LIFE BELOW ZERO...

terryswails1
2 minutes ago
4 min read

A few days ago, I mowed my grass. Today, it's under 10 inches of snow and my little corner of the world, (and for that matter the Midwest as a whole) has been whitewashed. Talk about a transformation, what an entirely different look. As you can see, 4–8 inches (in some cases as much as 12 inches) covers most of Iowa, southern Wisconsin, and northern Illinois.

One of the things about snow cover, especially deep snow cover, is that it makes the world we live in colder. Without snow, sunlight reaching the Earth’s surface causes temperatures to increase throughout the day. When snow covers the ground, the incoming radiation is reflected into space. The amount of solar radiation that an object reflects is known as its albedo. For a fresh snowpack, the albedo can be as high as 80-90%. Therefore, much of the incoming radiation is reflected into space, keeping the surface colder. Because the snow tends to reflect this radiation, high temperatures are almost always lower than what they would be without snow cover.

On the other end of the spectrum, snow cover can also affect overnight low temperatures. After the sun goes down, what "diminished" heat was absorbed by the snow cover is radiated back into the atmosphere, allowing temperatures to fall more than if there was no snow on the ground. Also, snowfall tends to act as a blanket, preventing the heat in the ground from escaping, which leads to overnight lows that are colder than they would typically be. That can be dramatically true when winds are light.

Starting Wednesday, we're going to get the double whammy as a quick hitting Arctic air mass enters the region. Early Wednesday, the leading edge of the front is just entering northern Iowa. However, by mid-afternoon it will have passed through the entire region. That allows some time for temperatures to warm to about 29 in the north to 34 in the south before winds switch to the north and the chill invades in the afternoon. By evening, temperatures are 10-15 degrees colder and wind chills of 0 to 10 are in place. A few snow showers could attend the front, but they look scattered, brief, and light, maybe just enough to track a cat in spots.

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SUB-ZERO LOWS THURSDAY.

After a blustery cold evening Wednesday with wind chills of 10 to 20 below by midnight, clear skies, decoupling winds, and fresh, deep snow cover will allow temperatures to plummet. By Thursday morning, the GFS shows lows over the snow fields of -6 to -14 degrees.

Temperatures will be 36 to 46 degrees colder than just 24 hours earlier. Welcome to life below zero.

Later in the day Thursday, despite sunshine, the reflective property of the snow will keep highs in the range of 7 to 13 degrees. Fortunately, winds until late in the afternoon will remain light, keeping wind chills in check. Despite it being only December 3rd, highs will be more typical of a mid-January day, due in large part to the expansive snow pack.

Friday, ahead of another fast moving front, readings will quickly rebound from lows of zero to 6 below, to highs in the range of 26 to 32 from north to south. The return flow is cut short with the passage of that front Friday night, and colder readings in the low 20s north to upper 20s south are back in place for Saturday.

Later Saturday night and Sunday, a couple weak disturbances ripple southeast through eastern Nebraska along a baroclinic boundary. Moisture and dynamics are not impressive, but there should be enough lift for occasional periods of light snow or flurries. The most likely period for any accumulating snow locally would be late Saturday night and early Sunday, and again later Sunday night, even then it all looks rather light. Very early in the game, it seems the best axis for accumulating snow would be over my southwestern counties and points west in central Iowa. Here's what models are currently suggesting for snow.

The EURO

The GFS

The NBMv5 comprised of 30 models and ensembles. It's only shown at a 10:1 ratio, but is noticeably further NE with its snow. The EURO and GFS were compiled with the Kuchera method, which accounts for expected higher snow ratios.

Next week, and for that matter much of the next 2 weeks, NW flow of varying degrees is expected to hold sway. Assuming that's the case, below normal temperatures are anticipated. The ensembles of the EURO show this for the week one temperature departures through December 9th

A less amplified flow during the week 2 period leaves temperatures cold but at least several degrees warmer than the previous week 1.

Snowfall would likely be relegated to clippers, which are fast movers with limited moisture. The ensembles comprised of many solutions produces this averaged depiction of 14 day snow.

The EURO has the same idea, but is a little lower on totals.

Long range, I see a lot of contradictions regarding the 500mb pattern which drives the storm track and the temperatures associated with it. There are signs of a major warm-up mid-December, but the possibility that the mild period could be followed by a strong cool-down by Christmas, with the MJO locked in phase 8. That's something I will be watching for in coming days. I would say chances are about 65 percent it happens, compared to 35 percent it won't. Just a hunch. Have a solid day and get ready for the big chill later Wednesday night. Thursday morning, we'll be living life below zero. Roll weather...TS