From Rain To Snow, Narrowing Down Our Next Storm
by Angela Schilling, Meteorologist
February 18, 2012 9:02 PM
Rain or snow continues to be the main question for Monday, but as we get closer to tomorrow snow totals become more and more easy to narrow down. Not a ton of cold air is behind the cold front, with temperatures hovering right at the freezing mark right ahead of the front. The cold air will remain north of highway 14, and as a result that is where most of the snow will be, with 3 to 5 inches possible. Snow totals will greatly diminish as you head farther south, with a slushly mix of winter weather expected. The timing of the precipitation and its exact type remains a challenge, but in the southeast we’ll start off with some sleet or a rain/snow mix in the morning followed by a brief period of snow mid day, and a rain snow mix in the afternoon. If the storm has any more moisture left overnight, it would fall as snow. Winter Weather Advisories remain in place for counties east of the Missouri River, and will expire by Monday afternoon. Make sure to read the rest of the blog below.
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Some storms are more straightforward to predict than others when it comes to precipitation type and snow amounts. Our next storm looks to roll through the Northern Plains beginning Sunday night and extending through Monday afternoon. This time around moisture is not the limiting factor, but rather the amount of cold air in place. As we head into the next couple of days timing will also play a huge role, as the sooner the cold front comes through, the sooner we will have some cold air in place to produce snow.
To get snow you have to have cold air (temperatures below freezing) throughout basically the entire column of air. Have a layer with temperatures above freezing and particles will either partially melt or completely melt. If you get the crystals to completely melt you can either get freezing rain or rain. Freezing rain occurs with both complete melting and freezing temperatures at the surface. Sleet occurs with partial melting followed by refreezing.
On Sunday temperatures are expected to be well above average with temperatures into the 40’s and 50’s, all thanks to a southerly wind out ahead of our next cold front. The cold front to our west and another area of low pressure to our south will be the two major players over the next couple of days. The cold front will provide the cold air and the low to our south will provide the majority of the moisture. With southerly flow in place warm air will continue to build into the region, and temperatures could rise as the night goes on heading into Monday morning, depending on how fast the cold front gets here.
Notice on the image below how our winds are still coming out of the south by Monday morning. Also notice how warm air is moving into colder air, in weather terms this is called warm air advection and is a classic way to get air to rise and form precipitation. Also interesting to note are temperatures, many of us in the southeast are hovering around the freezing mark, which makes the precipitation type a close call. Which means you have to get your high and temperatures right in order to get your precipitation type right as well. So here are some things to think about. When will the cold air arrive? Is evaporative cooling possible? How are models handling temperatures? Over the last several days models have been underachieving, forecasting highs a couple degrees too cold.
850 temperatures (right above the surface for Monday Morning...GFS model)
For many storms cold air arrives as the cold front swings through and we get some northeasterly flow wrapping around the low, which then funnels down the cold air. What makes this system so unique is the extended period of time where the southeast is under a southerly flow with temperatures right at the freezing mark. By the time the front moves through and cold air arrives temperatures will clearly be below freezing, it’s out ahead of the front where the tricky part is.
Precipitation Amount, as of Monday afternoon...GFS Model
With clouds on the rise and southerly flow temperatures will be hard to drop Sunday night in the southeast, which means it wont’ take much during the day on Monday to get above freezing, unless we get a decent amount of rain and evaporative cooling occurs. Through evaporative cooling the column of air will hence begin to cool, and if we cool enough the precipitation will transition over to snow. Rain on the ground will also make it hard for snow to stick, and therefore hinder totals. So what can you expect at this point in time? We can expect a mix bag of precipitation to start things off West River, before transitioning all over to snow once the cold air arrives. In the southeast we’ll start Monday morning off with a mixed bag of winter weather before transitioning over to light snow towards the afternoon. Throughout the day we could go in and out of snow due to evaporative cooling and the heat of the day. Rain totals will stay under a quarter of an inch with snow totals between 1 to 3 inches in the southeast with 2 to 4 inches possible just north of Sioux Falls into Marshall, MN and as far southeast as Spencer, IA.
Make sure to stay tuned to KDLT and KDLT.com and we’ll keep you updated as the storm progresses.