAA and the center of the low is less tight… meaning it’s less organized and strong. It may also suggest more of a northeasterly track versus north/northeasterly track which may take the snow farther east. As stated above, where WAA occurs ahead of the center of circulation is where meteorologists typically see the low moves as it follows falling heights aka lower pressure (cold air at 850 millibars creates rising heights at the surface). This is one of the biggest factors we’ll be watching as we continue to look at incoming data.
One way, visually, to look at this is at MSLP maps and to look at the 540 line. This line is a combination of temperature as well as moisture and show the thickness of the atmosphere between 500 and 1000 millibars. Usually, however topography like mountains can affect this, lower heights (so 534) mean that precipitation will freeze and fall, unless the layers below are warmer, as snow.

Jan 18th 00z GFS Run, 850mb Temp Advection

06z Jan 18th GFS Run, 850mb Temp Advection

Winds will also play an important role in the path of this incoming system, both at the surface as well as in the upper atmosphere. Stronger winds at the surface and at 850mb may move warm air, or cold air, into an area faster which would then impact where the low would track. Stronger, southerly winds would also move up more moisture which could then turn over to snow, or remain as rain, and be heavy at times. While lots of moisture isn’t needed for snow to develop, more moisture available in the atmosphere would allow for higher snow fall/rain fall rates thus leading to larger snow/rain accumulations. While we are looking at wind speeds and directions days ahead of this next low pressure system, at the surface through 300 millibars (where the jet stream is located), it’ll be during the actual event, unfortunately, that we’ll see where strong winds are and where those heavier snow bands are setting up.

06z Jan 18th GFS Run, MSLP

Even though we are still four days, if you consider Thursday day one, away from our next winter system. Will it bring significant snow fall is the question on everyone’s mind. Myself, Joe and Alex are carefully watching all of the incoming data and looking at not only the factors listed above but other factors as well like 500mb jet maxes, CVA and AVA (where there’s rising motion), etc. We’ll not only be looking at these factors in each model but comparing them to each other as well, especially as our longer range models like the NAM and RPM start to have this low in their forecasting period. By comparing between models, as well as within the individual models themselves, we can see not only how these factors are changing but also how they are trending; are winds trending stronger or lighter or is warm air moving in sooner rather than later then we can build a forecast are what we know what that does to a low pressure system.

Like last time, we thank you again for being patience when it comes to developing this forecast. Weather, as we’ve explained, is not an exact science and is difficult to forecast… no matter how long you’ve been forecasting. We pride ourselves here in being honest and transparent about an upcoming forecast so that you, at home, know what is going to be happening today, tonight and for the next 7 days with as less confusion/questions as possible. As of Thursday morning, it does look like the Sioux Empire will see snow as we go into the weekend, starting Saturday the farther northwest you live. The snow will continue into Monday morning, with those across the southeast under the greatest threat for heavy snow, before tapering off. The question, though, we still do not know who’ll see the heaviest snow and possible accumulations. We should have a clearer image on that starting Friday evening… as you can see below, it’s the tale of two different storms.

The GFS versus the EURO Snowfall Forecast for Monday at 5pm




Blaise Keller
KDLT Morning Meteorologist
Twitter – @blaisekellerr

Categories: Weather, Weather Blog